V4L2 VIDIOC_REQBUFS cannot allocate enough memory - c

I am writing a MIPI driver without using the I2C functionality, since it is not possible for me to use it. I am writing this for the Google Coral.
To write this new driver I looked at this example and adjusted it to only use the MMAP functionality.
My new code is this:
/*
* V4L2 video capture example
*
* This program can be used and distributed without restrictions.
*
* This program is provided with the V4L2 API
* see http://linuxtv.org/docs.php for more information
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <getopt.h> /* getopt_long() */
#include <fcntl.h> /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>
#define CLEAR(x) memset(&(x), 0, sizeof(x))
#ifndef V4L2_PIX_FMT_H264
#define V4L2_PIX_FMT_H264 v4l2_fourcc('H', '2', '6', '4') /* H264 with start codes */
#endif
struct buffer {
void *start;
size_t length;
};
static char *dev_name;
static int fd = -1;
struct buffer *buffers;
static unsigned int n_buffers;
static int out_buf;
static int force_format;
static int frame_count = 200;
static int frame_number = 0;
static void errno_exit(const char *s)
{
fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
exit(EXIT_FAILURE);
}
static int xioctl(int fh, int request, void *arg)
{
int r;
do {
r = ioctl(fh, request, arg);
} while (-1 == r && EINTR == errno);
return r;
}
static void process_image(const void *p, int size)
{
printf("processing image\n");
frame_number++;
char filename[15];
sprintf(filename, "frame-%d.raw", frame_number); // filename becomes frame-x.raw
FILE *fp=fopen(filename,"wb");
if (out_buf)
fwrite(p, size, 1, fp); // write data to file fp
fflush(fp);
fclose(fp);
}
static int read_frame(void)
{
printf("reading frame\n");
struct v4l2_buffer buf;
unsigned int i;
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
switch (errno) {
case EAGAIN:
return 0;
case EIO:
/* Could ignore EIO, see spec. */
/* fall through */
default:
errno_exit("VIDIOC_DQBUF");
}
}
assert(buf.index < n_buffers);
process_image(buffers[buf.index].start, buf.bytesused);
if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
return 1;
}
static void mainloop(void)
{
printf("mainloop\n");
unsigned int count;
count = frame_count;
while (count-- > 0) {
printf("count number = %d\n", count );
for (;;) {
fd_set fds;
struct timeval tv;
int r;
FD_ZERO(&fds); // clear file descriptor
FD_SET(fd, &fds); // set file descriptors to the descriptor fd
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(fd + 1, &fds, NULL, NULL, &tv); // select uses a timeout, allows program to monitor file descriptors waiting untill files becomes "ready"
// returns the number of file descriptors changed. This maybe zero if timeout expires.
// probably watching reafds descriptor to change?
if (-1 == r) {
if (EINTR == errno)
continue;
errno_exit("select");
}
if (0 == r) {
fprintf(stderr, "select timeout\n");
exit(EXIT_FAILURE);
}
if (read_frame()) // if one of the descriptors is set, a frame can be read.
break;
/* EAGAIN - continue select loop. */
}
}
printf("mainloop ended\n");
}
static void stop_capturing(void)
{
printf("stop capturing\n");
enum v4l2_buf_type type;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
errno_exit("VIDIOC_STREAMOFF");
printf("capturing stopped\n");
}
static void start_capturing(void)
{
printf("initiating capturing\n");
unsigned int i;
enum v4l2_buf_type type;
for (i = 0; i < n_buffers; ++i) {
struct v4l2_buffer buf;
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)){
errno_exit("VIDIOC_STREAMON");
}
printf("capturing initiated\n");
}
static void uninit_device(void)
{
unsigned int i;
for (i = 0; i < n_buffers; ++i){
if (-1 == munmap(buffers[i].start, buffers[i].length)){
errno_exit("munmap");
}
}
free(buffers);
}
static void init_mmap(void)
{
printf("initiating mmap buffer\n");
struct v4l2_requestbuffers req; //struct with details of the buffer to compose
CLEAR(req);
req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) { // initiate buffer
if (EINVAL == errno) {
fprintf(stderr, "%s does not support "
"memory mapping\n", dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}
printf("memory allocated\n");
if (req.count < 2) {
fprintf(stderr, "Insufficient buffer memory on %s\n",
dev_name);
exit(EXIT_FAILURE);
}
buffers = calloc(req.count, sizeof(*buffers)); // make the amount of buffers available
if (!buffers) {
fprintf(stderr, "Out of memory\n");
exit(EXIT_FAILURE);
}
for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { // go through buffers and adjust struct in it
struct v4l2_buffer buf;
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
errno_exit("VIDIOC_QUERYBUF");
buffers[n_buffers].length = buf.length;
buffers[n_buffers].start =
mmap(NULL /* start anywhere */,
buf.length,
PROT_READ | PROT_WRITE /* required */,
MAP_SHARED /* recommended */,
fd, buf.m.offset);
if (MAP_FAILED == buffers[n_buffers].start)
errno_exit("mmap");
}
printf("mmap buffer initiated\n");
}
static void init_device(void)
{
printf("initiating device\n");
struct v4l2_capability cap;
struct v4l2_cropcap cropcap;
struct v4l2_crop crop;
struct v4l2_format fmt;
unsigned int min;
if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) { // gets information about driver and harware capabilities
if (EINVAL == errno) { // driver is not compatible with specifications
fprintf(stderr, "%s is no V4L2 device\n",
dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_QUERYCAP");
}
}
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
fprintf(stderr, "%s is no video capture device\n",
dev_name);
exit(EXIT_FAILURE);
}
if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
fprintf(stderr, "%s does not support streaming i/o\n",
dev_name);
exit(EXIT_FAILURE);
}
/* Select video input, video standard and tune here. */
CLEAR(cropcap);
cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) { // used to get cropping limits, pixel aspects, ... fill in type field and get all this information back
crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
crop.c = cropcap.defrect; /* reset to default */
if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) { // get cropping rectangle
switch (errno) {
case EINVAL:
printf("EINVAL in VIDIOC_S_CROP\n");
/* Cropping not supported. */
break;
default:
printf("other error in VIDIOC_S_CROP\n");
/* Errors ignored. */
break;
}
}
} else {
/* Errors ignored. */
}
CLEAR(fmt); // set the format of the v4l2 video
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (force_format) {
fprintf(stderr, "Set H264\r\n");
fmt.fmt.pix.width = 640; //replace
fmt.fmt.pix.height = 480; //replace
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_H264; //replace
fmt.fmt.pix.field = V4L2_FIELD_ANY;
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");
/* Note VIDIOC_S_FMT may change width and height. */
} else {
/* Preserve original settings as set by v4l2-ctl for example */
if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt))
errno_exit("VIDIOC_G_FMT");
}
/* Buggy driver paranoia. */
min = fmt.fmt.pix.width * 2;
if (fmt.fmt.pix.bytesperline < min)
fmt.fmt.pix.bytesperline = min;
min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
if (fmt.fmt.pix.sizeimage < min)
fmt.fmt.pix.sizeimage = min;
init_mmap();
printf("device inititiated\n");
}
static void close_device(void)
{
printf("closing device\n");
if (-1 == close(fd))
errno_exit("close");
fd = -1;
printf("device closed\n");
}
/*
struct stat {
dev_t st_dev; ID of device containing file
ino_t st_ino; Inode number
mode_t st_mode; File type and mode
nlink_t st_nlink; Number of hard links
uid_t st_uid; User ID of owner
gid_t st_gid; Group ID of owner
dev_t st_rdev; Device ID (if special file)
off_t st_size; Total size, in bytes
blksize_t st_blksize; Block size for filesystem I/O
blkcnt_t st_blocks; Number of 512B blocks allocated
Since Linux 2.6, the kernel supports nanosecond
precision for the following timestamp fields.
For the details before Linux 2.6, see NOTES.
struct timespec st_atim; Time of last access
struct timespec st_mtim; Time of last modification
struct timespec st_ctim; Time of last status change
#define st_atime st_atim.tv_sec Backward compatibility
#define st_mtime st_mtim.tv_sec
#define st_ctime st_ctim.tv_sec
};
*/
static void open_device(void)
{
printf("openening device\n");
struct stat st;
if (-1 == stat(dev_name, &st)) { // stat() returns info about file into struct
fprintf(stderr, "Cannot identify '%s': %d, %s\n",
dev_name, errno, strerror(errno));
exit(EXIT_FAILURE);
}
if (!S_ISCHR(st.st_mode)) {
fprintf(stderr, "%s is no device\n", dev_name);
exit(EXIT_FAILURE);
}
fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0); // open the file dev/video0, returns a file descriptor
// if fd == -1, the file could not be opened.
if (-1 == fd) {
fprintf(stderr, "Cannot open '%s': %d, %s\n",
dev_name, errno, strerror(errno));
exit(EXIT_FAILURE);
}
printf("device opened\n");
}
int main(int argc, char **argv)
{
printf("main begins\n");
dev_name = "/dev/video0";
for (;;) {
printf("back here\n");
break;
}
open_device();
init_device();
start_capturing();
mainloop();
stop_capturing();
uninit_device();
close_device();
fprintf(stderr, "\n");
return 0;
}
However I get the following error:
VIDIOC_REQBUFS error 12, Cannot allocate memory
The entire output is:
main begins
back here
openening device
device opened
initiating device
initiating mmap buffer
VIDIOC_REQBUFS error 12, Cannot allocate memory
make: *** [makefile:3: all] Error 1
In the above code this is caused by:
if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) { // initiate buffer
if (EINVAL == errno) {
fprintf(stderr, "%s does not support "
"memory mapping\n", dev_name);
exit(EXIT_FAILURE);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}
Thus the ioctl(fd, VIDIOC_REQBUFS, &req) causes this error.
I have already looked on StackOverflow and found 1 other person with the same mistake.
He suggested to change CONFIG_CMA_SIZE_MBYTES to 32 from 16. I tried this by looking where I could find this setting. I found it in: boot/config-4.14.98-imx . However, it was already 320. (yes tenfold). I am now rather stuck on this. Is there a problem in my code, or do I need to change the setting from 320 to 32 (which seems counterintuitive).
With kind regards.

Related

Why not able to find second new event using inotifyd in c language

I am trying check new event created or deleted in the specific directory.
If event is created then need to do some operation using thread and this thread should be in initiate wile loop .
Main thread should look for another event creation or deletion.
I have developed application , but I could not able to second event is created or not.
Code flow is always in child thread.
Please find below code :
#include <errno.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/inotify.h>
#include <unistd.h>
#include <string.h>
#define PATH_MAX 4096
#define O_RDONLY 00
int main()
{
//char buf;
char buf[4096]
__attribute__ ((aligned(__alignof__(struct inotify_event))));
int fd, i, poll_num;
int *wd;
nfds_t nfds;
struct pollfd fds[0];
char *device_path = "/home/home/test";
ssize_t len;
const struct inotify_event *event;
int counter=0;
char getdata[10];
char devname[PATH_MAX];
char *filename;
int thread_ret = 0;
static pthread_t inotify_pthread;
/* Create the file descriptor for accessing the inotify API */
fd = inotify_init1(IN_NONBLOCK);
printf("fd = %d",fd);
if (fd == -1) {
perror("inotify_init1");
exit(EXIT_FAILURE);
}
/* Mark directories for events
- file was opened
- file was closed */
wd = inotify_add_watch(fd, device_path,
IN_OPEN | IN_CLOSE | IN_CREATE | IN_DELETE);
printf("wd = %d ",wd);
if (wd == -1) {
fprintf(stderr, "Cannot watch '%s': %s\n",
device_path, strerror(errno));
exit(EXIT_FAILURE);
}
/* Prepare for polling */
nfds = 1;
/* Inotify input */
fds[0].fd = fd;
fds[0].events = POLLIN;
/* Wait for events and/or terminal input */
printf("Listening for events.\n");
while (1) {
poll_num = poll(fds, nfds, -1);
if (poll_num == -1) {
if (errno == EINTR)
continue;
perror("poll");
exit(EXIT_FAILURE);
}
if (poll_num > 0) {
if (fds[0].revents & POLLIN) {
/* Inotify events are available */
len = read(fd, buf, sizeof(buf));
if (len == -1 && errno != EAGAIN) {
perror("read");
exit(EXIT_FAILURE);
}
if (len <= 0)
break;
for (char *ptr = buf; ptr < buf + len;
ptr += sizeof(struct inotify_event) + event->len) {
event = (struct inotify_event *) ptr;
if ( event->len ) {
/* Print event type */
if (event->mask & IN_CREATE){
printf("IN_CREATE: \n");
if (event->len){
counter++;
printf("IN_CREATE: created file name : %s , counter no = %d \n", event->name,counter);
thread_ret = pthread_create(&inotify_pthread, NULL, event_read_data(),NULL);
if (thread_ret < 0) {
printf("can't create inotify thread");
exit(EXIT_FAILURE);
}
}
}
else if (event->mask & IN_DELETE){
counter--;
printf( "IN_DELETE : Deleted File name %s , counter no = %d \n", event->name,counter );
}
}
printf("counter number : %d \n",counter);
}
}
}
}
printf("Listening for events stopped.\n");
close(fd);
free(wd);
exit(EXIT_SUCCESS);
}
event_read_data(){
while(1){
printf("Child Thread");
sleep(3);
}
}
Compiled like below:
gcc fine_name.c -lpthread

How to stop the repetition of inotify result?

In this code, I am trying to monitor two paths at the same time. I used while(1) for this purpose. But the problem that I am facing is that whenever I run the code, it gives me the same result two times like this.
Giving result
Pathname1 "file" is modified
Pathname1 "file" is modified
Expected result
Pathname1 "file" is modified
I debugged the code. After breaking the main function and stepping over it, the next command stops at this line length = read(fd, buffer, EVENT_BUF_LEN ). Whenever I break a line after this length variable command, the program starts and after modifying the file, the program stops at this line struct inotify_event *event = ( struct inotify_event *)&buffer[i]; Although the program should not break.
I also used IN_CLOSE_WRITE instead of IN_MODIFY but no change in the result.
typedef struct{
int length, fd, wd1, wd2;
char buffer[4096] __attribute__ ((aligned(__alignof__(struct inotify_event))));
} notification;
notification inotify;
int getNotified(char *pathname1, char *pathname2){
inotify.fd = inotify_init();
inotify.wd1 = inotify_add_watch(inotify.fd, pathname1, IN_MODIFY);
inotify.wd2 = inotify_add_watch(inotify.fd, pathname2, IN_MODIFY);
while(1){
inotify.length = read(inotify.fd, inotify.buffer, EVENT_BUF_LEN);
int i = 0;
while(i < inotify.length){
struct inotify_event *event = (struct inotify_event *)&inotify.buffer[i];
if(event->len){
if(event->mask & IN_MODIFY){
if(event->wd == inotify.wd1){
printf("Pathname1 '%s' is modified\n", event->name);
break;
}
if(event->wd == inotify.wd2){
printf("Pathname2 '%s' is modified\n", event->name);
break;
}
}
}
i += EVENT_SIZE + event->len;
}
}
inotify_rm_watch(inotify.fd, inotify.wd1);
inotify_rm_watch(inotify.fd, inotify.wd2);
close(inotify.fd);
exit(0);
}
Some remarks:
You should not "break" as you go out of the inside "while" loop and call read() again
The IN_MODIFY event does not fill the event->name field (i.e. event->len = 0)
The number of IN_MODIFY events depends on how you modify the files ("echo xxx >> file" = write only = 1 IN_MODIFY; "echo xxx > file" = truncate + write = 2 IN_MODIFY)
Here is a proposition for your program (with additional prints):
#include <stdio.h>
#include <sys/inotify.h>
#include <unistd.h>
#include <stdlib.h>
#define EVENT_BUF_LEN 4096
#define EVENT_SIZE sizeof(struct inotify_event)
typedef struct{
int length, fd, wd1, wd2;
char buffer[EVENT_BUF_LEN] __attribute__ ((aligned(__alignof__(struct inotify_event))));
} notification;
notification inotify;
int getNotified(char *pathname1, char *pathname2){
inotify.fd = inotify_init();
inotify.wd1 = inotify_add_watch(inotify.fd, pathname1, IN_MODIFY);
printf("wd1 = %d\n", inotify.wd1);
inotify.wd2 = inotify_add_watch(inotify.fd, pathname2, IN_MODIFY);
printf("wd2 = %d\n", inotify.wd2);
while(1){
inotify.length = read(inotify.fd, inotify.buffer, EVENT_BUF_LEN);
int i = 0;
printf("read() = %d\n", inotify.length);
while(i < inotify.length){
struct inotify_event *event = (struct inotify_event *)&inotify.buffer[i];
printf("event->len = %u\n", event->len);
if(event->mask & IN_MODIFY){
if(event->wd == inotify.wd1){
printf("Pathname1 is modified\n");
} else if (event->wd == inotify.wd2){
printf("Pathname2 is modified\n");
}
}
i += (EVENT_SIZE + event->len);
printf("i=%d\n", i);
}
}
inotify_rm_watch(inotify.fd, inotify.wd1);
inotify_rm_watch(inotify.fd, inotify.wd2);
close(inotify.fd);
exit(0);
}
int main(void)
{
getNotified("/tmp/foo", "/tmp/bar");
return 0;
} // main
Here is an example of execution:
$ gcc notif.c -o notif
$ > /tmp/foo
$ > /tmp/bar
$ ./notif
wd1 = 1
wd2 = 2
====== Upon "> /tmp/foo": 1 event (truncate operation)
read() = 16
event->len = 0
Pathname1 is modified
i=16
====== Upon "echo qwerty > /tmp/foo": 2 events (write operation, one event for truncate operation and one for the write of "qwerty" at the beginning of the file)
read() = 16
event->len = 0
Pathname1 is modified
i=16
read() = 16
event->len = 0
Pathname1 is modified
i=16
====== Upon "echo qwerty >> /tmp/foo": 1 event (write of "qwerty" at the end of the file)
read() = 16
event->len = 0
Pathname1 is modified
i=16
If the two pathnames refer to the same inode, then inotify.wd1 == inotify.wd2. In that case, because you have
if (event->wd == inotify.wd1) {
printf("Pathname1 '%s' is modified\n", event->name);
}
if (event->wd == inotify.wd2) {
printf("Pathname2 '%s' is modified\n", event->name);
}
both bodies would be executed; but the outputs would differ (Pathname1 ... and Pathname2 ...).
You really should be monitoring the directories the files reside in, rather than the actual pathnames, so you can catch rename events also. (Many editors create a temporary file, and rename or hardlink the temporary file over the old file, so that programs see either the old or the new file, and never a mix of the two.)
Consider the following program, which does not exhibit any undue duplication of events:
// SPDX-License-Identifier: CC0-1.0
#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/inotify.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
static volatile sig_atomic_t done = 0;
static void handle_done(int signum)
{
done = signum;
}
static int install_done(int signum)
{
struct sigaction act;
memset(&act, 0, sizeof act);
sigemptyset(&act.sa_mask);
act.sa_handler = handle_done;
act.sa_flags = 0;
return sigaction(signum, &act, NULL);
}
struct monitor {
/* Supplied by caller */
const char *directory;
const char *pathname;
int (*modified)(struct monitor *);
int (*completed)(struct monitor *);
/* Reserved for internal use */
int dirwatch;
};
int monitor_files(struct monitor *const list, const size_t count)
{
char *events_ptr = NULL;
size_t events_len = 65536;
size_t i;
int err;
/* Verify sane parameters */
if (count < 1) {
errno = ENOENT;
return -1;
} else
if (!list) {
errno = EINVAL;
return -1;
}
for (i = 0; i < count; i++) {
if (!list[i].directory || !list[i].directory[0]) {
errno = EINVAL;
return -1;
}
if (!list[i].pathname || !list[i].pathname[0]) {
errno = EINVAL;
return -1;
}
list[i].dirwatch = -1;
}
/* Obtain a descriptor for inotify event queue */
int queue = inotify_init1(IN_CLOEXEC);
if (queue == -1) {
/* errno set by inotify_init1() */
return -1;
}
/* Use a reasonable dynamically allocated buffer for events */
events_ptr = malloc(events_len);
if (!events_ptr) {
close(queue);
errno = ENOMEM;
return -1;
}
/* Add a watch for each directory to be watched */
for (i = 0; i < count; i++) {
list[i].dirwatch = inotify_add_watch(queue, list[i].directory, IN_CLOSE_WRITE | IN_MOVED_TO | IN_MODIFY);
if (list[i].dirwatch == -1) {
err = errno;
close(queue);
free(events_ptr);
errno = err;
return -1;
}
}
/* inotify event loop */
err = 0;
while (!done) {
ssize_t len = read(queue, events_ptr, events_len);
if (len == -1) {
/* Interrupted due to signal delivery? */
if (errno == EINTR)
continue;
/* Error */
err = errno;
break;
} else
if (len < -1) {
/* Should never occur */
err = EIO;
break;
} else
if (len == 0) {
/* No events watched anymore */
err = 0;
break;
}
char *const end = events_ptr + len;
char *ptr = events_ptr;
while (ptr < end) {
struct inotify_event *event = (struct inotify_event *)ptr;
/* Advance buffer pointer for next event */
ptr += sizeof (struct inotify_event) + event->len;
if (ptr > end) {
close(queue);
free(events_ptr);
errno = EIO;
return -1;
}
/* Call all event handlers, even duplicate ones */
for (i = 0; i < count; i++) {
if (event->wd == list[i].dirwatch && !strcmp(event->name, list[i].pathname)) {
if ((event->mask & (IN_MOVED_TO | IN_CLOSE_WRITE)) && list[i].completed) {
err = list[i].completed(list + i);
if (err)
break;
} else
if ((event->mask & IN_MODIFY) && list[i].modified) {
err = list[i].modified(list + i);
if (err)
break;
}
}
}
if (err)
break;
}
if (err)
break;
}
close(queue);
free(events_ptr);
errno = 0;
return err;
}
static int report_modified(struct monitor *m)
{
printf("%s/%s: Modified\n", m->directory, m->pathname);
fflush(stdout);
return 0;
}
static int report_completed(struct monitor *m)
{
printf("%s/%s: Completed\n", m->directory, m->pathname);
fflush(stdout);
return 0;
}
int main(void)
{
struct monitor watch[2] = {
{ .directory = ".",
.pathname = "file1",
.modified = report_modified,
.completed = report_completed },
{ .directory = ".",
.pathname = "file2",
.modified = report_modified,
.completed = report_completed }
};
int err;
if (install_done(SIGINT) == -1 ||
install_done(SIGHUP) == -1 ||
install_done(SIGTERM) == -1) {
fprintf(stderr, "Cannot set signal handlers: %s.\n", strerror(errno));
return EXIT_FAILURE;
}
fprintf(stderr, "To stop this program, press Ctrl+C, or send\n");
fprintf(stderr, "INT, HUP, or TERM signal (to process %ld).\n", (long)getpid());
fflush(stderr);
err = monitor_files(watch, 2);
if (err == -1) {
fprintf(stderr, "Error monitoring files: %s.\n", strerror(errno));
return EXIT_FAILURE;
} else
if (err) {
fprintf(stderr, "Monitoring files failed [%d].\n", err);
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
If you compile it using e.g. gcc -Wall -Wextra -O2 example.c -o example and run it via ./example, it will report IN_MODIFY events (as "Modified") and IN_CLOSE_WRITE and IN_MOVED_TO events (as "Completed") for file1 and file2 in the same directory (current working directory). To exit the program, press Ctrl+C.
(Note that we should probably add third event type, "Deleted", corresponding to IN_DELETE and IN_MOVED_FROM events.)
If you open file1 or file2 in say a text editor, saving the file generates one or more Modified (IN_MODIFY) events, and exactly one Completed (IN_CLOSE_WRITE or IN_MOVED_TO) event. This is because each open()/truncate()/ftruncate() syscall that causes the file to be truncated, generates one IN_MODIFY event for that file; as does every underlying write() syscall that modifies the file contents. Thus, it is natural to receive multiple IN_MODIFY events when some process modifies the file.
If you have multiple struct monitor entries in the list with the same effective directory and the same pathname, the example program will provide multiple events for them. If you wish to avoid this, just make sure that whenever .pathname matches, the two get differing .dirwatches.
rewriting the while() loop into a for() loop, and flattening out the if()s"
while(1){
int i ;
struct inotify_event *event ;
inotify.length = read(inotify.fd, inotify.buffer, EVENT_BUF_LEN);
for(i=0; i < inotify.length; i += EVENT_SIZE + event->len ) {
event = (struct inotify_event *)&inotify.buffer[i];
if (!event->len) continue;
if (!(event->mask & IN_MODIFY)) continue;
if (event->wd == inotify.wd1){
printf("Pathname1 '%s' is modified\n", event->name);
continue;
}
if (event->wd == inotify.wd2){
printf("Pathname2 '%s' is modified\n", event->name);
continue;
}
}
}

file mapping vs file system synchronization

I have a file with some data, which is also memory-mapped. So that I have both file descriptor and the pointer to the mapped pages. Mostly the data is only read from the mapping, but eventually it's also modified.
The modification consists of modifying some data within the file (sort of headers update), plus appending some new data (i.e. writing post the current end of the file).
This data structure is accessed from different threads, and to prevent collisions I synchronize access to it (mutex and friends).
During the modification I use both the file mapping and the file descriptor. Headers are updated implicitly by modifying the mapped memory, whereas the new data is written to the file by the appropriate API (WriteFile on windows, write on posix). Worth to note that the new data and the headers belong to different pages.
Since the modification changes the file size, the memory mapping is re-initialized after every such a modification. That is, it's unmapped, and then mapped again (with the new size).
I realize that writes to the mapped memory are "asynchronous" wrt file system, and order is not guaranteed, but I thought there was no problem because I explicitly close the file mapping, which should (IMHO) act as a sort of a flushing point.
Now this works without problem on windows, but on linux (android to be exact) eventually the mapped data turns-out to be inconsistent temporarily (i.e. data is ok when retrying). Seems like it doesn't reflect the newly-appended data.
Do I have to call some synchronization API to ensure the data if flushed properly? If so, which one should I use: sync, msync, syncfs or something different?
Thanks in advance.
EDIT:
This is a pseudo-code that illustrates the scenario I'm dealing with.
(The real code is more complex of course)
struct CompressedGrid
{
mutex m_Lock;
int m_FileHandle;
void* m_pMappedMemory;
Hdr* get_Hdr() { return /* the mapped memory with some offset*/; }
void SaveGridCell(int idx, const Cell& cCompressed)
{
AutoLock scope(m_Lock);
// Write to mapped memory
get_Hdr()->m_pCellOffset[Idx] = /* current end of file */;
// Append the data
lseek64(m_FileHandle, 0, FILE_END);
write(m_FileHandle, cCompressed.pPtr, cCompressed.nSize);
// re-map
munmap(...);
m_pMappedMemory = mmap(...); // specify the new file size of course
}
bool DecodeGridCell(int idx, Cell& cRaw)
{
AutoLock scope(m_Lock);
uint64_t nOffs = get_Hdr()->m_pCellOffset[Idx] = /* ;
if (!nOffs)
return false; // unavail
const uint8_t* p = m_pMappedMemory + nOffs;
cRaw.DecodeFrom(p); // This is where the problem appears!
return true;
}
Use addr = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_NORESERVE, fd, offset) to map the file.
If the size of the file changes, use newaddr = mremap(addr, len, newlen, MREMAP_MAYMOVE) to update the mapping to reflect it. To extend the file, use ftruncate(fd, newlen) before remapping the file.
You can use mprotect(addr, len, protflags) to change the protection (read/write) on any pages in the mapping (both must be aligned on a page boundary). You can also tell the kernel about your future accesses via madvise(), if the mapping is too large to fit in memory at once, but the kernel seems pretty darned good at managing readahead etc. even without those.
When you make changes to the mapping, use msync(partaddr, partlen, MS_SYNC | MS_INVALIDATE) or msync(partaddr, partlen, MS_ASYNC | MS_INVALIDATE) to ensure the changes int partlen chars from partaddr forward are visible to other mappings and file readers. If you use MS_SYNC, the call returns only when the update is complete. The MS_ASYNC call tells the kernel to do the update, but won't wait until it is done. If there are no other memory maps of the file, the MS_INVALIDATE does nothing; but if there are, that tells the kernel to ensure the changes are reflected in those too.
In Linux kernels since 2.6.19, MS_ASYNC does nothing, as the kernel tracks the changes properly anyway (no msync() is needed, except possibly before munmap()). I don't know if Android kernels have patches that change that behaviour; I suspect not. It is still a good idea to keep them in the code, for portability across POSIXy systems.
mapped data turns-out to be inconsistent temporarily
Well, unless you do use msync(partaddr, partlen, MS_SYNC | MS_INVALIDATE), the kernel will do the update when it sees best.
So, if you need some changes to be visible to file readers before proceeding, use msync(areaptr, arealen, MS_SYNC | MS_INVALIDATE) in the process doing those updates.
If you don't care about the exact moment, use msync(areaptr, arealen, MS_ASYNC | MS_INVALIDATE). It'll be a no-op on current Linux kernels, but it's a good idea to keep them for portability (perhaps commented out, if necessary for performance) and to remind developers about the (lack of) synchronization expectations.
As I commented to OP, I cannot observe the synchronization issues on Linux at all. (That does not mean it does not happen on Android, because Android kernels are derivatives of Linux kernels, not exactly the same.)
I do believe the msync() call is not needed on Linux kernels since 2.6.19 at all, as long as the mapping uses flags MAP_SHARED | MAP_NORESERVE, and the underlying file is not opened using the O_DIRECT flag. The reason for this belief is that in this case, both mapping and file accesses should use the exact same page cache pages.
Here are two test programs, that can be used to explore this on Linux. First, a single-process test, test-single.c:
#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
static inline int read_from(const int fd, void *const to, const size_t len, const off_t offset)
{
char *p = (char *)to;
char *const q = (char *)to + len;
ssize_t n;
if (lseek(fd, offset, SEEK_SET) != offset)
return errno = EIO;
while (p < q) {
n = read(fd, p, (size_t)(q - p));
if (n > 0)
p += n;
else
if (n != -1)
return errno = EIO;
else
if (errno != EINTR)
return errno;
}
return 0;
}
static inline int write_to(const int fd, const void *const from, const size_t len, const off_t offset)
{
const char *const q = (const char *)from + len;
const char *p = (const char *)from;
ssize_t n;
if (lseek(fd, offset, SEEK_SET) != offset)
return errno = EIO;
while (p < q) {
n = write(fd, p, (size_t)(q - p));
if (n > 0)
p += n;
else
if (n != -1)
return errno = EIO;
else
if (errno != EINTR)
return errno;
}
return 0;
}
int main(int argc, char *argv[])
{
unsigned long tests, n, merrs = 0, werrs = 0;
size_t page;
long *map, data[2];
int fd;
char dummy;
if (argc != 3) {
fprintf(stderr, "\n");
fprintf(stderr, "Usage: %s FILENAME COUNT\n", argv[0]);
fprintf(stderr, "\n");
fprintf(stderr, "This program will test synchronization between a memory map\n");
fprintf(stderr, "and reading/writing the underlying file, COUNT times.\n");
fprintf(stderr, "\n");
return EXIT_FAILURE;
}
if (sscanf(argv[2], " %lu %c", &tests, &dummy) != 1 || tests < 1) {
fprintf(stderr, "%s: Invalid number of tests to run.\n", argv[2]);
return EXIT_FAILURE;
}
/* Create the file. */
page = sysconf(_SC_PAGESIZE);
fd = open(argv[1], O_RDWR | O_CREAT | O_EXCL, 0644);
if (fd == -1) {
fprintf(stderr, "%s: Cannot create file: %s.\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
if (ftruncate(fd, page) == -1) {
fprintf(stderr, "%s: Cannot resize file: %s.\n", argv[1], strerror(errno));
unlink(argv[1]);
return EXIT_FAILURE;
}
/* Map it. */
map = mmap(NULL, page, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_NORESERVE, fd, 0);
if (map == MAP_FAILED) {
fprintf(stderr, "%s: Cannot map file: %s.\n", argv[1], strerror(errno));
unlink(argv[1]);
close(fd);
return EXIT_FAILURE;
}
/* Test loop. */
for (n = 0; n < tests; n++) {
/* Update map. */
map[0] = (long)(n + 1);
map[1] = (long)(~n);
/* msync(map, 2 * sizeof map[0], MAP_SYNC | MAP_INVALIDATE); */
/* Check the file contents. */
if (read_from(fd, data, sizeof data, 0)) {
fprintf(stderr, "read_from() failed: %s.\n", strerror(errno));
munmap(map, page);
unlink(argv[1]);
close(fd);
return EXIT_FAILURE;
}
werrs += (data[0] != (long)(n + 1) || data[1] != (long)(~n));
/* Update data. */
data[0] = (long)(n * 386131);
data[1] = (long)(n * -257);
if (write_to(fd, data, sizeof data, 0)) {
fprintf(stderr, "write_to() failed: %s.\n", strerror(errno));
munmap(map, page);
unlink(argv[1]);
close(fd);
return EXIT_FAILURE;
}
merrs += (map[0] != (long)(n * 386131) || map[1] != (long)(n * -257));
}
munmap(map, page);
unlink(argv[1]);
close(fd);
if (!werrs && !merrs)
printf("No errors detected.\n");
else {
if (!werrs)
printf("Detected %lu times (%.3f%%) when file contents were incorrect.\n",
werrs, 100.0 * (double)werrs / (double)tests);
if (!merrs)
printf("Detected %lu times (%.3f%%) when mapping was incorrect.\n",
merrs, 100.0 * (double)merrs / (double)tests);
}
return EXIT_SUCCESS;
}
Compile and run using e.g.
gcc -Wall -O2 test-single -o single
./single temp 1000000
to test a million times, whether the mapping and the file contents stay in sync, when both accesses are done in the same process. Note that the msync() call is commented out, because on my machine it is not needed: I never see any errors/desynchronization during testing even without it.
The test rate on my machine is about 550,000 tests per second. Note that each tests does it both ways, so includes a read and a write. I just cannot get this to detect any errors. It is written to be quite sensitive to errors, too.
The second test program uses two child processes and a POSIX realtime signal to tell the other process to check the contents. test-multi.c:
#define _POSIX_C_SOURCE 200809L
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#define NOTIFY_SIGNAL (SIGRTMIN+0)
int mapper_process(const int fd, const size_t len)
{
long value = 1, count[2] = { 0, 0 };
long *data;
siginfo_t info;
sigset_t sigs;
int signum;
if (fd == -1) {
fprintf(stderr, "mapper_process(): Invalid file descriptor.\n");
return EXIT_FAILURE;
}
data = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_NORESERVE, fd, 0);
if (data == MAP_FAILED) {
fprintf(stderr, "mapper_process(): Cannot map file.\n");
return EXIT_FAILURE;
}
sigemptyset(&sigs);
sigaddset(&sigs, NOTIFY_SIGNAL);
sigaddset(&sigs, SIGINT);
sigaddset(&sigs, SIGHUP);
sigaddset(&sigs, SIGTERM);
while (1) {
/* Wait for the notification. */
signum = sigwaitinfo(&sigs, &info);
if (signum == -1) {
if (errno == EINTR)
continue;
fprintf(stderr, "mapper_process(): sigwaitinfo() failed: %s.\n", strerror(errno));
munmap(data, len);
return EXIT_FAILURE;
}
if (signum != NOTIFY_SIGNAL)
break;
/* A notify signal was received. Check the write counter. */
count[ (data[0] == value) ]++;
/* Update. */
data[0] = value++;
data[1] = -(value++);
/* Synchronize */
/* msync(data, 2 * sizeof (data[0]), MS_SYNC | MS_INVALIDATE); */
/* And let the writer know. */
kill(info.si_pid, NOTIFY_SIGNAL);
}
/* Print statistics. */
printf("mapper_process(): %lu errors out of %lu cycles (%.3f%%)\n",
count[0], count[0] + count[1], 100.0 * (double)count[0] / (double)(count[0] + count[1]));
fflush(stdout);
munmap(data, len);
return EXIT_SUCCESS;
}
static inline int read_from(const int fd, void *const to, const size_t len, const off_t offset)
{
char *p = (char *)to;
char *const q = (char *)to + len;
ssize_t n;
if (lseek(fd, offset, SEEK_SET) != offset)
return errno = EIO;
while (p < q) {
n = read(fd, p, (size_t)(q - p));
if (n > 0)
p += n;
else
if (n != -1)
return errno = EIO;
else
if (errno != EINTR)
return errno;
}
return 0;
}
static inline int write_to(const int fd, const void *const from, const size_t len, const off_t offset)
{
const char *const q = (const char *)from + len;
const char *p = (const char *)from;
ssize_t n;
if (lseek(fd, offset, SEEK_SET) != offset)
return errno = EIO;
while (p < q) {
n = write(fd, p, (size_t)(q - p));
if (n > 0)
p += n;
else
if (n != -1)
return errno = EIO;
else
if (errno != EINTR)
return errno;
}
return 0;
}
int writer_process(const int fd, const size_t len, const pid_t other)
{
long data[2] = { 0, 0 }, count[2] = { 0, 0 };
long value = 0;
siginfo_t info;
sigset_t sigs;
int signum;
sigemptyset(&sigs);
sigaddset(&sigs, NOTIFY_SIGNAL);
sigaddset(&sigs, SIGINT);
sigaddset(&sigs, SIGHUP);
sigaddset(&sigs, SIGTERM);
while (1) {
/* Update. */
data[0] = ++value;
data[1] = -(value++);
/* then write the data. */
if (write_to(fd, data, sizeof data, 0)) {
fprintf(stderr, "writer_process(): write_to() failed: %s.\n", strerror(errno));
return EXIT_FAILURE;
}
/* Let the mapper know. */
kill(other, NOTIFY_SIGNAL);
/* Wait for the notification. */
signum = sigwaitinfo(&sigs, &info);
if (signum == -1) {
if (errno == EINTR)
continue;
fprintf(stderr, "writer_process(): sigwaitinfo() failed: %s.\n", strerror(errno));
return EXIT_FAILURE;
}
if (signum != NOTIFY_SIGNAL || info.si_pid != other)
break;
/* Reread the file. */
if (read_from(fd, data, sizeof data, 0)) {
fprintf(stderr, "writer_process(): read_from() failed: %s.\n", strerror(errno));
return EXIT_FAILURE;
}
/* Check the read counter. */
count[ (data[1] == -value) ]++;
}
/* Print statistics. */
printf("writer_process(): %lu errors out of %lu cycles (%.3f%%)\n",
count[0], count[0] + count[1], 100.0 * (double)count[0] / (double)(count[0] + count[1]));
fflush(stdout);
return EXIT_SUCCESS;
}
int main(int argc, char *argv[])
{
struct timespec duration;
double seconds;
pid_t mapper, writer, p;
size_t page;
siginfo_t info;
sigset_t sigs;
int fd, status;
char dummy;
if (argc != 3) {
fprintf(stderr, "\n");
fprintf(stderr, "Usage: %s FILENAME SECONDS\n", argv[0]);
fprintf(stderr, "\n");
fprintf(stderr, "This program will test synchronization between a memory map\n");
fprintf(stderr, "and reading/writing the underlying file.\n");
fprintf(stderr, "The test will run for the specified time, or indefinitely\n");
fprintf(stderr, "if SECONDS is zero, but you can also interrupt it with\n");
fprintf(stderr, "Ctrl+C (INT signal).\n");
fprintf(stderr, "\n");
return EXIT_FAILURE;
}
if (sscanf(argv[2], " %lf %c", &seconds, &dummy) != 1) {
fprintf(stderr, "%s: Invalid number of seconds to run.\n", argv[2]);
return EXIT_FAILURE;
}
if (seconds > 0) {
duration.tv_sec = (time_t)seconds;
duration.tv_nsec = (long)(1000000000 * (seconds - (double)(duration.tv_sec)));
} else {
duration.tv_sec = 0;
duration.tv_nsec = 0;
}
/* Block INT, HUP, CHLD, and the notification signal. */
sigemptyset(&sigs);
sigaddset(&sigs, SIGINT);
sigaddset(&sigs, SIGHUP);
sigaddset(&sigs, SIGCHLD);
sigaddset(&sigs, NOTIFY_SIGNAL);
if (sigprocmask(SIG_BLOCK, &sigs, NULL) == -1) {
fprintf(stderr, "Cannot block the necessary signals: %s.\n", strerror(errno));
return EXIT_FAILURE;
}
/* Create the file. */
page = sysconf(_SC_PAGESIZE);
fd = open(argv[1], O_RDWR | O_CREAT | O_EXCL, 0644);
if (fd == -1) {
fprintf(stderr, "%s: Cannot create file: %s.\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
if (ftruncate(fd, page) == -1) {
fprintf(stderr, "%s: Cannot resize file: %s.\n", argv[1], strerror(errno));
unlink(argv[1]);
return EXIT_FAILURE;
}
close(fd);
fd = -1;
/* Ensure streams are flushed before forking. They should be, we're just paranoid here. */
fflush(stdout);
fflush(stderr);
/* Fork the mapper child process. */
mapper = fork();
if (mapper == -1) {
fprintf(stderr, "Cannot fork mapper child process: %s.\n", strerror(errno));
unlink(argv[1]);
return EXIT_FAILURE;
}
if (!mapper) {
fd = open(argv[1], O_RDWR);
if (fd == -1) {
fprintf(stderr, "mapper_process(): %s: Cannot open file: %s.\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
status = mapper_process(fd, page);
close(fd);
return status;
}
/* For the writer child process. (mapper contains the PID of the mapper process.) */
writer = fork();
if (writer == -1) {
fprintf(stderr, "Cannot fork writer child process: %s.\n", strerror(errno));
unlink(argv[1]);
kill(mapper, SIGKILL);
return EXIT_FAILURE;
}
if (!writer) {
fd = open(argv[1], O_RDWR);
if (fd == -1) {
fprintf(stderr, "writer_process(): %s: Cannot open file: %s.\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
status = writer_process(fd, page, mapper);
close(fd);
return status;
}
/* Wait for a signal. */
if (duration.tv_sec || duration.tv_nsec)
status = sigtimedwait(&sigs, &info, &duration);
else
status = sigwaitinfo(&sigs, &info);
/* Whatever it was, we kill the child processes. */
kill(mapper, SIGHUP);
kill(writer, SIGHUP);
do {
p = waitpid(-1, NULL, 0);
} while (p != -1 || errno == EINTR);
/* Cleanup. */
unlink(argv[1]);
printf("Done.\n");
return EXIT_SUCCESS;
}
Note that the child processes open the temporary file separately. To compile and run, use e.g.
gcc -Wall -O2 test-multi.c -o multi
./multi temp 10
The second parameter is the duration of the test, in seconds. (You can interrupt the testing safely using SIGINT (Ctrl+C) or SIGHUP.)
On my machine, the test rate is roughly 120,000 tests per second; the msync() call is commented out here also, because I don't ever see any errors/desynchronization even without it. (Plus, msync(ptr, len, MS_SYNC) and msync(ptr, len, MS_SYNC | MS_INVALIDATE) are horribly slow; with either, I can get less than 1000 tests per second, with absolutely no difference in the results. That's a 100x slowdown.)
The MAP_NORESERVE flag to mmap tells it to use the file itself as backing storage when under memory pressure, rather than swap. If you compile the code on a system that does not recognize that flag, you can omit it. As long as the mapping is not evicted from RAM, the flag does not affect the operation at all.

How to properly set up ALSA device

Edit: This question is different than the proposed duplicate because I'm asking How do you set the period/buffer size that will work with multiple targets each with different sound hardware?.
I have created some code that attempts to set up ALSA before playback of an OGG file. The code below works on one embedded Linux platform, but on another it fails with the following output:
Error setting buffersize.
Playback open error: Operation not permitted
I've included only the code that demonstrates the issue. setup_alsa() is not complete and won't completely configure an alsa device.
#include <alsa/asoundlib.h>
char *buffer;
static char *device = "default";
snd_pcm_uframes_t periodsize = 8192; /* Periodsize (bytes) */
int setup_alsa(snd_pcm_t *handle)
{
int rc;
int dir = 0;
snd_pcm_uframes_t periods; /* Number of fragments/periods */
snd_pcm_hw_params_t *params;
snd_pcm_sw_params_t *sw_params;
int rate = 44100;
int exact_rate;
int i = 0;
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(&params);
/* Fill it in with default values. */
if (snd_pcm_hw_params_any(handle, params) < 0)
{
fprintf(stderr, "Can not configure this PCM device.\n");
snd_pcm_close(handle);
return(-1);
}
/* Set number of periods. Periods used to be called fragments. */
periods = 4;
if ( snd_pcm_hw_params_set_periods(handle, params, periods, 0) < 0 )
{
fprintf(stderr, "Error setting periods.\n");
snd_pcm_close(handle);
return(-1);
}
/* Set buffer size (in frames). The resulting latency is given by */
/* latency = periodsize * periods / (rate * bytes_per_frame) */
if (snd_pcm_hw_params_set_buffer_size(handle, params, (periodsize * periods)>>2) < 0)
{
fprintf(stderr, "Error setting buffersize.\n");
snd_pcm_close(handle);
return(-1);
}
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0)
{
fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc));
snd_pcm_close(handle);
return -1;
}
snd_pcm_hw_params_free(params);
What is the normal way to setup ALSA that doesn't require a specific buffer/period size be set that provides smooth audio playback?**
As it turns out, I can program my ALSA setup routine to let ALSA determine what the nearest working period/buffer size is by using snd_pcm_hw_params_set_buffer_size_near() instead of snd_pcm_hw_params_set_buffer_size().
The following code now works on both platforms:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <vorbis/vorbisfile.h>
#include <alsa/asoundlib.h>
char *buffer;
//static char *device = "default";
static char *device = "plughw:0,0";
snd_pcm_uframes_t periodsize = 4096; /* Periodsize (bytes) */
int setup_alsa(snd_pcm_t *handle)
{
int rc;
int dir = 0;
snd_pcm_uframes_t periods; /* Number of fragments/periods */
snd_pcm_hw_params_t *params;
snd_pcm_sw_params_t *sw_params;
int rate = 44100;
int exact_rate;
int i = 0;
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_malloc(&params);
/* Fill it in with default values. */
if (snd_pcm_hw_params_any(handle, params) < 0)
{
fprintf(stderr, "Can not configure this PCM device.\n");
snd_pcm_close(handle);
return(-1);
}
/* Set the desired hardware parameters. */
/* Non-Interleaved mode */
snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_NONINTERLEAVED);
snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
/* 44100 bits/second sampling rate (CD quality) */
/* Set sample rate. If the exact rate is not supported */
/* by the hardware, use nearest possible rate. */
exact_rate = rate;
if (snd_pcm_hw_params_set_rate_near(handle, params, &exact_rate, 0) < 0)
{
fprintf(stderr, "Error setting rate.\n");
snd_pcm_close(handle);
return(-1);
}
if (rate != exact_rate)
{
fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n==> Using %d Hz instead.\n", rate, exact_rate);
}
/* Set number of channels to 1 */
if( snd_pcm_hw_params_set_channels(handle, params, 1 ) < 0 )
{
fprintf(stderr, "Error setting channels.\n");
snd_pcm_close(handle);
return(-1);
}
/* Set number of periods. Periods used to be called fragments. */
periods = 4;
if ( snd_pcm_hw_params_set_periods(handle, params, periods, 0) < 0 )
{
fprintf(stderr, "Error setting periods.\n");
snd_pcm_close(handle);
return(-1);
}
snd_pcm_uframes_t size = (periodsize * periods) >> 2;
if( (rc = snd_pcm_hw_params_set_buffer_size_near( handle, params, &size )) < 0)
{
fprintf(stderr, "Error setting buffersize: [%s]\n", snd_strerror(rc) );
snd_pcm_close(handle);
return(-1);
}
else
{
printf("Buffer size = %lu\n", (unsigned long)size);
}
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0)
{
fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc));
snd_pcm_close(handle);
return -1;
}
snd_pcm_hw_params_free(params);
/* Allocate a software parameters object. */
rc = snd_pcm_sw_params_malloc(&sw_params);
if( rc < 0 )
{
fprintf (stderr, "cannot allocate software parameters structure (%s)\n", snd_strerror(rc) );
return(-1);
}
rc = snd_pcm_sw_params_current(handle, sw_params);
if( rc < 0 )
{
fprintf (stderr, "cannot initialize software parameters structure (%s)\n", snd_strerror(rc) );
return(-1);
}
if((rc = snd_pcm_sw_params_set_avail_min(handle, sw_params, 1024)) < 0)
{
fprintf (stderr, "cannot set minimum available count (%s)\n", snd_strerror (rc));
return(-1);
}
rc = snd_pcm_sw_params_set_start_threshold(handle, sw_params, 1);
if( rc < 0 )
{
fprintf(stderr, "Error setting start threshold\n");
snd_pcm_close(handle);
return -1;
}
if((rc = snd_pcm_sw_params(handle, sw_params)) < 0)
{
fprintf (stderr, "cannot set software parameters (%s)\n", snd_strerror (rc));
return(-1);
}
snd_pcm_sw_params_free(sw_params);
return 0;
}
/* copied from libvorbis source */
int ov_fopen(const char *path, OggVorbis_File *vf)
{
int ret = 0;
FILE *f = fopen(path, "rb");
if( f )
{
ret = ov_open(f, vf, NULL, 0);
if( ret )
{
fclose(f);
}
}
else
{
ret = -1;
}
return( ret );
}
int main(int argc, char *argv[])
{
// sample rate * bytes per sample * channel count * seconds
//int bufferSize = 44100 * 2 * 1 * 2;
int err;
snd_pcm_t *handle;
snd_pcm_sframes_t frames;
buffer = (char *) malloc( periodsize );
if( buffer )
{
if((err = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0)) < 0)
{
printf("Playback open error #1: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
if(err = setup_alsa(handle))
{
printf("Playback open error #2: %s\n", snd_strerror(err));
exit(EXIT_FAILURE);
}
OggVorbis_File vf;
int eof = 0;
int current_section;
err = ov_fopen(argv[1], &vf);
if(err != 0)
{
perror("Error opening file");
}
else
{
vorbis_info *vi = ov_info(&vf, -1);
fprintf(stderr, "Bitstream is %d channel, %ldHz\n", vi->channels, vi->rate);
fprintf(stderr, "Encoded by: %s\n\n", ov_comment(&vf, -1)->vendor);
while(!eof)
{
long ret = ov_read(&vf, buffer, periodsize, 0, 2, 1, &current_section);
if(ret == 0)
{
/* EOF */
eof = 1;
}
else if(ret < 0)
{
/* error in the stream. */
fprintf( stderr, "ov_read error %l", ret );
}
else
{
frames = snd_pcm_writen(handle, (void *)&buffer, ret/2);
if(frames < 0)
{
printf("snd_pcm_writen failed: %s\n", snd_strerror(frames));
if( frames == -EPIPE )
{
snd_pcm_prepare(handle);
//frames = snd_pcm_writen(handle, (void *)&buffer, ret/2);
}
else
{
break;
}
}
}
}
ov_clear(&vf);
}
free( buffer );
snd_pcm_drain(handle);
snd_pcm_close(handle);
}
return 0;
}

Webcam library for C on Linux? [closed]

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Is there any c library to get a video from the webcam on linux?
A lot of us use OpenCV (cross-platform Computer Vision library, currently on v2.1)
The following snippet grabs frames from camera, converts them to grayscale and displays them on the screen:
#include <stdio.h>
#include "cv.h"
#include "highgui.h"
typedef IplImage* (*callback_prototype)(IplImage*);
/*
* make_it_gray: custom callback to convert a colored frame to its grayscale version.
* Remember that you must deallocate the returned IplImage* yourself after calling this function.
*/
IplImage* make_it_gray(IplImage* frame)
{
// Allocate space for a new image
IplImage* gray_frame = 0;
gray_frame = cvCreateImage(cvSize(frame->width, frame->height), frame->depth, 1);
if (!gray_frame)
{
fprintf(stderr, "!!! cvCreateImage failed!\n" );
return NULL;
}
cvCvtColor(frame, gray_frame, CV_RGB2GRAY);
return gray_frame;
}
/*
* process_video: retrieves frames from camera and executes a callback to do individual frame processing.
* Keep in mind that if your callback takes too much time to execute, you might loose a few frames from
* the camera.
*/
void process_video(callback_prototype custom_cb)
{
// Initialize camera
CvCapture *capture = 0;
capture = cvCaptureFromCAM(-1);
if (!capture)
{
fprintf(stderr, "!!! Cannot open initialize webcam!\n" );
return;
}
// Create a window for the video
cvNamedWindow("result", CV_WINDOW_AUTOSIZE);
IplImage* frame = 0;
char key = 0;
while (key != 27) // ESC
{
frame = cvQueryFrame(capture);
if(!frame)
{
fprintf( stderr, "!!! cvQueryFrame failed!\n" );
break;
}
// Execute callback on each frame
IplImage* processed_frame = (*custom_cb)(frame);
// Display processed frame
cvShowImage("result", processed_frame);
// Release resources
cvReleaseImage(&processed_frame);
// Exit when user press ESC
key = cvWaitKey(10);
}
// Free memory
cvDestroyWindow("result");
cvReleaseCapture(&capture);
}
int main( int argc, char **argv )
{
process_video(make_it_gray);
return 0;
}
v4l2 official examples
What you get:
./v4l2grab: capture a few snapshots to files outNNN.ppm
./v4l2gl: show video live on a window using an OpenGL texture (immediate rendering, hey!) and raw X11 windowing (plus GLUT's gluLookAt for good measure).
How to get it on Ubuntu 16.04:
sudo apt-get install libv4l-dev
sudo apt-get build-dep libv4l-dev
git clone git://linuxtv.org/v4l-utils.git
cd v4l-utils
# Matching the installed version of dpkg -s libv4l-dev
git checkout v4l-utils-1.10.0
./bootstrap.sh
./configure
make
# TODO: fails halfway, but it does not matter for us now.
cd contrib/tests
make
It is also easy to use those examples outside of the Git tree, just copy them out, make relative includes "" absolute <>, and remove config.h. I've done that for you at: https://github.com/cirosantilli/cpp-cheat/tree/09fe73d248f7da2e9c9f3eff2520a143c259f4a6/v4l2
Minimal example from docs
The docs 4.9.0 contain what appears to be a minimal version of ./v4l2grab at https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/v4l2grab-example.html. I needed to patch it minimally and I've sent the patch to http://www.spinics.net/lists/linux-media/ (their docs live in the Linux kernel tree as rst, neat), where it was dully ignored.
Usage:
gcc v4l2grab.c -lv4l2
./a.out
Patched code:
/* V4L2 video picture grabber
Copyright (C) 2009 Mauro Carvalho Chehab <mchehab#infradead.org>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <libv4l2.h>
#define CLEAR(x) memset(&(x), 0, sizeof(x))
struct buffer {
void *start;
size_t length;
};
static void xioctl(int fh, int request, void *arg)
{
int r;
do {
r = v4l2_ioctl(fh, request, arg);
} while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
if (r == -1) {
fprintf(stderr, "error %d, %s\\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
int main(int argc, char **argv)
{
struct v4l2_format fmt;
struct v4l2_buffer buf;
struct v4l2_requestbuffers req;
enum v4l2_buf_type type;
fd_set fds;
struct timeval tv;
int r, fd = -1;
unsigned int i, n_buffers;
char *dev_name = "/dev/video0";
char out_name[256];
FILE *fout;
struct buffer *buffers;
fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
if (fd < 0) {
perror("Cannot open device");
exit(EXIT_FAILURE);
}
CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = 640;
fmt.fmt.pix.height = 480;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
xioctl(fd, VIDIOC_S_FMT, &fmt);
if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) {
printf("Libv4l didn't accept RGB24 format. Can't proceed.\\n");
exit(EXIT_FAILURE);
}
if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480))
printf("Warning: driver is sending image at %dx%d\\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
CLEAR(req);
req.count = 2;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
xioctl(fd, VIDIOC_REQBUFS, &req);
buffers = calloc(req.count, sizeof(*buffers));
for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
xioctl(fd, VIDIOC_QUERYBUF, &buf);
buffers[n_buffers].length = buf.length;
buffers[n_buffers].start = v4l2_mmap(NULL, buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, buf.m.offset);
if (MAP_FAILED == buffers[n_buffers].start) {
perror("mmap");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < n_buffers; ++i) {
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
xioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
xioctl(fd, VIDIOC_STREAMON, &type);
for (i = 0; i < 20; i++) {
do {
FD_ZERO(&fds);
FD_SET(fd, &fds);
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(fd + 1, &fds, NULL, NULL, &tv);
} while ((r == -1 && (errno = EINTR)));
if (r == -1) {
perror("select");
return errno;
}
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
xioctl(fd, VIDIOC_DQBUF, &buf);
sprintf(out_name, "out%03d.ppm", i);
fout = fopen(out_name, "w");
if (!fout) {
perror("Cannot open image");
exit(EXIT_FAILURE);
}
fprintf(fout, "P6\n%d %d 255\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
fclose(fout);
xioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
xioctl(fd, VIDIOC_STREAMOFF, &type);
for (i = 0; i < n_buffers; ++i)
v4l2_munmap(buffers[i].start, buffers[i].length);
v4l2_close(fd);
return 0;
}
Header only object oriented version for reuse
Extracted from the example in the docs, but in a form that makes it super easy to reuse.
common_v4l2.h
#ifndef COMMON_V4L2_H
#define COMMON_V4L2_H
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <sys/types.h>
#include <libv4l2.h>
#include <linux/videodev2.h>
#define COMMON_V4L2_CLEAR(x) memset(&(x), 0, sizeof(x))
typedef struct {
void *start;
size_t length;
} CommonV4l2_Buffer;
typedef struct {
int fd;
CommonV4l2_Buffer *buffers;
struct v4l2_buffer buf;
unsigned int n_buffers;
} CommonV4l2;
void CommonV4l2_xioctl(int fh, unsigned long int request, void *arg)
{
int r;
do {
r = v4l2_ioctl(fh, request, arg);
} while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
if (r == -1) {
fprintf(stderr, "error %d, %s\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
void CommonV4l2_init(CommonV4l2 *this, char *dev_name, unsigned int x_res, unsigned int y_res) {
enum v4l2_buf_type type;
struct v4l2_format fmt;
struct v4l2_requestbuffers req;
unsigned int i;
this->fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
if (this->fd < 0) {
perror("Cannot open device");
exit(EXIT_FAILURE);
}
COMMON_V4L2_CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = x_res;
fmt.fmt.pix.height = y_res;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
CommonV4l2_xioctl(this->fd, VIDIOC_S_FMT, &fmt);
if ((fmt.fmt.pix.width != x_res) || (fmt.fmt.pix.height != y_res))
printf("Warning: driver is sending image at %dx%d\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
COMMON_V4L2_CLEAR(req);
req.count = 2;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
CommonV4l2_xioctl(this->fd, VIDIOC_REQBUFS, &req);
this->buffers = calloc(req.count, sizeof(*this->buffers));
for (this->n_buffers = 0; this->n_buffers < req.count; ++this->n_buffers) {
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
this->buf.index = this->n_buffers;
CommonV4l2_xioctl(this->fd, VIDIOC_QUERYBUF, &this->buf);
this->buffers[this->n_buffers].length = this->buf.length;
this->buffers[this->n_buffers].start = v4l2_mmap(NULL, this->buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED, this->fd, this->buf.m.offset);
if (MAP_FAILED == this->buffers[this->n_buffers].start) {
perror("mmap");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < this->n_buffers; ++i) {
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
this->buf.index = i;
CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
CommonV4l2_xioctl(this->fd, VIDIOC_STREAMON, &type);
}
void CommonV4l2_update_image(CommonV4l2 *this) {
fd_set fds;
int r;
struct timeval tv;
do {
FD_ZERO(&fds);
FD_SET(this->fd, &fds);
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(this->fd + 1, &fds, NULL, NULL, &tv);
} while ((r == -1 && (errno == EINTR)));
if (r == -1) {
perror("select");
exit(EXIT_FAILURE);
}
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
CommonV4l2_xioctl(this->fd, VIDIOC_DQBUF, &this->buf);
CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
}
char * CommonV4l2_get_image(CommonV4l2 *this) {
return ((char *)this->buffers[this->buf.index].start);
}
size_t CommonV4l2_get_image_size(CommonV4l2 *this) {
return this->buffers[this->buf.index].length;
}
void CommonV4l2_deinit(CommonV4l2 *this) {
unsigned int i;
enum v4l2_buf_type type;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
CommonV4l2_xioctl(this->fd, VIDIOC_STREAMOFF, &type);
for (i = 0; i < this->n_buffers; ++i)
v4l2_munmap(this->buffers[i].start, this->buffers[i].length);
v4l2_close(this->fd);
free(this->buffers);
}
#endif
main.c
#include <stdio.h>
#include <stdlib.h>
#include "common_v4l2.h"
static void save_ppm(
unsigned int i,
unsigned int x_res,
unsigned int y_res,
size_t data_lenght,
char *data
) {
FILE *fout;
char out_name[256];
sprintf(out_name, "out%03d.ppm", i);
fout = fopen(out_name, "w");
if (!fout) {
perror("error: fopen");
exit(EXIT_FAILURE);
}
fprintf(fout, "P6\n%d %d 255\n", x_res, y_res);
fwrite(data, data_lenght, 1, fout);
fclose(fout);
}
int main(void) {
CommonV4l2 common_v4l2;
char *dev_name = "/dev/video0";
struct buffer *buffers;
unsigned int
i,
x_res = 640,
y_res = 480
;
CommonV4l2_init(&common_v4l2, dev_name, x_res, y_res);
for (i = 0; i < 20; i++) {
CommonV4l2_update_image(&common_v4l2);
save_ppm(
i,
x_res,
y_res,
CommonV4l2_get_image_size(&common_v4l2),
CommonV4l2_get_image(&common_v4l2)
);
}
CommonV4l2_deinit(&common_v4l2);
return EXIT_SUCCESS;
}
Upstream: https://github.com/cirosantilli/cpp-cheat/blob/be5d6444bddab93e95949b3388d92007b5ca916f/v4l2/common_v4l2.h
SDL
Video capture is in their roadmap: https://wiki.libsdl.org/Roadmap and I bet it will wrap v4l on Linux.
It will be sweet when we get that portability layer, with less bloat than OpenCV.
Your best bet is probably: video4linux (V4L)
It's easy to use, and powerful.

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