I am trying to read a file by the parent process, send the content to two child processes and child processes write content to a shared memory segment. However, at each run, I get different outputs and I cannot figure out why.
I use two named pipes and after writing to shared memory, the parent process opens the shared memory and reads the content of each memory.
The first child writes to memory as it gets but the second child converts to hexadecimal.
Here is my main function; assume that stringtohex() works correctly.
int main()
{
pid_t pid_1, pid_2;
int fd, sd; // pipes
const int SIZE = 4096;
const char infile[] = "in.txt";
FILE *tp; // file pointers
pid_1 = fork();
if (pid_1 < 0)
{
fprintf(stderr, "Fork 1 failed");
return(1);
}
if (pid_1 > 0)
{
pid_2 = fork();
if (pid_2 < 0)
{
fprintf(stderr, "Fork 2 failed");
return(1);
}
if (pid_2 > 0) // parent
{
tp = fopen(infile, "r");
if (tp == 0)
{
fprintf(stderr, "Failed to open %s for reading", infile);
return(1);
}
mknod(PIPE_NAME_1, S_IFIFO | 0666, 0);
mknod(PIPE_NAME_2, S_IFIFO | 0666, 0);
fd = open(PIPE_NAME_1, O_WRONLY);
sd = open(PIPE_NAME_2, O_WRONLY);
if (fd > 0 && sd > 0)
{
char line[300];
while (fgets(line, sizeof(line), tp))
{
int len = strlen(line);
int num_1 = write(fd, line, len);
int num_2 = write(sd, line, len);
if (num_1 != len || num_2 != len)
perror("write");
else
printf("Ch 1: wrote %d bytes\n", num_1);
printf("Ch 2: wrote %d bytes\n", num_2);
}
close(fd);
close(sd);
}
fclose(tp);
wait(NULL);
int shm_fd = shm_open("Ch_1", O_RDONLY, 0666);
if (shm_fd == -1)
{
fprintf(stderr, "Failed: Shared Memory 1");
exit(-1);
}
int shm_sd = shm_open("Ch_2", O_RDONLY, 0666);
if (shm_sd == -1)
{
fprintf(stderr, "Failed: Shared Memory 2");
exit(-1);
}
void *ptr = mmap(0, SIZE, PROT_READ, MAP_SHARED, shm_fd, 0);
if (ptr == MAP_FAILED)
{
printf("Map failed 1\n");
return -1;
}
void *ptr2 = mmap(0, SIZE, PROT_READ, MAP_SHARED, shm_sd, 0);
if (ptr2 == MAP_FAILED)
{
printf("Map failed 2\n");
return -1;
}
fprintf(stdout, "Normal input: \n%s\n", ptr);
fprintf(stderr, "Hexadecimal: \n%s\n", ptr2);
}
else // second child
{
// open shared memory segment
int shm_child_2 = shm_open("Ch_2", O_CREAT | O_RDWR, 0666);
// configure the size of the shared memory segment
ftruncate(shm_child_2, SIZE);
// map the pointer to the segment
void *ptr_child_2 = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_child_2, 0);
if (ptr_child_2 == MAP_FAILED)
{
printf("Map failed 3\n");
return -1;
}
// configure named pipe
mknod(PIPE_NAME_2, S_IFIFO | 0666, 0);
sd = open(PIPE_NAME_2, O_RDONLY);
if (sd > 0) // reading from pipe
{
int num;
char s[300];
while ((num = read(sd, s, sizeof(s))) > 0)
{
// convert to hexadecimal
char hex[strlen(s) * 2 + 1];
stringtohex(s, hex);
// write into segment
sprintf(ptr_child_2, "%s", hex);
ptr_child_2 += strlen(s) * 2;
}
close(sd);
}
exit(0);
}
}
else // first child
{
// create shared memory segment
int shm_child_1 = shm_open("Ch_1", O_CREAT | O_RDWR, 0666);
// configure the size of the shared memory segment
ftruncate(shm_child_1, SIZE);
// map the pointer to the segment
void *ptr_child_1 = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_child_1, 0);
if (ptr_child_1 == MAP_FAILED)
{
printf("Map failed 4\n");
return -1;
}
// configure named pipe
mknod(PIPE_NAME_1, S_IFIFO | 0666, 0);
fd = open(PIPE_NAME_1, O_RDONLY);
if (fd > 0) // reading from pipe
{
int num;
char s[300];
while ((num = read(fd, s, strlen(s))) > 0)
{
// write into segment
sprintf(ptr_child_1, "%s", s);
ptr_child_1 += strlen(s);
}
close(fd);
}
exit(0);
}
return 0;
}
For example input file has:
Harun
sasmaz
59900
1234
Aaaa
Results are:
Normal input:
HARUN
sasmaz
59900
1234
Aaaa4
Hexadecimal:
484152554E0A7361736D617A0A35393930300A313233340A41616161
or
Normal input:
HARUN
sasmaz
asmaz59900
1234
Aaaa
Hexadecimal:
484152554E0A7361736D617A0A35393930300A0A313233340A41616161FF03
Related
I'm trying to create a function that duplicates a file given a file descriptor and a file name:
int filedup(int fd1, char *cpyfile)
{
int fd;
size_t rd;
char buff;
if (fd1 < 0 || fd1 > OPEN_MAX)
return (-1);
if (!validfname(fname))
return (-1);
fd = open(cpyfile, O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fd == -1)
return (-1);
rd = read(fd1, &buff, 1);
while (rd > 0)
{
write(fd, &buff, 1);
rd = read(fd1, &buff, 1);
}
close(fd);
return (0);
}
int main(void)
{
int fd;
fd = open("/tmp/cpyfromfile", O_RDWR | O_CREAT | O_TRUNC, 0644);
if (fd == -1)
return (-1);
putstr_fd(strdup("hello world\n"), fd);
filedup(fd, "cpyfile");
close(fd);
return (0);
}
I tried to debug it, and the problem was rd == 0 even though the file contains data.
$ cat ./cpyfile
$ (nothing)
I'm not sure what's the problem ? what am i doing wrong ?
I'm trying to code a simple program to copy a file into another using 2 processes.
I want to use shared memory to open both files and get a piece of shared memory of 1Byte to be used as exchange memory in a mutually exclusive way.
So the main process should open both files and put them in shared memories;
fork twice, I obtain 2 processes A and B.
Process A should read 1 byte of the first file, put it in the shared exchange memory and unlock the mutex for process B.
Process B should copy the file from the shared exchange memory and put it in its file and unlock the mutex for process A.
And so on.
#define SIZE 4096
void reader_process(FILE* fptr,char*exch, sem_t*mut){
while(1){
sem_wait(mut);
*exch = (char) getc(fptr);
sem_post(mut+1);
}
}
void writer_process(FILE* fptr,char*exch, sem_t*mut){
if(*exch == EOF){
printf("done\n");
exit(0);
}
while(1){
sem_wait(mut);
putc((int)*exch,fptr);
sem_post(mut-1);
}
}
int main(int argc, char *argv[]){
FILE* shared_f_ptr[2];
pid_t pid;
//2 files name.
char *files[2];
int fd[2];
//open files.
files[0] = argv[1];
printf("%s\n",files[0]);
FILE* fpointer1 = fopen(files[0],"r+");
if (fpointer1 == NULL){
perror("fopen\n");
exit(-1);
}
fd[0] = fileno(fpointer1);
files[1] = argv[2];
printf("%s\n",files[1]);
FILE* fpointer2 = fopen(files[1],"r+");
if (fpointer2 == NULL){
perror("fopen\n");
exit(-1);
}
fd[1] = fileno(fpointer2);
//shared File pointers.
shared_f_ptr[0] = (FILE*)mmap(NULL, SIZE*sizeof(char),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
fd[0], 0);
if (shared_f_ptr[0] == MAP_FAILED){
perror("mmap\n");
exit(-1);
}
shared_f_ptr[1] = (FILE*)mmap(NULL, SIZE*sizeof(char),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
fd[1], 0);
if (shared_f_ptr[1] == MAP_FAILED){
perror("mmap\n");
exit(-1);
}
//shared mem for 1B exchange.
char *shared_exchange = (char*)mmap(NULL, sizeof(char),
PROT_READ | PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS,
-1, 0);
if (shared_exchange == MAP_FAILED){
perror("mmap\n");
exit(-1);
}
//mutex.
sem_t *mut = (sem_t*)mmap(NULL, 2*sizeof(sem_t),
PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS,
-1, 0);
sem_init(&mut[0],1,0);
sem_init(&mut[1],1,0);
//fork.
pid = fork();
if (pid == 0) {
reader_process(shared_f_ptr[0],
shared_exchange, &mut[0]);
}
if (pid == -1){
perror("fork\n");
exit(-1);
}
else pid = fork();
if (pid == 0) writer_process(shared_f_ptr[1],
shared_exchange, &mut[1]);
if (pid == -1){
perror("fork\n");
exit(-1);
}
else{
sem_post(&mut[0]);
}
}
I don't expect the error i am getting Fatal error: glibc detected an invalid stdio handle but i don't really know how to find what's causing the problem.
Don't do this:
//shared File pointers.
shared_f_ptr[0] = (FILE*)mmap(NULL, SIZE*sizeof(char),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
fd[0], 0);
if (shared_f_ptr[0] == MAP_FAILED){
perror("mmap\n");
exit(-1);
}
shared_f_ptr[1] = (FILE*)mmap(NULL, SIZE*sizeof(char),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
fd[1], 0);
if (shared_f_ptr[1] == MAP_FAILED){
perror("mmap\n");
exit(-1);
}
Use this instead:
shared_f_ptr[0] = fpointer1;
shared_f_ptr[1] = fpointer2;
Don't use the file descriptors underlying each FILE. Instead, simply use the FILE itself.
Also, instead of using fpointer1 and fpointer2, just use shared_f_ptr[0] and shared_f_ptr[1].
This is a possible definition of the FILE structure:
typedef struct _IO_FILE
{
int __fd;
int __flags;
int __unget;
char *__buffer;
struct {
size_t __orig;
size_t __size;
size_t __written;
} __bufsiz;
fpos_t __fpos;
} FILE;
As you can see, it's a structure, not just a flat pointer.
I'm try to read from the physical address.
the output of the printf function is empty:"value="
What I did wrong?
int counter;
int fd;
char* mmap_res;
fd = open("/dev/mem", O_RDWR);
if (fd == -1)
{
printf("can not access /dev/mem\n" );
return -1;
}
mmap_res =
(char*)mmap(NULL, 4096, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, 0x92000000);
for (counter = 0; counter < 10 ; counter++)
printf("value=%c\n",mmap_res[counter]);
if (mmap_res == MAP_FAILED)
{
printf("mmap failed\n" );
return -1;
}
I am trying to create an empty file if it does not exists. And than map it using mmap() so, that i can pass it to my other program for writing. I am not sure which arguments for mmap are suitable for an empty file. My code works for non empty files but gives error "Invalid argument" if file is empty
Code program1 (only creates an empty file if not exists)
int i;
int fd = open("/home/sungmin/dummy_programs/dummy.txt", O_RDONLY | O_CREAT, 0777);
char *pmap;
pid_t child;
if (fd == -1)
{
perror("Error opening file for writing");
exit(EXIT_FAILURE);
}
struct stat fileInfo = {0};
if (fstat(fd, &fileInfo) == -1)
{
perror("Error getting the file size");
exit(EXIT_FAILURE);
}
/*if (fileInfo.st_size == 0)
{
fprintf(stderr, "Error: File is empty, nothing to do\n");
exit(EXIT_FAILURE);
}*/
pmap = mmap(0, fileInfo.st_size, PROT_READ | PROT_EXEC , MAP_ANONYMOUS, fd, 0);
if (pmap == MAP_FAILED)
{
close(fd);
perror("Error mmapping the file");
exit(EXIT_FAILURE);
}
/* Calling fork function */
if((child=fork())==0){
printf("Iam Child process\n\n");
static char *argv[]={"This is some sample text. I need to write this text in my dummy file.","/home/sungmin/dummy_programs/dummy.txt",NULL};
execv("/home/sungmin/dummy_programs/pro2",argv);
exit(127);
}
else {
printf("Iam parent, waiting for child process to exit\n\n");
waitpid(child,0,0);
printf("Existing parent\n\n");
}
/* Don't forget to free the mmapped memory*/
if (munmap(pmap, fileInfo.st_size) == -1)
{
close(fd);
perror("Error un-mmapping the file");
exit(EXIT_FAILURE);
}
/* Un-mmaping doesn't close the file, so we still need to do that.*/
close(fd);
Code program2 (opens same file as program1 and writes text passed by program1)
size_t i;
int fd;
char *pmap;
pid_t child;
struct stat fileInfo = {0};
const char *text = argv[0];
fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, (mode_t)0600);
if (fd == -1)
{
perror("Error opening file for writing");
exit(EXIT_FAILURE);
}
size_t textsize = strlen(text) + 1; // + \0 null character
if (lseek(fd, textsize-1, SEEK_SET) == -1)
{
close(fd);
perror("Error calling lseek() to 'stretch' the file");
exit(EXIT_FAILURE);
}
if (write(fd, "", 1) == -1)
{
close(fd);
perror("Error writing last byte of the file");
exit(EXIT_FAILURE);
}
pmap = mmap(0, textsize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (pmap == MAP_FAILED)
{
close(fd);
perror("Error mmapping the file");
exit(EXIT_FAILURE);
}
/* Writting users text to file */
for (i = 0; i < textsize; i++)
{
pmap[i] = text[i];
}
// Write it now to disk
if (msync(pmap, textsize, MS_SYNC) == -1)
{
perror("Could not sync the file to disk");
}
/* Don't forget to free the mmapped memory*/
if (munmap(pmap, textsize) == -1)
{
close(fd);
perror("Error un-mmapping the file");
exit(EXIT_FAILURE);
}
/* Un-mmaping doesn't close the file, so we still need to do that.*/
close(fd);
You need to use truncate to extend the file length after creating it before mapping it.
Yes, the function name sounds wrong, but truncate can actually set the file length to any number. Be sure to use a multiple of 4K for best results.
Then, if you want to keep the mapping open to see data between Program 1 and 2, you need to get rid of ANONYMOUS and map with MAP_SHARED in Program 1. A mapping that isn't shared will not show changes made by other programs. Or it might, if it has to reload from disk. It's weird, don't mix SHARED and not-SHARED mappings.
Once you've changed Program 1 to use truncate, take that lseek and write code out of Program 2. The file will already have been created and extended by Program 1.
I'm having problems with writing to shared memory segment. Here's the code:
EDIT: after I removed that == (mistake), now I'm getting Bus Error (Core Dumped), here's the edited code:
// Struct for data from shared memory
typedef struct {
pthread_mutex_t shared_mutex;
int last_used_job_id;
} shared1;
static void *job_generator(void *param)
{
int J = *((int *) param);
shared1 *shd;
int shm;
int job_id;
// Open shared memory, don't create it if doesn't exist
shm = shm_open("/lab5", O_RDWR, 00600);
// Check
if (shm == -1) {
// Open shared memory, create it if doesn't exist (O_CREAT)
shm = shm_open(q_name, O_RDWR | O_CREAT, 00600);
// Map space for struct
shd = mmap(NULL, sizeof(shared1), PROT_READ | PROT_WRITE, MAP_SHARED, shm, 0);
if (shd == (void *) -1) {
perror ( "mmap" );
exit(1);
}
// Initialize mutex
if (pthread_mutex_init(&(shd->shared_mutex), NULL) != 0)
{
printf("Mutex initialization failed!\n");
exit(1);
}
}
else
{
// Map space for struct
shd = mmap(NULL, sizeof(shared1), PROT_READ | PROT_WRITE, MAP_SHARED, shm, 0);
if (shd == (void *) -1) {
perror ( "mmap" );
exit(1);
}
}
// Lock mutex
pthread_mutex_lock(&(shd->shared_mutex));
job_id = shd->last_used_job_id + 1;
shd->last_used_job_id = job_id + J;
printf("a: %d\n", shd->last_used_job_id);
return NULL;
}
it's caused by any of the instructions which are using shd, so any of these:
// Lock mutex
pthread_mutex_lock(&(shd->shared_mutex));
job_id = shd->last_used_job_id + 1;
shd->last_used_job_id = job_id + J;
printf("a: %d\n", shd->last_used_job_id);
I think this is where your problem lies:
shd == mmap(NULL, sizeof(shared1), PROT_READ | PROT_WRITE, MAP_SHARED, shm, 0);
You're comparing shd to the return value of mmap with '=='. I think you meant to use a single '=' which would assign the return value to shd.