FUSE file system crashed at opening file (only in release mode) - c

Question

I have some problem, and i can't find solution of this :/ I need to open a text file inside my fuse filesystem. In debug everything works fine, but in release system is crashing. I made a simples example, with this. Could anybody tell what's wrong in this code?
/*
FUSE: Filesystem in Userspace
Copyright (C) 2001-2007 Miklos Szeredi <miklos#szeredi.hu>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
gcc -Wall `pkg-config fuse --cflags --libs` hello.c -o hello
*/
# define FUSE_USE_VERSION 26
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
void stripnl(char *str) {
while(strlen(str) && ( (str[strlen(str) - 1] == 13) ||
( str[strlen(str) - 1] == 10 ))) {
str[strlen(str) - 1] = 0;
}
}
static const char *hello_str = "Hello World!\n";
static const char *hello_path = "/hello";
static int hello_getattr(const char *path, struct stat *stbuf)
{
int res = 0;
memset(stbuf, 0, sizeof(struct stat));
if (strcmp(path, "/") == 0) {
stbuf->st_mode = S_IFDIR | 0755;
stbuf->st_nlink = 2;
} else if (strcmp(path, hello_path) == 0) {
stbuf->st_mode = S_IFREG | 0444;
stbuf->st_nlink = 1;
stbuf->st_size = strlen(hello_str);
} else
res = -ENOENT;
return res;
}
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
off_t offset, struct fuse_file_info *fi)
{
(void) offset;
(void) fi;
if (strcmp(path, "/") != 0)
return -ENOENT;
filler(buf, ".", NULL, 0);
filler(buf, "..", NULL, 0);
filler(buf, hello_path + 1, NULL, 0);
FILE *infile;
char fname[40];
char line[100];
int lcount;
/* We need to get rid of the newline char. */
stripnl(fname);
/* Open the file. If NULL is returned there was an error */
if((infile = fopen("ex.txt", "r")) == NULL) {
printf("Error Opening File.\n");
}
while( fgets(line, sizeof(line), infile) != NULL ) {
/* Get each line from the infile */
lcount++;
/* print the line number and data */
printf("Line %d: %s", lcount, line);
filler(buf, line, NULL, 0);
}
fclose(infile); /* Close the file */
return 0;
}
static int hello_open(const char *path, struct fuse_file_info *fi)
{
if (strcmp(path, hello_path) != 0)
return -ENOENT;
if ((fi->flags & 3) != O_RDONLY)
return -EACCES;
return 0;
}
static int hello_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
size_t len;
(void) fi;
if(strcmp(path, hello_path) != 0)
return -ENOENT;
len = strlen(hello_str);
if (offset < len) {
if (offset + size > len)
size = len - offset;
memcpy(buf, hello_str + offset, size);
} else
size = 0;
return size;
}
static struct fuse_operations hello_oper = {
.getattr = hello_getattr,
.readdir = hello_readdir,
.open = hello_open,
.read = hello_read,
};
int main(int argc, char *argv[])
{
return fuse_main(argc, argv, &hello_oper, NULL);
}
Update
Ok, i've found solution, path must be absolute file path (not sure is this is proper sentence), but here is example code, which is working in release as well as in debug:
/*
FUSE: Filesystem in Userspace
Copyright (C) 2001-2007 Miklos Szeredi <miklos#szeredi.hu>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
gcc -Wall `pkg-config fuse --cflags --libs` hello.c -o hello
*/
# define FUSE_USE_VERSION 26
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
void stripnl(char *str) {
while(strlen(str) && ( (str[strlen(str) - 1] == 13) ||
( str[strlen(str) - 1] == 10 ))) {
str[strlen(str) - 1] = 0;
}
}
static const char *hello_str = "Hello World!\n";
static const char *hello_path = "/hello";
static int hello_getattr(const char *path, struct stat *stbuf)
{
int res = 0;
memset(stbuf, 0, sizeof(struct stat));
if (strcmp(path, "/") == 0) {
stbuf->st_mode = S_IFDIR | 0755;
stbuf->st_nlink = 2;
} else if (strcmp(path, hello_path) == 0) {
stbuf->st_mode = S_IFREG | 0444;
stbuf->st_nlink = 1;
stbuf->st_size = strlen(hello_str);
} else
res = -ENOENT;
return res;
}
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
off_t offset, struct fuse_file_info *fi)
{
(void) offset;
(void) fi;
if (strcmp(path, "/") != 0)
return -ENOENT;
filler(buf, ".", NULL, 0);
filler(buf, "..", NULL, 0);
filler(buf, hello_path + 1, NULL, 0);
FILE *infile;
char line[100];
if((infile = fopen("/root/Desktop/fexamples/ex.txt", "rb")) == NULL)
{
return -1;
}
while( fgets(line, sizeof(line), infile) != NULL )
{
filler(buf, line, NULL, 0);
}
fclose(infile); /* Close the file */
return 0;
}
static int hello_open(const char *path, struct fuse_file_info *fi)
{
if (strcmp(path, hello_path) != 0)
return -ENOENT;
if ((fi->flags & 3) != O_RDONLY)
return -EACCES;
return 0;
}
static int hello_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
size_t len;
(void) fi;
if(strcmp(path, hello_path) != 0)
return -ENOENT;
len = strlen(hello_str);
if (offset < len) {
if (offset + size > len)
size = len - offset;
memcpy(buf, hello_str + offset, size);
} else
size = 0;
return size;
}
static struct fuse_operations hello_oper = {
.getattr = hello_getattr,
.readdir = hello_readdir,
.open = hello_open,
.read = hello_read,
};
int main(int argc, char *argv[])
{
return fuse_main(argc, argv, &hello_oper, NULL);
}

Answer 1

There are at least two issues in your readdir implementation.
char fname[40];
char line[100];
int lcount;
/* We need to get rid of the newline char. */
stripnl(fname);
You're acting on the contents of fname that you're not initializing anywhere. This could do just about anything. The fact that you're not using fname after that is irrelevant, you could be modifying completely random data with that stripnl call.
/* Open the file. If NULL is returned there was an error */
if((infile = fopen("ex.txt", "r")) == NULL) {
printf("Error Opening File.\n");
}
If fopen fails, you should error out (or just leave) this function. Otherwise the next line will call fgets with NULL as its file argument.

Answer 2

Ok, i've found solution, path must be absolute file path (not sure is this is proper sentence), but here is example code, which is working in release as well as in debug:
/*
FUSE: Filesystem in Userspace
Copyright (C) 2001-2007 Miklos Szeredi <miklos#szeredi.hu>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
gcc -Wall `pkg-config fuse --cflags --libs` hello.c -o hello
*/
# define FUSE_USE_VERSION 26
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
void stripnl(char *str) {
while(strlen(str) && ( (str[strlen(str) - 1] == 13) ||
( str[strlen(str) - 1] == 10 ))) {
str[strlen(str) - 1] = 0;
}
}
static const char *hello_str = "Hello World!\n";
static const char *hello_path = "/hello";
static int hello_getattr(const char *path, struct stat *stbuf)
{
int res = 0;
memset(stbuf, 0, sizeof(struct stat));
if (strcmp(path, "/") == 0) {
stbuf->st_mode = S_IFDIR | 0755;
stbuf->st_nlink = 2;
} else if (strcmp(path, hello_path) == 0) {
stbuf->st_mode = S_IFREG | 0444;
stbuf->st_nlink = 1;
stbuf->st_size = strlen(hello_str);
} else
res = -ENOENT;
return res;
}
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
off_t offset, struct fuse_file_info *fi)
{
(void) offset;
(void) fi;
if (strcmp(path, "/") != 0)
return -ENOENT;
filler(buf, ".", NULL, 0);
filler(buf, "..", NULL, 0);
filler(buf, hello_path + 1, NULL, 0);
FILE *infile;
char line[100];
if((infile = fopen("/root/Desktop/fexamples/ex.txt", "rb")) == NULL)
{
return -1;
}
while( fgets(line, sizeof(line), infile) != NULL )
{
filler(buf, line, NULL, 0);
}
fclose(infile); /* Close the file */
return 0;
}
static int hello_open(const char *path, struct fuse_file_info *fi)
{
if (strcmp(path, hello_path) != 0)
return -ENOENT;
if ((fi->flags & 3) != O_RDONLY)
return -EACCES;
return 0;
}
static int hello_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
size_t len;
(void) fi;
if(strcmp(path, hello_path) != 0)
return -ENOENT;
len = strlen(hello_str);
if (offset < len) {
if (offset + size > len)
size = len - offset;
memcpy(buf, hello_str + offset, size);
} else
size = 0;
return size;
}
static struct fuse_operations hello_oper = {
.getattr = hello_getattr,
.readdir = hello_readdir,
.open = hello_open,
.read = hello_read,
};
int main(int argc, char *argv[])
{
return fuse_main(argc, argv, &hello_oper, NULL);
}