mjhjmtu

I would like to check if USB disk is mounted in a C application. I know that in a script I can accomplish this via mount | grep /mnt (the mount point where udev mounts the USB drive) but I need to do this in a C application. Earlier I used to accomplish this using system("sh script.sh") but doing this is causing some serious issues as this code runs in a very time critical thread.

If you need to check the full list of mount points, use getmntent(3) or its thread-safe GNU extension getmntent_r(3).

If you just want to quickly check whether a given directory has a filesystem mounted on it or not, then use one of the functions in the stat(2) family. For example, if you want to check if /mnt has a filesystem mounted or not, you could do something like this:

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

struct stat mountpoint;
struct stat parent;

/* Get the stat structure of the directory...*/
if stat("/mnt", &mountpoint) == -1) 
 perror("failed to stat mountpoint:");
 exit(EXIT_FAILURE);


/* ... and its parent. */
if stat("/mnt/..", &parent) == -1) 
 perror("failed to stat parent:");
 exit(EXIT_FAILURE);


/* Compare the st_dev fields in the results: if they are
 equal, then both the directory and its parent belong 
 to the same filesystem, and so the directory is not 
 currently a mount point.
*/
if (mountpoint.st_dev == parent.st_dev) 
 printf("No, there is nothing mounted in that directory.n");
 else 
 printf("Yes, there is currently a filesystem mounted.n");