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Btrfs-progs: fix resolving of loop devices

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The LOOP_GET_STATUS ioctl truncates filenames to 64 characters. We should get
the backing file for a given loop device from /sys/. This is how losetup does it
as well.

Signed-off-by: Nirbheek Chauhan <nirbheek.chauhan@collabora.co.uk>
Signed-off-by: Gene Czarcinski <gene@czarc.net>
Tested-By: Hector Oron <hector.oron@collabora.co.uk>
This commit is contained in:
Nirbheek Chauhan 2013-01-20 16:04:07 -05:00 committed by David Sterba
parent c88c2f52fe
commit abdb0ced01
1 changed files with 14 additions and 12 deletions
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26
utils.c
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@ -20,6 +20,7 @@
#define __USE_XOPEN2K
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifndef __CHECKER__
#include <sys/ioctl.h>
#include <sys/mount.h>
@ -652,21 +653,22 @@ int is_loop_device (const char* device) {
* the associated file (e.g. /images/my_btrfs.img) */
int resolve_loop_device(const char* loop_dev, char* loop_file, int max_len)
{
int loop_fd;
int ret_ioctl;
struct loop_info loopinfo;
int ret;
FILE *f;
char fmt[20];
char p[PATH_MAX];
char real_loop_dev[PATH_MAX];
if ((loop_fd = open(loop_dev, O_RDONLY)) < 0)
if (!realpath(loop_dev, real_loop_dev))
return -errno;
snprintf(p, PATH_MAX, "/sys/block/%s/loop/backing_file", strrchr(real_loop_dev, '/'));
if (!(f = fopen(p, "r")))
return -errno;
ret_ioctl = ioctl(loop_fd, LOOP_GET_STATUS, &loopinfo);
close(loop_fd);
if (ret_ioctl == 0) {
strncpy(loop_file, loopinfo.lo_name, max_len);
if (max_len > 0)
loop_file[max_len-1] = 0;
} else
snprintf(fmt, 20, "%%%i[^\n]", max_len-1);
ret = fscanf(f, fmt, loop_file);
fclose(f);
if (ret == EOF)
return -errno;
return 0;