From: Nirbheek Chauhan nirbheek.chauhan at collabora.co.uk
If the path to a given loopback file is longer than 64 characters, none of the
Btrfs-progs tools can use it. This is because the size of loopinfo.lo_name
returned by the LOOP_GET_STATUS ioctl is 64.
The attached patch fixes this by fetching the backing file for a loopback device
from /sys/block; which is how `losetup` from util-linux does it as well.
Nirbheek Chauhan (1):
Btrfs-progs: fix resolving of loop devices
utils.c | 26 ++
1 files changed, 14 insertions(+), 12 deletions(-)
Tested-By: Hector Oron hector.o...@collabora.co.uk
diff --git a/utils.c b/utils.c
index 205e667..cdd6f7d 100644
--- a/utils.c
+++ b/utils.c
@@ -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
@@ -651,21 +652,22 @@ 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;
--
1.7.8.6
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