New patch is attached. On 11/10/2015 12:50 PM, Karel Zak wrote: > > Yep, first try /sys/... and when unsuccessful then try ioctl. > > losetup example: > https://github.com/karelzak/util-linux/blob/master/lib/loopdev.c#L686 > > (it's probably too complex, but the basic idea is obvious) > > Maybe we need libloop.so to share all these things between various > project :-)
That would be lovely indeed. > > Karel > Regards, -- Florian Margaine Product Engineer @ Platform.sh https://platform.sh https://keybase.io/fmargaine
When using partitions on a loop device, the device's name can be
/dev/loop0p1 or similar, and no relevant entry exists in the /sys
filesystem, so the current resolve_loop_device function fails.
This patch adds a fallback to using loopdev API which will get the
correct backing file even for partitioned loop devices, at the expense
of using more memory, hence using it as a fallback only.
---
utils.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/utils.c b/utils.c
index d546bea..5e4813d 100644
--- a/utils.c
+++ b/utils.c
@@ -1170,2 +1170,2 @@ static int is_loop_device (const char* device) {
MAJOR(statbuf.st_rdev) == LOOP_MAJOR);
}
+/*
+ * Takes a loop device path (e.g. /dev/loop0) and returns
+ * the associated file (e.g. /images/my_btrfs.img) using
+ * loopdev API
+ */
+static int resolve_loop_device_with_loopdev(const char* loop_dev, char* loop_file)
+{
+ int fd;
+ struct loop_info64 lo64;
+
+ if (!(fd = open(loop_dev, O_RDONLY | O_NONBLOCK)))
+ return -errno;
+ if (ioctl(fd, LOOP_GET_STATUS64, &lo64) != 0)
+ return -errno;
+
+ memcpy(loop_file, lo64.lo_file_name, strlen(lo64.lo_file_name) + 1);
+ if (close(fd) != 0)
+ return -errno;
+
+ return 0;
+}
/* Takes a loop device path (e.g. /dev/loop0) and returns
* the associated file (e.g. /images/my_btrfs.img) */
@@ -1185,5 +1206,10 @@ static int resolve_loop_device(const char* loop_dev, char* loop_file,
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")))
+ if (!(f = fopen(p, "r"))) {
+ if (errno == ENOENT)
+ /* It's possibly a partitioned loop device, which
+ is resolvable with loopdev API. */
+ return resolve_loop_device_with_loopdev(loop_dev, loop_file);
return -errno;
+ }
snprintf(fmt, 20, "%%%i[^\n]", max_len-1);
ret = fscanf(f, fmt, loop_file);
--
2.6.1
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