loopdev: sync capacity after setting it

I recently tried to mount an hfsplus file system from an image file with
a partition table by using the loop offset and sizelimit options to specify
the location of the file system.

hfsplus stores some metadata at a set offset from the end of the partition,
so it's sensitive to the device size reported by the kernel.

It worked with this:

But failed with this:

/dev/loop0: [0089]:2 (<imagefile>), offset 32768, sizelimit 102400000
/dev/loop1: [0089]:2 (<imagefile>), offset 32768, sizelimit 102400000

/proc/partitions shows the correct number of blocks to match the sizelimit.

But if I set a breakpoint in mount before the mount syscall, I could see:
102400000
102432768

The kernel loop driver will set the gendisk capacity of the device at
LOOP_SET_STATUS64 but won't sync it to the block device until one of two
conditions are met: All open file descriptors referring to the device are
closed (and it will sync when re-opened) or if the LOOP_SET_CAPACITY ioctl
is called to sync it. Since mount opens the device and passes it directly
to the mount syscall after LOOP_SET_STATUS64 without closing and reopening
it, the sizelimit argument is effectively ignroed. The capacity needs to
be synced immediately for it to work as expected.

This patch adds the LOOP_SET_CAPACITY call to loopctx_setup_device since
the device isn't yet released to the user, so it's safe to sync the capacity
immediately.

[kzak@redhat.com: - port to the current git HEAD,
                  - use uint64_t]

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 4 insertions, 15 deletions

diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c
index 8f3614e1f..ccf120e9f 100644
--- a/sys-utils/losetup.c
+++ b/sys-utils/losetup.c
@@ -183,20 +183,6 @@ static int show_all_loops(struct loopdev_cxt *lc, const char *file,
 	return 0;
 }
 
-static int set_capacity(struct loopdev_cxt *lc)
-{
-	int fd = loopcxt_get_fd(lc);
-
-	if (fd < 0)
-		warn(_("cannot open %s"), loopcxt_get_device(lc));
-	else if (ioctl(fd, LOOP_SET_CAPACITY) != 0)
-		warnx(_("%s: set capacity failed"), loopcxt_get_device(lc));
-	else
-		return 0;
-
-	return -1;
-}
-
 static int delete_loop(struct loopdev_cxt *lc)
 {
 	if (loopcxt_delete_device(lc))
@@ -685,7 +671,10 @@ int main(int argc, char **argv)
 			warn(_("%s"), loopcxt_get_device(&lc));
 		break;
 	case A_SET_CAPACITY:
-		res = set_capacity(&lc);
+		res = loopcxt_set_capacity(&lc);
+		if (res)
+			warn(_("%s: set capacity failed"),
+			        loopcxt_get_device(&lc));
 		break;
 	default:
 		usage(stderr);