[PATCH 3/3] mount: Handle EROFS before calling mount() syscall

[Stanislav Brabec <sbrabec@suse.cz>]

If the loop device is already initialized read-only, the new code for loop
device reuse returns -EROFS. There is no solution of this situation. But mount
can behave in the same way, as it does for EROFS returned by mount syscall: Try
again in read-only mode.

Before:
mount: /mnt/2: mount failed: Read-only file system

After:
mount: /btrfs.img is used as read only loop, mounting read-only

Note: It would be nice to mention loop device name in the warning message, but
it is not available in the mount context.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
---
 sys-utils/mount.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sys-utils/mount.c b/sys-utils/mount.c
index 9c4729e..3e90fcc 100644
--- a/sys-utils/mount.c
+++ b/sys-utils/mount.c
@@ -402,6 +402,15 @@ try_readonly:
 		case -EBUSY:
 			warnx(_("%s is already mounted"), src);
 			return MOUNT_EX_USAGE;
+		/* -EROFS before syscall can happen only for loop mount */
+		case -EROFS:
+			warnx(_("%s is used as read only loop, mounting read-only"), src);
+			mnt_context_reset_status(cxt);
+			mnt_context_set_mflags(cxt, mflags | MS_RDONLY);
+			rc = mnt_context_mount(cxt);
+			if (!rc)
+				rc = mnt_context_finalize_mount(cxt);
+			goto try_readonly;
 		case -MNT_ERR_NOFSTAB:
 			if (mnt_context_is_swapmatch(cxt)) {
 				warnx(_("can't find %s in %s"),
-- 
2.8.1

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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