Stanislav Brabec wrote:
In mountinfo of cifs filesystem, root is filled with a relative path to the root
of the exported volume. There is no reasonable way to compare it without making
a network look-up.
This is an original problem of "mount -a", see How to reproduce below.
This causes false negative result in some cases.
Skipping root comparison in mnt_table_is_fs_mounted() makes things better,
however it still does not cover all possible setups.
I just compared behavior of cifs and nfs4 in this situation.
cifs and nfs4 provide different mountinfo. So maybe it is more an
inconsistency of procinfo root entry than problem of mount.
Sending mail also to linux-cifs to get an opinion.
When mounting subdirectory of exported nfs4 volume, 4th record (root)
remains "/".
When mounting subdirectory of exported cifs volume, 4th record (root) is
the "/subdir", and 9th record (source) contains fill path
"//server/volume/subdir".
And for comparison, when bind mounting cifs subdirectory out of volume
mount, 4th record is "/subdir" as well, but the string in 9th record
(source) does not contain trailing "/subdir", just "//server/volume".
And for completness, when bind mounting subdirectory of a btrfs
subvolume, 4th record (root) contains full path to the subdirectory
relative to the volume root (i. e. including subvolume path). Content of
9th record (source) is not relevant for comparison, as it contains
/dev/sd* node.
How to reproduce:
1) Create and export a cifs volume (with guest allowed).
2) Make a subdirectory in this volume.
3) Mount this subdirectory using fstab:
//server/volume/subdir /mnt cifs guest 0 0
4) Call mount -a twice.
Depending on a system running, you either get:
mount error(16): Device or resource busy
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
or you get a volume mounted twice.
Signed-off-by: Stanislav Brabec <sbrabec@xxxxxxx>
---
Here is the proposed patch for util-linux:
libmount/src/tab.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/libmount/src/tab.c b/libmount/src/tab.c
index 155c65e..aa9185a 100644
--- a/libmount/src/tab.c
+++ b/libmount/src/tab.c
@@ -1562,7 +1562,10 @@ int mnt_table_is_fs_mounted(struct libmnt_table *tb, struct libmnt_fs *fstab_fs)
#endif
}
- if (root) {
+ /* For cifs, root contains a relative path to the exported volume,
+ * i. e. something we cannot compare.
+ */
+ if (root && strcmp(mnt_fs_get_fstype(fs), "cifs")) {
const char *r = mnt_fs_get_root(fs);
if (!r || strcmp(r, root) != 0)
continue;
--
Best Regards / S pozdravem,
Stanislav Brabec
software developer
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