patch looks reasonable to me.
On Wed, Aug 3, 2016 at 12:23 PM, Stanislav Brabec <sbrabec@xxxxxxx> wrote:
> 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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--
Thanks,
Steve
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