fix mount -a on btrfs bind mount
If I have a fstab that contains:
UUID=1f976144-6c23-4622-bf6c-cd9821acc49d /var/log btrfs
subvol=@/var/log 0 0/var/log /local/nfsv4/log none bind,private
When calling "mount -a" multiple times, it mounts the bind mount again and again.
Here are related mountinfo entries with my kernel:
44 34 0:30 /@/var/log /var/log rw,relatime shared:27 - btrfs /dev/vda2 rw,space_cache,subvolid=269,subvol=/@/var/log 95 34 0:30 /@/var/log /local/nfsv4/log rw,relatime - btrfs /dev/vda2 rw,space_cache,subvolid=269,subvol=/@/var/log
Debugging this case, I found that the btrfs specific code in mnt_table_get_fs_root() returns bad value:
after remove_mountpoint_from_path() root is "/" mnt_table_find_target(tb, "/var/log", MNT_ITER_BACKWARD) returns src_root set to "/@/var/log". startswith() does not match and the snprintf() attempts to construct the final root value by concatenating of both strings:
FS root result: /@/var/log/
It looks strange, and it does not work:
Then it returns to mnt_table_is_fs_mounted(), and the iterator while (mnt_table_next_fs(tb, &itr, &fs) == 0)
could never get a match.
In section starting with if (root)
and mnt_fs_get_root(fs) returns "/@/var/log"
This is compared with "/@/var/log/" above, and match is never got.
Here is a possible easy fix. If it is correct, the code should be simplified to remove string copying there.
I am not sure whether it has any side effect, but it helps in my case.
Note that 41510d26ddd9a4c83f8589dded539e2985535dcf added a patch to "else if" part of this if, that is also a bit
suspicious: btrfs path should not contain "//" instead of "/{subvolume}/", at least not in a correct use.
--- libmount/src/tab.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
libmount/src/tab.c +1 -1
@@ -1252,7 +1252,7 @@ struct libmnt_fs *mnt_table_get_fs_root(struct libmnt_table *tb,if (!tmp) goto err; -snprintf (tmp, sz,"%s%s" , src_root, root); +snprintf (tmp, sz,"%s" , src_root);free (root); root = tmp; }
Signature · 13 lines
2.6.3 -- Best Regards / S pozdravem, Stanislav Brabec software developer --------------------------------------------------------------------- SUSE LINUX, s. r. o. e-mail: [email protected] Lihovarská 1060/12 tel: +49 911 7405384547 190 00 Praha 9 fax: +420 284 084 001 Czech Republic http://www.suse.cz/ PGP: 830B 40D5 9E05 35D8 5E27 6FA3 717C 209F A04F CD76
PATCH 1/1 fix mount -a on btrfs bind mount
Do not prepend src_root to root for bind mounts on btrfs.
root has to be literally the same as src_root, which is already the path prefixed by /{subvolume}. Otherwise it will not match in mnt_fs_streq_target(fs, xtgt) inside mnt_table_is_fs_mounted() and repeated "mount -a" will mount it again and again.
--- libmount/src/tab.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
libmount/src/tab.c +1 -4
@@ -1247,12 +1247,9 @@ struct libmnt_fs *mnt_table_get_fs_root(struct libmnt_table *tb,*/ src_root =mnt_fs_get_root (src_fs);if (src_root && !startswith (root, src_root)) { -size_t sz =strlen (root) +strlen (src_root) +1 ; -char *tmp =malloc (sz); - +char *tmp =strdup (src_root);if (!tmp) goto err; -snprintf (tmp, sz,"%s%s" , src_root, root);free (root); root = tmp; }
Signature · 13 lines
2.6.3 -- Best Regards / S pozdravem, Stanislav Brabec software developer --------------------------------------------------------------------- SUSE LINUX, s. r. o. e-mail: [email protected] Lihovarská 1060/12 tel: +49 911 7405384547 190 00 Praha 9 fax: +420 284 084 001 Czech Republic http://www.suse.cz/ PGP: 830B 40D5 9E05 35D8 5E27 6FA3 717C 209F A04F CD76
Karel Zak
maintainerQuoted 4 lines · Stanislav Brabec
root has to be literally the same as
src_root, which is already the path prefixed by /{subvolume}. Otherwise it will not match inmnt_fs_streq_target(fs, xtgt)insidemnt_table_is_fs_mounted()and repeated "mount -a" will mount it again and again.
yes
libmount/src/tab.c struct libmnt_fs *mnt_table_get_fs_root(struct libmnt_table *tb, · line 1255
Quoted 11 lines
libmount/src/tab.c +1
-4if (src_root && !startswith (root, src_root)) { -size_t sz =strlen (root) +strlen (src_root) +1 ; -char *tmp =malloc (sz); - +char *tmp =strdup (src_root);if (!tmp) goto err; -snprintf (tmp, sz,"%s%s" , src_root, root);free (root); root = tmp; }
but this code is there for another use case. The problem is when the fstab_fs source is *sub-directory* on btrfs subvolume (or another bind mount). For example imagine:
/dev/sdc /mnt/test btrfs subvol=/anydir /mnt/test/foo /mnt/test2 auto bind
then FS root for /mnt/test2 is /anydir/foo on /dev/sdc. The problem is that the code does not recognize your use-case with "/" (no sub-directory on source FS).
My bugfix:
https://github.com/karelzak/util-linux/commit/352740e88e2c9cb180fe845ce210b1c7b5ad88c7
try it :-)
Anyway, we need more regression tests for these crazy use-cases.
Karel
Signature · 2 lines
Karel Zak <[email protected]> http://karelzak.blogspot.com
Quoted 6 lines · Karel Zak
My bugfix:
https://github.com/karelzak/util-linux/commit/352740e88e2c9cb180fe845ce210b1c7b5ad88c7
try it :-)
If also fixed my problem.
Thanks.
Signature · 10 lines
Best Regards / S pozdravem, Stanislav Brabec software developer --------------------------------------------------------------------- SUSE LINUX, s. r. o. e-mail: [email protected] Lihovarská 1060/12 tel: +49 911 7405384547 190 00 Praha 9 fax: +420 284 084 001 Czech Republic http://www.suse.cz/ PGP: 830B 40D5 9E05 35D8 5E27 6FA3 717C 209F A04F CD76
Quoted 24 lines · Karel Zak
Quoted 4 lines · Stanislav Brabec
root has to be literally the same as
src_root, which is already the path prefixed by /{subvolume}. Otherwise it will not match inmnt_fs_streq_target(fs, xtgt)insidemnt_table_is_fs_mounted()and repeated "mount -a" will mount it again and again.yes
libmount/src/tab.c struct libmnt_fs *mnt_table_get_fs_root(struct libmnt_table *tb, · line 1255
Quoted 11 lines
libmount/src/tab.c +1
-4if (src_root && !startswith (root, src_root)) { -size_t sz =strlen (root) +strlen (src_root) +1 ; -char *tmp =malloc (sz); - +char *tmp =strdup (src_root);if (!tmp) goto err; -snprintf (tmp, sz,"%s%s" , src_root, root);free (root); root = tmp; }but this code is there for another use case. The problem is when the
fstab_fssource is *sub-directory* on btrfs subvolume (or another bind mount). For example imagine:
Quoted 1 line
/dev/sdc/mnt/testbtrfs subvol=/anydir
Only subvolumes are accepted as parameter for 'subvol=', otherwise bind mount needs to be used.