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Fix nfs snapdir automount

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The current implementation for allowing nfs to access snapdir is very buggy.
It uses a special fh for snapdirs, such that the next time nfsd does
fh_to_dentry, it actually returns the root inode inside the snapshot. So nfsd
never knows it cross a mountpoint.

The problem is that nfsd will not hold a reference on the vfsmount of the
snapshot. This cause auto unmounter to unmount the snapshot even though nfs is
still holding dentries in it.

To fix this, we return the inode for the snapdirs themselves. However, we also
trigger automount upon fh_to_dentry, and return ESTALE so nfsd will revalidate
and see the mountpoint and do crossmnt.

Because nfsd will now be aware that these are different filesystems users
must add crossmnt to their export options to access snapshot directories.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #3794
Closes #4716
Closes #5810 
Closes #5833
This commit is contained in:
Chunwei Chen
2017-03-08 09:26:33 -08:00
committed by Brian Behlendorf
parent 463009865f
commit 9b77d1c958
6 changed files with 94 additions and 107 deletions
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include/sys/zfs_ctldir.h
+2 -2
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@@ -78,8 +78,8 @@ extern int zfsctl_snapshot_mount(struct path *path, int flags);
extern int zfsctl_snapshot_unmount(char *snapname, int flags);
extern int zfsctl_snapshot_unmount_delay(spa_t *spa, uint64_t objsetid,
int delay);
extern int zfsctl_lookup_objset(struct super_block *sb, uint64_t objsetid,
zfs_sb_t **zsb);
extern int zfsctl_snapdir_vget(struct super_block *sb, uint64_t objsetid,
int gen, struct inode **ipp);
/* zfsctl '.zfs/shares' functions */
extern int zfsctl_shares_lookup(struct inode *dip, char *name,