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An intermittent problem with NFSv4 exporting of ZFS snapshots was

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reported to the freebsd-fs mailing list. I believe the problem was
caused by the Readdir operation using VFS_VGET() for a snapshot file entry
instead of VOP_LOOKUP(). This would not occur for NFSv3, since it
will do a VFS_VGET() of "." which fails with ENOTSUPP at the beginning
of the directory, whereas NFSv4 does not check "." or "..". This
patch adds a call to VFS_VGET() for the directory being read to check
for ENOTSUPP.
I also observed that the mount_on_fileid and fsid attributes were
not correct at the snapshot's auto mountpoints when looking at packet
traces for the Readdir. This patch fixes the attributes by doing a check
for different v_mount structure, even if the vnode v_mountedhere is not
set.

Reported by:	jas@cse.yorku.ca
Tested by:	jas@cse.yorku.ca
Reviewed by:	asomers
MFC after:	1 week
This commit is contained in:
Rick Macklem 2013-12-24 22:24:17 +00:00
parent bd28fb4d4c
commit 0c695afb96
1 changed files with 37 additions and 0 deletions
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37
sys/fs/nfsserver/nfs_nfsdport.c
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@ -1983,6 +1983,27 @@ nfsrvd_readdirplus(struct nfsrv_descript *nd, int isdgram,
goto out;
}
/*
* Check to see if entries in this directory can be safely acquired
* via VFS_VGET() or if a switch to VOP_LOOKUP() is required.
* ZFS snapshot directories need VOP_LOOKUP(), so that any
* automount of the snapshot directory that is required will
* be done.
* This needs to be done here for NFSv4, since NFSv4 never does
* a VFS_VGET() for "." or "..".
*/
if (not_zfs == 0) {
r = VFS_VGET(mp, at.na_fileid, LK_SHARED, &nvp);
if (r == EOPNOTSUPP) {
usevget = 0;
cn.cn_nameiop = LOOKUP;
cn.cn_lkflags = LK_SHARED | LK_RETRY;
cn.cn_cred = nd->nd_cred;
cn.cn_thread = p;
} else if (r == 0)
vput(nvp);
}
/*
* Save this position, in case there is an error before one entry
* is created.
@ -2120,6 +2141,22 @@ nfsrvd_readdirplus(struct nfsrv_descript *nd, int isdgram,
if (!r)
r = nfsvno_getattr(nvp, nvap,
nd->nd_cred, p, 1);
if (r == 0 && not_zfs == 0 &&
nfsrv_enable_crossmntpt != 0 &&
(nd->nd_flag & ND_NFSV4) != 0 &&
nvp->v_type == VDIR &&
vp->v_mount != nvp->v_mount) {
/*
* For a ZFS snapshot, there is a
* pseudo mount that does not set
* v_mountedhere, so it needs to
* be detected via a different
* mount structure.
*/
at_root = 1;
if (new_mp == mp)
new_mp = nvp->v_mount;
}
}
} else {
nvp = NULL;