An intermittent problem with NFSv4 exporting of ZFS snapshots was

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

1 files changed, 37 insertions, 0 deletions

diff --git a/sys/fs/nfsserver/nfs_nfsdport.c b/sys/fs/nfsserver/nfs_nfsdport.c
index 2f9d40a..89fc66e 100644
--- a/sys/fs/nfsserver/nfs_nfsdport.c
+++ b/sys/fs/nfsserver/nfs_nfsdport.c
@@ -1984,6 +1984,27 @@ again:
 	}
 
 	/*
+	 * 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 @@ again:
 					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;