Fix automount for root filesystems

Commit 093bb64 resolved an automount failures for chroot'd processes
but inadvertently broke automounting for root filesystems where the
vfs_mntpoint is NULL.  Resolve the issue by checking for NULL in order
to generate the correct path.

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #9381
Closes #9384

diff --git a/module/os/linux/zfs/zfs_ctldir.c b/module/os/linux/zfs/zfs_ctldir.c
index 1e61ef06d003736a871d8fd2a8d7f1ddcfe16130..3b2a6eb8273f059553eef9be5fae8ed41345c5c5 100644 (file)
--- a/module/os/linux/zfs/zfs_ctldir.c
+++ b/module/os/linux/zfs/zfs_ctldir.c
@@ -1053,7 +1053,8 @@ zfsctl_snapshot_mount(struct path *path, int flags)
         * on mount.zfs(8).
         */
        snprintf(full_path, MAXPATHLEN, "%s/.zfs/snapshot/%s",
-           zfsvfs->z_vfs->vfs_mntpoint, dname(dentry));
+           zfsvfs->z_vfs->vfs_mntpoint ? zfsvfs->z_vfs->vfs_mntpoint : "",
+           dname(dentry));
 
        /*
         * Multiple concurrent automounts of a snapshot are never allowed.