Add .zfs control directory

Add support for the .zfs control directory.  This was accomplished
by leveraging as much of the existing ZFS infrastructure as posible
and updating it for Linux as required.  The bulk of the core
functionality is now all there with the following limitations.

*) The .zfs/snapshot directory automount support requires a 2.6.37
   or newer kernel.  The exception is RHEL6.2 which has backported
   the d_automount patches.

*) Creating/destroying/renaming snapshots with mkdir/rmdir/mv
   in the .zfs/snapshot directory works as expected.  However,
   this functionality is only available to root until zfs
   delegations are finished.

      * mkdir - create a snapshot
      * rmdir - destroy a snapshot
      * mv    - rename a snapshot

The following issues are known defeciences, but we expect them to
be addressed by future commits.

*) Add automount support for kernels older the 2.6.37.  This should
   be possible using follow_link() which is what Linux did before.

*) Accessing the .zfs/snapshot directory via NFS is not yet possible.
   The majority of the ground work for this is complete.  However,
   finishing this work will require resolving some lingering
   integration issues with the Linux NFS kernel server.

*) The .zfs/shares directory exists but no futher smb functionality
   has yet been implemented.

Contributions-by: Rohan Puri <[email protected]>
Contributiobs-by: Andrew Barnes <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #173

1 files changed, 38 insertions, 50 deletions

diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 532f17aa1..d2ad1af71 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -58,6 +58,7 @@
 #include <sys/mount.h>
 #include <sys/sdt.h>
 #include <sys/fs/zfs.h>
+#include <sys/zfs_ctldir.h>
 #include <sys/zfs_dir.h>
 #include <sys/zfs_onexit.h>
 #include <sys/zvol.h>
@@ -2690,33 +2691,6 @@ zfs_ioc_get_fsacl(zfs_cmd_t *zc)
 	return (error);
 }
 
-#ifdef HAVE_SNAPSHOT
-/*
- * Search the vfs list for a specified resource.  Returns a pointer to it
- * or NULL if no suitable entry is found. The caller of this routine
- * is responsible for releasing the returned vfs pointer.
- */
-static vfs_t *
-zfs_get_vfs(const char *resource)
-{
-	struct vfs *vfsp;
-	struct vfs *vfs_found = NULL;
-
-	vfs_list_read_lock();
-	vfsp = rootvfs;
-	do {
-		if (strcmp(refstr_value(vfsp->vfs_resource), resource) == 0) {
-			mntget(vfsp);
-			vfs_found = vfsp;
-			break;
-		}
-		vfsp = vfsp->vfs_next;
-	} while (vfsp != rootvfs);
-	vfs_list_unlock();
-	return (vfs_found);
-}
-#endif /* HAVE_SNAPSHOT */
-
 /* ARGSUSED */
 static void
 zfs_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx)
@@ -3067,38 +3041,52 @@ out:
 	return (error);
 }
 
+/*
+ * inputs:
+ * name		dataset name, or when 'arg == NULL' the full snapshot name
+ * arg		short snapshot name (i.e. part after the '@')
+ */
 int
 zfs_unmount_snap(const char *name, void *arg)
 {
-#ifdef HAVE_SNAPSHOT
-	vfs_t *vfsp = NULL;
+	zfs_sb_t *zsb = NULL;
+	char *dsname;
+	char *snapname;
+	char *fullname;
+	char *ptr;
+	int error;
 
 	if (arg) {
-		char *snapname = arg;
-		char *fullname = kmem_asprintf("%s@%s", name, snapname);
-		vfsp = zfs_get_vfs(fullname);
-		strfree(fullname);
-	} else if (strchr(name, '@')) {
-		vfsp = zfs_get_vfs(name);
+		dsname = strdup(name);
+		snapname = strdup(arg);
+	} else {
+		ptr = strchr(name, '@');
+		if (ptr) {
+			dsname = strdup(name);
+			dsname[ptr - name] = '\0';
+			snapname = strdup(ptr + 1);
+		} else {
+			return (0);
+		}
 	}
 
-	if (vfsp) {
-		/*
-		 * Always force the unmount for snapshots.
-		 */
-		int flag = MS_FORCE;
-		int err;
+	fullname = kmem_asprintf("%s@%s", dsname, snapname);
 
-		if ((err = vn_vfswlock(vfsp->vfs_vnodecovered)) != 0) {
-			mntput(vfsp);
-			return (err);
-		}
-		mntput(vfsp);
-		if ((err = dounmount(vfsp, flag, kcred)) != 0)
-			return (err);
+	error = zfs_sb_hold(dsname, FTAG, &zsb, B_FALSE);
+	if (error == 0) {
+		error = zfsctl_unmount_snapshot(zsb, fullname, MNT_FORCE);
+		zfs_sb_rele(zsb, FTAG);
+
+		/* Allow ENOENT for consistency with upstream */
+		if (error == ENOENT)
+			error = 0;
 	}
-#endif /* HAVE_SNAPSHOT */
-	return (0);
+
+	strfree(dsname);
+	strfree(snapname);
+	strfree(fullname);
+
+	return (error);
 }
 
 /*