Linux compat 2.6.39: mount_nodev()

The .get_sb callback has been replaced by a .mount callback
in the file_system_type structure.  When using the new
interface the caller must now use the mount_nodev() helper.

Unfortunately, the new interface no longer passes the vfsmount
down to the zfs layers.  This poses a problem for the existing
implementation because we currently save this pointer in the
super block for latter use.  It provides our only entry point
in to the namespace layer for manipulating certain mount options.

This needed to be done originally to allow commands like
'zfs set atime=off tank' to work properly.  It also allowed me
to keep more of the original Solaris code unmodified.  Under
Solaris there is a 1-to-1 mapping between a mount point and a
file system so this is a fairly natural thing to do.  However,
under Linux they many be multiple entries in the namespace
which reference the same filesystem.  Thus keeping a back
reference from the filesystem to the namespace is complicated.

Rather than introduce some ugly hack to get the vfsmount and
continue as before.  I'm leveraging this API change to update
the ZFS code to do things in a more natural way for Linux.
This has the upside that is resolves the compatibility issue
for the long term and fixes several other minor bugs which
have been reported.

This commit updates the code to remove this vfsmount back
reference entirely.  All modifications to filesystem mount
options are now passed in to the kernel via a '-o remount'.
This is the expected Linux mechanism and allows the namespace
to properly handle any options which apply to it before passing
them on to the file system itself.

Aside from fixing the compatibility issue, removing the
vfsmount has had the benefit of simplifying the code.  This
change which fairly involved has turned out nicely.

Closes #246
Closes #217
Closes #187
Closes #248
Closes #231

1 files changed, 35 insertions, 6 deletions

diff --git a/lib/libzfs/libzfs_dataset.c b/lib/libzfs/libzfs_dataset.c
index 378bbc7b1..5f8847a93 100644
--- a/lib/libzfs/libzfs_dataset.c
+++ b/lib/libzfs/libzfs_dataset.c
@@ -1313,6 +1313,25 @@ zfs_setprop_error(libzfs_handle_t *hdl, zfs_prop_t prop, int err,
 	}
 }
 
+static boolean_t
+zfs_is_namespace_prop(zfs_prop_t prop)
+{
+	switch (prop) {
+
+	case ZFS_PROP_ATIME:
+	case ZFS_PROP_DEVICES:
+	case ZFS_PROP_EXEC:
+	case ZFS_PROP_SETUID:
+	case ZFS_PROP_READONLY:
+	case ZFS_PROP_XATTR:
+	case ZFS_PROP_NBMAND:
+		return (B_TRUE);
+
+	default:
+		return (B_FALSE);
+	}
+}
+
 /*
  * Given a property name and value, set the property for the given dataset.
  */
@@ -1408,12 +1427,22 @@ zfs_prop_set(zfs_handle_t *zhp, const char *propname, const char *propval)
 		if (do_prefix)
 			ret = changelist_postfix(cl);
 
-		/*
-		 * Refresh the statistics so the new property value
-		 * is reflected.
-		 */
-		if (ret == 0)
+		if (ret == 0) {
+			/*
+			 * Refresh the statistics so the new property
+			 * value is reflected.
+			 */
 			(void) get_stats(zhp);
+
+			/*
+			 * Remount the filesystem to propagate the change
+			 * if one of the options handled by the generic
+			 * Linux namespace layer has been modified.
+			 */
+			if (zfs_is_namespace_prop(prop) &&
+			    zfs_is_mounted(zhp, NULL))
+				ret = zfs_mount(zhp, MNTOPT_REMOUNT, 0);
+		}
 	}
 
 error:
@@ -1530,7 +1559,7 @@ error:
  * True DSL properties are stored in an nvlist.  The following two functions
  * extract them appropriately.
  */
-static uint64_t
+uint64_t
 getprop_uint64(zfs_handle_t *zhp, zfs_prop_t prop, char **source)
 {
 	nvlist_t *nv;