Honor xattr=sa dataset property

ZFS incorrectly uses directory-based extended attributes even when
xattr=sa is specified as a dataset property or mount option. Support to
honor temporary mount options including "xattr" was added in commit
0282c41. There are two issues with the
mount option handling:

* Libzfs has historically included "xattr" in its list of default mount
  options with no value specified. Omitting the value implies xattr=on or
  directory-based xattrs, so the dataset is configured to use
  directory-based xattrs regardless of the xattr dataset property value.
  Address this by removing "xattr" from the list of default mount
  options.

* The option parser incorrectly treats the xattr mount option as a
  boolean value. Even if xattr=sa is specified, the parser translates
  that to xattr=on. Address this by treating the option as a scalar
  value.

Issue #3787

Signed-off-by: Ned Bass <bass6@llnl.gov>

include/sys/zfs_vfsops.h

@@ -44,6 +44,7 @@ struct znode;
 typedef struct zfs_mntopts {
 	char		*z_osname;	/* Objset name */
 	char		*z_mntpoint;	/* Primary mount point */
+	uint64_t	z_xattr;
 	boolean_t	z_readonly;
 	boolean_t	z_do_readonly;
 	boolean_t	z_setuid;
@@ -52,7 +53,6 @@ typedef struct zfs_mntopts {
 	boolean_t	z_do_exec;
 	boolean_t	z_devices;
 	boolean_t	z_do_devices;
-	boolean_t	z_xattr;
 	boolean_t	z_do_xattr;
 	boolean_t	z_atime;
 	boolean_t	z_do_atime;

lib/libzfs/libzfs_mount.c

@@ -371,8 +371,6 @@ zfs_add_options(zfs_handle_t *zhp, char *options, int len)
 	    ZFS_PROP_READONLY, MNTOPT_RO, MNTOPT_RW);
 	error = error ? error : zfs_add_option(zhp, options, len,
 	    ZFS_PROP_SETUID, MNTOPT_SETUID, MNTOPT_NOSETUID);
-	error = error ? error : zfs_add_option(zhp, options, len,
-	    ZFS_PROP_XATTR, MNTOPT_XATTR, MNTOPT_NOXATTR);
 	error = error ? error : zfs_add_option(zhp, options, len,
 	    ZFS_PROP_NBMAND, MNTOPT_NBMAND, MNTOPT_NONBMAND);
 

module/zfs/zpl_super.c

@@ -264,11 +264,30 @@ zpl_parse_option(char *option, int token, substring_t *args,
 		zmo->z_do_devices = B_TRUE;
 		break;
 	case TOKEN_XATTR:
-		zmo->z_xattr = B_TRUE;
+	{
+		char *xattr_val;
+		uint64_t index;
+
+		xattr_val = match_strdup(&args[0]);
+		if (xattr_val == NULL)
+			return (-ENOMEM);
+
+		if (strlen(xattr_val) == 0) {
+			index = ZFS_XATTR_DIR;
+		} else if (zfs_prop_string_to_index(ZFS_PROP_XATTR,
+		    xattr_val, &index) != 0) {
+			strfree(xattr_val);
+			return (-EINVAL);
+		}
+
+		zmo->z_xattr = index;
 		zmo->z_do_xattr = B_TRUE;
+		strfree(xattr_val);
+
 		break;
+	}
 	case TOKEN_NOXATTR:
-		zmo->z_xattr = B_FALSE;
+		zmo->z_xattr = ZFS_XATTR_OFF;
 		zmo->z_do_xattr = B_TRUE;
 		break;
 	case TOKEN_ATIME: