Honor CONFIG_FS_POSIX_ACL kernel option

The required Posix ACL interfaces are only available for kernels
with CONFIG_FS_POSIX_ACL defined.  Therefore, only enable Posix
ACL support for these kernels.  All major distribution kernels
enable CONFIG_FS_POSIX_ACL by default.

If your kernel does not support Posix ACLs the following warning
will be printed at ZFS module load time.

  "ZFS: Posix ACLs disabled by kernel"

Signed-off-by: Massimo Maggi <me@massimo-maggi.eu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1825

include/linux/vfs_compat.h

@@ -174,6 +174,7 @@ lseek_execute(struct file *filp, struct inode *inode,
 }
 #endif /* SEEK_HOLE && SEEK_DATA && !HAVE_LSEEK_EXECUTE */
 
+#if defined(CONFIG_FS_POSIX_ACL)
 /*
  * These functions safely approximates the behavior of posix_acl_release()
  * which cannot be used because it calls the GPL-only symbol kfree_rcu().
@@ -315,5 +316,6 @@ typedef umode_t zpl_equivmode_t;
 #else
 typedef mode_t zpl_equivmode_t;
 #endif /* HAVE_POSIX_ACL_EQUIV_MODE_UMODE_T */
+#endif /* CONFIG_FS_POSIX_ACL */
 
 #endif /* _ZFS_VFS_H */

include/sys/zpl.h

@@ -71,6 +71,7 @@ extern struct file_system_type zpl_fs_type;
 extern ssize_t zpl_xattr_list(struct dentry *dentry, char *buf, size_t size);
 extern int zpl_xattr_security_init(struct inode *ip, struct inode *dip,
     const struct qstr *qstr);
+#if defined(CONFIG_FS_POSIX_ACL)
 extern int zpl_set_acl(struct inode *ip, int type, struct posix_acl *acl);
 extern struct posix_acl *zpl_get_acl(struct inode *ip, int type);
 #if !defined(HAVE_GET_ACL)
@@ -87,6 +88,19 @@ extern int zpl_permission(struct inode *ip, int mask);
 
 extern int zpl_init_acl(struct inode *ip, struct inode *dir);
 extern int zpl_chmod_acl(struct inode *ip);
+#else
+static inline int
+zpl_init_acl(struct inode *ip, struct inode *dir)
+{
+	return (0);
+}
+
+static inline int
+zpl_chmod_acl(struct inode *ip)
+{
+	return (0);
+}
+#endif /* CONFIG_FS_POSIX_ACL */
 
 extern xattr_handler_t *zpl_xattr_handlers[];