fs: xattr_handler table should be const

The entries in xattr handler table should be immutable (ie const)
like other operation tables.

Later patches convert common filesystems. Uncoverted filesystems
will still work, but will generate a compiler warning.

Signed-off-by: Stephen Hemminger <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/generic_acl.c

···
 	return -EAGAIN;
 }
 
-struct xattr_handler generic_acl_access_handler = {
+const struct xattr_handler generic_acl_access_handler = {
 	.prefix = POSIX_ACL_XATTR_ACCESS,
 	.flags	= ACL_TYPE_ACCESS,
 	.list	= generic_acl_list,
···
 	.set	= generic_acl_set,
 };
 
-struct xattr_handler generic_acl_default_handler = {
+const struct xattr_handler generic_acl_default_handler = {
 	.prefix = POSIX_ACL_XATTR_DEFAULT,
 	.flags	= ACL_TYPE_DEFAULT,
 	.list	= generic_acl_list,

fs/xattr.c

···
 /*
  * Find the xattr_handler with the matching prefix.
  */
-static struct xattr_handler *
-xattr_resolve_name(struct xattr_handler **handlers, const char **name)
+static const struct xattr_handler *
+xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
 {
-	struct xattr_handler *handler;
+	const struct xattr_handler *handler;
 
 	if (!*name)
 		return NULL;
···
 ssize_t
 generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
 {
-	struct xattr_handler *handler;
+	const struct xattr_handler *handler;
 
 	handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 	if (!handler)
···
 ssize_t
 generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
 {
-	struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
+	const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
 	unsigned int size = 0;
 
 	if (!buffer) {
···
 int
 generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
 {
-	struct xattr_handler *handler;
+	const struct xattr_handler *handler;
 
 	if (size == 0)
 		value = "";  /* empty EA, do not remove */
···
 int
 generic_removexattr(struct dentry *dentry, const char *name)
 {
-	struct xattr_handler *handler;
+	const struct xattr_handler *handler;
 
 	handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
 	if (!handler)

include/linux/fs.h

···
 #ifdef CONFIG_SECURITY
 	void                    *s_security;
 #endif
-	struct xattr_handler	**s_xattr;
+	const struct xattr_handler **s_xattr;
 
 	struct list_head	s_inodes;	/* all inodes */
 	struct hlist_head	s_anon;		/* anonymous dentries for (nfs) exporting */

include/linux/generic_acl.h

···
 
 struct inode;
 
-extern struct xattr_handler generic_acl_access_handler;
-extern struct xattr_handler generic_acl_default_handler;
+extern const struct xattr_handler generic_acl_access_handler;
+extern const struct xattr_handler generic_acl_default_handler;
 
 int generic_acl_init(struct inode *, struct inode *);
 int generic_acl_chmod(struct inode *);

include/linux/xattr.h

···
 struct dentry;
 
 struct xattr_handler {
-	char *prefix;
+	const char *prefix;
 	int flags;	/* fs private flags passed back to the handlers */
 	size_t (*list)(struct dentry *dentry, char *list, size_t list_size,
 		       const char *name, size_t name_len, int handler_flags);

mm/shmem.c

···
 					  size, flags);
 }
 
-static struct xattr_handler shmem_xattr_security_handler = {
+static const struct xattr_handler shmem_xattr_security_handler = {
 	.prefix = XATTR_SECURITY_PREFIX,
 	.list   = shmem_xattr_security_list,
 	.get    = shmem_xattr_security_get,
 	.set    = shmem_xattr_security_set,
 };
 
-static struct xattr_handler *shmem_xattr_handlers[] = {
+static const struct xattr_handler *shmem_xattr_handlers[] = {
 	&generic_acl_access_handler,
 	&generic_acl_default_handler,
 	&shmem_xattr_security_handler,