afs: Add metadata xattrs

Add xattrs to allow the user to get/set metadata in lieu of having pioctl()
available.  The following xattrs are now available:

 - "afs.cell"

   The name of the cell in which the vnode's volume resides.

 - "afs.fid"

   The volume ID, vnode ID and vnode uniquifier of the file as three hex
   numbers separated by colons.

 - "afs.volume"

   The name of the volume in which the vnode resides.

For example:

	# getfattr -d -m ".*" /mnt/scratch
	getfattr: Removing leading '/' from absolute path names
	# file: mnt/scratch
	afs.cell="mycell.myorg.org"
	afs.fid="10000b:1:1"
	afs.volume="scratch"

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/afs/Makefile

@@ -27,6 +27,7 @@ kafs-objs := \
 	vlocation.o \
 	vnode.o \
 	volume.o \
-	write.o
+	write.o \
+	xattr.o
 
 obj-$(CONFIG_AFS_FS)  := kafs.o

fs/afs/dir.c

@@ -61,6 +61,7 @@ const struct inode_operations afs_dir_inode_operations = {
 	.permission	= afs_permission,
 	.getattr	= afs_getattr,
 	.setattr	= afs_setattr,
+	.listxattr	= afs_listxattr,
 };
 
 const struct dentry_operations afs_fs_dentry_operations = {

fs/afs/file.c

@@ -46,6 +46,7 @@ const struct inode_operations afs_file_inode_operations = {
 	.getattr	= afs_getattr,
 	.setattr	= afs_setattr,
 	.permission	= afs_permission,
+	.listxattr	= afs_listxattr,
 };
 
 const struct address_space_operations afs_fs_aops = {

fs/afs/inode.c

@@ -28,6 +28,11 @@ struct afs_iget_data {
 	struct afs_volume	*volume;	/* volume on which resides */
 };
 
+static const struct inode_operations afs_symlink_inode_operations = {
+	.get_link	= page_get_link,
+	.listxattr	= afs_listxattr,
+};
+
 /*
  * map the AFS file status to the inode member variables
  */
@@ -67,7 +72,7 @@ static int afs_inode_map_status(struct afs_vnode *vnode, struct key *key)
 			inode->i_fop	= &afs_mntpt_file_operations;
 		} else {
 			inode->i_mode	= S_IFLNK | vnode->status.mode;
-			inode->i_op	= &page_symlink_inode_operations;
+			inode->i_op	= &afs_symlink_inode_operations;
 		}
 		inode_nohighmem(inode);
 		break;

fs/afs/internal.h

@@ -731,6 +731,11 @@ extern int afs_writeback_all(struct afs_vnode *);
 extern int afs_flush(struct file *, fl_owner_t);
 extern int afs_fsync(struct file *, loff_t, loff_t, int);
 
+/*
+ * xattr.c
+ */
+extern const struct xattr_handler *afs_xattr_handlers[];
+extern ssize_t afs_listxattr(struct dentry *, char *, size_t);
 
 /*****************************************************************************/
 /*

fs/afs/mntpt.c

@@ -35,6 +35,7 @@ const struct inode_operations afs_mntpt_inode_operations = {
 	.lookup		= afs_mntpt_lookup,
 	.readlink	= page_readlink,
 	.getattr	= afs_getattr,
+	.listxattr	= afs_listxattr,
 };
 
 const struct inode_operations afs_autocell_inode_operations = {

fs/afs/super.c

@@ -319,6 +319,7 @@ static int afs_fill_super(struct super_block *sb,
 	sb->s_blocksize_bits	= PAGE_SHIFT;
 	sb->s_magic		= AFS_FS_MAGIC;
 	sb->s_op		= &afs_super_ops;
+	sb->s_xattr		= afs_xattr_handlers;
 	ret = super_setup_bdi(sb);
 	if (ret)
 		return ret;

fs/afs/xattr.c

@@ -0,0 +1,121 @@
+/* Extended attribute handling for AFS.  We use xattrs to get and set metadata
+ * instead of providing pioctl().
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/xattr.h>
+#include "internal.h"
+
+static const char afs_xattr_list[] =
+	"afs.cell\0"
+	"afs.fid\0"
+	"afs.volume";
+
+/*
+ * Retrieve a list of the supported xattrs.
+ */
+ssize_t afs_listxattr(struct dentry *dentry, char *buffer, size_t size)
+{
+	if (size == 0)
+		return sizeof(afs_xattr_list);
+	if (size < sizeof(afs_xattr_list))
+		return -ERANGE;
+	memcpy(buffer, afs_xattr_list, sizeof(afs_xattr_list));
+	return sizeof(afs_xattr_list);
+}
+
+/*
+ * Get the name of the cell on which a file resides.
+ */
+static int afs_xattr_get_cell(const struct xattr_handler *handler,
+			      struct dentry *dentry,
+			      struct inode *inode, const char *name,
+			      void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct afs_cell *cell = vnode->volume->cell;
+	size_t namelen;
+
+	namelen = strlen(cell->name);
+	if (size == 0)
+		return namelen;
+	if (namelen > size)
+		return -ERANGE;
+	memcpy(buffer, cell->name, size);
+	return namelen;
+}
+
+static const struct xattr_handler afs_xattr_afs_cell_handler = {
+	.name	= "afs.cell",
+	.get	= afs_xattr_get_cell,
+};
+
+/*
+ * Get the volume ID, vnode ID and vnode uniquifier of a file as a sequence of
+ * hex numbers separated by colons.
+ */
+static int afs_xattr_get_fid(const struct xattr_handler *handler,
+			     struct dentry *dentry,
+			     struct inode *inode, const char *name,
+			     void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	char text[8 + 1 + 8 + 1 + 8 + 1];
+	size_t len;
+
+	len = sprintf(text, "%x:%x:%x",
+		      vnode->fid.vid, vnode->fid.vnode, vnode->fid.unique);
+	if (size == 0)
+		return len;
+	if (len > size)
+		return -ERANGE;
+	memcpy(buffer, text, len);
+	return len;
+}
+
+static const struct xattr_handler afs_xattr_afs_fid_handler = {
+	.name	= "afs.fid",
+	.get	= afs_xattr_get_fid,
+};
+
+/*
+ * Get the name of the volume on which a file resides.
+ */
+static int afs_xattr_get_volume(const struct xattr_handler *handler,
+			      struct dentry *dentry,
+			      struct inode *inode, const char *name,
+			      void *buffer, size_t size)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	const char *volname = vnode->volume->vlocation->vldb.name;
+	size_t namelen;
+
+	namelen = strlen(volname);
+	if (size == 0)
+		return namelen;
+	if (namelen > size)
+		return -ERANGE;
+	memcpy(buffer, volname, size);
+	return namelen;
+}
+
+static const struct xattr_handler afs_xattr_afs_volume_handler = {
+	.name	= "afs.volume",
+	.get	= afs_xattr_get_volume,
+};
+
+const struct xattr_handler *afs_xattr_handlers[] = {
+	&afs_xattr_afs_cell_handler,
+	&afs_xattr_afs_fid_handler,
+	&afs_xattr_afs_volume_handler,
+	NULL
+};