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>

8 files changed, 138 insertions, 2 deletions

diff --git a/fs/afs/Makefile b/fs/afs/Makefile
index 4f64b95d57bd..095c54165dfd 100644
--- a/fs/afs/Makefile
+++ b/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
diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 949f960337f5..613a77058263 100644
--- a/fs/afs/dir.c
+++ b/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 = {
diff --git a/fs/afs/file.c b/fs/afs/file.c
index 0d5b8508869b..510cba15fa56 100644
--- a/fs/afs/file.c
+++ b/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 = {
diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index aae55dd15108..342316a9e3e0 100644
--- a/fs/afs/inode.c
+++ b/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;
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 4e2556606623..82e16556afea 100644
--- a/fs/afs/internal.h
+++ b/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);
 
 /*****************************************************************************/
 /*
diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
index bd3b65cde282..690fea9d84c3 100644
--- a/fs/afs/mntpt.c
+++ b/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 = {
diff --git a/fs/afs/super.c b/fs/afs/super.c
index c79633e5cfd8..67680c2d96cf 100644
--- a/fs/afs/super.c
+++ b/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;
diff --git a/fs/afs/xattr.c b/fs/afs/xattr.c
new file mode 100644
index 000000000000..2830e4f48d85
--- /dev/null
+++ b/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;
+