ext4: support xattr gnu.* namespace for the Hurd

The Hurd gained[0] support for moving the translator and author
fields out of the inode and into the "gnu.*" xattr namespace.

In anticipation of that, an xattr INDEX was reserved[1].  The Hurd has
now been brought into compliance[2] with that.

This patch adds support for reading and writing such attributes from
Linux; you can now do something like

    mkdir -p hurd-root/servers/socket
    touch hurd-root/servers/socket/1
    setfattr --name=gnu.translator --value='"/hurd/pflocal\0"' \
        hurd-root/servers/socket/1
    getfattr --name=gnu.translator hurd-root/servers/socket/1
    # file: 1
    gnu.translator="/hurd/pflocal"

to setup a pipe translator, which is being used to create[3] a
vm-image for the Hurd from GNU Guix.

[0] https://summerofcode.withgoogle.com/projects/#5869799859027968
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3980bd3b406addb327d858aebd19e229ea340b9a
[2] https://git.savannah.gnu.org/cgit/hurd/hurd.git/commit/?id=a04c7bf83172faa7cb080fbe3b6c04a8415ca645
[3] https://git.savannah.gnu.org/cgit/guix.git/log/?h=wip-hurd-vm

Signed-off-by: Jan Nieuwenhuizen <janneke@gnu.org>
Link: https://lore.kernel.org/r/20200525193940.878-1-janneke@gnu.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 4ccb3c9..2e42f47 100644 (file)
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -9,7 +9,8 @@ ext4-y  := balloc.o bitmap.o block_validity.o dir.o ext4_jbd2.o extents.o \
                extents_status.o file.o fsmap.o fsync.o hash.o ialloc.o \
                indirect.o inline.o inode.o ioctl.o mballoc.o migrate.o \
                mmp.o move_extent.o namei.o page-io.o readpage.o resize.o \
-               super.o symlink.o sysfs.o xattr.o xattr_trusted.o xattr_user.o
+               super.o symlink.o sysfs.o xattr.o xattr_hurd.o xattr_trusted.o \
+               xattr_user.o
 
 ext4-$(CONFIG_EXT4_FS_POSIX_ACL)       += acl.o
 ext4-$(CONFIG_EXT4_FS_SECURITY)                += xattr_security.o

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 9b29a40..7d2f657 100644 (file)
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -93,6 +93,7 @@ static const struct xattr_handler * const ext4_xattr_handler_map[] = {
 #ifdef CONFIG_EXT4_FS_SECURITY
        [EXT4_XATTR_INDEX_SECURITY]          = &ext4_xattr_security_handler,
 #endif
+       [EXT4_XATTR_INDEX_HURD]              = &ext4_xattr_hurd_handler,
 };
 
 const struct xattr_handler *ext4_xattr_handlers[] = {
@@ -105,6 +106,7 @@ const struct xattr_handler *ext4_xattr_handlers[] = {
 #ifdef CONFIG_EXT4_FS_SECURITY
        &ext4_xattr_security_handler,
 #endif
+       &ext4_xattr_hurd_handler,
        NULL
 };
 

diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index ffe21ac..730b91f 100644 (file)
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -124,6 +124,7 @@ struct ext4_xattr_inode_array {
 extern const struct xattr_handler ext4_xattr_user_handler;
 extern const struct xattr_handler ext4_xattr_trusted_handler;
 extern const struct xattr_handler ext4_xattr_security_handler;
+extern const struct xattr_handler ext4_xattr_hurd_handler;
 
 #define EXT4_XATTR_NAME_ENCRYPTION_CONTEXT "c"
 

diff --git a/fs/ext4/xattr_hurd.c b/fs/ext4/xattr_hurd.c
new file mode 100644 (file)
index 0000000..8cfa74a
--- /dev/null
+++ b/fs/ext4/xattr_hurd.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext4/xattr_hurd.c
+ * Handler for extended gnu attributes for the Hurd.
+ *
+ * Copyright (C) 2001 by Andreas Gruenbacher, <a.gruenbacher@computer.org>
+ * Copyright (C) 2020 by Jan (janneke) Nieuwenhuizen, <janneke@gnu.org>
+ */
+
+#include <linux/init.h>
+#include <linux/string.h>
+#include "ext4.h"
+#include "xattr.h"
+
+static bool
+ext4_xattr_hurd_list(struct dentry *dentry)
+{
+       return test_opt(dentry->d_sb, XATTR_USER);
+}
+
+static int
+ext4_xattr_hurd_get(const struct xattr_handler *handler,
+                   struct dentry *unused, struct inode *inode,
+                   const char *name, void *buffer, size_t size)
+{
+       if (!test_opt(inode->i_sb, XATTR_USER))
+               return -EOPNOTSUPP;
+
+       return ext4_xattr_get(inode, EXT4_XATTR_INDEX_HURD,
+                             name, buffer, size);
+}
+
+static int
+ext4_xattr_hurd_set(const struct xattr_handler *handler,
+                   struct dentry *unused, struct inode *inode,
+                   const char *name, const void *value,
+                   size_t size, int flags)
+{
+       if (!test_opt(inode->i_sb, XATTR_USER))
+               return -EOPNOTSUPP;
+
+       return ext4_xattr_set(inode, EXT4_XATTR_INDEX_HURD,
+                             name, value, size, flags);
+}
+
+const struct xattr_handler ext4_xattr_hurd_handler = {
+       .prefix = XATTR_HURD_PREFIX,
+       .list   = ext4_xattr_hurd_list,
+       .get    = ext4_xattr_hurd_get,
+       .set    = ext4_xattr_hurd_set,
+};

diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
index c1395b5..9463db2 100644 (file)
--- a/include/uapi/linux/xattr.h
+++ b/include/uapi/linux/xattr.h
@@ -7,6 +7,7 @@
   Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
   Copyright (c) 2001-2002 Silicon Graphics, Inc.  All Rights Reserved.
   Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
+  Copyright (c) 2020 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 */
 
 #include <linux/libc-compat.h>
@@ -31,6 +32,9 @@
 #define XATTR_BTRFS_PREFIX "btrfs."
 #define XATTR_BTRFS_PREFIX_LEN (sizeof(XATTR_BTRFS_PREFIX) - 1)
 
+#define XATTR_HURD_PREFIX "gnu."
+#define XATTR_HURD_PREFIX_LEN (sizeof(XATTR_HURD_PREFIX) - 1)
+
 #define XATTR_SECURITY_PREFIX  "security."
 #define XATTR_SECURITY_PREFIX_LEN (sizeof(XATTR_SECURITY_PREFIX) - 1)