[PATCH] ext2fs: Update to upstream Hurd-reserved xattr index for "gnu.*".

[Jan Nieuwenhuizen]

Hello,

I have looked a bit further into upstream xattr support and and have
been testing that using the two attached patches.  As you can see,
upstream reserved INDEX 10 for the Hurd, but the Hurd has been using
INDEX 7.

The (trivial) patch for the Hurd to change this should be OK, but until
this all fully works I'm just a bit less certain about the Linux patch.

Anyway, using the patched Linux we can add gnu.translator attributes to
files that are recognized by Linux (on a Hurd file system) as well as by
the Hurd.

So now we can actually do this

--8<---------------cut here---------------start------------->8---
dd if=/dev/zero of=file bs=1k count=1000
losetup /dev/loop0 file
mke2fs -t ext2 -o hurd -O ext_attr /dev/loop0
mount -t ext2 -o x-xattr-translator-records /dev/loop0 /mnt
mkdir -p /mnt/servers/socket
touch /mnt/servers/socket/1
setfattr --name=gnu.translator --value='/hurd/pflocal\0' /mnt/servers/socket/1
getfattr --name=gnu.translator /mnt/servers/socket/1
# file: 1
gnu.translator="/hurd/pflocal"
--8<---------------cut here---------------end--------------->8---

(on GNU/Linux), and I am using that now in Guix to cross build a
vm-image for the Hurd.

So far, so good.  However, combining these does not work yet.  When I
reduce libexec/runsystem to something like this

--8<---------------cut here---------------start------------->8---
#! /gnu/store/s8pcby4hjxf7d4pfzrwd3ngd813i8skw-bash-minimal-5.0.16/bin/bash

# XXX Guile needs pipe support for its finalizer thread to start
PATH=/gnu/store/6is7b5xjdfdwzym5cfhjf7jpa3824h42-hurd-0.9-1.91a5167/bin:/gnu/store/6is7b5xjdfdwzym5cfhjf7jpa3824h42-hurd-0.9-1.91a5167/sbin:/gnu/store/a4vdhbfflmbpc346lsvl3v0plplmg5ma-attr-2.4.48/bin:/gnu/store/y9vicb9spdy9lfsipv75yy5aavwf5xyn-coreutils-8.32/bin:/gnu/store/s5kx9yqqqqbvdkxcyg1243rl4fdq139b-sed-4.8/bin:/gnu/store/wy7k8v4iik6kzh9vw1fjzcnj7jhsh5fv-util-linux-2.35.1/sbin

echo foo | sed s/o/O/
echo Starting 
/gnu/store/6is7b5xjdfdwzym5cfhjf7jpa3824h42-hurd-0.9-1.91a5167/libexec/rc ...
exec /gnu/store/6is7b5xjdfdwzym5cfhjf7jpa3824h42-hurd-0.9-1.91a5167/libexec/rc
--8<---------------cut here---------------end--------------->8---

the Hurd says

    /gnu/store/6is7b5xjdfdwzym5cfhjf7jpa3824h42-hurd-0.9-1.91a5167/runsystem: 
pipe error: Translator died

When I leave out the echo | sed pipe, starting Guile just hangs.

When I insert this

--8<---------------cut here---------------start------------->8---
fsck --yes --force /
fsysopts / --writable
mv /servers/socket/1 /servers/socket/1-linux
touch /servers/socket/1
setfattr --name=gnu.translator --value='/hurd/pflocal\0' /servers/socket/1
--8<---------------cut here---------------end--------------->8---

it works: So, we're getting real close! \o/

And I guess there must be an incompatibility between Linux and the Hurd
in how setfattr embeds the xattr attributes into the file system.

How to best "diff" this aspect in the file system; how to proceed?
Inspired by Shengyu's GSoC code that simply seemed to use fprintf for
debbugging, I tried adding some debug printing in inode.c

    fprintf (stderr, "gnu.translator[%d,%d]=%s\n", datalen, strlen (*namep), 
*namep);

but that does not seem to work, or I am looking in the wrong place.  Ideas?

Greetings,
janneke

>From 75cb948c575fca3962c4cce115d31dd178bc389f Mon Sep 17 00:00:00 2001
From: "Jan (janneke) Nieuwenhuizen" <address@hidden>
Date: Tue, 12 May 2020 07:39:59 +0200
Subject: [PATCH] ext2fs: Update to upstream Hurd-reserved xattr index for
 "gnu.*".

See
    
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3980bd3b406addb327d858aebd19e229ea340b9a

This supports setting (and reading) of passive trasnlators from
GNU/Linux, e.g.

    dd if=/dev/zero of=file bs=1k count=1000
    losetup /dev/loop0 file
    mke2fs -t ext2 -o hurd -O ext_attr /dev/loop0
    mount -t ext2 -o x-xattr-translator-records /dev/loop0 /mnt
    mkdir -p /mnt/servers/socket
    touch /mnt/servers/socket/1
    setfattr --name=gnu.translator --value='/hurd/pflocal\0' 
/mnt/servers/socket/1
    getfattr --name=gnu.translator /mnt/servers/socket/1
    # file: 1
    gnu.translator="/hurd/pflocal"

* ext2fs/xattr.c (struct _xattr_prefix): For "gnu.*", use index for
the Hurd (10).
---
 ext2fs/xattr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ext2fs/xattr.c b/ext2fs/xattr.c
index f6ea0f39..78458214 100644
--- a/ext2fs/xattr.c
+++ b/ext2fs/xattr.c
@@ -1,6 +1,6 @@
  /* Ext2 support for extended attributes
 
-   Copyright (C) 2006, 2016 Free Software Foundation, Inc.
+   Copyright (C) 2006, 2016, 2020 Free Software Foundation, Inc.
 
    Written by Thadeu Lima de Souza Cascardo <address@hidden>
    and Shengyu Zhang <address@hidden>
@@ -39,7 +39,7 @@ xattr_prefixes[] =
   {
   1, "user.", sizeof "user." - 1},
   {
-  7, "gnu.", sizeof "gnu." - 1},
+  10, "gnu.", sizeof "gnu." - 1},
   {
   0, NULL, 0}
 };
-- 
2.26.0

>From 475eb7cfae390d9118a5420df90b979b4ec78aa3 Mon Sep 17 00:00:00 2001
From: "Jan (janneke) Nieuwenhuizen" <address@hidden>
Date: Mon, 11 May 2020 18:43:44 +0200
Subject: [PATCH] ext4: Support gnu.* namespace for Hurd file systems.

The Hurd has experimental code to move the translator and author
fields out of the inode, into the "gnu.*" xattr namespace.

This patch adds support for reading and writing such attributes.

For more information please see:
    https://summerofcode.withgoogle.com/projects/#5869799859027968
---
 fs/ext4/Kconfig            | 11 ++++++++
 fs/ext4/Makefile           |  1 +
 fs/ext4/xattr.c            |  6 ++++
 fs/ext4/xattr.h            |  1 +
 fs/ext4/xattr_hurd.c       | 57 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/xattr.h |  4 +++
 6 files changed, 80 insertions(+)
 create mode 100644 fs/ext4/xattr_hurd.c

diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index 2de970cfc33c..324082dec6ee 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -98,6 +98,17 @@ config EXT4_FS_SECURITY
          If you are not using a security module that requires using
          extended attributes for file security labels, say N.
 
+config EXT4_FS_HURD
+       bool "Ext4 xattr gnu.* namespace support for the Hurd"
+       depends on EXT4_FS
+       help
+         Extended attributes are name:value pairs associated with inodes by
+         the kernel or by users (see the attr(5) manual page for details).
+          This option adds support for the gnu.* namespace ext4 file
+          systems for the Hurd.
+
+         If you don't know what the GNU Hurd is, say N
+
 config EXT4_DEBUG
        bool "Ext4 debugging support"
        depends on EXT4_FS
diff --git a/fs/ext4/Makefile b/fs/ext4/Makefile
index 4ccb3c9189d8..3c2c43167dbf 100644
--- a/fs/ext4/Makefile
+++ b/fs/ext4/Makefile
@@ -16,3 +16,4 @@ ext4-$(CONFIG_EXT4_FS_SECURITY)               += 
xattr_security.o
 ext4-inode-test-objs                   += inode-test.o
 obj-$(CONFIG_EXT4_KUNIT_TESTS)         += ext4-inode-test.o
 ext4-$(CONFIG_FS_VERITY)               += verity.o
+ext4-$(CONFIG_EXT4_FS_HURD)            += xattr_hurd.o
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 8966a5439a22..6353034c5f56 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -93,6 +93,9 @@ static const struct xattr_handler * const 
ext4_xattr_handler_map[] = {
 #ifdef CONFIG_EXT4_FS_SECURITY
        [EXT4_XATTR_INDEX_SECURITY]          = &ext4_xattr_security_handler,
 #endif
+#ifdef CONFIG_EXT4_FS_HURD
+       [EXT4_XATTR_INDEX_HURD]              = &ext4_xattr_hurd_handler,
+#endif
 };
 
 const struct xattr_handler *ext4_xattr_handlers[] = {
@@ -104,6 +107,9 @@ const struct xattr_handler *ext4_xattr_handlers[] = {
 #endif
 #ifdef CONFIG_EXT4_FS_SECURITY
        &ext4_xattr_security_handler,
+#endif
+#ifdef CONFIG_EXT4_FS_HURD
+       &ext4_xattr_hurd_handler,
 #endif
        NULL
 };
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index f39cad2abe2a..c5e865f14133 100644
--- 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
index 000000000000..ee31557308a9
--- /dev/null
+++ b/fs/ext4/xattr_hurd.c
@@ -0,0 +1,57 @@
+// 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, <address@hidden>
+ * Copyright (C) 2020 by Jan (janneke) Nieuwenhuizen, <address@hidden>
+ */
+
+#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) &&
+               EXT4_SB(dentry->d_sb)->s_es->s_creator_os ==
+               cpu_to_le32(EXT4_OS_HURD);
+}
+
+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) ||
+            EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
+            cpu_to_le32(EXT4_OS_HURD))
+               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) ||
+            EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
+            cpu_to_le32(EXT4_OS_HURD))
+               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 c1395b5bd432..9463db2dfa9d 100644
--- a/include/uapi/linux/xattr.h
+++ b/include/uapi/linux/xattr.h
@@ -7,6 +7,7 @@
   Copyright (C) 2001 by Andreas Gruenbacher <address@hidden>
   Copyright (c) 2001-2002 Silicon Graphics, Inc.  All Rights Reserved.
   Copyright (c) 2004 Red Hat, Inc., James Morris <address@hidden>
+  Copyright (c) 2020 Jan (janneke) Nieuwenhuizen <address@hidden>
 */
 
 #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)
 
-- 
2.26.0

-- 
Jan Nieuwenhuizen <address@hidden> | GNU LilyPond http://lilypond.org
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