[PATCH] shmem: support xattr gnu.* namespace for the Hurd

[Janneke Nieuwenhuizen <janneke@gnu.org>]

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].  In 2020, the
Hurd has been brought into compliance[2] with that, and so has ext4[3].

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

    mkdir -p hurd-root
    mount -t tmpfs -o size=2M tmpfs hurd-root
    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 an initial
file-system image for the Hurd from GNU Guix[4].

[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.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=88ee9d571b6d8ed345f877e05f685814412e359b
[4] https://codeberg.org/guix/guix/pulls/8632
---
 mm/shmem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 3b5dc21b323c..5d60aa4dba92 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -15,6 +15,7 @@
  * Extended attribute support for tmpfs:
  * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
  * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
+ * Copyright (C) 2026 Janneke Nieuwenhuizen <janneke@gnu.org>
  *
  * tiny-shmem:
  * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
@@ -4371,10 +4372,17 @@ static const struct xattr_handler shmem_user_xattr_handler = {
 	.set = shmem_xattr_handler_set,
 };
 
+static const struct xattr_handler shmem_hurd_xattr_handler = {
+	.prefix = XATTR_HURD_PREFIX,
+	.get = shmem_xattr_handler_get,
+	.set = shmem_xattr_handler_set,
+};
+
 static const struct xattr_handler * const shmem_xattr_handlers[] = {
 	&shmem_security_xattr_handler,
 	&shmem_trusted_xattr_handler,
 	&shmem_user_xattr_handler,
+	&shmem_hurd_xattr_handler,
 	NULL
 };
 
-- 
2.54.0


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