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9A8376012B; Tue, 3 Mar 2026 12:41:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A327C116C6; Tue, 3 Mar 2026 12:41:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772541662; bh=VP3JX/y7oHBrbuT3Z5WJTKU4TP0CvwWXeHSRvhRDUa4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Zvz0oQM923J04EpBWJnh25hhi1uji/p9u147a6lunY/FvMUKCcB35+UyrQ0TMgEa5 GdwqkMNsNHk7uOP5gamt+yaACOgsqZbyv8Q6aXl/q5ROkvBu87FNOVYXK8CpHIxmEm DiteLwJWuRDYIJ3IgaK/HoVWBG06sjQe0n34B1+PNE6XDMKpiXq5/bkfI3YvyOLjL5 xu53HCqTB8sVkttFXX0uh9wl9fmZToNs05cXE4Ea9br9f+WmAEhi6+QXnESXgGFt0d 9iDNZgv2JJ+8YSmo8OGVtxnPp0u/cZ+lalNTtSSkojp+G+/VCnuhFBbEDHV/dEz9rq DkEeRpA2ASGUQ== Message-ID: <1df344e68aca20c24d447318ff93db3f359043ee.camel@kernel.org> Subject: Re: [PATCH 00/14] xattr: rework simple xattrs and support user.* xattrs on sockets From: Jeff Layton To: Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Josef Bacik , Alexander Viro , Jan Kara , linux-kernel@vger.kernel.org, Hugh Dickins , linux-mm@kvack.org, Greg Kroah-Hartman , Tejun Heo , Eric Dumazet , Jakub Kicinski , Jann Horn , netdev@vger.kernel.org Date: Tue, 03 Mar 2026 07:40:58 -0500 In-Reply-To: <20260216-work-xattr-socket-v1-0-c2efa4f74cb7@kernel.org> References: <20260216-work-xattr-socket-v1-0-c2efa4f74cb7@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ 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U2FsdGVkX1+ua2/XHzv+cMHLOzHpzhAyiIK9xHzZxCmn+v9I8by3OYemeFpKtHjTMrJqOunF9rg9LjjzYXWvwf2Q2FZ9yA7DsHLJ762avXBgfzD2rg6EjgP8htIlS3UTMEjJnoherATnKXKH4l2Yz2ZxFmJ11i1Jz1iZjSjrJNopxroBLEPnzGcwpwDMkdkwswMNSqum109wKU5hmCbwnMYVGq2OAXeEFoPaA8tdwNu2zNgLO9adRMawxxApemhdWO/Hb+8oBXoFQpzkO0IJemngs4ldtb7eb6oeVck5dTnjrnWITHOjulTqM1g/3EA9eH3QyaQJPzeOaJOrXrW21cmLkMPkp7R+KpxUkmoh/6ourtnB5yLG2B6ZMN2sq4GJjh9CmNArjxoXalcfC5UTRzxuVogH7XKdBlRPLLdxVOVcohmlhfC2UEOwmO8Ueg0KNt01o6OKNakCahpFlBL+oBHuKs5ieN45QXRKRVLDLZAkFu9NSxI7NOpgqLVEeQ8hk/en8tKeNgWcWxOxHMtYznTHoTYP/FDumSu9+Fq3sj3MXcUsbk7rZwRljCp4MW0MgLUfIee52r8ctrh6w5VRiTnAOC8oQYeDi8bDzselcLdO65zLu3Z730AkP4MpsA6kPzoPMTxjC7f/maIbALidq9dVM69jR1em1ZwzJQX1tjtZW0WyzW/tVPGDHdb4+1HosVpCeGYZwSEZbMWF+jcA+EuvBKDPNHYlWaO6LaU7rqT61GVFfsUwcN20H/uWgVlEYHRvkLhu8hb01GFR1mwmTmPu5ebr5E1d+aX5dZ30TgdQc04L3vmeP38xQlgEt4BSVGnVPTGl0Iq7dL8SwfQC3IhGVunWnE6W+iI0zs+62t1bSLVBZJFAQdprTIqJKzMx6tfgsHcw8C2h/yoLEFcXKjc7MEzBj712LBtUDmFlojjPlj7+s1tjtPK22g4Tij729x/LInrrnCRiSqmuVZ3 ER02oEnk UG2f+I+3cPk8Wf2bPf4gRWECyyWSXc1YmcSjcsSRGYTglKjrf2/+/wsUJanmIT4DR3X+G86N3t+z0OytLk8Gfu2rSJJuo8s1AfO5Yu6l2r0ummAgneaBeKfHVIX7own9ONEaN5T0/BMPtvv80uP71/MkbTXry0jQDqI7R4sGS7WlDYFYfVd32rwXc+8hwKfa31tPf0yxI8qOQjXpYnpaBK9vpLR2CBkG8lQxJUgMp5szuf0p25Wy8b90HlQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2026-02-16 at 14:31 +0100, Christian Brauner wrote: > Hey, >=20 > This reworks the simple_xattr infrastructure and adds support for > user.* extended attributes on sockets. >=20 > The simple_xattr subsystem currently uses an rbtree protected by a > reader-writer spinlock. This series replaces the rbtree with an > rhashtable giving O(1) average-case lookup with RCU-based lockless > reads. This sped up concurrent access patterns on tmpfs quite a bit and > it's an overall easy enough conversion to do and gets rid or rwlock_t. >=20 > The conversion is done incrementally: a new rhashtable path is added > alongside the existing rbtree, consumers are migrated one at a time > (shmem, kernfs, pidfs), and then the rbtree code is removed. All three > consumers switch from embedded structs to pointer-based lazy allocation > so the rhashtable overhead is only paid for inodes that actually use > xattrs. >=20 > With this infrastructure in place the series adds support for user.* > xattrs on sockets. Path-based AF_UNIX sockets inherit xattr support > from the underlying filesystem (e.g. tmpfs) but sockets in sockfs - > that is everything created via socket() including abstract namespace > AF_UNIX sockets - had no xattr support at all. >=20 > The xattr_permission() checks are reworked to allow user.* xattrs on > S_IFSOCK inodes. Sockfs sockets get per-inode limits of 128 xattrs and > 128KB total value size matching the limits already in use for kernfs. >=20 > The practical motivation comes from several directions. systemd and > GNOME are expanding their use of Varlink as an IPC mechanism. For D-Bus > there are tools like dbus-monitor that can observe IPC traffic across > the system but this only works because D-Bus has a central broker. For > Varlink there is no broker and there is currently no way to identify > which sockets speak Varlink. With user.* xattrs on sockets a service > can label its socket with the IPC protocol it speaks (e.g., > user.varlink=3D1) and an eBPF program can then selectively capture > traffic on those sockets. Enumerating bound sockets via netlink combined > with these xattr labels gives a way to discover all Varlink IPC > entrypoints for debugging and introspection. >=20 > Similarly, systemd-journald wants to use xattrs on the /dev/log socket > for protocol negotiation to indicate whether RFC 5424 structured syslog > is supported or whether only the legacy RFC 3164 format should be used. >=20 > In containers these labels are particularly useful as high-privilege or > more complicated solutions for socket identification aren't available. >=20 > The series comes with comprehensive selftests covering path-based > AF_UNIX sockets, sockfs socket operations, per-inode limit enforcement, > and xattr operations across multiple address families (AF_INET, > AF_INET6, AF_NETLINK, AF_PACKET). >=20 > Christian >=20 > Signed-off-by: Christian Brauner > --- > Christian Brauner (14): > xattr: add rcu_head and rhash_head to struct simple_xattr > xattr: add rhashtable-based simple_xattr infrastructure > shmem: adapt to rhashtable-based simple_xattrs with lazy allocation > kernfs: adapt to rhashtable-based simple_xattrs with lazy allocatio= n > pidfs: adapt to rhashtable-based simple_xattrs > xattr: remove rbtree-based simple_xattr infrastructure > xattr: add xattr_permission_error() > xattr: switch xattr_permission() to switch statement > xattr: move user limits for xattrs to generic infra > xattr,net: support limited amount of extended attributes on sockfs = sockets > xattr: support extended attributes on sockets > selftests/xattr: path-based AF_UNIX socket xattr tests > selftests/xattr: sockfs socket xattr tests > selftests/xattr: test xattrs on various socket families >=20 > fs/kernfs/dir.c | 15 +- > fs/kernfs/inode.c | 99 +---- > fs/kernfs/kernfs-internal.h | 5 +- > fs/pidfs.c | 65 +-- > fs/xattr.c | 423 +++++++++++++--= ---- > include/linux/kernfs.h | 2 - > include/linux/shmem_fs.h | 2 +- > include/linux/xattr.h | 47 ++- > mm/shmem.c | 46 +- > net/socket.c | 119 ++++-- > .../testing/selftests/filesystems/xattr/.gitignore | 3 + > tools/testing/selftests/filesystems/xattr/Makefile | 6 + > .../filesystems/xattr/xattr_socket_test.c | 470 +++++++++++++++= ++++++ > .../filesystems/xattr/xattr_socket_types_test.c | 177 ++++++++ > .../filesystems/xattr/xattr_sockfs_test.c | 363 +++++++++++++++= + > 15 files changed, 1547 insertions(+), 295 deletions(-) > --- > base-commit: 72c395024dac5e215136cbff793455f065603b06 > change-id: 20260211-work-xattr-socket-c85f4d3b8847 Reviewed-by: Jeff Layton