From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A269D219EB for ; Mon, 9 Jun 2025 12:57:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749473821; cv=none; b=BasSHxq4MDvRnftWuTDJk5mwu82USSqYc+ngqUOYnYWYCqoKjT0+FvnVxoLVJHOAs/aXnh52MwIRFOGgYkDhhuqumK7ErBY8xgTbajgj9RGOxmp91gvmQ9rvLov7dY6m/Y8bkP14RblZ3edLoyWl5+UDUnG2XNffJ1df5LHJoWY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749473821; c=relaxed/simple; bh=isO2jMs/4okLVwzv7EBFcIFtPGUXMpykw2TzGvbjL7A=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=etaD+q/pLwzdbkWY3NQiX10UFyj+G9yKQhJpDPboO2HvcTpMe2XpPn1QtEjTm0k9dOnAXbT1pME3EaLVRR4vvqJ6ocsSn5PDO91Dxc1kX0/FWLluVaj0yCkI/mLlRnQldzH+TQplsVxULVItihS4rYD+ZNm2ve6q2KX14CsYegY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=T9HrEXt3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="T9HrEXt3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2330AC4CEEB; Mon, 9 Jun 2025 12:57:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749473821; bh=isO2jMs/4okLVwzv7EBFcIFtPGUXMpykw2TzGvbjL7A=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=T9HrEXt3tAAonInje2GlRTa8GClt7MLovLWvZsb/DttcQeW0MNwbqNesZI5OlxCzn W8FUEpkvljliGVctxuOiqmjk0A1YoNAeVPvqH96qiijtsUtrn6wDB5CZ9i9ypwol29 GdFhHyeVsZrJA5asOhCF2Gf9vCW9F/X4h08R5k9xL09t/G8IPGCILvzuljI/YoR7tR Amac1tClUrGneclw3SZJ8J2XEAckciva6t2msTEqGPNSNE5RI4KZ5KBurs9rcauCBV kFQXN8WuNHsmlFES87Hv41/NsB7VEOhwgqc9KR0/txCcz+R8bBF9+f8M6R0yrnN2MC zESad44JZ4wUA== Message-ID: Subject: Re: [PATCH v2 0/5] coredump: allow for flexible coredump handling From: Jeff Layton To: Christian Brauner , linux-fsdevel@vger.kernel.org, Jann Horn Cc: Josef Bacik , Alexander Viro , Daan De Meyer , Jan Kara , Lennart Poettering , Mike Yuan , Zbigniew =?UTF-8?Q?J=C4=99drzejewski-Szmek?= , Alexander Mikhalitsyn Date: Mon, 09 Jun 2025 08:56:58 -0400 In-Reply-To: <20250603-work-coredump-socket-protocol-v2-0-05a5f0c18ecc@kernel.org> References: <20250603-work-coredump-socket-protocol-v2-0-05a5f0c18ecc@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Tue, 2025-06-03 at 15:31 +0200, Christian Brauner wrote: > In addition to the extensive selftests I've already written a > (non-production ready) simple Rust coredump server for this in > userspace: >=20 > https://github.com/brauner/dumdum.git > > Extend the coredump socket to allow the coredump server to tell the > kernel how to process individual coredumps. This allows for fine-grained > coredump management. Userspace can decide to just let the kernel write > out the coredump, or generate the coredump itself, or just reject it. > > When the crashing task connects to the coredump socket the kernel will > send a struct coredump_req to the coredump server. The kernel will set > the size member of struct coredump_req allowing the coredump server how > much data can be read. >=20 > The coredump server uses MSG_PEEK to peek the size of struct > coredump_req. If the kernel uses a newer struct coredump_req the > coredump server just reads the size it knows and discard any remaining > bytes in the buffer. If the kernel uses an older struct coredump_req > the coredump server just reads the size the kernel knows. >=20 > The returned struct coredump_req will inform the coredump server what > features the kernel supports. The coredump_req->mask member is set to > the currently know features. >=20 > The coredump server may only use features whose bits were raised by the > kernel in coredump_req->mask. >=20 > In response to a coredump_req from the kernel the coredump server sends > a struct coredump_ack to the kernel. The kernel informs the coredump > server what version of struct coredump_ack it supports by setting struct > coredump_req->size_ack to the size it knows about. The coredump server > may only send as many bytes as coredump_req->size_ack indicates (a > smaller size is fine of course). The coredump server must set > coredump_ack->size accordingly. >=20 > The coredump server sets the features it wants to use in struct > coredump_ack->mask. Only bits returned in struct coredump_req->mask may > be used. >=20 > In case an invalid struct coredump_ack is sent to the kernel an > out-of-band byte will be sent by the kernel indicating the reason why > the coredump_ack was rejected. >=20 > The out-of-band markers allow advanced userspace to infer failure. They > are optional and can be ignored by not listening for POLLPRI events and > aren't necessary for the coredump server to function correctly. >=20 > In the initial version the following features are supported in > coredump_{req,ack}->mask: >=20 > * COREDUMP_KERNEL > The kernel will write the coredump data to the socket. >=20 > * COREDUMP_USERSPACE > The kernel will not write coredump data but will indicate to the > parent that a coredump has been generated. This is used when userspace > generates its own coredumps. >=20 > * COREDUMP_REJECT > The kernel will skip generating a coredump for this task. >=20 > * COREDUMP_WAIT > The kernel will prevent the task from exiting until the coredump > server has shutdown the socket connection. >=20 How do you envision COREDUMP_WAIT being used? I took a look at the trivial server, but it wasn't clear to me why you'd want to block the task from exiting. > The flexible coredump socket can be enabled by using the "@@" prefix > instead of the single "@" prefix for the regular coredump socket: >=20 > @@/run/systemd/coredump.socket >=20 > will enable flexible coredump handling. Current kernels already enforce > that "@" must be followed by "/" and will reject anything else. So > extending this is backward and forward compatible. >=20 > Signed-off-by: Christian Brauner > --- > Changes in v2: > - Add epoll-based concurrent coredump handling selftests. > - Improve cover letter. > - Ensure that enum coredump_oob is packed aka a single byte and add a > static_assert() verifying that. > - Simplify helper functions making the patch even smaller. > - Link to v1: https://lore.kernel.org/20250530-work-coredump-socket-proto= col-v1-0-20bde1cd4faa@kernel.org >=20 > --- > Christian Brauner (5): > coredump: allow for flexible coredump handling > selftests/coredump: fix build > selftests/coredump: cleanup coredump tests > tools: add coredump.h header > selftests/coredump: add coredump server selftests >=20 > fs/coredump.c | 130 +- > include/uapi/linux/coredump.h | 104 ++ > tools/include/uapi/linux/coredump.h | 104 ++ > tools/testing/selftests/coredump/Makefile | 2 +- > tools/testing/selftests/coredump/config | 4 + > tools/testing/selftests/coredump/stackdump_test.c | 1705 +++++++++++++++= +++--- > 6 files changed, 1799 insertions(+), 250 deletions(-) > --- > base-commit: 3e406741b19890c3d8a2ed126aa7c23b106ca9e1 > change-id: 20250520-work-coredump-socket-protocol-6980d1f54c2f --=20 Jeff Layton