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Message-ID: <20241101135452.19359-1-erin.shepherd@e43.eu>
Date: Fri, 1 Nov 2024 13:54:48 +0000
From: Erin Shepherd <erin.shepherd@....eu>
To: linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Cc: christian@...uner.io,
paul@...l-moore.com,
bluca@...ian.org,
erin.shepherd@....eu
Subject: [PATCH 0/4] pidfs: implement file handle support
Since the introduction of pidfs, we have had 64-bit process identifiers
that will not be reused for the entire uptime of the system. This greatly
facilitates process tracking in userspace.
There are two limitations at present:
* These identifiers are currently only exposed to processes on 64-bit
systems. On 32-bit systems, inode space is also limited to 32 bits and
therefore is subject to the same reuse issues.
* There is no way to go from one of these unique identifiers to a pid or
pidfd.
Patch 1 & 2 in this stack implements fh_export for pidfs. This means
userspace can retrieve a unique process identifier even on 32-bit systems
via name_to_handle_at.
Patch 3 & 4 in this stack implement fh_to_dentry for pidfs. This means
userspace can convert back from a file handle to the corresponding pidfd.
To support us going from a file handle to a pidfd, we have to store a pid
inside the file handle. To ensure file handles are invariant and can move
between pid namespaces, we stash a pid from the initial namespace inside
the file handle.
I'm not quite sure if stashing an initial-namespace pid inside the file
handle is the right approach here; if not, I think that patch 1 & 2 are
useful on their own.
Erin Shepherd (4):
pseudofs: add support for export_ops
pidfs: implement file handle export support
pid: introduce find_get_pid_ns
pidfs: implement fh_to_dentry
fs/libfs.c | 1 +
fs/pidfs.c | 57 +++++++++++++++++++++++++++++++++++++++
include/linux/pid.h | 1 +
include/linux/pseudo_fs.h | 1 +
kernel/pid.c | 10 +++++--
5 files changed, 68 insertions(+), 2 deletions(-)
--
2.46.1
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