1b074abe88
-----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRAhzRXHqcMeLMyaSiRxhvAZXjcogUCZpEHFAAKCRCRxhvAZXjc olb9AQDsA6PLSHsRIVGO3E+syvL+lXC21QdsbAkSgADbqbSC5wEA+nfG2adiWKXc 8CKGMrqXb3j75UfIRIHnM6D03wm0ywo= =ybN0 -----END PGP SIGNATURE----- Merge tag 'vfs-6.11.nsfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs Pull namespace-fs updates from Christian Brauner: "This adds ioctls allowing to translate PIDs between PID namespaces. The motivating use-case comes from LXCFS which is a tiny fuse filesystem used to virtualize various aspects of procfs. LXCFS is run on the host. The files and directories it creates can be bind-mounted by e.g. a container at startup and mounted over the various procfs files the container wishes to have virtualized. When e.g. a read request for uptime is received, LXCFS will receive the pid of the reader. In order to virtualize the corresponding read, LXCFS needs to know the pid of the init process of the reader's pid namespace. In order to do this, LXCFS first needs to fork() two helper processes. The first helper process setns() to the readers pid namespace. The second helper process is needed to create a process that is a proper member of the pid namespace. The second helper process then creates a ucred message with ucred.pid set to 1 and sends it back to LXCFS. The kernel will translate the ucred.pid field to the corresponding pid number in LXCFS's pid namespace. This way LXCFS can learn the init pid number of the reader's pid namespace and can go on to virtualize. Since these two forks() are costly LXCFS maintains an init pid cache that caches a given pid for a fixed amount of time. The cache is pruned during new read requests. However, even with the cache the hit of the two forks() is singificant when a very large number of containers are running. So this adds a simple set of ioctls that let's a caller translate PIDs from and into a given PID namespace. This significantly improves performance with a very simple change. To protect against races pidfds can be used to check whether the process is still valid" * tag 'vfs-6.11.nsfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: nsfs: add pid translation ioctls
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.