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Christian Brauner 7063c229a8 Merge patch series "fhandle: expose u64 mount id to name_to_handle_at(2)"
Aleksa Sarai <cyphar@cyphar.com> says:

Now that we provide a unique 64-bit mount ID interface in statx(2), we
can now provide a race-free way for name_to_handle_at(2) to provide a
file handle and corresponding mount without needing to worry about
racing with /proc/mountinfo parsing or having to open a file just to do
statx(2).

While this is not necessary if you are using AT_EMPTY_PATH and don't
care about an extra statx(2) call, users that pass full paths into
name_to_handle_at(2) need to know which mount the file handle comes from
(to make sure they don't try to open_by_handle_at a file handle from a
different filesystem) and switching to AT_EMPTY_PATH would require
allocating a file for every name_to_handle_at(2) call, turning

  err = name_to_handle_at(-EBADF, "/foo/bar/baz", &handle, &mntid,
                          AT_HANDLE_MNT_ID_UNIQUE);

into

  int fd = openat(-EBADF, "/foo/bar/baz", O_PATH | O_CLOEXEC);
  err1 = name_to_handle_at(fd, "", &handle, &unused_mntid, AT_EMPTY_PATH);
  err2 = statx(fd, "", AT_EMPTY_PATH, STATX_MNT_ID_UNIQUE, &statxbuf);
  mntid = statxbuf.stx_mnt_id;
  close(fd);

Also, this series adds a patch to clarify how AT_* flag allocation
should work going forwards.

* patches from https://lore.kernel.org/r/20240828-exportfs-u64-mount-id-v3-0-10c2c4c16708@cyphar.com:
  fhandle: expose u64 mount id to name_to_handle_at(2)
  uapi: explain how per-syscall AT_* flags should be allocated

Link: https://lore.kernel.org/r/20240828-exportfs-u64-mount-id-v3-0-10c2c4c16708@cyphar.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
History 2024-09-05 11:39:20 +02:00
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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.