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| author | Kees Cook <kees+treewide@kernel.org> | 2026-09-02 15:31:14 -0700 |
|---|---|---|
| committer | Kees Cook <kees@kernel.org> | 2026-09-04 21:37:00 -0700 |
| commit | 3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d (patch) | |
| tree | c65086f9bdcd48c6360fb7cb4598bca084da1f32 /Documentation/filesystems/virtiofs.rst | |
| download | linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.tar.gz linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.zip | |
treewide: refresh kmalloc_obj() conversionsgrafted
This is another run of the Coccinelle script for converting kmalloc()
family of allocations to kmalloc_obj() via the existing rules in
scripts/coccinelle/api/kmalloc_objs.cocci
This catches both the set of kmalloc() uses added since the first
kmalloc_obj() conversions in v7.0 and adds a large group missed in the
first pass due to Coccinelle not interacting well with the cleanup.h
scoped_...() family of macros[1]. I worked around this with spatch's
"--macro-file" argument to a file with all the scoped_...() macros mapped
to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control
flow indicator I could find.
Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc,
riscv, and s390 with no new warnings.
Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1]
Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2]
Signed-off-by: Kees Cook <kees+treewide@kernel.org>
Diffstat (limited to 'Documentation/filesystems/virtiofs.rst')
| -rw-r--r-- | Documentation/filesystems/virtiofs.rst | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/Documentation/filesystems/virtiofs.rst b/Documentation/filesystems/virtiofs.rst new file mode 100644 index 000000000..fd4d2484e --- /dev/null +++ b/Documentation/filesystems/virtiofs.rst @@ -0,0 +1,76 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _virtiofs_index: + +=================================================== +virtiofs: virtio-fs host<->guest shared file system +=================================================== + +- Copyright (C) 2019 Red Hat, Inc. + +Introduction +============ +The virtiofs file system for Linux implements a driver for the paravirtualized +VIRTIO "virtio-fs" device for guest<->host file system sharing. It allows a +guest to mount a directory that has been exported on the host. + +Guests often require access to files residing on the host or remote systems. +Use cases include making files available to new guests during installation, +booting from a root file system located on the host, persistent storage for +stateless or ephemeral guests, and sharing a directory between guests. + +Although it is possible to use existing network file systems for some of these +tasks, they require configuration steps that are hard to automate and they +expose the storage network to the guest. The virtio-fs device was designed to +solve these problems by providing file system access without networking. + +Furthermore the virtio-fs device takes advantage of the co-location of the +guest and host to increase performance and provide semantics that are not +possible with network file systems. + +Usage +===== +Mount file system with tag ``myfs`` on ``/mnt``: + +.. code-block:: sh + + guest# mount -t virtiofs myfs /mnt + +Please see https://virtio-fs.gitlab.io/ for details on how to configure QEMU +and the virtiofsd daemon. + +Mount options +------------- + +virtiofs supports general VFS mount options, for example, remount, +ro, rw, context, etc. It also supports FUSE mount options. + +atime behavior +^^^^^^^^^^^^^^ + +The atime-related mount options, for example, noatime, strictatime, +are ignored. The atime behavior for virtiofs is the same as the +underlying filesystem of the directory that has been exported +on the host. + +Internals +========= +Since the virtio-fs device uses the FUSE protocol for file system requests, the +virtiofs file system for Linux is integrated closely with the FUSE file system +client. The guest acts as the FUSE client while the host acts as the FUSE +server. The /dev/fuse interface between the kernel and userspace is replaced +with the virtio-fs device interface. + +FUSE requests are placed into a virtqueue and processed by the host. The +response portion of the buffer is filled in by the host and the guest handles +the request completion. + +Mapping /dev/fuse to virtqueues requires solving differences in semantics +between /dev/fuse and virtqueues. Each time the /dev/fuse device is read, the +FUSE client may choose which request to transfer, making it possible to +prioritize certain requests over others. Virtqueues have queue semantics and +it is not possible to change the order of requests that have been enqueued. +This is especially important if the virtqueue becomes full since it is then +impossible to add high priority requests. In order to address this difference, +the virtio-fs device uses a "hiprio" virtqueue specifically for requests that +have priority over normal requests. |
