Re: [PATCH] docs: add virtiofsd(1) man page

[Christophe de Dinechin <dinechin@redhat.com>]

Stefan Hajnoczi writes:

> Document the virtiofsd(1) program and its command-line options.  This
> man page is a rST conversion of the original texi documentation that I
> wrote.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> Based-on: 20200124162606.8787-1-peter.maydell@linaro.org
>           ("[PATCH v2 0/8] qemu-img, qemu-trace-stap, virtfs-proxy-helper: convert to rST")
> ---
>  MAINTAINERS                |   1 +
>  Makefile                   |   8 ++-
>  docs/interop/conf.py       |   5 +-
>  docs/interop/index.rst     |   1 +
>  docs/interop/virtiofsd.rst | 123 +++++++++++++++++++++++++++++++++++++
>  5 files changed, 136 insertions(+), 2 deletions(-)
>  create mode 100644 docs/interop/virtiofsd.rst
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 83fb32b860..1da0709129 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1603,6 +1603,7 @@ S: Supported
>  F: tools/virtiofsd/*
>  F: hw/virtio/vhost-user-fs*
>  F: include/hw/virtio/vhost-user-fs.h
> +F: docs/interop/virtiofsd.rst
>
>  virtio-input
>  M: Gerd Hoffmann <kraxel@redhat.com>
> diff --git a/Makefile b/Makefile
> index 539f9ef079..ecd26044bc 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -348,6 +348,9 @@ DOCS=qemu-doc.html qemu-doc.txt qemu.1
>  DOCS+=$(MANUAL_BUILDDIR)/interop/qemu-img.1
>  DOCS+=$(MANUAL_BUILDDIR)/interop/qemu-nbd.8
>  DOCS+=$(MANUAL_BUILDDIR)/interop/qemu-ga.8
> +ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP)$(CONFIG_LIBCAP_NG),yyy)
> +DOCS+=$(MANUAL_BUILDDIR)/interop/virtiofsd.1
> +endif
>  DOCS+=$(MANUAL_BUILDDIR)/system/qemu-block-drivers.7
>  DOCS+=docs/interop/qemu-qmp-ref.html docs/interop/qemu-qmp-ref.txt docs/interop/qemu-qmp-ref.7
>  DOCS+=docs/interop/qemu-ga-ref.html docs/interop/qemu-ga-ref.txt docs/interop/qemu-ga-ref.7
> @@ -861,6 +864,9 @@ ifdef CONFIG_VIRTFS
>  	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man1"
>  	$(INSTALL_DATA) $(MANUAL_BUILDDIR)/interop/virtfs-proxy-helper.1 "$(DESTDIR)$(mandir)/man1"
>  endif
> +ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP)$(CONFIG_LIBCAP_NG),yyy)
> +	$(INSTALL_DATA) docs/interop/virtiofsd.1 "$(DESTDIR)$(mandir)/man1"
> +endif
>
>  install-datadir:
>  	$(INSTALL_DIR) "$(DESTDIR)$(qemu_datadir)"
> @@ -1052,7 +1058,7 @@ $(MANUAL_BUILDDIR)/system/index.html: $(call manual-deps,system)
>
>  $(call define-manpage-rule,interop,\
>         qemu-ga.8 qemu-img.1 qemu-nbd.8 qemu-trace-stap.1\
> -       virtfs-proxy-helper.1,\
> +       virtiofsd.1 virtfs-proxy-helper.1,\
>         $(SRC_PATH/qemu-img-cmds.hx))
>
>  $(call define-manpage-rule,system,qemu-block-drivers.7)
> diff --git a/docs/interop/conf.py b/docs/interop/conf.py
> index b0f322207c..b3cda17042 100644
> --- a/docs/interop/conf.py
> +++ b/docs/interop/conf.py
> @@ -27,5 +27,8 @@ man_pages = [
>       [], 1),
>      ('virtfs-proxy-helper', 'virtfs-proxy-helper',
>       u'QEMU 9p virtfs proxy filesystem helper',
> -     ['M. Mohan Kumar'], 1)
> +     ['M. Mohan Kumar'], 1),
> +    ('virtiofsd', 'virtiofsd', u'QEMU virtio-fs shared file system daemon',
> +     ['Stefan Hajnoczi <stefanha@redhat.com>',
> +      'Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>'], 1),
>  ]
> diff --git a/docs/interop/index.rst b/docs/interop/index.rst
> index 3b763b1eeb..e8455b4270 100644
> --- a/docs/interop/index.rst
> +++ b/docs/interop/index.rst
> @@ -24,3 +24,4 @@ Contents:
>     vhost-user
>     vhost-user-gpu
>     virtfs-proxy-helper
> +   virtiofsd
> diff --git a/docs/interop/virtiofsd.rst b/docs/interop/virtiofsd.rst
> new file mode 100644
> index 0000000000..51a657ac0c
> --- /dev/null
> +++ b/docs/interop/virtiofsd.rst
> @@ -0,0 +1,123 @@
> +QEMU virtio-fs shared file system daemon
> +========================================
> +
> +Synopsis
> +--------
> +
> +**virtiofsd** [*OPTIONS*]
> +
> +Description
> +-----------
> +
> +Share a host directory tree with a guest through a virtio-fs device.  This
> +program is a vhost-user backend that implements the virtio-fs device.  Each
> +virtio-fs device instance requires its own virtiofsd process.
> +
> +This program is designed to work with QEMU's ``--device vhost-user-fs-pci``
> +but should work with any virtual machine monitor (VMM) that supports
> +vhost-user.  See the Examples section below.
> +
> +This program must be run as the root user.  Upon startup the program will
> +switch into a new file system namespace with the shared directory tree as its
> +root.  This prevents "file system escapes" due to symlinks and other file
> +system objects that might lead to files outside the shared directory.  The
> +program also sandboxes itself using seccomp(2) to prevent ptrace(2) and other
> +vectors that could allow an attacker to compromise the system after gaining
> +control of the virtiofsd process.
> +
> +Options
> +-------
> +
> +.. program:: virtiofsd
> +
> +.. option:: -h, --help
> +
> +  Print help.
> +
> +.. option:: -V, --version
> +
> +  Print version.
> +
> +.. option:: -d
> +
> +  Enable debug output.
> +
> +.. option:: --syslog
> +
> +  Print log messages to syslog instead of stderr.
> +
> +.. option:: -o OPTION
> +
> +  * debug -
> +    Enable debug output.
> +
> +  * flock|no_flock -
> +    Enable/disable flock.  The default is ``no_flock``.
> +
> +  * log_level=LEVEL -
> +    Print only log messages matching LEVEL or more severe.  LEVEL is one of
> +    ``err``, ``warn``, ``info``, or ``debug``.  The default is ``info``.
> +
> +  * norace -
> +    Disable racy fallback.  The default is false.

It's not a problem with the doc, but seeing it exposes that options are
not overly consistent in their spelling. "norace" has no _ but no_flock
does (as does no_writeback).

> +
> +  * posix_lock|no_posix_lock -
> +    Enable/disable remote POSIX locks.  The default is ``posix_lock``.
> +
> +  * readdirplus|no_readdirplus -
> +    Enable/disable readdirplus.  The default is ``readdirplus``.
> +
> +  * source=PATH -
> +    Share host directory tree located at PATH.  This option is required.
> +
> +  * timeout=TIMEOUT -
> +    I/O timeout in seconds.  The default depends on cache= option.
> +
> +  * vhost_user_socket=PATH -
> +    Listen on vhost-user UNIX domain socket at PATH.

I believe that this option has been removed.

> +
> +  * writeback|no_writeback -
> +    Enable/disable writeback cache. The cache alows the FUSE client to buffer
> +    and merge write requests.  The default is ``no_writeback``.
> +
> +  * xattr|no_xattr -
> +    Enable/disable extended attributes (xattr) on files and directories.  The
> +    default is ``no_xattr``.
> +
> +.. option:: --socket-path=PATH
> +
> +  Listen on vhost-user UNIX domain socket at PATH.

Not related to the doc, but this looks like an option that might deserve
a short form.

> +
> +.. option:: --fd=FDNUM
> +
> +  Accept connections from vhost-user UNIX domain socket file descriptor FDNUM.
> +  The file descriptor must already be listening for connections.

Not directly related to the manual itself, but any reason why it's
"socket-path" and "fd" (as opposed e.g. to "socket-path" and
"socket-fd"?


> +
> +.. option:: --thread-pool-size=NUM
> +
> +  Restrict the number of worker threads per request queue to NUM.  The default
> +  is 64.
> +
> +.. option:: --cache=none|auto|always
> +
> +  Select the desired trade-off between coherency and performance.  ``none``
> +  forbids the FUSE client from caching to achieve best coherency at the cost of
> +  performance.  ``auto`` acts similar to NFS with a 1 second metadata cache
> +  timeout.  ``always`` sets a long cache lifetime at the expense of coherency.
> +
> +Examples
> +--------
> +
> +Export ``/var/lib/fs/vm001/`` on vhost-user UNIX domain socket
> +``/var/run/vm001-vhost-fs.sock``:
> +
> +::
> +
> +  host# virtiofsd --socket-path=/var/run/vm001-vhost-fs.sock -o source=/var/lib/fs/vm001
> +  host# qemu-system-x86_64 \
> +      -chardev socket,id=char0,path=/var/run/vm001-vhost-fs.sock \
> +      -device vhost-user-fs-pci,chardev=char0,tag=myfs \
> +      -object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on \
> +      -numa node,memdev=mem \
> +      ...
> +  guest# mount -t virtio_fs myfs /mnt


--
Cheers,
Christophe de Dinechin (IRC c3d)