Re: [PATCH] virtiofsd: support setting multiple request virtqueues

[Stefan Hajnoczi]

On Sun, 11 Dec 2022 at 05:49, Jiachen Zhang
<zhangjiachen.jaycee@bytedance.com> wrote:
>
> Add an option '-o num_request_queues' to configure the queue number,
> currently the total number of vqs should be (1 hiprio queue +
> num_request_queues).
>
> The code is based on Connor's previous version in the virtio-fs
> mailing-list [1], but change the semantic of the new option from total
> queue number to request queue number.
>
> The corresponding virtio-fs kernel part modification can be found at the
> mail [2].
>
> Link:
> [1] https://www.mail-archive.com/virtio-fs@redhat.com/msg03333.html
> [2] 
> https://lore.kernel.org/linux-fsdevel/20221211103857.25805-1-zhangjiachen.jaycee@bytedance.com/
> Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Connor Kuehl <ckuehl@redhat.com>
> Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
> ---
>  tools/virtiofsd/fuse_lowlevel.c  |  4 ++--
>  tools/virtiofsd/fuse_lowlevel.h  |  2 +-
>  tools/virtiofsd/fuse_virtio.c    | 20 +++-----------------
>  tools/virtiofsd/fuse_virtio.h    |  2 +-
>  tools/virtiofsd/helper.c         |  4 ++++
>  tools/virtiofsd/passthrough_ll.c | 12 +++++++++++-
>  6 files changed, 22 insertions(+), 22 deletions(-)

QEMU's C virtiofsd is no longer actively developed. New development
happens in the Rust https://gitlab.com/virtio-fs/virtiofsd codebase.
Are you sure you want to continue using C virtiofsd?

>
> diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
> index 2f08471627..528492d2cf 100644
> --- a/tools/virtiofsd/fuse_lowlevel.c
> +++ b/tools/virtiofsd/fuse_lowlevel.c
> @@ -2708,9 +2708,9 @@ out1:
>      return NULL;
>  }
>
> -int fuse_session_mount(struct fuse_session *se)
> +int fuse_session_mount(struct fuse_session *se, unsigned int num_queues)
>  {
> -    return virtio_session_mount(se);
> +    return virtio_session_mount(se, num_queues);
>  }
>
>  int fuse_session_fd(struct fuse_session *se)
> diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h
> index b889dae4de..aee02d3e91 100644
> --- a/tools/virtiofsd/fuse_lowlevel.h
> +++ b/tools/virtiofsd/fuse_lowlevel.h
> @@ -1856,7 +1856,7 @@ struct fuse_session *fuse_session_new(struct fuse_args 
> *args,
>   *
>   * @return 0 on success, -1 on failure.
>   **/
> -int fuse_session_mount(struct fuse_session *se);
> +int fuse_session_mount(struct fuse_session *se, unsigned int num_queues);
>
>  /**
>   * Enter a single threaded, blocking event loop.
> diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
> index 9368e292e4..a3ebcbea8e 100644
> --- a/tools/virtiofsd/fuse_virtio.c
> +++ b/tools/virtiofsd/fuse_virtio.c
> @@ -762,20 +762,6 @@ static void fv_queue_set_started(VuDev *dev, int qidx, 
> bool started)
>               started);
>      assert(qidx >= 0);
>
> -    /*
> -     * Ignore additional request queues for now.  passthrough_ll.c must be
> -     * audited for thread-safety issues first.  It was written with a
> -     * well-behaved client in mind and may not protect against all types of
> -     * races yet.
> -     */
> -    if (qidx > 1) {
> -        fuse_log(FUSE_LOG_ERR,
> -                 "%s: multiple request queues not yet implemented, please 
> only "
> -                 "configure 1 request queue\n",
> -                 __func__);
> -        exit(EXIT_FAILURE);
> -    }

Please include an explanation of why it's safe to drop this now. Have
the thread-safety issues mentioned in the comment been resolved?

> -
>      if (started) {
>          /* Fire up a thread to watch this queue */
>          if (qidx >= vud->nqueues) {
> @@ -1011,7 +997,7 @@ static int fv_create_listen_socket(struct fuse_session 
> *se)
>      return 0;
>  }
>
> -int virtio_session_mount(struct fuse_session *se)
> +int virtio_session_mount(struct fuse_session *se, unsigned int num_queues)
>  {
>      int ret;
>
> @@ -1057,8 +1043,8 @@ int virtio_session_mount(struct fuse_session *se)
>      se->vu_socketfd = data_sock;
>      se->virtio_dev->se = se;
>      pthread_rwlock_init(&se->virtio_dev->vu_dispatch_rwlock, NULL);
> -    if (!vu_init(&se->virtio_dev->dev, 2, se->vu_socketfd, fv_panic, NULL,
> -                 fv_set_watch, fv_remove_watch, &fv_iface)) {
> +    if (!vu_init(&se->virtio_dev->dev, num_queues, se->vu_socketfd,
> +                fv_panic, NULL, fv_set_watch, fv_remove_watch, &fv_iface)) {
>          fuse_log(FUSE_LOG_ERR, "%s: vu_init failed\n", __func__);
>          return -1;
>      }
> diff --git a/tools/virtiofsd/fuse_virtio.h b/tools/virtiofsd/fuse_virtio.h
> index 111684032c..a0e78b9b84 100644
> --- a/tools/virtiofsd/fuse_virtio.h
> +++ b/tools/virtiofsd/fuse_virtio.h
> @@ -18,7 +18,7 @@
>
>  struct fuse_session;
>
> -int virtio_session_mount(struct fuse_session *se);
> +int virtio_session_mount(struct fuse_session *se, unsigned int num_queues);
>  void virtio_session_close(struct fuse_session *se);
>  int virtio_loop(struct fuse_session *se);
>
> diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
> index f5f66f292c..b5138ce17d 100644
> --- a/tools/virtiofsd/helper.c
> +++ b/tools/virtiofsd/helper.c
> @@ -191,6 +191,10 @@ void fuse_cmdline_help(void)
>             "    -o killpriv_v2/no_killpriv_v2\n"
>             "                               Enable/Disable 
> FUSE_HANDLE_KILLPRIV_V2.\n"
>             "                               (default: enabled as long as 
> client supports it)\n"
> +           "    -o num_request_queues=<num>\n"
> +           "                               set maximum number of request 
> virtqueues\n"
> +           "                               supported by virtiofsd"
> +           "                               default: 1\n"
>             );
>  }
>
> diff --git a/tools/virtiofsd/passthrough_ll.c 
> b/tools/virtiofsd/passthrough_ll.c
> index 20f0f41f99..f9d8075835 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -182,6 +182,7 @@ struct lo_data {
>      /* Keeps track if /proc/<pid>/attr/fscreate should be used or not */
>      bool use_fscreate;
>      int user_security_label;
> +    int num_request_queues;
>  };
>
>  static const struct fuse_opt lo_opts[] = {
> @@ -218,6 +219,8 @@ static const struct fuse_opt lo_opts[] = {
>      { "no_posix_acl", offsetof(struct lo_data, user_posix_acl), 0 },
>      { "security_label", offsetof(struct lo_data, user_security_label), 1 },
>      { "no_security_label", offsetof(struct lo_data, user_security_label), 0 
> },
> +    { "num_request_queues=%d",
> +      offsetof(struct lo_data, num_request_queues), 1 },
>      FUSE_OPT_END
>  };
>  static bool use_syslog = false;
> @@ -4479,6 +4482,12 @@ int main(int argc, char *argv[])
>
>      lo.use_statx = true;
>
> +    if (lo.num_request_queues < 1) {
> +        fuse_log(FUSE_LOG_ERR, "num_request_queues must be at least 1 (got 
> %d)"
> +                 "\n", lo.num_request_queues);
> +        exit(1);
> +    }
> +
>      se = fuse_session_new(&args, &lo_oper, sizeof(lo_oper), &lo);
>      if (se == NULL) {
>          goto err_out1;
> @@ -4488,7 +4497,8 @@ int main(int argc, char *argv[])
>          goto err_out2;
>      }
>
> -    if (fuse_session_mount(se) != 0) {
> +    /* There will be 1 hirpio queue plus lo.num_request_queues request 
> queues */

s/hirpio/hiprio/

> +    if (fuse_session_mount(se, lo.num_request_queues + 1) != 0) {
>          goto err_out3;
>      }
>
> --
> 2.20.1
>
>