Re: [Virtio-fs] [PATCH v2] virtiofsd: Prevent multiply running with same vhost_user_socket

[piaojun <piaojun@huawei.com>]

Hi Masayoshi,

On 2019/8/12 6:55, Masayoshi Mizuma wrote:
> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> 
> virtiofsd can run multiply even if the vhost_user_socket is
> same path.
> 
>   ]# ./virtiofsd -o vhost_user_socket=/tmp/vhostqemu -o source=/tmp/share &
>   [1] 244965
>   virtio_session_mount: Waiting for vhost-user socket connection...
>   ]# ./virtiofsd -o vhost_user_socket=/tmp/vhostqemu -o source=/tmp/share &
>   [2] 244966
>   virtio_session_mount: Waiting for vhost-user socket connection...
>   ]#
> 
> The user will get confused about the situation and maybe the cause of the
> unexpected problem. So it's better to prevent the multiple running.
> 
> Create a regular file under localstatedir directory to exclude the
> vhost_user_socket. To create and lock the file, use qemu_write_pidfile()
> because the API has some sanity checks and file lock.
> 
> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> ---
>  contrib/virtiofsd/fuse_i.h        |  1 +
>  contrib/virtiofsd/fuse_lowlevel.c |  3 ++
>  contrib/virtiofsd/fuse_virtio.c   | 50 +++++++++++++++++++++++++++++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/contrib/virtiofsd/fuse_i.h b/contrib/virtiofsd/fuse_i.h
> index ff6e1b75ba..d31c675469 100644
> --- a/contrib/virtiofsd/fuse_i.h
> +++ b/contrib/virtiofsd/fuse_i.h
> @@ -72,6 +72,7 @@ struct fuse_session {
>          char *vu_socket_path;
>          int   vu_listen_fd;
>          int   vu_socketfd;
> +        char *vu_socket_lock_file;

I prefer char *vu_socket_lock which is just a personal habit.

>          struct fv_VuDev *virtio_dev;
>  };
>  
> diff --git a/contrib/virtiofsd/fuse_lowlevel.c b/contrib/virtiofsd/fuse_lowlevel.c
> index 8adc4b1ab8..ab18b86435 100644
> --- a/contrib/virtiofsd/fuse_lowlevel.c
> +++ b/contrib/virtiofsd/fuse_lowlevel.c
> @@ -2587,6 +2587,9 @@ void fuse_session_destroy(struct fuse_session *se)
>  	free(se->vu_socket_path);
>  	se->vu_socket_path = NULL;
>  
> +	unlink(se->vu_socket_lock_file);
> +	free(se->vu_socket_lock_file);
> +
>  	free(se);
>  }
>  
> diff --git a/contrib/virtiofsd/fuse_virtio.c b/contrib/virtiofsd/fuse_virtio.c
> index 083e4fc317..4999f95b63 100644
> --- a/contrib/virtiofsd/fuse_virtio.c
> +++ b/contrib/virtiofsd/fuse_virtio.c
> @@ -32,6 +32,9 @@
>  
>  #include "contrib/libvhost-user/libvhost-user.h"
>  
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +
>  struct fv_VuDev;
>  struct fv_QueueInfo {
>          pthread_t thread;
> @@ -862,6 +865,47 @@ int virtio_loop(struct fuse_session *se)
>         return 0;
>  }
>  
> +static void strreplace(char *s, char old, char new)
> +{
> +        for (; *s; ++s)
> +                if (*s == old)
> +                        *s = new;
> +}
> +
> +static int fv_create_socket_lock_file(struct fuse_session *se)
> +{
> +        char *dir, *socket_name;
> +        Error *local_err = NULL;
> +
> +        dir = qemu_get_local_state_pathname("run/virtiofsd");
> +
> +        if (g_mkdir_with_parents(dir, S_IRWXU) < -1) {
> +                fuse_err("%s: Failed to create directory %s: %s",
> +                        __func__, dir, strerror(errno));
> +                return -1;
> +        }
> +
> +        socket_name = malloc(strlen(se->vu_socket_path) + 1);
> +        memset(socket_name, 0, strlen(se->vu_socket_path) + 1);
> +        memcpy(socket_name, se->vu_socket_path, strlen(se->vu_socket_path));
> +        strreplace(socket_name, '/', '.');

Shall we use a local var to replace the long *se->vu_socket_path*? And
I wonder if we could just place the lock file in the same dir level of
socket file which could save some code work?

> +
> +        se->vu_socket_lock_file = malloc(NAME_MAX);
> +        memset(se->vu_socket_lock_file, 0, NAME_MAX);
> +        snprintf(se->vu_socket_lock_file, NAME_MAX, "%s/%s.pid",
> +			dir, socket_name);
> +
> +        if (!qemu_write_pidfile(se->vu_socket_lock_file, &local_err)) {
> +                error_report_err(local_err);

Memory leak here.

> +                return -1;
> +        }
> +
> +        free(socket_name);
> +        g_free(dir);
> +
> +        return 0;
> +}
> +
>  static int fv_create_listen_socket(struct fuse_session *se)
>  {
>          struct sockaddr_un un;
> @@ -876,6 +920,12 @@ static int fv_create_listen_socket(struct fuse_session *se)
>                  return -1;
>          }
>  
> +        /* Check the vu_socket_path is already used */
> +        if (fv_create_socket_lock_file(se) == -1) {
> +                fuse_err("%s: Socket lock file creation failed\n", __func__);
> +                return -1;
> +        }
> +
>          /* Create the Unix socket to communicate with qemu
>           * based on QEMU's vhost-user-bridge
>           */
>