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

[Masayoshi Mizuma]

Hi Jun,

On Mon, Aug 12, 2019 at 11:12:52AM +0800, piaojun wrote:
> Hi Masayoshi,
> 
> On 2019/8/12 6:55, Masayoshi Mizuma wrote:
> > From: Masayoshi Mizuma <m.mizuma at 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 at 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'll add a local var to replace strlen(se->vu_socket_path).

> I wonder if we could just place the lock file in the same dir level of
> socket file which could save some code work?

Thank you for the suggestion but I prefer the lock file is in
localstatedir, for example /var/run/virtiofsd, because if the
lock file in the same dir and the dir is used in common, for example
/tmp, users may delete the lock file...

> 
> > +
> > +        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.

I'll fix this.

Thanks!
Masa

> 
> > +                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
> >           */
> >