Libguestfs - Apr 2017 - Re: [PATCH 1/2] daemon: run 'udevadm settle' with --exit-if-exists option

On Wed, Apr 12, 2017 at 05:01:10PM +0300, Pavel Butsykin
wrote:
> Add udev_settle_file() to run 'udevadm settle' with
--exit-if-exists option. It
> will slightly reduce the waiting-time for pending events if we need to wait
> for events related to a particular device/file.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  daemon/daemon.h   |  2 ++
>  daemon/guestfsd.c | 20 ++++++++++++++++----
>  2 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/daemon/daemon.h b/daemon/daemon.h
> index 79a5288f6..90ebaafbe 100644
> --- a/daemon/daemon.h
> +++ b/daemon/daemon.h
> @@ -141,6 +141,8 @@ extern int parse_btrfsvol (const char *desc,
mountable_t *mountable);
>  
>  extern int prog_exists (const char *prog);
>  
> +extern void udev_settle_file (const char *file);
> +
>  extern void udev_settle (void);
>  
>  extern int random_name (char *template);
> diff --git a/daemon/guestfsd.c b/daemon/guestfsd.c
> index 85ce5d2ad..dccfa15bc 100644
> --- a/daemon/guestfsd.c
> +++ b/daemon/guestfsd.c
> @@ -1213,13 +1213,18 @@ random_name (char *template)
>   * fussed if it fails.
>   */
>  void
> -udev_settle (void)
> +udev_settle_file (const char *file)
>  {
> -  char cmd[80];
> +  size_t cmd_size = strlen (str_udevadm) +
> +                    sizeof (" settle")   +
> +                    sizeof (" --debug")  +
> +                    (file ? sizeof (" --exit-if-exists=") +
strlen (file) : 0);
> +  char *cmd = malloc (cmd_size);
>    int r;
>  
> -  snprintf (cmd, sizeof cmd, "%s%s settle",
> -            str_udevadm, verbose ? " --debug" : "");
> +  snprintf(cmd, cmd_size, "%s%s settle%s%s",
> +           str_udevadm, verbose ? " --debug" : "",
> +           file ? " --exit-if-exists=" : "", file ?
file : "");
>    if (verbose)
>      printf ("%s\n", cmd);
>    r = system (cmd);
> @@ -1227,6 +1232,13 @@ udev_settle (void)
>      perror ("system");
>    else if (!WIFEXITED (r) || WEXITSTATUS (r) != 0)
>      fprintf (stderr, "warning: udevadm command failed\n");
> +  free (cmd);
There are some ugly quoting (and hence, possibly, security) problems
with this patch.

It's more secure and also much simpler to call ADD_ARG + commandv
here.  For an example of how to use it, see:

  https://github.com/libguestfs/libguestfs/blob/master/daemon/mkfs.c#L41-L247

Rich.

-- 
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