Re: [PATCH v3] qga: fence guest-set-time if hwclock not available

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Cornelia,

On 12/5/19 12:53 PM, Cornelia Huck wrote:
> The Posix implementation of guest-set-time invokes hwclock to
> set/retrieve the time to/from the hardware clock. If hwclock
> is not available, the user is currently informed that "hwclock
> failed to set hardware clock to system time", which is quite
> misleading. This may happen e.g. on s390x, which has a different
> timekeeping concept anyway.
> 
> Let's check for the availability of the hwclock command and
> return QERR_UNSUPPORTED for guest-set-time if it is not available.
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
> 
> v2->v3:
>    - added 'static' keyword to hwclock_path
> 
> Not sure what tree this is going through; if there's no better place,
> I can also take this through the s390 tree.

s390 or trivial trees seems appropriate.

> 
> ---
>   qga/commands-posix.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 1c1a165daed8..0be301a4ea77 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -156,6 +156,17 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
>       pid_t pid;
>       Error *local_err = NULL;
>       struct timeval tv;
> +    static const char hwclock_path[] = "/sbin/hwclock";
> +    static int hwclock_available = -1;
> +
> +    if (hwclock_available < 0) {
> +        hwclock_available = (access(hwclock_path, X_OK) == 0);
> +    }
> +
> +    if (!hwclock_available) {
> +        error_setg(errp, QERR_UNSUPPORTED);

In include/qapi/qmp/qerror.h we have:

/*
  * These macros will go away, please don't use in new code, and do not
  * add new ones!
  */

Maybe we can replace it by "this feature is not supported on this 
architecture"? (or without 'on this architecture').

> +        return;
> +    }
>   
>       /* If user has passed a time, validate and set it. */
>       if (has_time) {
> @@ -195,7 +206,7 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
>   
>           /* Use '/sbin/hwclock -w' to set RTC from the system time,
>            * or '/sbin/hwclock -s' to set the system time from RTC. */
> -        execle("/sbin/hwclock", "hwclock", has_time ? "-w" : "-s",
> +        execle(hwclock_path, "hwclock", has_time ? "-w" : "-s",
>                  NULL, environ);
>           _exit(EXIT_FAILURE);
>       } else if (pid < 0) {
>