[libvirt] [Libguestfs] [PATCH libguestfs v3] lib: Handle slow USB devices more gracefully.

[Daniel P. Berrange]

On Tue, Jan 19, 2016 at 04:18:46PM +0000, Richard W.M. Jones wrote:
> Libvirt has a fixed 15 second timeout for qemu to exit.  If qemu is
> writing to a slow USB key, it can hang (in D state) for much longer
> than this - many minutes usually.
> 
> The solution is to check specifically for the libvirt EBUSY error when
> this happens, and retry the virDomainDestroyFlags operation
> (indefinitely).
> 
> See also the description here:
> https://www.redhat.com/archives/libvir-list/2016-January/msg00767.html
> 
> Similar to the following OpenStack Nova commit:
> http://git.openstack.org/cgit/openstack/nova/commit/?id=3907867
> 
> Thanks: Kashyap Chamarthy and Daniel Berrange.
> ---
>  src/launch-libvirt.c | 45 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 35 insertions(+), 10 deletions(-)
> 
> diff --git a/src/launch-libvirt.c b/src/launch-libvirt.c
> index 8215e02..90b6c49 100644
> --- a/src/launch-libvirt.c
> +++ b/src/launch-libvirt.c
> @@ -25,6 +25,7 @@
>  #include <unistd.h>
>  #include <fcntl.h>
>  #include <grp.h>
> +#include <errno.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
>  #include <assert.h>
> @@ -2015,6 +2016,8 @@ ignore_errors (void *ignore, virErrorPtr ignore2)
>    /* empty */
>  }
>  
> +static int destroy_domain (guestfs_h *g, virDomainPtr dom, int check_for_errors);
> +
>  static int
>  shutdown_libvirt (guestfs_h *g, void *datav, int check_for_errors)
>  {
> @@ -2023,23 +2026,14 @@ shutdown_libvirt (guestfs_h *g, void *datav, int check_for_errors)
>    virDomainPtr dom = data->dom;
>    size_t i;
>    int ret = 0;
> -  int flags;
>  
>    /* Note that we can be called back very early in launch (specifically
>     * from launch_libvirt itself), when conn and dom might be NULL.
>     */
> -
>    if (dom != NULL) {
> -    flags = check_for_errors ? VIR_DOMAIN_DESTROY_GRACEFUL : 0;
> -    debug (g, "calling virDomainDestroy \"%s\" flags=%s",
> -           data->name, check_for_errors ? "VIR_DOMAIN_DESTROY_GRACEFUL" : "0");
> -    if (virDomainDestroyFlags (dom, flags) == -1) {
> -      libvirt_error (g, _("could not destroy libvirt domain"));
> -      ret = -1;
> -    }
> +    ret = destroy_domain (g, dom, check_for_errors);
>      virDomainFree (dom);
>    }
> -
>    if (conn != NULL)
>      virConnectClose (conn);
>  
> @@ -2068,6 +2062,37 @@ shutdown_libvirt (guestfs_h *g, void *datav, int check_for_errors)
>    return ret;
>  }
>  
> +/* Wrapper around virDomainDestroy which handles errors and retries.. */
> +static int
> +destroy_domain (guestfs_h *g, virDomainPtr dom, int check_for_errors)
> +{
> +  const int flags = check_for_errors ? VIR_DOMAIN_DESTROY_GRACEFUL : 0;
> +  virErrorPtr err;
> +
> + again:
> +  debug (g, "calling virDomainDestroy flags=%s",
> +         check_for_errors ? "VIR_DOMAIN_DESTROY_GRACEFUL" : "0");
> +  if (virDomainDestroyFlags (dom, flags) == -1) {
> +    err = virGetLastError ();
> +
> +    /* Second chance if we're just waiting for qemu to shut down.  See:
> +     * https://www.redhat.com/archives/libvir-list/2016-January/msg00767.html
> +     */
> +    if ((flags & VIR_DOMAIN_DESTROY_GRACEFUL) &&
> +        err && err->code == VIR_ERR_SYSTEM_ERROR && err->int1 == EBUSY)
> +      goto again;

NB, you could get that error even if you don't specify
VIR_DOMAIN_DESTROY_GRACEFUL, because even SIGKILL can
fail to kill QEMU if it is in an uninterruptable sleep
on a dead NFS server for example and hard,nointr is used
as mount options.

So perhaps you don't want to check flags here ?

> +
> +    /* "Domain not found" is not treated as an error. */
> +    if (err && err->code == VIR_ERR_NO_DOMAIN)
> +      return 0;
> +
> +    libvirt_error (g, _("could not destroy libvirt domain"));
> +    return -1;
> +  }
> +
> +  return 0;
> +}

I don't know the use context from libguestfs POV, but is there any
scenario in which a user would want a way to time out this, instead
of making libguestfs wait forever ?

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|