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Re: [libvirt] [PATCH 1/6] libxl: Fix handling of timeouts



On Thu, Jan 24, 2013 at 12:55:09PM -0700, Jim Fehlig wrote:
> Jim Fehlig wrote:
> > xen-unstable commit XXXX makes changes wrt modifying and deregistering
> > timeouts.
> >
> > First, timeout modify callbacks will only be invoked with an
> > abs_t of {0,0}, i.e. make the timeout fire immediately.  Prior to this
> > commit, timeout modify callbacks were never invoked.
> >
> > Second, timeout deregister hooks will no longer be called.
> >
> > This patch makes changes in the libvirt libxl driver that should be
> > compatible before and after commit XXXX.
> >
> > While at it, fix a potential overflow in the timeout register callback.
> > ---
> >
> > 'commit XXXX' will be replaced with a proper commit id once committed
> > to xen-unstable.
> >   
> 
> libxl patch as been committed to xen-unstable now, changeset 26469. 
> I've updated this patch accordingly.
> 
> Regards,
> Jim
> 
> 

> >From 451c84284fa1b4f311f2ceb052c8e9f25ffa0cf0 Mon Sep 17 00:00:00 2001
> From: Jim Fehlig <jfehlig suse com>
> Date: Mon, 21 Jan 2013 09:59:28 -0700
> Subject: [PATCH 1/6] libxl: Fix handling of timeouts
> 
> xen-unstable changeset 26469 makes changes wrt modifying and deregistering
> timeouts.
> 
> First, timeout modify callbacks will only be invoked with an
> abs_t of {0,0}, i.e. make the timeout fire immediately.  Prior to this
> commit, timeout modify callbacks were never invoked.
> 
> Second, timeout deregister hooks will no longer be called.
> 
> This patch makes changes in the libvirt libxl driver that should be
> compatible before and after changeset 26469.
> 
> While at it, fix a potential overflow in the timeout register callback.
> ---
>  src/libxl/libxl_driver.c | 39 ++++++++++++++++++++++++++++++---------
>  1 file changed, 30 insertions(+), 9 deletions(-)
> 
> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
> index a8c4cae..77026fc 100644
> --- a/src/libxl/libxl_driver.c
> +++ b/src/libxl/libxl_driver.c
> @@ -186,7 +186,13 @@ libxlTimerCallback(int timer ATTRIBUTE_UNUSED, void *timer_info)
>  {
>      struct libxlOSEventHookTimerInfo *info = timer_info;
>  
> +    /* libxl expects the event to be deregistered when calling
> +       libxl_osevent_occurred_timeout, but we dont want the event info
> +       destroyed.  Disable the timeout and only remove it after returning
> +       from libxl. */
> +    virEventUpdateTimeout(info->id, -1);
>      libxl_osevent_occurred_timeout(info->priv->ctx, info->xl_priv);
> +    virEventRemoveTimeout(info->id);
>  }
>  
>  static void
> @@ -202,6 +208,8 @@ libxlTimeoutRegisterEventHook(void *priv,
>                                void *xl_priv)
>  {
>      struct timeval now;
> +    struct timeval res;
> +    static struct timeval zero;
>      struct libxlOSEventHookTimerInfo *timer_info;
>      int timeout, timer_id;
>  
> @@ -211,8 +219,15 @@ libxlTimeoutRegisterEventHook(void *priv,
>      }
>  
>      gettimeofday(&now, NULL);
> -    timeout = (abs_t.tv_usec - now.tv_usec) / 1000;
> -    timeout += (abs_t.tv_sec - now.tv_sec) * 1000;
> +    timersub(&abs_t, &now, &res);
> +    /* Ensure timeout is not overflowed */
> +    if (timercmp(&res, &zero, <)) {
> +        timeout = 0;
> +    } else if (res.tv_sec > INT_MAX / 1000) {
> +        timeout = INT_MAX;
> +    } else {
> +        timeout = res.tv_sec * 1000 + (res.tv_usec + 999) / 1000;
> +    }
>      timer_id = virEventAddTimeout(timeout, libxlTimerCallback,
>                                    timer_info, libxlTimerInfoFree);
>      if (timer_id < 0) {
> @@ -227,19 +242,25 @@ libxlTimeoutRegisterEventHook(void *priv,
>      return 0;
>  }
>  
> +/*
> + * Note:  There are two changes wrt timeouts starting with xen-unstable
> + * changeset 26469:
> + *
> + * 1. Timeout modify callbacks will only be invoked with an abs_t of {0,0},
> + * i.e. make the timeout fire immediately.  Prior to this commit, timeout
> + * modify callbacks were never invoked.
> + *
> + * 2. Timeout deregister hooks will no longer be called.
> + */
>  static int
>  libxlTimeoutModifyEventHook(void *priv ATTRIBUTE_UNUSED,
>                              void **hndp,
> -                            struct timeval abs_t)
> +                            struct timeval abs_t ATTRIBUTE_UNUSED)
>  {
> -    struct timeval now;
> -    int timeout;
>      struct libxlOSEventHookTimerInfo *timer_info = *hndp;
>  
> -    gettimeofday(&now, NULL);
> -    timeout = (abs_t.tv_usec - now.tv_usec) / 1000;
> -    timeout += (abs_t.tv_sec - now.tv_sec) * 1000;
> -    virEventUpdateTimeout(timer_info->id, timeout);
> +    /* Make the timeout fire */
> +    virEventUpdateTimeout(timer_info->id, 0);
>      return 0;
>  }
>  

  ACK, I assume you tested with the older libxl, right ?

Daniel

-- 
Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | virtualization library  http://libvirt.org/


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