Re: [Xen-devel] [PATCH 2 of 3] tools/libxl: suspend/postflush/commit callbacks

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-01-25 at 23:15 +0000, Shriram Rajagopalan wrote:
> On Wed, Jan 25, 2012 at 3:22 AM, Ian Campbell
> <Ian.Campbell@xxxxxxxxxx> wrote:
>         On Mon, 2012-01-23 at 22:46 +0000, rshriram@xxxxxxxxx wrote:
>         > # HG changeset patch
>         > # User Shriram Rajagopalan <rshriram@xxxxxxxxx>
>         > # Date 1327358640 28800
>         > # Node ID 0446591bee86eb4e767d75b70c885549c7a3cfef
>         > # Parent  11fb1dfda7de4d6759dec87d80cd16cf137f7369
>         > tools/libxl: suspend/postflush/commit callbacks
>         >
>         >  * Add libxl callbacks for Remus checkpoint suspend,
>         postflush (aka resume)
>         >    and checkpoint commit callbacks.
>         >  * suspend callback just bounces off
>         libxl__domain_suspend_common_callback
>         >  * resume callback directly calls xc_domain_resume instead
>         of re-using
>         >    libxl_domain_resume (as the latter does not set the fast
>         suspend argument
>         >    to xc_domain_resume - aka suspend_cancel support).
>         >  * commit callback just sleeps for the checkpoint interval
>         (for the moment).
>         >
>         >  * Future patches will augument these callbacks with more
>         functionalities like
>         >    issuing network buffer plug/unplug commands, disk
>         checkpoint commands, etc.
>         >
>         > Signed-off-by: Shriram Rajagopalan <rshriram@xxxxxxxxx>
>         >
>         
>         
>         
>         > +static int libxl__remus_domain_resume_callback(void *data)
>         > +{
>         > +    struct suspendinfo *si = data;
>         > +    libxl_ctx *ctx = libxl__gc_owner(si->gc);
>         > +
>         > +    /* Assumes that SUSPEND_CANCEL is available - just like
>         > +     * xm version of Remus. Without that, remus wont work.
>         > +     * Since libxl_domain_resume calls xc_domain_resume
>         with
>         > +     * fast_suspend = 0, we cant re-use that api.
>         
>         
>         You could modify that API which would be better than
>         duplicating its
>         content. I think the "fast" flag is useful to expose to users
>         of libxl
>         but if not then you could refactor into an internal function
>         which takes
>         the flag and call it from both here and libxl_domain_resume.
>         
>         
> 
> I didnt want to touch any existing public interfaces, structures, etc,
> especially something so common like domain_resume.

Until Xen 4.2 it is fine to improve the public interface of libxl,
including adding a new parameter here if you think that is best.

>  While users of xl resume (or unpause) wont see any difference, other
> libraries using the libxl API might be affected.

So long as they can still ask for the current behaviour that is fine.

>  But I am in favor of "exposing" the flag instead of hiding it in an
> internal function,  if there are no objections :).

None.

Ian.





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