Re: [Xen-devel] [libvirt] [PATCH] libxl: detect support for save and restore

[Jim Fehlig <jfehlig@xxxxxxxx>]

Eric Blake wrote:
> On 06/25/2014 12:13 PM, Jim Fehlig wrote:
>   
>> libxl does not support save, restore, or migrate on all architectures,
>> notably ARM.  Detect whether libxl supports these operations using
>> LIBXL_HAVE_NO_SUSPEND_RESUME.  If not supported, drop advertisement of
>> <migration_features>.
>>
>> Found by Ian Campbell while improving Xen's OSSTEST infrastructure
>>
>> http://lists.xen.org/archives/html/xen-devel/2014-06/msg02171.html
>> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
>> ---
>>
>> Derived from a test patch I sent to Ian Campbell
>>
>> http://lists.xen.org/archives/html/xen-devel/2014-06/msg03150.html
>>
>> Includes fixups Ian provided later in the thread.
>>
>>  src/libxl/libxl_conf.c   | 4 ++++
>>  src/libxl/libxl_driver.c | 8 ++++++++
>>  2 files changed, 12 insertions(+)
>>     
>
>   
>>  
>> +#ifndef LIBXL_HAVE_NO_SUSPEND_RESUME
>>     
>
> Double negative logic is hard to read. Oh well.
>
>
>   
>>  
>>  static virDriver libxlDriver = {
>> @@ -4594,10 +4598,12 @@ static virDriver libxlDriver = {
>>      .domainSetMemoryFlags = libxlDomainSetMemoryFlags, /* 0.9.0 */
>>      .domainGetInfo = libxlDomainGetInfo, /* 0.9.0 */
>>      .domainGetState = libxlDomainGetState, /* 0.9.2 */
>> +#ifndef LIBXL_HAVE_NO_SUSPEND_RESUME
>>      .domainSave = libxlDomainSave, /* 0.9.2 */
>>      .domainSaveFlags = libxlDomainSaveFlags, /* 0.9.4 */
>>      .domainRestore = libxlDomainRestore, /* 0.9.2 */
>>      .domainRestoreFlags = libxlDomainRestoreFlags, /* 0.9.4 */
>> +#endif
>>     
>
> Hmm - do we do conditional registration in any other driver based on
> configure-time results?  I'd almost rather always provide the driver
> registration, and then use #ifdefs in the body of that function to
> either provide a sane result or else report that the compilation
> environment was too old, rather than omit the support altogether.

I sent a V2 which takes your preferred approach

https://www.redhat.com/archives/libvir-list/2014-June/msg01305.html

> Maybe get Dan's opinion on this?
>   

Ok.  I lean towards V2 since it avoids the double negative.

Regards,
Jim


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