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Re: [Xen-devel] [PATCH v3 10/10] libxl: fix caller of libxl_cpupool functions

On 07/16/2015 11:07 AM, Wei Liu wrote:
On Thu, Jul 16, 2015 at 10:57:24AM +0200, Dario Faggioli wrote:
[Adding Juergen]                

On Wed, 2015-07-15 at 18:16 +0100, Wei Liu wrote:
On Tue, Jul 14, 2015 at 06:33:22PM +0100, Ian Jackson wrote:
Wei Liu writes ("[PATCH v3 10/10] libxl: fix caller of libxl_cpupool 

--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -771,8 +771,11 @@ libxl_cpupoolinfo * libxl_list_cpupool(libxl_ctx *ctx, int 

      poolid = 0;
      for (i = 0;; i++) {
-        if (cpupool_info(gc, &info, poolid, false))
+        libxl_cpupoolinfo_init(&info);
+        if (cpupool_info(gc, &info, poolid, false)) {
+            libxl_cpupoolinfo_dispose(&info);
+        }

I'm not convinced by this change.

I think that this function has broken error handling: if cpupool_info
fails, it simply ignores the error.

I think the semantics of this function is to get back as many cpupool
info as it can.

Yes, I also think this is the case.

Unfortunately the failing of cpupool_info can either mean the cpupool id
does not exist or other internal errors.  So not cleaning up is the
right thing to do (speaking from semantics point of view).


I think I need to overhaul cpupool_info a bit if we want to make this
API better.

Well, perhaps having cpupool_info() treating specially the situation
where the pool ID is not there may help... However, what would you do
once you have this additional piece of information available?

See below.

Maybe, depending on the error, we can cleanup the whole array? Is it
this that we are after?

I'm not sure if it is possible to interleave pool ids. If so, we need a
way to get back the exact number of cpupools. Dario?

Sorry, what you mean by 'interleave pool ids'?

For example, pools have ids 0 1 4 6. In this case when should we stop
querying hypervisor about cpu pools? Current model will stop at id 2.

No, it won't. cpupool_info(..., poolid, false) will return the next
cpupool with an id >= poolid. Only with the last parameter being "true"
an exact match is required.


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