[Xen-devel] Re: [PATCH 5/7] mm: New XENMEM space, XENMAPSPACE_gmfn_range

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.11.11 at 18:37, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote:
> On 10/11 12:47, Jan Beulich wrote:
>> >>> On 10.11.11 at 12:35, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote:
>> >@@ -4716,6 +4748,17 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE(void) 
> arg)
>> >         }
>> > 
>> >         rc = xenmem_add_to_physmap(d, &xatp);
>> >+        if ( rc == -EAGAIN )
>> 
>>         if ( rc )
>> 
>> >+        {
>> >+            if ( copy_to_guest(arg, &xatp, 1) )
>> >+            {
>> >+                rcu_unlock_domain(d);
>> >+                return -EFAULT;
>> >+            }
>> 
>>         }
>>         if ( rc == -EAGAIN )
>> 
>> (with some room for further simplification). Without that (or the minimal
>> alternative of copying back just .size or yet some other mechanism), as
>> pointed out before, the caller won't have a way to know how far into
>> the batch things succeeded.
>> 
> 
> In xenmem_add_to_physmap I modify xatp in place so when I exit this
> function xatp will contain the updated value (new start value in
> .gpfn and .idx, how far do I need to go in .size).
> 
> The idea here was to call the copy_to_guest only when we got preempted.
> If I copy xatp back to the guest I should get the updated value
> in xatp from the copy_from_guest when I'll be called by the continuation.

I understand the continuation aspect. But you appear to have not read
my comments completely: I'm asking how your caller, in the event of
failure, would know how much of the batch was processed successfully.

Jan


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