Re: [Xen-devel] [PATCH] tools/libxc: Fix error checking for xc_get_{cpu, node}map_size() callers

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/12/2013 14:56, Dario Faggioli wrote:
> On gio, 2013-12-12 at 14:24 +0000, Ian Campbell wrote:
>> On Wed, 2013-12-11 at 15:47 +0000, Andrew Cooper wrote:
>>> c/s 2e82c18cd850592ae9a1f682eb93965a868b5f2f changed the error returns of
>>> xc_get_{cpu,node}map_size() to now include returning -1.  This invalidated 
>>> the
>>> error checks from callers, which expected 0 to be the only error case.
>> I don't think 0 is a valid error value any more. Neither xc_get_max_cpus
>> nor xc_get_max_nodes can return 0 and the map_size functions will round
>> to 1 or more.
>>
> Yep, I confirm that, after that changeset, neither
> xc_get_max_{cpus,nodes}() nor xc_get_{cpu,node}map_size() return 0 as an
> error anymore.

Zero might not be "the error condition" any more, but it is certainly an
error from any of these functions (and possible as
xc_get_max_{cpus,nodes}() is capable of returning 0 if Xen hands back -1
for physinfo.max_{cpu,node}_id)

>
>> So these could all be "< 0" tests think.
>>
> Indeed.
>
> Anyway, looks like, while I fixed the callers of the xx_get_max_xx
> things in that very comment, I didn't do the same for the xx_get_*map_xx
> ones. Weird, as ISTR doing so too... :-/
>
> Anyway, thanks to Coverity for caching this and to Andrew for the patch.
>
> I'll reply to v2 (if you're posting it) but, with the conditions
> converted to "< 0", this can have my:
>
> Reviewed-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
>
> Regards,
> Dario
>

xc_{cpu/node}map_alloc() must strictly still be "<= 0" checks to avoid
the issue where calloc(1, 0) returns a non-NULL pointer.


Currently, I am of the opinion that the patch is better as is, than
changing some of the checks to being strictly "< 0"

~Andrew

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