On Thu, Jun 21, 2018 at 03:47 PM +0200, Marc Hartmayer <mhartmay@linux.ibm.com> wrote:
On Wed, Jun 13, 2018 at 03:11 PM +0200, John Ferlan <jferlan@redhat.com> wrote:
On 06/07/2018 08:17 AM, Marc Hartmayer wrote:
On Wed, May 09, 2018 at 09:51 PM +0200, John Ferlan <jferlan@redhat.com> wrote:
On 05/07/2018 11:24 AM, Marc Hartmayer wrote:
On Mon, Apr 30, 2018 at 03:20 PM +0200, John Ferlan <jferlan@redhat.com> wrote:
On 04/25/2018 11:55 AM, Marc Hartmayer wrote: > 1. Don't allocate if there is nothing that needs to be > allocated. Especially as the result of calling calloc(0, ...) is > implementation-defined.
uh oh - another memory recollection challenge ;-)
Following VIR_ALLOC_N one finds :
VIR_ALLOC_N(params_val, nparams)
which equates to
# define VIR_ALLOC_N(ptr, count) \ virAllocN(&(ptr), sizeof(*(ptr)), (count), true, \ VIR_FROM_THIS, __FILE__, __FUNCTION__, __LINE__)
or
virAllocN(¶ms_val, sizeof(params_val), nparams, true, ...)
and eventually/essentially
*params_val = calloc(sizeof(params_val), nparams)
If the returned value is NULL then we error w/ OOM (4th param=true).
So, unless @params_val had no elements, it won't be calloc(0,...) and
I'm talking about the case that nparams == 0 => calloc(sizeof(…), 0).
And I was thinking is there a specific consumer/caller of virTypedParamsSerialize that was passing something incorrectly.
thus the question becomes is there a more specific path you are referencing here?
It’s a “generic” serializer so it should work for every (valid) case. What happens, for example, if params == NULL and nparams == 0? In that case I would expect *remote_params_val = NULL and *remote_params_len = 0.
Going through the callers to virTypedParamsSerialize can/does anyone pass params == NULL and nparams == 0? Would that be reasonable and/or expected?
My look didn't find any - either some caller checks that the passed @params != NULL (usually via virCheckNonNullArgGoto in the external API call) or @params is built up on the fly and wouldn't be NULL because there'd be an error causing failure beforehand. Although I'll admit the migration ones are also crazy to look at.
I could have made a mistake too; hence, the is there a specific instance that I missed? Or perhaps this is a result of some branched/private code that had that error which I don't have access to?
It was the result of private code but actually it was intended and no error :)
To answer your "What happens, for example, if params == NULL and nparams == 0?", well supposedly "VIR_ALLOC_N(params_val, 0)" should return NULL, so params_val and thus *remote_params_val == NULL.
Did you try what 'VIR_ALLOC_N(params_val, 0)' actually returns? At least for me, it doesn’t return a NULL pointer.
I think I already determined that NULL isn't returned; otherwise, we would have failed w/ OOM. I do recall trying this and seeing a non NULL value returned.
IIRC: I found no way into [de]serialize w/ a 0 parameter, so having that guard didn't seem necessary,
I used the libvirt-python APIs for some testing. I called an (own) API with 'None' as argument and this resulted in 0 parameters.
Maybe it was an empty dictionary. […snip] -- Beste Grüße / Kind regards Marc Hartmayer IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen Registergericht: Amtsgericht Stuttgart, HRB 243294