Hi Zoltan,
On 07/19/2016 05:59 PM, Zoltan Kiss wrote:
>
>
> On 19/07/16 16:37, Olivier Matz wrote:
>> Hi Zoltan,
>>
>> On 07/19/2016 04:37 PM, Zoltan Kiss wrote:
>>> A recent fix brought up an issue about the size of the 'name' fields:
>>>
>>> 85cf0079 mem: avoid memzone/mempool/ring name truncation
>>>
>>> These relations should be observed:
>>>
>>> RTE_RING_NAMESIZE <= RTE_MEMZONE_NAMESIZE - strlen(RTE_RING_MZ_PREFIX)
>>> RTE_MEMPOOL_NAMESIZE <= RTE_RING_NAMESIZE -
>>> strlen(RTE_MEMPOOL_MZ_PREFIX)
>>>
>>> Setting all of them to 32 hides this restriction from the application.
>>> This patch increases the memzone string size to accomodate for these
>>> prefixes, and the same happens with the ring name string. The ABI
>>> needs to
>>> be broken to fix this API issue, this way doesn't break applications
>>> previously not failing due to the truncating bug now fixed.
>>>
>>> Signed-off-by: Zoltan Kiss <zoltan.kiss at schaman.hu>
>>
>> I agree it is a problem for an application because it cannot know what
>> is the maximum name length. On the other hand, breaking the ABI for this
>> looks a bit overkill. Maybe we could reduce RTE_MEMPOOL_NAMESIZE and
>> RTE_RING_NAMESIZE instead of increasing RTE_MEMZONE_NAMESIZE? That way,
>> we could keep the ABI as is.
>
> But that would break the ABI too, wouldn't it? Unless you keep the array
> the same size (32 bytes) by using RTE_MEMZONE_NAMESIZE.
Yes, that was the idea.
> And even then, the API breaks anyway. There are applications - I have at
> least some - which use all 32 bytes to store the name. Decrease that
> would cause headache to change the naming scheme, because it's a 30
> character long id, and chopping the last few chars would cause name
> collisions and annoying bugs.
Before my patch (85cf0079), long names were silently truncated when
mempool created its ring and/or memzones. Now, it returns an error.
I'm not getting why changing the struct to something like below would
break the API, since it would already return an error today.
#define RTE_MEMPOOL_NAMESIZE \
(RTE_MEMZONE_NAMESIZE - sizeof(pool_prefix) - sizeof(ring prefix))
struct rte_mempool {
union {
char name[RTE_MEMPOOL_NAMESIZE];
char pad[32];
};
...
}
Anyway, it may not be the proper solution since it supposes that a
mempool includes a ring based on a memzone, which is not always true now
with mempool handlers.
>> It would even be better to get rid of this static char[] for the
>> structure names and replace it by an allocated const char *. I didn't
>> check it's feasible for memzones. What do you think?
>
> It would work too, but I don't think it would help a lot. We would still
> need max sizes for the names. Storing them somewhere else won't help us
> in this problem.
Why should we have a maximum length for the names?
Thanks,
Olivier
