Re: [PATCH v2] mempool: adjust name string size in related data types

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-07-21 16:25, Olivier Matz:
> On 07/21/2016 03:47 PM, Zoltan Kiss wrote:
> > On 21/07/16 14:40, Olivier Matz wrote:
> >> On 07/20/2016 07:16 PM, Zoltan Kiss wrote:
> >>> A recent patch brought up an issue about the size of the 'name' fields:
> >>>
> >>> 85cf0079 mem: avoid memzone/mempool/ring name truncation
> >>>
> >>> These relations should be observed:
> >>>
> >>> 1. Each ring creates a memzone with a prefixed name:
> >>> RTE_RING_NAMESIZE <= RTE_MEMZONE_NAMESIZE - strlen(RTE_RING_MZ_PREFIX)
> >>>
> >>> 2. There are some mempool handlers which create a ring with a prefixed
> >>> name:
> >>> RTE_MEMPOOL_NAMESIZE <= RTE_RING_NAMESIZE -
> >>> strlen(RTE_MEMPOOL_MZ_PREFIX)
> >>>
> >>> 3. A mempool can create up to RTE_MAX_MEMZONE pre and postfixed
> >>> memzones:
> >>> sprintf(postfix, "_%d", RTE_MAX_MEMZONE)
> >>> RTE_MEMPOOL_NAMESIZE <= RTE_MEMZONE_NAMESIZE -
> >>>     strlen(RTE_MEMPOOL_MZ_PREFIX) - strlen(postfix)
> >>>
> >>> Setting all of them to 32 hides this restriction from the application.
> >>> This patch decreases the mempool and ring string size to accommodate for
> >>> these prefixes, but it doesn't apply the 3rd constraint. Applications
> >>> relying on these constants need to be recompiled, otherwise they'll run
> >>> into ENAMETOOLONG issues.
> >>> The size of the arrays are kept 32 for ABI compatibility, it can be
> >>> decreased next time the ABI changes.
> >>>
> >>> Signed-off-by: Zoltan Kiss <zoltan.kiss@schaman.hu>
> >>
> >> Looks like to be a good compromise for the 16.07 release. One question
> >> however: why not taking in account the 3rd constraint? Because it may
> >> not completly fix the issue if the mempool is fragmented.
> >>
> >> We could define RTE_MEMPOOL_NAMESIZE to 24
> >>  = 32 - len('mp_') - len('_0123'))
> > 
> > I was trying to figure out a compile time macro for strlen(postfix), but
> > I could not. Your suggestion would work only until someone increases
> > RTE_MAX_MEMZONE above 9999. As the likelihood of fragmenting a pool over
> > 99 memzones seems small, I did not bother to fix this with an ugly hack,
> > but if you think we should include it, let me know!
> 
> Ok, looks fair, thanks for the clarification.
> 
> Acked-by: Olivier Matz <olivier.matz@6wind.com>

Applied, thanks