[dpdk-dev] [PATCH v2] mbuf: decrease refcnt when detaching

[Ananyev, Konstantin]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com]
> Sent: Tuesday, May 17, 2016 2:40 PM
> To: Ananyev, Konstantin
> Cc: dev at dpdk.org; Hiroyuki Mikita; olivier.matz at 6wind.com
> Subject: Re: [dpdk-dev] [PATCH v2] mbuf: decrease refcnt when detaching
> 
> 2016-05-17 12:59, Ananyev, Konstantin:
> > > > The rte_pktmbuf_detach() function should decrease refcnt on a direct
> > > > buffer.
> > >
> > > As you have noticed, "whenever the indirect buffer is detached,
> > > the reference counter on the direct buffer is decremented."
> > > So the current behaviour of rte_pktmbuf_detach() is buggy.
> > > Why not fix it without renaming?
> > > If you consider this behavioral bug is part of the API, we
> > > can fix it in a new function unattach and deprecate detach.
> > > But Konstantin, why do you want to keep a restore function?
> > > What is the need?
> >
> > I think it might be a useful functionality in some situations:
> > some users can attach/detach to external memory buffers (no mbufs)
> > and similar functionality is required.
> 
> Attach to external memory buffer (raw buffer) is not currently supported.
> 
> > Let say right now examples/vhost/main.c has its own pktmbuf_detach_zcp()
> 
> You should look at the commit http://dpdk.org/commit/68363d85
> 	"examples/vhost: remove the non-working zero copy code"
> 
> > which is doing pretty much the same - restore original values, after detaching
> > mbuf from external (virtio) memory buffer.
> > Would be good if we'll use a standard API function here.
> 
> You are welcome to implement mbuf attach to raw buffer.
> But it is not a requirement for this fix.

Hmm, still not sure why we can't keep an existing function?
Obviously it wouldn't cost anything and I still think might be useful.
Konstantin