From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon@6wind.com>
Subject: Re: [PATCH v2] mbuf: decrease refcnt when detaching
Date: Tue, 17 May 2016 15:39:55 +0200
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Cc: dev@dpdk.org, Hiroyuki Mikita <h.mikita89@gmail.com>,
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To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
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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.