Date: Sat, 14 Nov 2015 11:46:58 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: Stable Stable <freebsd-stable@freebsd.org> Subject: Re: NETMAP and off-by-one? Message-ID: <20151114084658.GZ31314@zxy.spb.ru> In-Reply-To: <CA%2BhQ2%2BjGrZXd5e_uR_3fBJNUeDo1eGB2hVoWJm4dsOze9KrYFA@mail.gmail.com> References: <20151113213039.GK48728@zxy.spb.ru> <CA%2BhQ2%2BjGrZXd5e_uR_3fBJNUeDo1eGB2hVoWJm4dsOze9KrYFA@mail.gmail.com>
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On Fri, Nov 13, 2015 at 03:40:04PM -0800, Luigi Rizzo wrote:
> On Fri, Nov 13, 2015 at 1:30 PM, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote:
> > I am see strange things: like NETMAP stop transmit after `head` and `cur`
> > touch `tail`.
> >
> > But:
> >
> > /*
> > * check if space is available in the ring.
> > */
> > static inline int
> > nm_ring_empty(struct netmap_ring *ring)
> > {
> > return (ring->cur == ring->tail);
> > }
> >
> > i.e. if cur == (tail-1) mod ring_size -- space is available in the
> > ring and I can put packet in output buffer.
>
> The design requires to leave at least one empty slot in the buffer.
> The name of the function is correct, the comment is probably not,
> unless a bug has creeped in recently the code was very careful
> in not using the free slot that separates the two regions.
Please, do some clarification, in case for transmit patch:
- can I put in txring in case cur == (tail-1) mod ring_size?
- can I use poll with only `events |= POLLIN` for transmiting?
in case for receive patch:
- can I detect input overflow?
> cheers
> luigi
>
> > After put this packet ring is full, but no transmiting.
> >
> > This is bug?
> > _______________________________________________
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> > https://lists.freebsd.org/mailman/listinfo/freebsd-stable
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>
>
>
> --
> -----------------------------------------+-------------------------------
> Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione
> http://www.iet.unipi.it/~luigi/ . Universita` di Pisa
> TEL +39-050-2217533 . via Diotisalvi 2
> Mobile +39-338-6809875 . 56122 PISA (Italy)
> -----------------------------------------+-------------------------------
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