From: Philippe Gerum <rpm@xenomai.org>
To: dietmar.schindler@domain.hid
Cc: xenomai@xenomai.org
Subject: Re: [Xenomai-help] message pipe message boundaries
Date: Wed, 27 Apr 2011 23:42:38 +0200 [thread overview]
Message-ID: <1303940558.1932.33.camel@domain.hid> (raw)
In-Reply-To: <1183078C0D064042B3AD2D03E3859EF174E43D@AREXCH02.mra.roland-man.biz>
On Wed, 2011-04-27 at 14:22 +0200, dietmar.schindler@domain.hid
wrote:
> > From: xenomai-help-bounces@domain.hid
> [mailto:xenomai-help-bounces@domain.hid]
> > On Behalf Of dietmar.schindler@domain.hid
> > Sent: Wednesday, April 27, 2011 10:50 AM
> >
> > > From: xenomai-help-bounces@domain.hid
> > > On Behalf Of Philippe Gerum
> > > Sent: Tuesday, April 26, 2011 10:28 PM
> > >
> > > ...
> > > One read() per rt_pipe_write() operation, always.
> >
> > Thank you for your answer. Is "One readv() per rt_pipe_write()
> > operation" supposed to be true also, or is there something special to
> be
> > taken into consideration regarding readv(2)?
>
> Meanwhile, I found some facts which allow me to elaborate on my
> question. The rtpipe device hasn't a readv file operation implemented,
> so the kernel substitutes the readv call by a series of read calls to
> the device driver; due to this, under certain circumstances readv(2)
> gathers more than a single rt_pipe_write() call's data. (I can provide
> an example case, if desired.) Wouldn't it be desirable to implement the
> readv file operation in the rtpipe driver so that the guarantee "One
> read() per rt_pipe_write()" could cover readv(2) also?
No objection to merge this. Patch welcome.
> (Besides, this
> would make the phrase "Operates just like read" in the readv(2) man page
> more correct.)
Having readv() operate like read() would not give any guarantee wrt
message boundaries, because it is the real-time write side which makes
the decision regarding this, not the read side. So you could have
readv() operate like read() and still have blurred boundaries in case
rt_pipe_stream() is used instead of rt_pipe_write().
--
Philippe.
next prev parent reply other threads:[~2011-04-27 21:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-26 9:48 [Xenomai-help] message pipe message boundaries dietmar.schindler
2011-04-26 20:27 ` Philippe Gerum
2011-04-27 8:50 ` dietmar.schindler
2011-04-27 12:22 ` dietmar.schindler
2011-04-27 21:42 ` Philippe Gerum [this message]
2011-04-29 6:30 ` dietmar.schindler
2011-05-03 8:15 ` dietmar.schindler
2011-05-03 11:00 ` Gilles Chanteperdrix
2011-05-03 11:27 ` dietmar.schindler
2011-05-03 17:35 ` Gilles Chanteperdrix
2011-05-04 6:36 ` dietmar.schindler
2011-05-04 6:40 ` Gilles Chanteperdrix
2011-05-04 14:34 ` dietmar.schindler
2011-05-05 8:14 ` Gilles Chanteperdrix
2011-05-09 7:36 ` dietmar.schindler
2011-05-11 9:12 ` Gilles Chanteperdrix
2011-05-11 9:20 ` Philippe Gerum
2011-05-11 10:48 ` dietmar.schindler
2011-05-11 10:55 ` Gilles Chanteperdrix
2011-05-11 11:02 ` Philippe Gerum
2011-05-19 13:09 ` dietmar.schindler
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