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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Linus Torvalds <torvalds@osdl.org>
Cc: linux@horizon.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Make pipe data structure be a circular list of pages, rather
Date: Sat, 08 Jan 2005 21:47:05 +0000	[thread overview]
Message-ID: <1105216050.10519.64.camel@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.58.0501081018271.2386@ppc970.osdl.org>

On Sad, 2005-01-08 at 18:41, Linus Torvalds wrote:
> For all of those that are valid (certainly the signal case), you need to
> put the pipe into nonblocking mode anyway, so I don't think coalescing is
> really needed. SuS certainly does _not_ seem guarantee that you can do
> many nonblocking writes (small _or_ big). Let's see if somebody reports 
> any trouble with the new world order.

It breaks netscape 3 if I simulate it (but thats picking an app I know
makes silly assumptions).

>From the rules pasted below I think the 1 byte at a time 4K write is
guaranteed or at least strongly implied. The single write atomicity is
guaranteed but that is if anything made easier by the changes.

(From pathconf)

	fpathconf(_PC_PATH_BUF)

             returns  the  size of the pipe buffer, where filedes must
refer
              to a pipe or FIFO and path must refer to  a  FIFO.  The 
corre-
              sponding macro is _POSIX_PIPE_BUF.

(From pwrite)

Write requests of {PIPE_BUF} bytes or less shall not be interleaved with
data from other processes doing writes on the same pipe. Writes of
greater than {PIPE_BUF} bytes may have data interleaved, on arbitrary
boundaries, with writes by other processes, whether or not the
O_NONBLOCK flag of the file status flags is set.

[of O_NDELAY for pipe]
A write request for {PIPE_BUF} or fewer bytes shall have the following
effect: if there is sufficient space available in the pipe, write()
shall transfer all the data and return the number of bytes requested.
Otherwise, write() shall transfer no data and return -1 with errno set
to [EAGAIN].



  reply	other threads:[~2005-01-08 22:51 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-01-08  8:25 Make pipe data structure be a circular list of pages, rather linux
2005-01-08 18:41 ` Linus Torvalds
2005-01-08 21:47   ` Alan Cox [this message]
2005-01-13 21:46   ` Ingo Oeser
2005-01-13 22:32     ` Linus Torvalds
2005-01-14 21:03       ` Ingo Oeser
2005-01-14 21:29         ` Linus Torvalds
2005-01-14 22:12           ` Ingo Oeser
2005-01-14 22:44             ` Linus Torvalds
2005-01-14 23:34               ` Ingo Oeser
2005-01-15  0:16                 ` Linus Torvalds
2005-01-16  2:59                   ` Linus Torvalds
2005-01-17 16:03                     ` Ingo Oeser
2005-01-19 21:12                     ` Make pipe data structure be a circular list of pages, rather than linux
2005-01-20  2:06                       ` Robert White
2005-01-15 23:42 Make pipe data structure be a circular list of pages, rather linux
2005-01-15 22:55 ` Alan Cox
2005-01-16  0:12   ` Linus Torvalds
2005-01-16  2:02     ` Miquel van Smoorenburg
2005-01-16  2:06     ` Jeff Garzik

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