Re: [PATCH] [2.5] Non-blocking write can block

From: Davide Libenzi (
Date: Wed Jun 04 2003 - 18:47:27 EST

On Thu, 5 Jun 2003, Russell King wrote:

> On Wed, Jun 04, 2003 at 08:46:51PM +0100, P. Benie wrote:
> > The problem isn't to do with large writes. It's to do with any sequence of
> > writes that fills up the receive buffer, which is only 4K for N_TTY. If
> > the receiving program is suspended, the buffer will fill sooner or later.
> If the tty drivers buffer fills, we don't sleep in tty->driver->write,
> but we return zero instead. If we are in non-blocking mode, and we
> haven't written any characters, we return -EAGAIN. If we have, we
> return the number of characters which the tty driver accepted.
> However, the problem you are referring to is what happens if you have
> a blocking process blocked in write_chan() in n_tty.c, and we have
> a non-blocking process trying to write to the same tty.
> Reading POSIX, it doesn't seem to be clear about our area of interest,
> and I'd even say that it seems to be unspecified.

Given that a problem exist for certain apps, and given that the proposed
fix will *at least* have existing apps to behave funny, couldn't this
implemented as a feature of the fd (default off).
Something like O_REALLYNONBLOCK :)

- Davide

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