Message-ID: <IvEM6Gxz0001IavmYU@andrew.cmu.edu>
Date: Tue,  3 Jul 2001 04:25:54 -0400 (EDT)
From: James R Bruce <bruce+@andrew.cmu.edu>
To: linux-kernel@vger.kernel.org
Subject: serial port O_SYNC functionality in 2.4.5
Sender: linux-kernel-owner@vger.kernel.org


As far as I can tell from observed operation and from perusing the
code, O_SYNC doesn't seem to be supported by the serial driver in
2.4.5.  Writes are forced as far as the serial.c's circular queue, but
O_SYNC seems to be ignored from there on, so any application trying to
do small synchronous writes to the serial port will end up backing it
up PAGE_SIZE bytes rather than getting synchronous operation (which is
incidentally what I was trying to do when I ran into this :).

I'm unfamiliar with the serial driver so I'm not sure the right way to
fix it is, but perhaps using a smaller value for WAKEUP_CHARS from
drivers/char/serial.c when the port is opened with O_SYNC
functionality might do the trick (i.e. 0 rather than 256).

Hopefully someone familiar with that part of the code please can tell
me what should be done... or if a patch or configuration option can
already get that functionality in another way.

Thanks,
  Jim Bruce

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/