Proposed patch tty_io.c/8K write split

Paul Fulghum (paulkf@microgate.com)
Tue, 24 Aug 1999 09:29:26 -0500

I have previously posted a suggestion to allow line disciplines
to avoid the splitting of write() calls into 8K chunks. No one objected
so I am posting the actual patch for comments. The patch is against 2.2.11.
The point of this change is to allow a line discipline I wrote to
process complete write() calls without interference from tty_io.c.

The change adds a new TTY flag that suppresses the write split
in tty_io.c. If this flag is not set then the behavior is unchanged. If set
then the line discipline write routine is called with the parameters of the
original write (no write split). When a line discipline is loaded (ldisc
open called)
then the ldisc can set the flag if necessary. When the ldisc is unloaded
(ldisc close called), then the flag can be restored.

This patch is very minimal and does not change the default behavior if the
new flag is not set. Please post any objections. If none are raised then
I will submit this patch.

diff -Naur linux-2.2.11/drivers/char/tty_io.c
linux-2.2.11-mg/drivers/char/tty_io.c
--- linux-2.2.11/drivers/char/tty_io.c Mon Aug 9 14:05:09 1999
+++ linux-2.2.11-mg/drivers/char/tty_io.c Mon Aug 23 15:36:41 1999
@@ -656,23 +656,27 @@
down(&inode->i_sem);
return -ERESTARTSYS;
}
- for (;;) {
- unsigned long size = PAGE_SIZE*2;
- if (size > count)
- size = count;
- ret = write(tty, file, buf, size);
- if (ret <= 0)
- break;
- written += ret;
- buf += ret;
- count -= ret;
- if (!count)
- break;
- ret = -ERESTARTSYS;
- if (signal_pending(current))
- break;
- if (current->need_resched)
- schedule();
+ if ( test_bit(TTY_NO_WRITE_SPLIT, &tty->flags) )
+ written = write(tty, file, buf, count);
+ else {
+ for (;;) {
+ unsigned long size = PAGE_SIZE*2;
+ if (size > count)
+ size = count;
+ ret = write(tty, file, buf, size);
+ if (ret <= 0)
+ break;
+ written += ret;
+ buf += ret;
+ count -= ret;
+ if (!count)
+ break;
+ ret = -ERESTARTSYS;
+ if (signal_pending(current))
+ break;
+ if (current->need_resched)
+ schedule();
+ }
}
if (written) {
file->f_dentry->d_inode->i_mtime = CURRENT_TIME;
diff -Naur linux-2.2.11/include/linux/tty.h
linux-2.2.11-mg/include/linux/tty.h
--- linux-2.2.11/include/linux/tty.h Mon Aug 23 14:52:57 1999
+++ linux-2.2.11-mg/include/linux/tty.h Mon Aug 23 15:34:43 1999
@@ -328,6 +328,7 @@
#define TTY_HW_COOK_OUT 14
#define TTY_HW_COOK_IN 15
#define TTY_PTY_LOCK 16
+#define TTY_NO_WRITE_SPLIT 17

#define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))

Paul Fulghum paulkf@microgate.com
Microgate Corporation www.microgate.com
9501 Capital of Texas Hwy
Austin, Texas 78759
(512)-345-7791

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