The previous console cleanup patch switched generic_read and
generic_write from calling os_{read,write}_file to calling read and
write directly. Because the calling convention is different, they
now need to get any error from errno rather than the return value. I
did this for generic_read, but forgot about generic_write.
While chasing some output corruption, I noticed that line_write was
unnecessarily calling flush_buffer, and deleted it. I don't understand
why, but the corruption disappeared. This is unneeded because there
already is a perfectly good mechanism for finding out when the host
output device has some room to write data - there is an interrupt that
comes in when writes can happen again. line_write calling
flush_buffer seemed to just be an attempt to opportunistically get some
data out to the host.
I also made write_chan short-circuit calling into the host-level code
for zero-length writes. Calling libc write with a length of zero
conflated write not being able to write anything with asking it not to
write anything. Better to just cut it off as soon as possible.
Signed-off-by: Jeff Dike <[email protected]>
--
arch/um/drivers/chan_kern.c | 3 +++
arch/um/drivers/chan_user.c | 11 ++++++++++-
arch/um/drivers/line.c | 5 +----
3 files changed, 14 insertions(+), 5 deletions(-)
Index: linux-2.6.21-mm/arch/um/drivers/chan_kern.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/drivers/chan_kern.c 2007-08-02 10:51:14.000000000 -0400
+++ linux-2.6.21-mm/arch/um/drivers/chan_kern.c 2007-08-03 11:11:18.000000000 -0400
@@ -291,6 +291,9 @@ int write_chan(struct list_head *chans,
struct chan *chan = NULL;
int n, ret = 0;
+ if (len == 0)
+ return 0;
+
list_for_each(ele, chans) {
chan = list_entry(ele, struct chan, list);
if (!chan->output || (chan->ops->write == NULL))
Index: linux-2.6.21-mm/arch/um/drivers/chan_user.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/drivers/chan_user.c 2007-08-03 11:02:42.000000000 -0400
+++ linux-2.6.21-mm/arch/um/drivers/chan_user.c 2007-08-03 11:04:23.000000000 -0400
@@ -38,7 +38,16 @@ int generic_read(int fd, char *c_out, vo
int generic_write(int fd, const char *buf, int n, void *unused)
{
- return write(fd, buf, n);
+ int err;
+
+ err = write(fd, buf, n);
+ if (err > 0)
+ return err;
+ else if (errno == EAGAIN)
+ return 0;
+ else if (err == 0)
+ return -EIO;
+ return -errno;
}
int generic_window_size(int fd, void *unused, unsigned short *rows_out,
Index: linux-2.6.21-mm/arch/um/drivers/line.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/drivers/line.c 2007-08-03 13:00:30.000000000 -0400
+++ linux-2.6.21-mm/arch/um/drivers/line.c 2007-08-03 13:00:49.000000000 -0400
@@ -216,18 +216,15 @@ int line_write(struct tty_struct *tty, c
{
struct line *line = tty->driver_data;
unsigned long flags;
- int n, err, ret = 0;
+ int n, ret = 0;
if(tty->stopped)
return 0;
spin_lock_irqsave(&line->lock, flags);
- if (line->head != line->tail) {
+ if (line->head != line->tail)
ret = buffer_data(line, buf, len);
- err = flush_buffer(line);
- if (err <= 0 && (err != -EAGAIN || !ret))
- ret = err;
- } else {
+ else {
n = write_chan(&line->chan_list, buf, len,
line->driver->write_irq);
if (n < 0) {