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uml: fix console writing bugs

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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 <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeff Dike 2007-10-16 01:26:42 -07:00 committed by Linus Torvalds
parent e99525f970
commit c59dbcadd5
3 changed files with 16 additions and 7 deletions
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3
arch/um/drivers/chan_kern.c
View file

@ -291,6 +291,9 @@ int write_chan(struct list_head *chans, const char *buf, int len,
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))

11
arch/um/drivers/chan_user.c
View file

@ -38,7 +38,16 @@ int generic_read(int fd, char *c_out, void *unused)
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,

9
arch/um/drivers/line.c
View file

@ -216,18 +216,15 @@ int line_write(struct tty_struct *tty, const unsigned char *buf, int len)
{
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) {