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Commit c59dbcad authored by Jeff Dike's avatar Jeff Dike Committed by Linus Torvalds
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uml: fix console writing bugs 



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: default avatarJeff Dike <jdike@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e99525f9

arch/um/drivers/chan_kern.c

+3 −0
Original line number Diff line number Diff line
@@ -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))

arch/um/drivers/chan_user.c

+10 −1
Original line number Diff line number Diff line
@@ -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,

arch/um/drivers/line.c

+3 −6
Original line number Diff line number Diff line
@@ -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) {