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: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/drivers/chan_kern.c b/arch/um/drivers/chan_kern.c
index c09dbdf..db3082b 100644
--- a/arch/um/drivers/chan_kern.c
+++ b/arch/um/drivers/chan_kern.c
@@ -291,6 +291,9 @@
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))
diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 77557e2..d29e56d 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -38,7 +38,16 @@
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,
diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 3e0b68e..b4538df 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -216,18 +216,15 @@
{
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) {