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))