From c59dbcadd5d125ba40595612dc91ab18924164d3 Mon Sep 17 00:00:00 2001
From: Jeff Dike <jdike@addtoit.com>
Date: Tue, 16 Oct 2007 01:26:42 -0700
Subject: 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>
---
arch/um/drivers/chan_user.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
(limited to 'arch/um/drivers/chan_user.c')
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_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,
--
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