[PATCH] hvc_console: returning 0 from put_chars is not an error

Timur Tabi timur at freescale.com
Thu Oct 15 08:53:46 EST 2009

hvc_console_print() calls the HVC client driver's put_chars() callback
to write some characters to the console.  If the callback returns 0, that
indicates that no characters were written (perhaps the output buffer is
full), but hvc_console_print() treats that as an error and discards the
rest of the buffer.

So change hvc_console_print() to just loop and call put_chars() again if it
returns a 0 return code.

This change makes hvc_console_print() behave more like hvc_push(), which does
check for a 0 return code and re-schedules itself.

Signed-off-by: Timur Tabi <timur at freescale.com>

This patch might cause a hang in drivers that return 0 in case of error, 
instead of a negative number, but those drivers are broken anyway.  This 
patch might fix drivers that return 0 to indicate that they're busy, such as
arch/powerpc/platforms/pseries/hvconsole.c.  It will break drivers that
return 0 if their output buffer is full, but where those buffers cannot be
emptied while the kernel is in a loop.

 drivers/char/hvc_console.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 25ce15b..0c94907 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -161,7 +161,7 @@ static void hvc_console_print(struct console *co, const char *b,
 		} else {
 			r = cons_ops[index]->put_chars(vtermnos[index], c, i);
-			if (r <= 0) {
+			if (r < 0) {
 				/* throw away chars on error */
 				i = 0;
 			} else if (r > 0) {

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