Xen devel - Sep 2009 - [PATCH]: Remove "buffer half full" check from guest_console_write

All,
     We''ve seen a case where booting Xen on a certain platform
configured with a
serial console takes an unreasonably long time to boot (on the order of hours).
 Now, on this particular piece of hardware, it was determined that the serial
firmware actually has a bug.  That being said, I''m not sure that
preventing boot
in the face of buggy serial hardware is a reasonable course of action.
Bare-metal Linux, for instance, boots fine although characters might be dropped
along the way.
     The problem seems to be the check in guest_console_write(), which has a
quench-type check at the top of the loop.  I assume the check is to prevent the
guest from completely flooding the serial console, but:

1)  It seems like a layering violation; a check here can (and does) prevent the
lower level serial code from doing the right thing.

2)  It seems redundant since c/s 17851.  That c/s added a very similar check
into __serial_putc(), so I don''t think we need it here anymore.

This patch just removes the check entirely.  With this patch and c/s 17851 in
place, the problematic hardware boots in a normal amount of time (although it
still might drop characters, but I think this is the best we can do).

Signed-off-by: Chris Lalancette <clalance@redhat.com>


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