tree 397b3930ea9effa60bc0c01b3071fd0b7f938956
parent 9b024b5f965a3c11aa65435df5b9e8f1cc24d3fa
author Anthony Liguori <aliguori@us.ibm.com> 1312831897 -0500
committer Anthony Liguori <aliguori@us.ibm.com> 1313155620 -0500

pc: make vgabios exit port more useful

We've always listened on port 501 for vgabios panic messages.  In the entire
time I've worked on QEMU, I've never actually seen a vgabios panic message :-)

If we change the semantics of this port a little bit, it makes it possible to
use it for more interesting use-cases.  I chose this approach instead of adding
a new I/O port because it avoids having a guest visible change.

This change allows single-byte access to port 501 and also uses the value
written to construct an exit code.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>