virtio: console: Don't block entire guest if host doesn't read data
authorAmit Shah <amit.shah@redhat.com>
Wed, 20 Oct 2010 03:15:43 +0000 (13:15 +1030)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 20 Oct 2010 20:18:04 +0000 (13:18 -0700)
commit531295e63be8c2b8b909d7400739e8b8df60d61f
tree1ae5e6429e3fb52104220e543534049a6832ba1a
parent30c278192f9ab06125fb042f6e46763e0fd7140a
virtio: console: Don't block entire guest if host doesn't read data

If the host is slow in reading data or doesn't read data at all,
blocking write calls not only blocked the program that called write()
but the entire guest itself.

To overcome this, let's not block till the host signals it has given
back the virtio ring element we passed it.  Instead, send the buffer to
the host and return to userspace.  This operation then becomes similar
to how non-blocking writes work, so let's use the existing code for this
path as well.

This code change also ensures blocking write calls do get blocked if
there's not enough room in the virtio ring as well as they don't return
-EAGAIN to userspace.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
CC: stable@kernel.org
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/char/virtio_console.c