[PATCH] fix reading from character devices

[Jan Kiszka <jan.kiszka-kv7WeFo6aLtBDgjK7y7TUQ@public.gmane.org>]

Hi Avi,

commit "kvm: qemu: consume all pending I/O in I/O loop"
(8ab8bb09f1115b9bf733f885cc92b6c63d83f420) broke reading data bursts
from serial devices (and maybe from other character devices as well) by
guests. Reason: serial devices do input flow control via fd_read_poll,
but qemu now ignores this fact by pushing all data into the virtual
device as soon as it is available.

Patch below is not really nice (just as the whole internal virtual I/O
interface at the moment, IMHO), but it re-enables the serial ports for
now.

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

---
 qemu/vl.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: kvm-userspace/qemu/vl.c
===================================================================
--- kvm-userspace.orig/qemu/vl.c
+++ kvm-userspace/qemu/vl.c
@@ -7751,7 +7751,10 @@ void main_loop_wait(int timeout)
         for(ioh = first_io_handler; ioh != NULL; ioh = ioh->next) {
             if (!ioh->deleted && ioh->fd_read && FD_ISSET(ioh->fd, &rfds)) {
                 ioh->fd_read(ioh->opaque);
-                more = 1;
+                if (!ioh->fd_read_poll || ioh->fd_read_poll(ioh->opaque))
+                    more = 1;
+                else
+                    FD_CLR(ioh->fd, &rfds);
             }
             if (!ioh->deleted && ioh->fd_write && FD_ISSET(ioh->fd, &wfds)) {
                 ioh->fd_write(ioh->opaque);

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