Re: [Qemu-devel] [PATCH] migrate.c: migrate_fd_put_buffer: Do not busyloop: stop writing if EWOULDBLOCK

[Dor Laor <dlaor@redhat.com>]

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Anthony Liguori wrote:
>
> This is whitespace damaged, presumably from copy/paste, can you resend?
>
Here is a better one.

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>From 2d875410cb168fa728dcde96885a3e4ddfd0bb58 Mon Sep 17 00:00:00 2001
From: Dor Laor <dor@redhat.com>
Date: Thu, 21 May 2009 12:29:39 +0300
Subject: [PATCH] The migration code is non-blocking, designed for live migration.

Practically migrate_fd_put_buffer busy-loops trying to write, as
on many machines EWOULDBLOCK==EAGAIN (look in include/asm-generic/errno.h).

Based on Uri Lublin's patch.
Signed-off-by: Dor Laor <dor@redhat.com>
---
 qemu/buffered_file.c |    4 ++--
 qemu/migration.c     |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/qemu/buffered_file.c b/qemu/buffered_file.c
index be5baea..34cde6e 100644
--- a/qemu/buffered_file.c
+++ b/qemu/buffered_file.c
@@ -86,7 +86,7 @@ static void buffered_flush(QEMUFileBuffered *s)
 
         ret = s->put_buffer(s->opaque, s->buffer + offset,
                             s->buffer_size - offset);
-        if (ret == -EAGAIN) {
+        if (ret == -EAGAIN || ret == -EWOULDBLOCK) {
             dprintf("backend not ready, freezing\n");
             s->freeze_output = 1;
             break;
@@ -132,7 +132,7 @@ static int buffered_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, in
         }
 
         ret = s->put_buffer(s->opaque, buf + offset, size - offset);
-        if (ret == -EAGAIN) {
+        if (ret == -EAGAIN || ret ==-EWOULDBLOCK) {
             dprintf("backend not ready, freezing\n");
             s->freeze_output = 1;
             break;
diff --git a/qemu/migration.c b/qemu/migration.c
index 85757c5..8846eee 100644
--- a/qemu/migration.c
+++ b/qemu/migration.c
@@ -174,7 +174,7 @@ ssize_t migrate_fd_put_buffer(void *opaque, const void *data, size_t size)
     if (ret == -1)
         ret = -(s->get_error(s));
 
-    if (ret == -EAGAIN)
+    if (ret == -EAGAIN || ret == -EWOULDBLOCK)
         qemu_set_fd_handler2(s->fd, NULL, NULL, migrate_fd_put_notify, s);
 
     return ret;
-- 
1.5.6.6