[Qemu-devel] [RESEND] [PATCH 1/2] migrate.c: migrate_fd_put_buffer(): Do not busyloop: stop writing if EWOULDBLOCK

[Qemu-devel] [RESEND] [PATCH 1/2] migrate.c: migrate_fd_put_buffer(): Do not busyloop: stop writing if EWOULDBLOCK

[Uri Lublin]

Theoretically the migration code is non-blocking, designed for live migration.

Practically migrate_fd_put_buffer busy-loops trying to write. That's since
on many machines EWOULDBLOCK==EAGAIN (e.g. look in
<linux>/include/asm-generic/errno.h).
Busy looping is much worse then blocking (in case a write actually blocks).

Fixed by removing "(s->get_error(s)) == EWOULDBLOCK)" from the while condition.

Signed-off-by: Uri Lublin <uril@redhat.com>
---
  migration.c |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/migration.c b/migration.c
index 0ef777a..e8bafa6 100644
--- a/migration.c
+++ b/migration.c
@@ -168,7 +168,7 @@ ssize_t migrate_fd_put_buffer(void *opaque, const void 
*data, size_t size)

      do {
          ret = s->write(s, data, size);
-    } while (ret == -1 && ((s->get_error(s)) == EINTR || (s->get_error(s)) == 
EWOULDBLOCK));
+    } while (ret == -1 && s->get_error(s) == EINTR);

      if (ret == -1)
          ret = -(s->get_error(s));
-- 
1.6.0.6