[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] migrate_fd_close: delete associated io-handler
From: |
Mark McLoughlin |
Subject: |
Re: [Qemu-devel] [PATCH] migrate_fd_close: delete associated io-handler before closing the fd |
Date: |
Mon, 08 Jun 2009 17:38:14 +0100 |
On Mon, 2009-06-08 at 18:56 +0300, Uri Lublin wrote:
> >> +
> >> + qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
> >
> > Looks good, but perhaps a comment explaining how the I/O handler could
> > possibly be registered here would be useful - at first glance, it seemed
> > to me that the I/O handler should always be de-registered in
> > migrate_fd_cleanup() before getting here.
> >
> > The key to understanding the problem is that qemu_fclose() on a buffered
> > file can cause I/O to be flushed.
>
> Do you mean in addition to the log-message (copy part of the log message as a
> comment in the code) ?
It's subtle, so yeah - I think it deserves a comment.
Would the below patch working equally well? But then again, we should
really remove the I/O handler before closing the fd.
(The close(s->fd) in migration_fd_cleanup() looks like it can never
happen - perhaps we should remove it)
Cheers,
Mark.
diff --git a/migration.c b/migration.c
index 401383c..078967f 100644
--- a/migration.c
+++ b/migration.c
@@ -154,13 +154,21 @@ void migrate_fd_error(FdMigrationState *s)
void migrate_fd_cleanup(FdMigrationState *s)
{
- qemu_set_fd_handler2(s->fd, NULL, NULL, NULL, NULL);
+ int fd;
+
+ /* qemu_fclose() can cause I/O to be flushed (see buffered_close())
+ * which, in turn, can cause an I/O handler to be registered. We
+ * need to delay removing the I/O handler until after qemu_fclose().
+ */
+ fd = s->fd;
if (s->file) {
dprintf("closing file\n");
qemu_fclose(s->file);
}
+ qemu_set_fd_handler2(fd, NULL, NULL, NULL, NULL);
+
if (s->fd != -1)
close(s->fd);