iohelper: fdatasync() at the end

Currently, when we are doing (managed) save, we insert the
iohelper between the qemu and OS. The pipe is created, the
writing end is passed to qemu and the reading end to the
iohelper. It reads data and write them into given file. However,
with write() being asynchronous data may still be in OS
caches and hence in some (corner) cases, all migration data
may have been read and written (not physically though). So
qemu will report success, as well as iohelper. However, with
some non local filesystems, where ENOSPACE is polled every X
time units, we may get into situation where all operations
succeeded but data hasn't reached the disk. And in fact will
never do. Therefore we ought sync caches to make sure data
has reached the block device on remote host.
(cherry picked from commit f32e3a2dd686f3692cd2bd3147c03e90f82df987)

diff --git a/src/util/iohelper.c b/src/util/iohelper.c
index c6542ed261846814e28c39a6b401bd2da5eca440..860e14a98f6c6c5b5330b8c9ebd96b5985dcb2ab 100644 (file)
--- a/src/util/iohelper.c
+++ b/src/util/iohelper.c
@@ -179,6 +179,12 @@ runIO(const char *path, int fd, int oflags, unsigned long long length)
         }
     }
 
+    /* Ensure all data is written */
+    if (fdatasync(fdout) < 0) {
+        virReportSystemError(errno, _("unable to fsync %s"), fdoutname);
+        goto cleanup;
+    }
+
     ret = 0;
 
 cleanup: