Thank you guys for responding!! > > > 1. Add a signal handler (like SIGHUP or SIGUSR1) to qemu-nbd which > > flushes all exports. > > That would be a useful addition anyway. > > Paolo
This is exactly what I was going to try today. I'm just getting familiar with Qemu source. I'll let you know how it goes.. Thanks again Paolo and Stefan. Regards, Mark Trumpold -----Original Message----- From: Paolo Bonzini [mailto:pbonz...@redhat.com] Sent: Wednesday, May 22, 2013 04:07 AM To: 'Stefan Hajnoczi' Cc: 'Mark Trumpold', qemu-devel@nongnu.org, ma...@tachyon.net Subject: Re: 'qemu-nbd' explicit flush Il 22/05/2013 11:47, Stefan Hajnoczi ha scritto: > On Tue, May 21, 2013 at 08:01:10PM +0000, Mark Trumpold wrote: >> Linux kernel 3.3.1 with Qemu patch to enable kernel flushing: >> http://thread.gmane.org/gmane.linux.drivers.nbd.general/1108 > > Did you check that the kernel is sending NBD_FLUSH commands? You can > use tcpdump and then check the captured network traffic. > >> Usage example: >> 'qemu-nbd --cache=writeback -c /dev/nbd0 /images/my-qcow.img' >> 'mount /dev/nbd0 /my-mount-point' >> >> Everything does flush correctly when I first unmount and then disconnect the >> device; however, in my case I am not able to unmount things before >> snapshotting. >> >> I tried several approaches externally to flush the device. For example: >> 'mount -o remount,ro /dev/nbd0' >> 'blockdev --flushbufs /dev/nbd0' > > Did you try plain old sync(1)? This could also work: dd if=/dev/zero of=dummy oflag=sync bs=512 count=1 > 1. Add a signal handler (like SIGHUP or SIGUSR1) to qemu-nbd which > flushes all exports. That would be a useful addition anyway. Paolo
