The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/crosvm/+/c79de2d0b2b75c18adf1b9f1779a6b482247531e

commit c79de2d0b2b75c18adf1b9f1779a6b482247531e
Author: Stephen Barber <smbarber@chromium.org>
Date: Thu Feb 22 06:26:53 2018

crosvm: add advisory locking for disk images

Disk images should never be mounted as writable by multiple VMs at once.
Add advisory locking to prevent this.

BUG= chromium:810576 
TEST=run crosvm twice with same rwdisk, check that second VM fails to start

Change-Id: I5e6c178515eafa570812a093449eef5a4edc1740
Reviewed-on: https://chromium-review.googlesource.com/929994
Commit-Ready: Stephen Barber <smbarber@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>

[modify] https://crrev.com/c79de2d0b2b75c18adf1b9f1779a6b482247531e/src/linux.rs
[modify] https://crrev.com/c79de2d0b2b75c18adf1b9f1779a6b482247531e/sys_util/src/lib.rs