Re: [Libguestfs] [Qemu-devel] [Qemu-block] [PATCH] tests: regressions: make test-big-heap use a temporary empty file

On 03/21/2018 03:44 PM, Kevin Wolf wrote: >>> >>>You're right that file locking on a character device like /dev/null is >>>not going to work as expected, but is it a case where fcntl() actually >>>fails, or is it worse where the fcntl() claiming the locks "succeeds" >>>but doesn't do what we want? That is, what were the actual error >>>messages you ran into? >> >>$ qemu-img --version >>qemu-img version 2.10.1(qemu-2.10.1-2.fc27) >>Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers >>$ qemu-img info /dev/null >>qemu-img: Could not open '/dev/null': Failed to get "consistent read" lock >>Is another process using the image? > >Not sure where the difference is, but I can't reproduce this on >upstream, neither git master nor the v2.10.1 tag: Is it a case where file locking actually works, and more than one process is trying to lock /dev/null at once? (qemu-img info is short-lived, but could there be another longer-lived process also using /dev/null)? Does using -r help (if the only reason you're telling qemu-img to operate on /dev/null is to probe qemu-img features, can you probe those same features without needing to write, which in turn requests less locking)?