Re: [libvirt] [PATCH 2/3] fdstream: introduce virFDStreamOpenBlockDevice

On Fri, Aug 15, 2014 at 12:55:58PM +0400, Roman Bogorodskiy wrote: > Daniel P. Berrange wrote: > > > On Fri, Aug 15, 2014 at 12:44:21PM +0400, Roman Bogorodskiy wrote: > > > virStorageBackendVolDownloadLocal and virStorageBackendVolUploadLocal > > > use virFDStreamOpenFile function to work with the volume fd. > > > > > > virFDStreamOpenFile calls virFDStreamOpenFileInternal that implements > > > handling of the non-blocking I/O. If a file is not a character device and > > > not a fifo, it uses libvirt_iohelper. > > > > > > On FreeBSD, it doesn't work as expected because disks are exposed as > > > character devices. > > > > Why does that cause a problem ? The reason we use iohelper is because > > POSIX does not have O_NONBLOCK work on plain files, so we need to use > > the iohelper so that we have a pipe we can set O_NONBLOCK on. If FreeBSD > > disks are character devices though, O_NONBLOCK should work fine on them > > avoiding the need for iohelper. > > O_NONBLOCK doesn't work for some reason, at least on ZFS volumes: > fcntl() fails with: > > fcntl: Inappropriate ioctl for device > > I have asked a question on an appropriate mailing list: > > https://lists.freebsd.org/pipermail/freebsd-fs/2014-August/019923.html > > I've also included a test program I use to reproduce that there. Ah ok, so can you update the commit message to explicitly mention that ZFS character devices are unusual in not supporting O_NOBLOBKJ

On FreeBSD, it doesn't work as expected because disks are exposed as character devices and do not support O_NONBLOCK.