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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



Regards,
Daniel
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