On Mon, Oct 12, 2015 at 9:26 AM, Eric Blake <ebl...@redhat.com> wrote: > On 10/12/2015 09:56 AM, John Snow wrote: > >>> What is the correct action here though? If the file is writeable should >>> we just allow the device to extend its size? Is that possible already? >>> Just zero-pad read-only? >>> >> >> Read-only seems like an easy case of append zeroes. > > Yes, allowing read-only with append-zero behavior seems sane. > >> >> Read-write ... well, we can't write-protect just half of a 512k block. > >> Probably just forcibly increasing the size on RW or refusing to use the >> file altogether are probably the sane deterministic things we want. > > I'd lean towards outright rejection if the file size isn't up to snuff > for use as read-write. Forcibly increasing the size (done > unconditionally) still feels like magic, and may not be possible if the > size is due to something backed by a block device rather than a file. >
Inability to extend is easily detectable and can become a failure mode in it's own right. If we cant extend the file perhaps we can just LOG_UNIMP the data writes? Having to include in your user instructions "dd your already-on-SATA file system to this container just so it can work for SD" is a pain. Regards, Peter > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org >
