On Tue, Apr 15, 2014 at 8:35 PM, Mark Fasheh <mfasheh@xxxxxxx> wrote: > On Tue, Apr 15, 2014 at 07:30:51PM +0100, Filipe David Manana wrote: >> On Tue, Apr 15, 2014 at 7:10 PM, Josef Bacik <jbacik@xxxxxx> wrote: >> > Just make a SUPPORTS_V2 flag that userspace can pass in through the existing flags to make the kernel spit out V2 commands. We don't want to break old user space, I still have to see distro guys in real life ;). Thanks, >> >> So would this flag named like "supports_v2" imply to send fallocate >> commands and data size computation/command? Right now I made data size >> optional, sent only if a new ioctl send flag is set, because for large >> fs trees it can take some time to compute data size. > > If it's already backwards-compatibilty you could keep the flag for data size computation as-is > and simply add another flag that gets passed in for the fallocate commands > (UNDERSTANDS_FALLOCATE or something lke that). Yep, exactly what I had in mind. > > > >> Also, would new btrfs-progs version send that flag (support_v2) >> always, without any option to use old v1, or not really that useful? > > > As far as btrfs-progs go you could go with many different approaches. For > the library interface to this we might just let the callers determine the > behavior they want. For the command processing (user runs the btrfs program > directly), you could do a couple things: > > - perhaps try once with the new flags, if you get an error (EINVAL right now > for bad flags) try with the old ones and only then throw an error out to > the caller? > > - have user specify whether new flags should be tried or not (this is > easiest) > > I would generally avoid breaking compatibility inside of btrfs-progs too so > just forcing the new flag seems the most 'breaking' option. Sounds good. Will probably try first to have the user explicitly pass a --stream-version=2 for e.g to btrfs send command, with v1 (current) being the default. I like the idea of clearing the SUPPORT_FALLOCATE/DATA_SIZE bits from the flags and retry if the ioctl returns -EINVAL too. Thanks Mark > > Thanks, > --Mark > > -- > Mark Fasheh -- Filipe David Manana, "Reasonable men adapt themselves to the world. Unreasonable men adapt the world to themselves. That's why all progress depends on unreasonable men." -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
