On Wed, Sep 29, 2010 at 10:04:31AM +0200, Kay Sievers wrote: > On Wed, Sep 29, 2010 at 09:25, Ric Wheeler <rwhee...@redhat.com> wrote: > > > Second question is why is checking in /sys a big deal, would ??you prefer an > > interface like we did for alignment in libblkid? > > It's about knowing what's behind the 'nodev' major == 0 of a btrfs > mount. There is no way to get that from /sys or anywhere else at the > moment. > > Usually filesystems backed by a disk have the dev_t of the device, or > the fake block devices like md/dm/raid have their own major and the > slaves/ directory pointing to the devices. > > This is not only about readahead, it's every other tool, that needs to > know what kind of disks are behind a btrfs 'nodev' major == 0 mount.
Thanks for explaining the problem. It's one that affects everything with more than one underlying block device, so adding a filesystem-specific ioctl hack is not a good idea. As mentioned in this mail we already have a solution for that - the block device slaves links used for raid and volume managers. The most logical fix is to re-use that for btrfs as well and stop it from abusing the anonymous block major that was never intended for block based filesystems (and already has caused trouble in other areas). One way to to this might be to allocate a block major for btrfs that only gets used for representing these links. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
