On Wed, Dec 01, 2010 at 03:09:52PM -0500, Josef Bacik wrote:
On Wed, Dec 01, 2010 at 03:00:08PM -0500, J. Bruce Fields wrote:
I think you're already fine:
# mkdir TMP
# dd if=/dev/zero of=TMP-image bs=1M count=512
# mkfs.btrfs TMP-image
# mount -oloop TMP-image TMP/
# btrfs subvolume create sub-a
# btrfs subvolume create sub-b
../readdir-inos .
. 256 256
.. 256 4130609
sub-a 256 256
sub-b 257 256
Where readdir-inos is my silly test program below, and the first
number is from readdir, the second from stat.
Heh as soon as I typed my email I went and actually looked at the
code, looks like for readdir we fill in the root id, which will be
unique, so hotdamn we are good and I don't have to use a stupid
incompat flag. Thanks for checking that :),
Except, aren't the inode numbers within a filesystem and the sunbvolume
tree IDs allocated out of separate namespaces? I don't think there's
anything preventing a file/directory from having an inode number that
clashes with one of the snapshots.
In fact, this already happens in the example above: "." (inode 256 in
the root subvolume) and "sub-a" (subvolume ID 256).
(Though I still don't understand the semantics well enough to say
whether we need all the inode numbers returned by readdir to be
distinct.)
--Michael Vrable
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