On 2010-03-11, at 06:30, Dmitry Monakhov wrote:
Christoph Hellwig <hch@xxxxxxxxxxxxx> writes:
I think you'd be much better off storing it inide the inode core
itself.
E.g. you could ue the never used fragment address in the ext2/3/4
disk
inode.
This was already discussed at the first RFC
http://patchwork.ozlabs.org/patch/38766
and Andreas was strongly against this idea.
I had written:
You can instead just store this data in an xattr (which will
normally be stored in the inode, so no performance impact), and
then you are free to store multiple values per inode.
I don't know if I would classify this as "strongly against", but it is
true that I'm hesitant to use up the last field in the inode for
something that may be used so rarely. There is also some desire to
use this field for an extended i_links_hi field, and/or an inode
checksum.
Part of my suggestion to use xattrs was that it would then be possible
to allow hard links to have different project IDs on the same file,
since the size of the xattr is flexible. Since the xattr is stored
inside the inode in ext3/ext4 if the inode was formatted with 256-byte
inodes this is a minimal performance hit.
A second possibility (if there is really no desire to have more than a
single project ID per inode) is to add a field to the "large" inode
for ext4, though that doesn't help filesystems that were not formatted
that way, and it also consumes space in all inodes even if this
feature is not used.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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