Neil Brown wrote:
On Tuesday June 26, nickpiggin@xxxxxxxxxxxx wrote:
Chris Mason wrote:
The block device pagecache isn't special, and certainly isn't that much
code. I would suggest keeping it buffer head specific and making a
second variant that does only fsblocks. This is mostly to keep the
semantics of PagePrivate sane, lets not fuzz the line.
That would require a new inode and address_space for the fsblock
type blockdev pagecache, wouldn't it? I just can't think of a
better non-intrusive way of allowing a buffer_head filesystem and
an fsblock filesystem to live on the same blkdev together.
I don't think they would ever try to. Both filesystems would bd_claim
the blkdev, and only one would win.
Hmm OK, I might have confused myself thinking about partitions...
The issue is more of a filesystem sharing a blockdev with the
block-special device (i.e. open("/dev/sda1"), read) isn't it?
If a filesystem wants to attach information to the blockdev pagecache
that is different to what blockdev want to attach, then I think "Yes"
- a new inode and address space is what it needs to create.
Then you get into consistency issues between the metadata and direct
blockdevice access. Do we care about those?
Yeah that issue is definitely a real one. The problem is not just
consistency, but "how do the block device aops even know that the
PG_private page they have has buffer heads or fsblocks", so it is
an oopsable condition rather than just a plain consistency issue
(consistency is already not guaranteed).
--
SUSE Labs, Novell Inc.
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