On Wed, 2007-07-11 at 15:05 +1000, Neil Brown wrote:
> It just occurred to me:
>
> If i_version is 64bit, then knfsd would need to be careful when
> reading it on a 32bit host. What are the locking rules?
How does knfsd use i_version? I would think that if all it was doing
was to compare (i_version == previous_version), then locking wouldn't
really matter. Well, theoretically, previous_version could be
0x100000000, and i_version could be 0x1ffffffff, knfsd checks the high
word, then ext4 updates i_version to 0x200000000, then knfsd checks the
low word, detecting no change. How likely is this? (I don't understand
why i_version even needs to be 64 bits in the first place.)
> Presumably it is only updated under i_mutex protection, but having to
> get i_mutex to read it would seem a little heavy handed.
How does knfsd protect itself from the inode changing after i_version is
checked? Is any locking being done otherwise?
> Should it use a seqlock like i_size?
> Could we use the same seqlock that i_size uses, or would we need a
> separate one?
>
> NeilBrown
--
David Kleikamp
IBM Linux Technology Center
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