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 - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
