Messages in this thread | | | Date | Wed, 14 Jan 2009 15:08:04 +0100 | From | Jens Axboe <> | Subject | Re: ext2 + -osync: not as easy as it seems |
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On Wed, Jan 14 2009, Jan Kara wrote: > > I'm not sure what you mean; if the barrier operation isn't flushing > > all of the caches all the way out to the iron oxide, it's not going to > > be working properly no matter where it is being called, whether it's > > in ext4_sync_file() or in jbd2's journal_submit_commit_record(). > Well, I thought that a barrier, as an abstraction, only guarantees that > any IO which happened before the barrier hits the iron before any IO which > has been submitted after a barrier. This is actually enough for a > journalling to work correctly but it's not enough for fsync() guarantees. > But I might be wrong...
It also guarentees that when you get a completion for that barrier write, it's on safe storage. Think of it as a flush-write-flush operation, in the presence of write back caching.
-- Jens Axboe
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