Re: Proposal for "proper" durable fsync() and fdatasync()

[Ric Wheeler <ric@emc.com>]

Jeff Garzik wrote:
> Jamie Lokier wrote:
>> By durable, I mean that fsync() should actually commit writes to
>> physical stable storage,
> 
> Yes, it should.
> 
> 
>> I was surprised that fsync() doesn't do this already.  There was a lot
>> of effort put into block I/O write barriers during 2.5, so that
>> journalling filesystems can force correct write ordering, using disk
>> flush cache commands.
>>
>> After all that effort, I was very surprised to notice that Linux 2.6.x
>> doesn't use that capability to ensure fsync() flushes the disk cache
>> onto stable storage.
> 
> It's surprising you are surprised, given that this [lame] fsync behavior 
> has remaining consistently lame throughout Linux's history.

Maybe I am confused, but isn't this is what fsync() does today whenever 
barriers are enabled (the fsync() invalidates the drive's write cache).

ric