Generic O_SYNC AIO DIO handling
 

Hi Jeff,

these patches implement generic way of handling O_SYNC AIO DIO. They work
for all filesystems except for ext4 and xfs. Thus together with your patches,
all filesystems should handle O_SYNC AIO DIO correctly. I've tested ext3,
btrfs, and xfs (to check that I didn't break anything when the generic code
is unused) and things seem to work fine. Will you add these patches to your
series please? Thanks.

Honza