Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi [off-list ref] wrote:

Currently fdatasync is identical to fsync in ext3,4.
I think fdatasync should skip journal flush in data=ordered and data=writeback mode
because this syscall is not required to synchronize the metadata.

I suppose so.  Although one wonders what earthly point there is in syncing
a file's data if we haven't yet written out the metadata which is required
for locating that data.

IOW, fdatasync() is only useful if the application knows that it is overwriting
already-instantiated blocks.

In which case it might as well have used fsync().  For ext2-style filesystems,
anyway.

hm.  It needs some thought.