Re: [RFC PATCH v2 0/5] Add buffered write-through support to iomap & xfs

[Christoph Hellwig]

On Mon, Jun 01, 2026 at 10:19:18PM +0530, Ojaswin Mujoo wrote:
> 
> So this week I spent some time looking into the failure of g/457. 
> I was able to replicate it in my setup and after analysing it, this is
> actually an issue in my xfstests patch. The issue is that to verify
> RWF_WRITETHROUGH support I do a 4kb write on the fd during the test prep
> phase. However "out-of-band" write makes the actual contents of the file
> different from what fsx expected (It reads it in before the problematic
> write), causing the test failure. 

Why does this get out of sync?  One of the arguments for RWF_WRITETHROUGH
vs direct I/O was that it avoids the content getting out of sync.