[PATCH RFC 1/3] xfs: debug mode forced buffered write failure

[Christoph Hellwig]

On Mon, Feb 29, 2016 at 09:29:28AM -0500, Brian Foster wrote:
> Add a DEBUG mode-only sysfs knob to enable forced buffered write
> failure. An additional side effect of this mode is brute force killing
> of delayed allocation blocks in the range of the write. The latter is
> the prime motiviation behind this patch, as userspace test
> infrastructure requires a reliable mechanism to create and split
> delalloc extents without causing extent conversion.
> 
> Certain fallocate operations (i.e., zero range) were used for this in
> the past, but the implementations have changed such that delalloc
> extents are flushed and converted to real blocks, rendering the test
> useless.

Looks harmless, but I'd add a inline function to check for the failed
writes field so that we can compile it away entirely for !DEBUG builds.