[PATCH] jffs2: Hook up splice_write callback

[Christoph Hellwig]

On Wed, Mar 31, 2021 at 12:15:37AM +1030, Joel Stanley wrote:
> overlayfs using jffs2 as the upper filesystem would fail in some cases
> since moving to v5.10. The test case used was to run 'touch' on a file
> that exists in the lower fs, causing the modification time to be
> updated. It returns EINVAL when the bug is triggered.
> 
> A bisection showed this was introduced in v5.9-rc1, with commit
> 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops").
> Reverting that commit restores the expected behaviour.
> 
> Some digging showed that this was due to jffs2 lacking an implementation
> of splice_write. (For unknown reasons the warn_unsupported that should
> trigger was not displaying any output).
> 
> Adding this patch resolved the issue and the test now passes.

Looks good:

Reviewed-by: Christoph Hellwig <hch at lst.de>