[Cluster-devel] [5.15 REGRESSION] iomap: Fix inline extent handling in iomap_readpage

[Christoph Hellwig]

On Wed, Nov 10, 2021 at 03:52:01PM +0100, Andreas Gruenbacher wrote:
> Hmm, that doesn't make sense to me: the filesystem doesn't know that
> iomap_readpage will pad to page boundaries. This happens at the iomap
> layer, so the iomap layer should also deal with the consequences.
> We're using different alignment rules here and for direct I/O, so that
> makes fake-aligning the extent size in iomap_begin even more
> questionable.
> 
> "Fixing" the extent size the filesystem returns would also break
> direct I/O. We could add some additional padding code to
> iomap_dio_inline_iter to deal with that, but currently, there's no
> need for that.

The iomap mapping sizes are read-only to iomap for a good reason.  You
can't just break that design.