[PATCH 04/33] vfs: Export rw_verify_area() for use by cachefiles

[David Howells]

Christoph Hellwig <hch at lst.de> wrote:

> > Export rw_verify_area() for so that cachefiles can use it before issuing
> > call_read_iter() and call_write_iter() to effect async DIO operations
> > against the cache.  This is analogous to aio_read() and aio_write().
> 
> I don't think this is the right thing to do.  Instead of calling
> into ->read_iter / ->write_iter directly this should be using helpers.
> 
> What prevents you from using vfs_iocb_iter_read and
> vfs_iocb_iter_write which seem the right level of abstraction for this?

I don't think they existed when I wrote this code.  Should aio use that too,
btw?  I modelled my code on aio_read() and aio_write().

But I can certainly switch to using vfs_iocb_iter_read/write, though the
trivial checks are redundant.  The fsnotify call, I guess I'm missing though
(and is that missing in aio_read/write() also?).

David