Re: [PATCH] fs/read_write: Enable copy_file_range for block device.

[Christoph Hellwig]

> > Change generic_copy_file_checks to use ->f_mapping->host for both inode_in
> > and inode_out. Allow block device in generic_file_rw_checks.
> 
> Why? copy_file_range() is for copying a range of a regular file to
> another regular file - why do we want to support block devices for
> somethign that is clearly intended for copying data files?

Nitesh has a series to add block layer copy offload, and uses that to
implement copy_file_range on block device nodes, which seems like a
sensible use case for copy_file_range on block device nodes, and that
series was hiding a change like this deep down in a "block" title
patch, so I asked for it to be split out.  It still really should
be in that series, as there's very little point in changing this
check without an actual implementation making use of it.