Re: [PATCH 02/10] fs: don't allow splice read/write without explicit ops

David Howells
2020-10-27T09:29:59Z

Christoph Hellwig <hch@lst.de> wrote:

> default_file_splice_write is the last piece of generic code that uses
> set_fs to make the uaccess routines operate on kernel pointers. It
> implements a "fallback loop" for splicing from files that do not actually
> provide a proper splice_read method. The usual file systems and other
> high bandwith instances all provide a ->splice_read, so this just removes
> support for various device drivers and procfs/debugfs files. If splice
> support for any of those turns out to be important it can be added back
> by switching them to the iter ops and using generic_file_splice_read.

Hmmm... this causes the copy_file_range() syscall to fail with EINVAL in some
places where before it used to work.

For my part, it causes the generic/112 xfstest to fail with afs, but there may
be other places.

Is this a regression we need to fix in the VFS core? Or is it something we
need to fix in xfstests and assume userspace will fallback to doing it itself?

David