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

[David Howells]

David Howells <dhowells at redhat.com> 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?

That said, for afs at least, the fix seems to be just this:

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 395075d7fe02..2bc6adfe351a 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -33,6 +33,7 @@ const struct file_operations afs_file_operations = {
 	.write_iter	= afs_file_write,
 	.mmap		= afs_file_mmap,
 	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
 	.fsync		= afs_fsync,
 	.lock		= afs_lock,
 	.flock		= afs_flock,

David