Re: [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof where appropriate

[Christoph Hellwig]

On Fri, May 19, 2023 at 11:27:51PM +0100, David Howells wrote:
> 	ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
> 					 struct pipe_inode_info *pipe, size_t len,
> 					 unsigned int flags)
> 	{
> 		if (unlikely(*ppos >= in->f_mapping->host->i_sb->s_maxbytes))
> 			return 0;
> 		if (unlikely(!len))
> 			return 0;
> 		return filemap_splice_read(in, ppos, pipe, len, flags);
> 	}
> 
> so I wonder if the tests in generic_file_splice_read() can be folded into
> vfs_splice_read(), pointers to generic_file_splice_read() be replaced with
> pointers to filemap_splice_read() and generic_file_splice_read() just be
> removed.
> 
> I suspect we can't quite do this because of the *ppos check - but I wonder if
> that's actually necessary since filemap_splice_read() checks against
> i_size... or if the check can be moved there if we definitely want to do it.
> 
> Certainly, the zero-length check can be done in vfs_splice_read().

The zero length check makes sense in vfs_splice_read.  The ppos check
I think makes sense for filemap_splice_read - after all we're dealing
with the page cache here, and the page cache needs a working maxbytes
and i_size.  What callers of filemap_splice_read that don't have the
checks do you have in your tree right now and how did you end up with
them?