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Date: Mon, 22 Oct 2018 13:29:53 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Olga Kornievskaia <olga.kornievskaia@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
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Subject: Re: [PATCH v1 02/11] VFS permit cross device vfs_copy_file_range
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On Mon, Oct 22, 2018 at 10:48:10PM +0300, Amir Goldstein wrote:
> On Mon, Oct 22, 2018 at 10:35 PM Olga Kornievskaia
> <olga.kornievskaia@gmail.com> wrote:
> > So remove the check all together for the VFS (that was my original
> > patch to begin with (like #1 not this one). So am I missing the point
> > again, I keep getting different corrections every time.
> 
> Because there are different opinions... although you did get the opinion
> of the VFS maintainer, which was: compare i_sb->s_type.
> 
> Jeff, Matthew, really, what's the use of "allowing" cross fs type copy inside
> filesystem code? and which method is going to be called?
> file_out->f_op->copy_file_range()?
> file_in->f_op->copy_file_range()?

The destination's method, as Olga originally had.

> Do we need to check if both are implemented? either?
> This is just confusing Olga and gives no real value to anyone.
> If we ever have a filesystem copy_file_range() method that can deal
> with cross fs type copy, we can change it then when we know the
> required semantics of that future call.

Wrong.  Go back and read my reasoning earlier this thread.

> That is not to say that we cannot relax same fs type from copy_file_range()
> syscall. That has already been done with the current patch, just not officially
> declared in commit message.
> 
> Thanks,
> Amir.