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Date: Mon, 22 Oct 2018 12:06:20 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Olga Kornievskaia <olga.kornievskaia@gmail.com>
Cc: Amir Goldstein <amir73il@gmail.com>, viro@zeniv.linux.org.uk,
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Subject: Re: [PATCH v1 02/11] VFS permit cross device vfs_copy_file_range
Message-ID: <20181022190620.GA8863@bombadil.infradead.org>
References: <20181019153018.32507-1-olga.kornievskaia@gmail.com>
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On Mon, Oct 22, 2018 at 02:45:04PM -0400, Olga Kornievskaia wrote:
> On Sat, Oct 20, 2018 at 4:54 AM Amir Goldstein <amir73il@gmail.com> wrote:
> > Another thing is the commit message claims to:
> > "Allow copy_file_range to copy between different superblocks but only
> > of the same file system types"
> >
> > But what the patch actually does is:
> > "Allow copy_file_range() syscall to copy between different filesystems
> > AND allow calling the filesystems' copy_file_range() method
> > between different superblocks but only of the same file system types"
> >
> > It's probably OK and quite useful to do the former, but maybe man page
> > should be fixed to explicitly mention that the copy is expected to work
> > across filesystems since kernel version XXX (?)
> >
> > If you don't wish to change cross filesystem type behavior and only
> > relax cross super block limitation, then you should replace the
> > same inode->i_sb check above with same inode->i_sb->s_type
> > check instead of doing the check only for calling the filesystem
> > copy_file_range() method.
> 
> Thank you for the feedback. In the next version, I will remove the
> check for the functions and instead check for the same file system
> types.

Jeff and I agree that this is the wrong way to go.  Instead, the
cross-device check should be in the individual instances, not the top
level code.