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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Thu, 25 Oct 2018 08:54:30 +0300
Message-ID: <CAOQ4uxiB5PLd9QjAp7pQerXOJdtkLbGAENhsGsAQehYWdK91PQ@mail.gmail.com>
Subject: Re: [PATCH v2 03/13] OverlayFS: add cross-device check for copy_file_range
To:     Olga Kornievskaia <olga.kornievskaia@gmail.com>
Cc:     trond.myklebust@hammerspace.com,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Steve French <smfrench@gmail.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-cifs@vger.kernel.org,
        overlayfs <linux-unionfs@vger.kernel.org>,
        linux-man@vger.kernel.org
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On Wed, Oct 24, 2018 at 10:59 PM Olga Kornievskaia
<olga.kornievskaia@gmail.com> wrote:
>
> From: Olga Kornievskaia <kolga@netapp.com>
>
> VFS copy_file_range was relaxed to allow for cross-device copy.
> Add a check for now, to disallow cross-device copy offload until
> appropriate support is added.
>
> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> `
> ---
>  fs/overlayfs/file.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index aeaefd2..5282853 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -483,6 +483,9 @@ static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
>                                    struct file *file_out, loff_t pos_out,
>                                    size_t len, unsigned int flags)
>  {
> +       if (file_in->f_inode->i_sb != file_out->f_inode->i_sb)
> +               return -EXDEV;
>

Note that this could be relaxed later on to same fs type
allowing for cross container copy_file_range() to be performced
as clone_file_range() when upper is a shared fs with clone support.

Don't worry about it though, I can make this change later after testing
the use case.

As long as this patch comes in the series *before* relaxing the VFS check,
You may add:
Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.