Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 18 Feb 2021 07:43:49 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Luis Henriques <lhenriques@suse.de>
Cc:     Amir Goldstein <amir73il@gmail.com>,
        Jeff Layton <jlayton@kernel.org>,
        Steve French <sfrench@samba.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Dave Chinner <dchinner@redhat.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Nicolas Boichat <drinkcat@chromium.org>,
        Ian Lance Taylor <iant@google.com>,
        Luis Lozano <llozano@chromium.org>, ceph-devel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-cifs@vger.kernel.org,
        samba-technical@lists.samba.org, linux-fsdevel@vger.kernel.org,
        linux-nfs@vger.kernel.org
Subject: Re: [PATCH v3] vfs: fix copy_file_range regression in cross-fs copies
Message-ID: <20210218074349.GB329605@infradead.org>
References: <CAOQ4uxii=7KUKv1w32VbjkwS+Z1a0ge0gezNzpn_BiY6MFWkpA@mail.gmail.com>
 <20210217172654.22519-1-lhenriques@suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210217172654.22519-1-lhenriques@suse.de>
Precedence: bulk

On Wed, Feb 17, 2021 at 05:26:54PM +0000, Luis Henriques wrote:
> A regression has been reported by Nicolas Boichat, found while using the
> copy_file_range syscall to copy a tracefs file.  Before commit
> 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
> kernel would return -EXDEV to userspace when trying to copy a file across
> different filesystems.  After this commit, the syscall doesn't fail anymore
> and instead returns zero (zero bytes copied), as this file's content is
> generated on-the-fly and thus reports a size of zero.
> 
> This patch restores some cross-filesystems copy restrictions that existed
> prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> devices").  It also introduces a flag (COPY_FILE_SPLICE) that can be used
> by filesystems calling directly into the vfs copy_file_range to override
> these restrictions.  Right now, only NFS needs to set this flag.

No need for the flag.  Jyst fall back to splicing in the only caller
that wants it.