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Re: [PATCH RFC 03/41] target: fileio: check that the backing file supports ->{read,write}_iter
- To: Christian Brauner <brauner@xxxxxxxxxx>
- From: Christoph Hellwig <hch@xxxxxx>
- Date: Wed, 11 Nov 2026 15:56:47 +0100
- Authentication-results: eu.smtp.expurgate.cloud; none
- Cc: linux-fsdevel@xxxxxxxxxxxxxxx, Jann Horn <jannh@xxxxxxxxxx>, Chris Mason <mason@xxxxxxxxxx>, Josef Bacik <josef@xxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxx>, linux-block@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-nvme@xxxxxxxxxxxxxxxxxxx, Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, linux-scsi@xxxxxxxxxxxxxxx, target-devel@xxxxxxxxxxxxxxx, driver-core@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, bpf@xxxxxxxxxxxxxxx, linux-security-module@xxxxxxxxxxxxxxx, selinux@xxxxxxxxxxxxxxx, apparmor@xxxxxxxxxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, fuse-devel@xxxxxxxxxxxxxxx, linux-efi@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, linux-usb@xxxxxxxxxxxxxxx, Amir Goldstein <amir73il@xxxxxxxxx>, linux-erofs@xxxxxxxxxxxxxxxx, linux-kselftest@xxxxxxxxxxxxxxx
- Delivery-date: Wed, 11 Nov 2026 14:56:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, Nov 10, 2026 at 10:14:19AM +0100, Christian Brauner wrote:
> With fd_async_io=1 the fileio backend calls ->read_iter() and
> ->write_iter() of the backing file directly. The synchronous path goes
> through vfs_iter_read() and vfs_iter_write() which check for them but
> the aio path doesn't. So a backing file without them calls a NULL
> pointer on its first I/O.
>
> Refuse such files when configuring the device. On the synchronous path
> every read or write that needed the missing method failed with EINVAL
> anyway.
Looks good:
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
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