[PATCH 1/1] backing-file: convert to using fops->splice_write

[Amir Goldstein]

Christian,

Would you mind picking up this fix via the vfs tree?
The reason that the Fixes tag points to fuse passthrough patch is twofold:

1. fuse passthrough is a new user of backing_file_splice_write() which
    can have a fuse or overlayfs backing file with custom ->splice_write()
2. overlayfs can have a backing upper file which is a fuse passthrough
    file with a custom ->splice_write()

Thanks,
Amir.

On Mon, Jul 8, 2024 at 9:23 AM <ed.tsai at mediatek.com> wrote:
>
> From: Ed Tsai <ed.tsai at mediatek.com>
>
> Filesystems may define their own splice write. Therefore, use the file
> fops instead of invoking iter_file_splice_write() directly.
>

Fixes: 5ca73468612d ("fuse: implement splice read/write passthrough")
Reviewed-by: Amir Goldstein <amir73il at gmail.com>

> Signed-off-by: Ed Tsai <ed.tsai at mediatek.com>
> ---
>  fs/backing-file.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/backing-file.c b/fs/backing-file.c
> index afb557446c27..8860dac58c37 100644
> --- a/fs/backing-file.c
> +++ b/fs/backing-file.c
> @@ -303,13 +303,16 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
>         if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
>                 return -EIO;
>
> +       if (!out->f_op->splice_write)
> +               return -EINVAL;
> +
>         ret = file_remove_privs(ctx->user_file);
>         if (ret)
>                 return ret;
>
>         old_cred = override_creds(ctx->cred);
>         file_start_write(out);
> -       ret = iter_file_splice_write(pipe, out, ppos, len, flags);
> +       ret = out->f_op->splice_write(pipe, out, ppos, len, flags);
>         file_end_write(out);
>         revert_creds(old_cred);
>
> --
> 2.18.0
>