Re: [PATCH 1/2] vfs: add vfs_iocb_iter_[read|write] helper functions

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Nov 19, 2019 at 4:14 AM Jiufei Xue <jiufei.xue@linux.alibaba.com> wrote:
>
> This isn't cause any behavior changes and will be used by overlay
> async IO implementation.
>
> Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
> ---
>  fs/read_write.c    | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h | 16 +++++++++++++++
>  2 files changed, 74 insertions(+)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 5bbf587..3dfbcec 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -984,6 +984,64 @@ ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
>  }
>  EXPORT_SYMBOL(vfs_iter_write);
>
> +ssize_t vfs_iocb_iter_read(struct file *file, struct kiocb *iocb,
> +                          struct iov_iter *iter)
> +{
> +       ssize_t ret = 0;
> +       ssize_t tot_len;
> +
> +       if (!file->f_op->read_iter)
> +               return -EINVAL;
> +       if (!(file->f_mode & FMODE_READ))
> +               return -EBADF;
> +       if (!(file->f_mode & FMODE_CAN_READ))
> +               return -EINVAL;
> +
> +       tot_len = iov_iter_count(iter);
> +       if (!tot_len)
> +               return 0;
> +
> +       ret = rw_verify_area(READ, file, &iocb->ki_pos, tot_len);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = call_read_iter(file, iocb, iter);
> +       if (ret >= 0)
> +               fsnotify_access(file);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(vfs_iocb_iter_read);
> +
> +ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
> +                           struct iov_iter *iter)
> +{
> +       ssize_t ret = 0;
> +       ssize_t tot_len;
> +
> +       if (!file->f_op->write_iter)
> +               return -EINVAL;
> +       if (!(file->f_mode & FMODE_WRITE))
> +               return -EBADF;
> +       if (!(file->f_mode & FMODE_CAN_WRITE))
> +               return -EINVAL;
> +
> +       tot_len = iov_iter_count(iter);
> +       if (!tot_len)
> +               return 0;
> +
> +       ret = rw_verify_area(WRITE, file, &iocb->ki_pos, tot_len);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = call_write_iter(file, iocb, iter);
> +       if (ret >= 0)
> +               fsnotify_modify(file);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(vfs_iocb_iter_write);
> +

If it was up to me, I would pass down an optional iocb pointer
to the do_iter_XXX static helpers, instead of duplicating the code.
Others may find your approach cleaner, so let's see what other
people think.

Thanks,
Amir.