Re: [PATCH] libceph: fix last_piece calculation in ceph_msg_data_pages_advance

[Alex Elder <elder@ieee.org>]

On 3/2/22 9:37 AM, Jeff Layton wrote:
> It's possible we'll have less than a page's worth of residual data, that
> is stradding the last two pages in the array. That will make it
> incorrectly set the last_piece boolean when it shouldn't.
> 
> Account for a non-zero cursor->page_offset when advancing.

It's been quite a while I looked at this code, but isn't
cursor->resid supposed to be the number of bytes remaining,
irrespective of the offset?

Have you found this to cause a failure?

					-Alex

> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>   net/ceph/messenger.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> index d3bb656308b4..3f8453773cc8 100644
> --- a/net/ceph/messenger.c
> +++ b/net/ceph/messenger.c
> @@ -894,10 +894,9 @@ static bool ceph_msg_data_pages_advance(struct ceph_msg_data_cursor *cursor,
>   		return false;   /* no more data */
>   
>   	/* Move on to the next page; offset is already at 0 */
> -
>   	BUG_ON(cursor->page_index >= cursor->page_count);
>   	cursor->page_index++;
> -	cursor->last_piece = cursor->resid <= PAGE_SIZE;
> +	cursor->last_piece = cursor->page_offset + cursor->resid <= PAGE_SIZE;
>   
>   	return true;
>   }