Re: [PATCH 4/5] migration: Make find_dirty_block() return a single parameter

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Juan Quintela (quintela@redhat.com) wrote:
> We used to return two bools, just return a single int with the
> following meaning:
> 
> old return / again / new return
> false        false   0
> false        true    1
> true         true    2  /* We don't care about again at all */

We shouldn't use magic numbers; if you want to return it in a single
value then it should be an enum so it is clear.

Dave

> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c | 37 +++++++++++++++++++------------------
>  1 file changed, 19 insertions(+), 18 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 1d4ff3185b..2c7289edad 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1481,13 +1481,16 @@ retry:
>   * find_dirty_block: find the next dirty page and update any state
>   * associated with the search process.
>   *
> - * Returns true if a page is found
> + * Returns:
> + *         0: no page found, give up
> + *         1: no page found, retry
> + *         2: page found
>   *
>   * @rs: current RAM state
>   * @pss: data about the state of the current dirty page scan
>   * @again: set to false if the search has scanned the whole of RAM
>   */
> -static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
> +static int find_dirty_block(RAMState *rs, PageSearchStatus *pss)
>  {
>      /* This is not a postcopy requested page */
>      pss->postcopy_requested = false;
> @@ -1499,8 +1502,7 @@ static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
>           * We've been once around the RAM and haven't found anything.
>           * Give up.
>           */
> -        *again = false;
> -        return false;
> +        return 0;
>      }
>      if (!offset_in_ramblock(pss->block,
>                              ((ram_addr_t)pss->page) << TARGET_PAGE_BITS)) {
> @@ -1529,13 +1531,10 @@ static bool find_dirty_block(RAMState *rs, PageSearchStatus *pss, bool *again)
>              }
>          }
>          /* Didn't find anything this time, but try again on the new block */
> -        *again = true;
> -        return false;
> +        return 1;
>      } else {
> -        /* Can go around again, but... */
> -        *again = true;
> -        /* We've found something so probably don't need to */
> -        return true;
> +        /* We've found something */
> +        return 2;
>      }
>  }
>  
> @@ -2270,18 +2269,20 @@ static int ram_find_and_save_block(RAMState *rs)
>          pss.block = QLIST_FIRST_RCU(&ram_list.blocks);
>      }
>  
> -    do {
> +    while (true){
>          if (!get_queued_page(rs, &pss)) {
>              /* priority queue empty, so just search for something dirty */
> -            bool again = true;
> -            if (!find_dirty_block(rs, &pss, &again)) {
> -                if (!again) {
> -                    break;
> -                }
> -            }
> +            int res = find_dirty_block(rs, &pss);
> +            if (res == 0) {
> +                break;
> +            } else if (res == 1)
> +                continue;
>          }
>          pages = ram_save_host_page(rs, &pss);
> -    } while (!pages);
> +        if (pages) {
> +            break;
> +        }
> +    }
>  
>      rs->last_seen_block = pss.block;
>      rs->last_page = pss.page;
> -- 
> 2.34.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK