Re: [PATCH 5/5] migration/ram: Merge save_zero_page functions

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 15, 2023 at 11:38:28AM -0300, Fabiano Rosas wrote:
> We don't need to do this in two pieces. One single function makes it
> easier to grasp, specially since it removes the indirection on the
> return value handling.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/ram.c | 41 +++++++++++------------------------------
>  1 file changed, 11 insertions(+), 30 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 8ec38f69e8..13935ead1c 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1128,32 +1128,6 @@ void ram_release_page(const char *rbname, uint64_t offset)
>      ram_discard_range(rbname, offset, TARGET_PAGE_SIZE);
>  }
>  
> -/**
> - * save_zero_page_to_file: send the zero page to the file
> - *
> - * Returns the size of data written to the file, 0 means the page is not
> - * a zero page
> - *
> - * @pss: current PSS channel
> - * @block: block that contains the page we want to send
> - * @offset: offset inside the block for the page
> - */
> -static int save_zero_page_to_file(PageSearchStatus *pss, RAMBlock *block,
> -                                  ram_addr_t offset)
> -{
> -    uint8_t *p = block->host + offset;
> -    QEMUFile *file = pss->pss_channel;
> -    int len = 0;
> -
> -    if (buffer_is_zero(p, TARGET_PAGE_SIZE)) {
> -        len += save_page_header(pss, file, block, offset | RAM_SAVE_FLAG_ZERO);
> -        qemu_put_byte(file, 0);
> -        len += 1;
> -        ram_release_page(block->idstr, offset);
> -    }
> -    return len;
> -}
> -
>  /**
>   * save_zero_page: send the zero page to the stream
>   *
> @@ -1167,12 +1141,19 @@ static int save_zero_page_to_file(PageSearchStatus *pss, RAMBlock *block,
>  static int save_zero_page(RAMState *rs, PageSearchStatus *pss, RAMBlock *block,
>                            ram_addr_t offset)
>  {
> -    int len = save_zero_page_to_file(pss, block, offset);
> +    uint8_t *p = block->host + offset;
> +    QEMUFile *file = pss->pss_channel;
> +    int len = 0;
>  
> -    if (!len) {
> -        return -1;
> +    if (!buffer_is_zero(p, TARGET_PAGE_SIZE)) {
> +        return 0;
>      }
>  
> +    len += save_page_header(pss, file, block, offset | RAM_SAVE_FLAG_ZERO);
> +    qemu_put_byte(file, 0);
> +    len += 1;
> +    ram_release_page(block->idstr, offset);
> +
>      stat64_add(&mig_stats.zero_pages, 1);
>      ram_transferred_add(len);
>  
> @@ -1186,7 +1167,7 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss, RAMBlock *block,
>          XBZRLE_cache_unlock();
>      }
>  
> -    return 1;
> +    return len;

I don't think it's correct.. We need to keep the retval definition (how
many pages were sent) rather than returning num of bytes, I think.

I'm curious how did this pass any form of test.. because I think we did
assert that:

            /* Be strict to return code; it must be 1, or what else? */
            if (migration_ops->ram_save_target_page(rs, pss) != 1) {
                error_report_once("%s: ram_save_target_page failed", __func__);
                ret = -1;
                goto out;
            }

Did I miss something?

-- 
Peter Xu