Re: [Qemu-devel] [PATCH 4/6] save_xbzrle_page: change calling convention

[Amit Shah]

On (Thu) 12 Feb 2015 [23:03:09], Juan Quintela wrote:
> Add a parameter to pass the number of bytes written, and make it return
> the number of pages written instead.
> 
> Signed-off-by: Juan Quintela <address@hidden>
> ---
>  arch_init.c | 44 +++++++++++++++++++++++++-------------------
>  1 file changed, 25 insertions(+), 19 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index f243c6e..834f40c 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -352,11 +352,27 @@ static void xbzrle_cache_zero_page(ram_addr_t 
> current_addr)
> 
>  #define ENCODING_FLAG_XBZRLE 0x1
> 
> +/**
> + * save_xbzrle_page: compress and send current page
> + *
> + * Returns: 1 means that we wrote the page
> + *          0 means that page is identical to the one already sent
> + *          -1 means that xbzrle would be longer than normal
> + *
> + * @f: QEMUFile where to send the data
> + * @current_data:
> + * @current_addr:
> + * @block: block that contains the page we want to send
> + * @offset: offset inside the block for the page
> + * @last_stage: if we are at the completion stage
> + * @bytes_transferred: increase it with the number of transferred bytes
> + */
>  static int save_xbzrle_page(QEMUFile *f, uint8_t **current_data,
>                              ram_addr_t current_addr, RAMBlock *block,
> -                            ram_addr_t offset, int cont, bool last_stage)
> +                            ram_addr_t offset, int cont, bool last_stage,
> +                            uint64_t *bytes_transferred)
>  {
> -    int encoded_len = 0, bytes_sent = -1;
> +    int encoded_len = 0, bytes_xbzrle;
>      uint8_t *prev_cached_page;
> 
>      if (!cache_is_cached(XBZRLE.cache, current_addr, bitmap_sync_count)) {

This patch exposes a bug in here:

    if (!cache_is_cached(XBZRLE.cache, current_addr, bitmap_sync_count)) {
        acct_info.xbzrle_cache_miss++;
        if (!last_stage) {
             if (cache_insert(XBZRLE.cache, current_addr, *current_data,
                              bitmap_sync_count) == -1) {
                                     return -1;
             } else {
                 /* update *current_data when the page has been
                    inserted into cache */
                 *current_data = get_cached_data(XBZRLE.cache, current_addr);
             }
        }
        return -1;
    }

The return -1 should not be done for a successful insert of page in
cache.

Also, return -1 for both cache overflow and cache miss are perhaps not
relevant for the caller but the doctext needs to be updated.

                Amit