Re: [Qemu-devel] [PATCH 3/8] migration: support to detect compressionand decompression errors

[jiang.biao2]

Hi, guangrong
> @@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream 
> *stream, RAMBlock *block,
> {
> RAMState *rs = ram_state;
> int bytes_sent, blen;
> -    uint8_t *p = block->host + (offset & TARGET_PAGE_MASK);
> +    uint8_t buf[TARGET_PAGE_SIZE], *p;

> +    p = block->host + (offset & TARGET_PAGE_MASK);
> bytes_sent = save_page_header(rs, f, block, offset |
> RAM_SAVE_FLAG_COMPRESS_PAGE);
> -    blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE);
> +    memcpy(buf, p, TARGET_PAGE_SIZE);
> +    blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE);
Memory copy operation for every page to be compressed is not cheap, especially
when the page number is huge, and it may be not necessary for pages never 
updated during migration. 
Is there any possibility that we can distinguish the real compress/decompress 
errors from those being caused by source VM updating? Such as the return 
value of qemu_uncompress(distinguish Z_DATA_ERROR and other error codes 
returned by inflate())? 

Jiang
Regards,