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Re: [libvirt] [PATCH] Compressed save image format for Qemu.



On Tue, Aug 11, 2009 at 01:25:59PM +0200, Chris Lalancette wrote:
> Implement a compressed save image format for qemu.  While ideally
> we would have the choice between compressed/non-compressed
> available to the libvirt API, unfortunately there is no "flags"
> parameter to the virDomainSave() API.  Therefore, implement this
> as a qemu.conf option.  Both gzip and bzip2 are implemented, and
> it should be very easy to implement additional compression
> methods.
> 
> One open question is if/how we should detect the gzip and bzip2
> binaries.  One way to do it is to do compile-time setting of the
> paths (via configure.in), but that doesn't seem like a great thing
> to do.  Another solution (my preferred solution) is not to detect
> at all; when we go to run the commands that need them, if they
> aren't available, or aren't available in one of the standard paths,
> then we'll fail.  Maybe somebody else has another option or
> opinion, though.
> 
> In the future, we'll have a more robust (managed) save/restore API,
> at which time we can expose this functionality properly in the API.
> 
> V2: get rid of redundant dd command and just use >> to append data.
> V3: Add back the missing pieces for the enum and bumping the save version.


> diff --git a/src/qemu_driver.c b/src/qemu_driver.c
> index 20906ef..8d700bf 100644
> --- a/src/qemu_driver.c
> +++ b/src/qemu_driver.c
> @@ -3411,18 +3411,26 @@ static char *qemudEscapeShellArg(const char *in)
>  }
>  
>  #define QEMUD_SAVE_MAGIC "LibvirtQemudSave"
> -#define QEMUD_SAVE_VERSION 1
> +#define QEMUD_SAVE_VERSION 2
> +
> +enum qemud_save_formats {
> +    QEMUD_SAVE_FORMAT_RAW,
> +    QEMUD_SAVE_FORMAT_GZIP,
> +    QEMUD_SAVE_FORMAT_BZIP2,
> +};
>  
>  struct qemud_save_header {
>      char magic[sizeof(QEMUD_SAVE_MAGIC)-1];
>      int version;
>      int xml_len;
>      int was_running;
> -    int unused[16];
> +    char compressed;
> +    int unused[15];
>  };

Little mistake here - you removed sizeof(int) bytes, but only
added sizeof(char) replacement.

Regards,
Daniel
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