Re: [Qemu-devel] [PATCH v5 3/8] fw_cfg: add vmcoreinfo file

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 07, 2017 at 08:16:13PM +0200, Marc-André Lureau wrote:
> diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
> index 08c00bdf44..37d0f9f40a 100644
> --- a/docs/specs/fw_cfg.txt
> +++ b/docs/specs/fw_cfg.txt
> @@ -136,6 +136,22 @@ struct FWCfgFile {		/* an individual file entry, 64 bytes total */
>      char name[56];		/* fw_cfg item name, NUL-terminated ascii */
>  };
>  
> +=== etc/vmcoreinfo ===
> +
> +A guest may use this entry to add information details to qemu
> +dumps. The entry gives location and size of an ELF note that is
> +appended in qemu dumps.
> +
> +The entry is of 12 bytes with this format:
> +
> +struct FWCfgVMCoreInfo {
> +    uint64_t paddr;             /* physical address of ELF note, LE */
> +    uint32_t size;              /* size of ELF note region, LE */
> +};
> +
> +The note format/class must be of the target bitness and the size must
> +be less than 1Mb.
> +

I would say adding a format bitmap would make sense for future compatibility.
How about:

struct FWCfgVMCoreInfo {
    uint16_t host_format;       /* Formats host supports. 0x1 LE - ELF note. Other bits - ignored. */
    uint16_t guest_format;      /* Formats guest supplies. Must be 0x1 LE */
    uint32_t size;              /* size of ELF note region, LE */
    uint64_t paddr;             /* physical address of ELF note, LE */
};


>  === All Other Data Items ===
>  
>  Please consult the QEMU source for the most up-to-date and authoritative list
> -- 
> 2.14.0.1.geff633fa0