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

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

On Fri, Sep 08, 2017 at 06:39:01PM +0300, Michael S. Tsirkin wrote:
> 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 */

.. to set the ELF note info, or 0x0 to reset the device.

>     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