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

[Marc-André Lureau]

Hi

----- Original Message -----
> 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. */

Could this be added later?

For ex, extend the entry to 16 bytes, with those 2 values appended?

If the size is 12, assume it is ELF note only, and that the host supports it.

> >     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
>