[Qemu-devel] Re: [PATCHv4 15/15] Pass boot device list to firmware.

[Michael S. Tsirkin]

On Sun, Nov 14, 2010 at 09:13:03PM +0000, Blue Swirl wrote:
> On Sun, Nov 14, 2010 at 8:54 PM, Michael S. Tsirkin <address@hidden> wrote:
> > On Sun, Nov 14, 2010 at 08:49:59PM +0000, Blue Swirl wrote:
> >> On Sun, Nov 14, 2010 at 3:39 PM, Gleb Natapov <address@hidden> wrote:
> >> >
> >> > Signed-off-by: Gleb Natapov <address@hidden>
> >> > ---
> >> >  hw/fw_cfg.c |   14 ++++++++++++++
> >> >  hw/fw_cfg.h |    4 +++-
> >> >  sysemu.h    |    1 +
> >> >  vl.c        |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >  4 files changed, 69 insertions(+), 1 deletions(-)
> >> >
> >> > diff --git a/hw/fw_cfg.c b/hw/fw_cfg.c
> >> > index 7b9434f..f6a67db 100644
> >> > --- a/hw/fw_cfg.c
> >> > +++ b/hw/fw_cfg.c
> >> > @@ -53,6 +53,7 @@ struct FWCfgState {
> >> >     FWCfgFiles *files;
> >> >     uint16_t cur_entry;
> >> >     uint32_t cur_offset;
> >> > +    Notifier machine_ready;
> >> >  };
> >> >
> >> >  static void fw_cfg_write(FWCfgState *s, uint8_t value)
> >> > @@ -315,6 +316,15 @@ int fw_cfg_add_file(FWCfgState *s,  const char 
> >> > *filename, uint8_t *data,
> >> >     return 1;
> >> >  }
> >> >
> >> > +static void fw_cfg_machine_ready(struct Notifier* n)
> >> > +{
> >> > +    uint32_t len;
> >> > +    char *bootindex = get_boot_devices_list(&len);
> >> > +
> >> > +    fw_cfg_add_bytes(container_of(n, FWCfgState, machine_ready),
> >> > +                     FW_CFG_BOOTINDEX, (uint8_t*)bootindex, len);
> >>
> >> I started to implement this to OpenBIOS but I noticed a small issue.
> >> First the first byte must be read to determine length. Then the read
> >> routine will be called again to read the correct amount of bytes. This
> >> would work, but since there is no shortage of IDs, I'd prefer a system
> >> where one ID is used to query the length and another ID is used to
> >> read the data, without the length byte. This is similar how command
> >> line, initrd etc. are handled.
> >>
> >> This would have the advantage that since fw_cfg uses little endian
> >> format, the length value would easily scale to for example 64 bits to
> >> support terabytes of boot device lists. ;-)
> >
> > Yea. Let's just print # of devices as a property, in ASCII.
> > No endian-ness, no nothing.
> > Also - can we just NULL-terminate each ID?
> 
> No, we should use LE numbers like other IDs. To be more specific, this
> is what I meant (instead of FW_CFG_BOOTINDEX):
> FW_CFG_BOOTINDEX_LEN: get LE integer length of the boot device data.
> FW_CFG_BOOTINDEX_DATA: get the boot device data as NUL terminated C
> strings, all strings back-to-back. The reader can determine number of
> strings.

Sounds good.