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

[Blue Swirl]

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.