Re: [SeaBIOS] [PATCH v7 7/8] bootdevice: FW_CFG interface for LCHS values

[Sam Eiderman]

Gentle Ping,

Philippe, John?

Just wondering if the series is okay, as Gerd pointed out this series
is a blocker for the corresponding changes in SeaBIOS for v 1.13

Sam


On Tue, Oct 8, 2019 at 2:51 PM Sam Eiderman <address@hidden> wrote:
>
>
>
> On Tue, Oct 8, 2019, 13:34 Philippe Mathieu-Daudé <address@hidden> wrote:
>>
>> Hi Sam,
>>
>> On 9/29/19 12:13 PM, Sam Eiderman wrote:
>> > Philippe, thanks for the fast review,
>>
>> Fast is not always the friend of careful.
>>
>> >
>> > John, thanks for picking up this hot potato :-)
>> >
>> > Sam
>> >
>> > On Thu, Sep 26, 2019 at 10:16 PM Philippe Mathieu-Daudé
>> > <address@hidden <mailto:address@hidden>> wrote:
>> >
>> >     On 9/26/19 9:09 PM, Philippe Mathieu-Daudé wrote:
>> >      > On 9/26/19 8:26 PM, John Snow wrote:
>> >      >> On 9/26/19 5:57 AM, Philippe Mathieu-Daudé wrote:
>> >      >>> Hi Sam,
>> >      >>>
>> >      >>> On 9/25/19 1:06 PM, Sam Eiderman wrote:
>> >      >>>> From: Sam Eiderman <address@hidden
>> >     <mailto:address@hidden>>
>> >      >>>>
>> >      >>>> Using fw_cfg, supply logical CHS values directly from QEMU to
>> >     the BIOS.
>> >      >>>>
>> >      >>>> Non-standard logical geometries break under QEMU.
>> >      >>>>
>> >      >>>> A virtual disk which contains an operating system which depends 
>> > on
>> >      >>>> logical geometries (consistent values being reported from BIOS
>> >     INT13
>> >      >>>> AH=08) will most likely break under QEMU/SeaBIOS if it has
>> >     non-standard
>> >      >>>> logical geometries - for example 56 SPT (sectors per track).
>> >      >>>> No matter what QEMU will report - SeaBIOS, for large enough
>> >     disks - will
>> >      >>>> use LBA translation, which will report 63 SPT instead.
>> >      >>>>
>> >      >>>> In addition we cannot force SeaBIOS to rely on physical
>> >     geometries at
>> >      >>>> all. A virtio-blk-pci virtual disk with 255 phyiscal heads cannot
>> >      >>>> report more than 16 physical heads when moved to an IDE
>> >     controller,
>> >      >>>> since the ATA spec allows a maximum of 16 heads - this is an
>> >     artifact of
>> >      >>>> virtualization.
>> >      >>>>
>> >      >>>> By supplying the logical geometries directly we are able to
>> >     support such
>> >      >>>> "exotic" disks.
>> >      >>>>
>> >      >>>> We serialize this information in a similar way to the "bootorder"
>> >      >>>> interface.
>> >      >>>> The new fw_cfg entry is "bios-geometry".
>> >      >>>>
>> >      >>>> Reviewed-by: Karl Heubaum <address@hidden
>> >     <mailto:address@hidden>>
>> >      >>>> Reviewed-by: Arbel Moshe <address@hidden
>> >     <mailto:address@hidden>>
>> >      >>>> Signed-off-by: Sam Eiderman <address@hidden
>> >     <mailto:address@hidden>>
>> >      >>>> ---
>> >      >>>>  bootdevice.c            | 32 ++++++++++++++++++++++++++++++++
>> >      >>>>  hw/nvram/fw_cfg.c       | 14 +++++++++++---
>> >      >>>>  include/sysemu/sysemu.h |  1 +
>> >      >>>>  3 files changed, 44 insertions(+), 3 deletions(-)
>> >      >>>>
>> >      >>>> diff --git a/bootdevice.c b/bootdevice.c
>> >      >>>> index 2b12fb85a4..b034ad7bdc 100644
>> >      >>>> --- a/bootdevice.c
>> >      >>>> +++ b/bootdevice.c
>> >      >>>> @@ -405,3 +405,35 @@ void del_boot_device_lchs(DeviceState
>> >     *dev, const char *suffix)
>> >      >>>>          }
>> >      >>>>      }
>> >      >>>>  }
>> >      >>>> +
>> >      >>>> +/* Serialized as: (device name\0 + lchs struct) x devices */
>>
>> I suppose the lchs struct is serialized in little-endian.
>
>
> Nice catch, that's just a bad comment, should be removed.
> There used to be a struct with 3 uint32_t values, Laszlo pointed out that 
> there is an endianess problem (this was fixed in v3) later Kevin suggested to 
> make it a textual interface and the struct was removed (in v4) but the 
> comment remained.
>>
>>
>> >      >>>> +char *get_boot_devices_lchs_list(size_t *size)
>> >      >>>> +{
>> >      >>>> +    FWLCHSEntry *i;
>> >      >>>> +    size_t total = 0;
>> >      >>>> +    char *list = NULL;
>> >      >>>> +
>> >      >>>> +    QTAILQ_FOREACH(i, &fw_lchs, link) {
>> >      >>>> +        char *bootpath;
>> >      >>>> +        char *chs_string;
>> >      >>>> +        size_t len;
>> >      >>>> +
>> >      >>>> +        bootpath = get_boot_device_path(i->dev, false,
>> >     i->suffix);
>> >      >>>> +        chs_string = g_strdup_printf("%s %" PRIu32 " %"
>> >     PRIu32 " %" PRIu32,
>> >      >>>> +                                     bootpath, i->lcyls,
>> >     i->lheads, i->lsecs);
>>
>> Sam. can you check if you don't need endianness conversion here?
>
>
> Hmm, since this is a textual interface, I believe this should work no?
>
> uint32_t a = 4;
> g_strdup_printf("%s" PRIu32, a);
>
> Should return "4" no matter the endianess? (Taken care of by glib?)
>
>>
>> >      >>>
>> >      >>> Hmm maybe we can g_free(bootpath) directly here.
>> >      >>>
>> >      >>
>> >      >> I think it's okay to do it at the bottom of the loop. No real
>> >     benefit to
>> >      >> being that eager to free resources in my mind. I expect setup at
>> >     the top
>> >      >> of a block and teardown at the bottom of a block.
>> >      >>
>> >      >> Trying to do too much in the middle gets messy in my opinion,
>> >     not that
>> >      >> it seems to matter here.
>> >      >
>> >      > No problem.
>> >      >
>> >      >>>> +
>> >      >>>> +        if (total) {
>> >      >>>> +            list[total - 1] = '\n';
>> >      >>>> +        }
>> >      >>>> +        len = strlen(chs_string) + 1;
>> >      >>>> +        list = g_realloc(list, total + len);
>> >      >>>> +        memcpy(&list[total], chs_string, len);
>> >      >>>> +        total += len;
>> >      >>>> +        g_free(chs_string);
>> >      >>>> +        g_free(bootpath);
>> >      >>>> +    }
>> >      >>>> +
>> >      >>>> +    *size = total;
>> >      >>>> +
>> >      >>>> +    return list;
>> >      >>>> +}
>> >      >>>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> >      >>>> index 7dc3ac378e..18aff658c0 100644
>> >      >>>> --- a/hw/nvram/fw_cfg.c
>> >      >>>> +++ b/hw/nvram/fw_cfg.c
>> >      >>>> @@ -920,13 +920,21 @@ void *fw_cfg_modify_file(FWCfgState *s,
>> >     const char *filename,
>> >      >>>>
>> >      >>>>  static void fw_cfg_machine_reset(void *opaque)
>> >      >>>>  {
>> >      >>>> +    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
>> >      >>>> +    FWCfgState *s = opaque;
>> >      >>>>      void *ptr;
>> >      >>>>      size_t len;
>> >      >>>> -    FWCfgState *s = opaque;
>> >      >>>> -    char *bootindex = get_boot_devices_list(&len);
>> >      >>>> +    char *buf;
>> >      >>>>
>> >      >>>> -    ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t
>> >     *)bootindex, len);
>> >      >>>> +    buf = get_boot_devices_list(&len);
>> >      >>>> +    ptr = fw_cfg_modify_file(s, "bootorder", (uint8_t *)buf,
>> >     len);
>> >      >>>>      g_free(ptr);
>> >      >>>> +
>> >      >>>> +    if (!mc->legacy_fw_cfg_order) {
>> >      >>>> +        buf = get_boot_devices_lchs_list(&len);
>> >      >>>> +        ptr = fw_cfg_modify_file(s, "bios-geometry", (uint8_t
>> >     *)buf, len);
>> >      >>>
>> >      >>> OK. Can you add a test in tests/fw_cfg-test.c please?
>> >      >>>
>> >      >>
>> >      >> :D
>> >      >>
>> >      >>>> +        g_free(ptr);
>> >      >>>> +    }
>> >      >>>>  }
>> >      >>>>
>> >      >>>>  static void fw_cfg_machine_ready(struct Notifier *n, void *data)
>> >      >>>> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
>> >      >>>> index 5bc5c79cbc..80c57fdc4e 100644
>> >      >>>> --- a/include/sysemu/sysemu.h
>> >      >>>> +++ b/include/sysemu/sysemu.h
>> >      >>>> @@ -106,6 +106,7 @@ void validate_bootdevices(const char
>> >     *devices, Error **errp);
>> >      >>>>  void add_boot_device_lchs(DeviceState *dev, const char *suffix,
>> >      >>>>                            uint32_t lcyls, uint32_t lheads,
>> >     uint32_t lsecs);
>> >      >>>>  void del_boot_device_lchs(DeviceState *dev, const char *suffix);
>> >      >>>> +char *get_boot_devices_lchs_list(size_t *size);
>> >      >>>
>> >      >>> Please add some documentation. At least 'size' must be non-NULL.
>> >      >>>
>> >      >>
>> >      >> Sure; but I wasn't going to gate on it because this series went
>> >     unloved
>> >      >> for so long. At this point, a follow-up patch is fine.
>> >      >
>> >      > OK
>> >      >
>> >      >>
>> >      >>> Ideally you should add doc for the other functions added in 3/8
>> >      >>> "bootdevice: Add interface to gather LCHS" too.
>> >      >>>
>> >      >>
>> >      >> Same thing here.
>> >      >>
>> >      >>> John, what do you think about extracting the *boot_device*
>> >     functions out
>> >      >>> of "sysemu.h"?
>> >      >>>
>> >      >>
>> >      >> Potentially worthwhile; but not critical at the moment. The
>> >     source tree
>> >      >> is not the best-organized thing as-is and I don't think it's fair 
>> > to
>> >      >> hold this series up for much longer for nice-to-haves, ultimately.
>> >      >>
>> >      >> More targeted improvements might avoid the "whose responsibility
>> >     is it
>> >      >> to stage this?" hot potato we played with this one; so I'd
>> >     rather have
>> >      >> smaller follow-up patches handled by the respective maintainers.
>> >      >
>> >      > Sure, fair enough.
>> >
>> >     I forgot:
>> >     Reviewed-by: Philippe Mathieu-Daudé <address@hidden
>> >     <mailto:address@hidden>>
>>
>> Meanwhile I withdraw my fast R-b :(
>>
>> Regards,
>>
>> Phil.