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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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 
> <philmd@redhat.com <mailto:philmd@redhat.com>> 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 <shmuel.eiderman@oracle.com
>     <mailto:shmuel.eiderman@oracle.com>>
>      >>>>
>      >>>> 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 <karl.heubaum@oracle.com
>     <mailto:karl.heubaum@oracle.com>>
>      >>>> Reviewed-by: Arbel Moshe <arbel.moshe@oracle.com
>     <mailto:arbel.moshe@oracle.com>>
>      >>>> Signed-off-by: Sam Eiderman <shmuel.eiderman@oracle.com
>     <mailto:shmuel.eiderman@oracle.com>>
>      >>>> ---
>      >>>>  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.

>      >>>> +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 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 <philmd@redhat.com
>     <mailto:philmd@redhat.com>>

Meanwhile I withdraw my fast R-b :(

Regards,

Phil.