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

[Philippe Mathieu-Daudé]

Hi Sam,

On 9/25/19 1:06 PM, Sam Eiderman wrote:
> From: Sam Eiderman <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>
> Reviewed-by: Arbel Moshe <address@hidden>
> Signed-off-by: Sam Eiderman <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 */
> +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);

Hmm maybe we can g_free(bootpath) directly here.

> +
> +        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?

> +        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.

Ideally you should add doc for the other functions added in 3/8
"bootdevice: Add interface to gather LCHS" too.

John, what do you think about extracting the *boot_device* functions out
of "sysemu.h"?

Thanks,

Phil.

>  
>  /* handler to set the boot_device order for a specific type of MachineClass 
> */
>  typedef void QEMUBootSetHandler(void *opaque, const char *boot_order,
>