Re: [Qemu-devel] [PATCH v2 6/6] geometry: Target specific hook for s390x in geometry guessing

[Markus Armbruster <armbru@redhat.com>]

Ekaterina Tumanova <tumanova@linux.vnet.ibm.com> writes:

> For target-s390x, the behaviour is chosen as follows:
> If no geo could be guessed from backing device, guess_disk_lchs (partition
> table guessing) is called.
> If this is not successful (e.g. image files) geometry is derived from the
> size of the disk (as before).
> We have no translation on s390, so we simply set in to NONE.
>
> Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
> ---
>  hw/block/Makefile.objs |  6 +++++-
>  hw/block/hd-geometry.c | 36 +++++++++++++++++++++++++++++++-----
>  2 files changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/hw/block/Makefile.objs b/hw/block/Makefile.objs
> index d4c3ab7..1f7da7a 100644
> --- a/hw/block/Makefile.objs
> +++ b/hw/block/Makefile.objs
> @@ -1,4 +1,4 @@
> -common-obj-y += block.o cdrom.o hd-geometry.o
> +common-obj-y += block.o cdrom.o
>  common-obj-$(CONFIG_FDC) += fdc.o
>  common-obj-$(CONFIG_SSI_M25P80) += m25p80.o
>  common-obj-$(CONFIG_NAND) += nand.o
> @@ -13,3 +13,7 @@ obj-$(CONFIG_SH4) += tc58128.o
>  
>  obj-$(CONFIG_VIRTIO) += virtio-blk.o
>  obj-$(CONFIG_VIRTIO) += dataplane/
> +
> +# geometry is target/architecture dependent and therefore needs to be built
> +# for every target platform
> +obj-y += hd-geometry.o
> diff --git a/hw/block/hd-geometry.c b/hw/block/hd-geometry.c
> index 4972114..b462225 100644
> --- a/hw/block/hd-geometry.c
> +++ b/hw/block/hd-geometry.c
> @@ -49,11 +49,12 @@ struct partition {
>  
>  /* try to guess the disk logical geometry from the MSDOS partition table.
>     Return 0 if OK, -1 if could not guess */
> -static int guess_disk_lchs(BlockBackend *blk,
> -                           int *pcylinders, int *pheads, int *psectors)
> +static int guess_disk_lchs(BlockBackend *blk, uint32_t *pcylinders,
> +                           uint32_t *pheads, uint32_t *psectors)
>  {
>      uint8_t buf[BDRV_SECTOR_SIZE];
> -    int i, heads, sectors, cylinders;
> +    int i;
> +    uint32_t heads, sectors, cylinders;
>      struct partition *p;
>      uint32_t nr_sects;
>      uint64_t nb_sectors;
> @@ -116,11 +117,11 @@ static void guess_chs_for_size(BlockBackend *blk,
>      *psecs = 63;
>  }
>  
> +#ifdef TARGET_S390X
>  void hd_geometry_guess(BlockBackend *blk,
>                         uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs,
>                         int *ptrans)
>  {
> -    int cylinders, heads, secs, translation;
>      struct ProbeGeometry geometry = blk_probe_geometry(blk);
>  
>      if (geometry.rc == 0) {
> @@ -129,7 +130,32 @@ void hd_geometry_guess(BlockBackend *blk,
>          *pheads = geometry.geo.heads;
>          goto done;
>      }
> +    if (guess_disk_lchs(blk, pcyls, pheads, psecs) == 0) {
> +        goto done;
> +    }
> +    guess_chs_for_size(blk, pcyls, pheads, psecs);
> +done:
> +    if (ptrans) {
> +        *ptrans = BIOS_ATA_TRANSLATION_NONE;
> +    }

The goto looks awkward...  What about

    if (guess_disk_lchs(blk, pcyls, pheads, psecs) < 0) {
        guess_chs_for_size(blk, pcyls, pheads, psecs);
    }

>  
> +    trace_hd_geometry_guess(blk, *pcyls, *pheads, *psecs,
> +                            BIOS_ATA_TRANSLATION_NONE);
> +}
> +#else
> +void hd_geometry_guess(BlockBackend *blk,
> +                       uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs,
> +                       int *ptrans)
> +{
> +    int cylinders, heads, secs, translation;
> +    struct ProbeGeometry geometry = blk_probe_geometry(blk);
> +
> +    if (geometry.rc == 0) {
> +        *pcyls = geometry.geo.cylinders;
> +        *psecs = geometry.geo.sectors;
> +        *pheads = geometry.geo.heads;
> +        goto done;
> +    }
>      if (guess_disk_lchs(blk, &cylinders, &heads, &secs) < 0) {
>          /* no LCHS guess: use a standard physical disk geometry  */
>          guess_chs_for_size(blk, pcyls, pheads, psecs);
> @@ -157,7 +183,7 @@ done:
>      }
>      trace_hd_geometry_guess(blk, *pcyls, *pheads, *psecs, translation);
>  }
> -
> +#endif

Please put the blank line after the #endif.

>  int hd_bios_chs_auto_trans(uint32_t cyls, uint32_t heads, uint32_t secs)
>  {
>      return cyls <= 1024 && heads <= 16 && secs <= 63

hd_geometry_guess() behavior before this series:

    If we can't guess LCHS from MSDOS partition table
        guess geometry on size
        translation is NONE for very small disk, else LBA
    Else if LCHS guess has heads > 16
        BIOS LBA translation must be active
        guess geometry on size
        translation is LARGE for sufficiently small disk, else LBA
    Else
        use LCHS guess
        translation is NONE

Afterwards, targets other than s390x:

    If backend has a geometry (currently only DASD has)
        use backend geometry
        translation is NONE
    Else behave like before this series

Incompatible change.  Why do we want it?

Afterwards, target s390x:

    If backend has a geometry (currently only DASD has)
        use backend geometry
        translation is NONE
    Else if we can't guess LCHS from MSDOS partition table
        guess geometry on size
    Else
        use LCHS guess
    Regardless, translation is NONE

Non-trivial incompatible change.  At least some of it is wanted.

Why do you still guess from an MS-DOS partition table with an s390x
target?

The only caller that passes non-null ptrans is ide_dev_initfn(), and the
only user of the value stored there is pc_cmos_init_late().  Thus,
what you store here doesn't matter.