Re: [Qemu-devel] [PATCH v3 3/6] pc/vl: Add units-per-default-bus property

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Oct 01, 2014 at 02:19:26PM -0400, John Snow wrote:
> This patch adds the 'units_per_default_bus' property which
> allows individual boards to declare their desired
> index => (bus,unit) mapping for their default HBA, so that
> boards such as Q35 can specify that its default if_ide HBA,
> AHCI, only accepts one unit per bus.
> 
> This property only overrides the mapping for drives matching
> the block_default_type interface.
> 
> This patch also adds this property to *all* past and present
> Q35 machine types. This retroactive addition is justified
> because the previous erroneous index=>(bus,unit) mappings
> caused by lack of such a property were not utilized due to
> lack of initialization code in the Q35 init routine.
> 
> Further, semantically, the Q35 board type has always had the
> property that its default HBA, AHCI, only accepts one unit per
> bus. The new code added to add devices to drives relies upon
> the accuracy of this mapping. Thus, the property is applied
> retroactively to reduce complexity of allowing IDE HBAs with
> different units per bus.
> 
> Examples:
> 
> Prior to this patch, all IDE HBAs were assumed to use 2 units
> per bus (Master, Slave). When using Q35 and AHCI, however, we
> only allow one unit per bus.
> 
> -hdb foo.qcow2 would become index=1, or bus=0,unit=1.
> -hdd foo.qcow2 would become index=3, or bus=1,unit=1.
> -drive file=foo.qcow2,index=5 becomes bus=2,unit=1.
> 
> These are invalid for AHCI. They now become, under Q35 only:
> 
> -hdb foo.qcow2 --> index=1, bus=1, unit=0.
> -hdd foo.qcow2 --> index=3, bus=3, unit=0.
> -drive file=foo.qcow2,index=5 --> bus=5,unit=0.
> 
> The mapping is adjusted based on the fact that the default IF
> for the Q35 machine type is IF_IDE, and units-per-default-bus
> overrides the IDE mapping from its default of 2 units per bus
> to just 1 unit per bus.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>


Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  hw/i386/pc.c        | 1 +
>  hw/i386/pc_q35.c    | 3 ++-
>  include/hw/boards.h | 2 ++
>  vl.c                | 8 ++++++++
>  4 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 82a7daa..d045e8b 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1524,6 +1524,7 @@ static void pc_generic_machine_class_init(ObjectClass *oc, void *data)
>      mc->hot_add_cpu = qm->hot_add_cpu;
>      mc->kvm_type = qm->kvm_type;
>      mc->block_default_type = qm->block_default_type;
> +    mc->units_per_default_bus = qm->units_per_default_bus;
>      mc->max_cpus = qm->max_cpus;
>      mc->no_serial = qm->no_serial;
>      mc->no_parallel = qm->no_parallel;
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index d4a907c..b28ddbb 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -344,7 +344,8 @@ static void pc_q35_init_1_4(MachineState *machine)
>  #define PC_Q35_MACHINE_OPTIONS \
>      PC_DEFAULT_MACHINE_OPTIONS, \
>      .desc = "Standard PC (Q35 + ICH9, 2009)", \
> -    .hot_add_cpu = pc_hot_add_cpu
> +    .hot_add_cpu = pc_hot_add_cpu, \
> +    .units_per_default_bus = 1
>  
>  #define PC_Q35_2_2_MACHINE_OPTIONS                      \
>      PC_Q35_MACHINE_OPTIONS,                             \
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index dfb6718..663f16a 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -28,6 +28,7 @@ struct QEMUMachine {
>      QEMUMachineHotAddCPUFunc *hot_add_cpu;
>      QEMUMachineGetKvmtypeFunc *kvm_type;
>      BlockInterfaceType block_default_type;
> +    int units_per_default_bus;
>      int max_cpus;
>      unsigned int no_serial:1,
>          no_parallel:1,
> @@ -86,6 +87,7 @@ struct MachineClass {
>      int (*kvm_type)(const char *arg);
>  
>      BlockInterfaceType block_default_type;
> +    int units_per_default_bus;
>      int max_cpus;
>      unsigned int no_serial:1,
>          no_parallel:1,
> diff --git a/vl.c b/vl.c
> index 6500472..940b149 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1588,6 +1588,7 @@ static void machine_class_init(ObjectClass *oc, void *data)
>      mc->hot_add_cpu = qm->hot_add_cpu;
>      mc->kvm_type = qm->kvm_type;
>      mc->block_default_type = qm->block_default_type;
> +    mc->units_per_default_bus = qm->units_per_default_bus;
>      mc->max_cpus = qm->max_cpus;
>      mc->no_serial = qm->no_serial;
>      mc->no_parallel = qm->no_parallel;
> @@ -4378,6 +4379,13 @@ int main(int argc, char **argv, char **envp)
>      blk_mig_init();
>      ram_mig_init();
>  
> +    /* If the currently selected machine wishes to override the units-per-bus
> +     * property of its default HBA interface type, do so now. */
> +    if (machine_class->units_per_default_bus) {
> +        override_max_devs(machine_class->block_default_type,
> +                          machine_class->units_per_default_bus);
> +    }
> +
>      /* open the virtual block devices */
>      if (snapshot)
>          qemu_opts_foreach(qemu_find_opts("drive"), drive_enable_snapshot, NULL, 0);
> -- 
> 1.9.3