Re: [Qemu-devel] [PATCH v2 16/17] s390x: initialize memory region for memory devices

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, May 11, 2018 at 03:34:05PM -0300, Murilo Opsfelder Araujo wrote:
> On Fri, May 11, 2018 at 03:19:52PM +0200, David Hildenbrand wrote:
> > While s390x has no real interface for communicating devices mapped into
> > the physical address space of the guest, paravirtualized devices can
> > easily expose the applicable address range themselves.
> > 
> > So let's use the difference between maxram_size and ram_size as the size
> > for our hotplug memory area (just as on other architectures).
> > 
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> > ---
> >  hw/s390x/s390-virtio-ccw.c | 28 ++++++++++++++++++++++++++--
> >  1 file changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> > index ee0a2b124f..09b755282b 100644
> > --- a/hw/s390x/s390-virtio-ccw.c
> > +++ b/hw/s390x/s390-virtio-ccw.c
> > @@ -157,9 +157,11 @@ static void virtio_ccw_register_hcalls(void)
> >  #define KVM_MEM_MAX_NR_PAGES ((1ULL << 31) - 1)
> >  #define SEG_MSK (~0xfffffULL)
> >  #define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) & SEG_MSK)
> > -static void s390_memory_init(ram_addr_t mem_size)
> > +static void s390_memory_init(MachineState *machine)
> >  {
> > +    S390CcwMachineState *ms = S390_CCW_MACHINE(machine);
> >      MemoryRegion *sysmem = get_system_memory();
> > +    ram_addr_t mem_size = machine->ram_size;
> >      ram_addr_t chunk, offset = 0;
> >      unsigned int number = 0;
> >      gchar *name;
> > @@ -181,6 +183,28 @@ static void s390_memory_init(ram_addr_t mem_size)
> >      }
> >      g_free(name);
> >  
> > +    /* always allocate the device memory information */
> > +    machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
> 
> Is there any QEMU guideline/preference/recommendation in using g_new0
> vs. g_malloc0?
> 
> I recall Paolo suggesting g_new0 instead of g_malloc0 in another patch:
> 
>   http://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg02372.html

I don't see any reason to not use g_new0() instead of
g_malloc0(sizeof(...)), as it's more readable.

But I don't think it's a problem that should block the patch from
being merged.  We have hundreds of g_malloc*(sizeof(...)) calls
in the tree.

-- 
Eduardo