Re: [Qemu-devel] [PATCH] memory: size can be different from ptr_size

[Juan Quintela <quintela@redhat.com>]

Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
> memory_region_init_ram*_ptr() take only the size of the MemoryRegion,
> and allocate a RAMBlock with the same size. However, it may be
> convenient to expose a smaller MemoryRegion (for ex: a few bytes) than
> the RAMBlock (which must be a multiple of TARGET_PAGE_SIZE).
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  include/exec/memory.h  |  8 ++++++--
>  exec.c                 |  3 +++
>  hw/display/g364fb.c    |  2 +-
>  hw/vfio/common.c       |  3 ++-
>  hw/virtio/vhost-user.c |  2 +-
>  memory.c               | 10 ++++++----
>  6 files changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index eb4f2fb249..03f257829b 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -700,6 +700,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
>   *        must be unique within any device
>   * @size: size of the region.
>   * @ptr: memory to be mapped; must contain at least @size bytes.
                                                       ^^^^^

this comment gets wrong with your patches

> + * @ptr_size: size of @ptr buffer

> diff --git a/exec.c b/exec.c
> index 6826c8337d..fcea614e79 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2361,6 +2361,9 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
>  RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>                                     MemoryRegion *mr, Error **errp)
>  {
> +    assert(size >= TARGET_PAGE_SIZE);
> +    assert(size % TARGET_PAGE_SIZE == 0);
> +
>      return qemu_ram_alloc_internal(size, size, NULL, host, false,
>                                     false, mr, errp);
>  }

ok with this bit.

But how about to change instead to:

void memory_region_init_ram_ptr(MemoryRegion *mr,
                                Object *owner,
                                const char *name,
                                uint64_t size,
                                void *ptr)
{
    uint64_t real_size = ROUND_UP_TARGET_PAGE_SIZE(size);
    memory_region_init(mr, owner, name, real_size);
    mr->ram = true;
    mr->terminates = true;
    mr->destructor = memory_region_destructor_ram;
    mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;

    /* qemu_ram_alloc_from_ptr cannot fail with ptr != NULL.  */
    assert(ptr != NULL);
    mr->ram_block = qemu_ram_alloc_from_ptr(size, ptr, mr, &error_fatal);
}

For a suitable ROUND_UP_TARGET_PAGE_SIZE() macro.  You get the idea.

And memory_region_device_ram_ptr() don't even need a change.
We need to adjust the comments, but it looks like an easier patch to me, no?

> diff --git a/hw/display/g364fb.c b/hw/display/g364fb.c
> index fbc2b2422d..f4f5643761 100644
> --- a/hw/display/g364fb.c
> +++ b/hw/display/g364fb.c
> @@ -475,7 +475,7 @@ static void g364fb_init(DeviceState *dev, G364State *s)
>  
>      memory_region_init_io(&s->mem_ctrl, NULL, &g364fb_ctrl_ops, s, "ctrl", 0x180000);
>      memory_region_init_ram_ptr(&s->mem_vram, NULL, "vram",
> -                               s->vram_size, s->vram);
> +                               s->vram_size, s->vram, s->vram_size);

Having to change all the devices that use the function with exactly the
same parameter looks weird to me.

What do you think?

Later, Juan.