Re: [Qemu-devel] [PATCH 05/22] memory: return bitmap from memory_region_is_logging

[Michael S. Tsirkin]

On Thu, Mar 26, 2015 at 06:38:23PM +0100, Paolo Bonzini wrote:
> For now it only returns (1 << DIRTY_MEMORY_VGA) or 0, but this
> will change soon so adjust the callers.
> 
> Listeners check for "any bit except migration", which is handled
> via the global start/stop listener callbacks.  This in practice
> means VGA because the code bitmap is TCG-specific; however, be
> explicit, as for example things would be different if vhost ever
> ran with TCG.
> 
> Instead, the VMware VGA is looking explicitly for DIRTY_MEMORY_VGA.
> 
> Cc: Michael S. Tsirkin <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>         This is the ugliest patch in the series.  My long-term plan
>         is to get rid of the global start/stop hooks in the
>         MemoryListeners.
> 
>  hw/display/vmware_vga.c | 2 +-
>  hw/virtio/vhost.c       | 3 ++-
>  include/exec/memory.h   | 5 +++--
>  kvm-all.c               | 3 ++-
>  memory.c                | 2 +-
>  xen-hvm.c               | 3 ++-
>  6 files changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c
> index c17ddd1..93d7426 100644
> --- a/hw/display/vmware_vga.c
> +++ b/hw/display/vmware_vga.c
> @@ -1124,7 +1124,7 @@ static void vmsvga_update_display(void *opaque)
>       * Is it more efficient to look at vram VGA-dirty bits or wait
>       * for the driver to issue SVGA_CMD_UPDATE?
>       */
> -    if (memory_region_is_logging(&s->vga.vram)) {
> +    if (memory_region_is_logging(&s->vga.vram) & (1 << DIRTY_MEMORY_VGA)) {
>          vga_sync_dirty_bitmap(&s->vga);
>          dirty = memory_region_get_dirty(&s->vga.vram, 0,
>              surface_stride(surface) * surface_height(surface),
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 5a12861..59321ee 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -377,7 +377,8 @@ static void vhost_set_memory(MemoryListener *listener,
>                                           memory_listener);
>      hwaddr start_addr = section->offset_within_address_space;
>      ram_addr_t size = int128_get64(section->size);
> -    bool log_dirty = memory_region_is_logging(section->mr);
> +    bool log_dirty =
> +        memory_region_is_logging(section->mr) & ~(1 << 
> DIRTY_MEMORY_MIGRATION);
>      int s = offsetof(struct vhost_memory, regions) +
>          (dev->mem->nregions + 1) * sizeof dev->mem->regions[0];
>      void *ram;
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 081f7d6..8d5feb2 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -569,11 +569,12 @@ const char *memory_region_name(const MemoryRegion *mr);
>  /**
>   * memory_region_is_logging: return whether a memory region is logging writes
>   *
> - * Returns %true if the memory region is logging writes
> + * Returns a bitmap of clients for which the memory region is logging writes.
> + * Right now this will be either 0 or (1 << DIRTY_MEMORY_VGA).
>   *
>   * @mr: the memory region being queried
>   */
> -bool memory_region_is_logging(MemoryRegion *mr);
> +uint8_t memory_region_is_logging(MemoryRegion *mr);
>  
>  /**
>   * memory_region_is_rom: check whether a memory region is ROM
> diff --git a/kvm-all.c b/kvm-all.c
> index 335438a..6962653 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -663,7 +663,8 @@ static void kvm_set_phys_mem(MemoryRegionSection 
> *section, bool add)
>      KVMSlot *mem, old;
>      int err;
>      MemoryRegion *mr = section->mr;
> -    bool log_dirty = memory_region_is_logging(mr);
> +    bool log_dirty =
> +        memory_region_is_logging(mr) & ~(1 << DIRTY_MEMORY_MIGRATION);
>      bool writeable = !mr->readonly && !mr->rom_device;
>      bool readonly_flag = mr->readonly || memory_region_is_romd(mr);
>      hwaddr start_addr = section->offset_within_address_space;
> diff --git a/memory.c b/memory.c
> index e688f5e..45606bc 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1318,7 +1318,7 @@ bool memory_region_is_skip_dump(MemoryRegion *mr)
>      return mr->skip_dump;
>  }
>  
> -bool memory_region_is_logging(MemoryRegion *mr)
> +uint8_t memory_region_is_logging(MemoryRegion *mr)
>  {
>      return mr->dirty_log_mask;
>  }

This API is pretty easy to misuse, and return
value is completely undocumented. In fact, if I see
"is" I assume a boolean return type.

As you are touching all users anyway, how about
wrappers that answer specific questions:
memory_region_is_logging_dirty_memory_vga
memory_region_is_logging_dirty_memory_migration
memory_region_is_logging_dirty_memory_except_migration
?

As a bonus, compiler will catch you if you forget to
change some caller.

> diff --git a/xen-hvm.c b/xen-hvm.c
> index 315864c..acd89c8 100644
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -488,7 +488,8 @@ static void xen_set_memory(struct MemoryListener 
> *listener,
>      XenIOState *state = container_of(listener, XenIOState, memory_listener);
>      hwaddr start_addr = section->offset_within_address_space;
>      ram_addr_t size = int128_get64(section->size);
> -    bool log_dirty = memory_region_is_logging(section->mr);
> +    bool log_dirty =
> +        memory_region_is_logging(section->mr) & ~(1 << 
> DIRTY_MEMORY_MIGRATION);
>      hvmmem_type_t mem_type;
>  
>      if (section->mr == &ram_memory) {
> -- 
> 2.3.3
>