Re: [Qemu-devel] [PATCH v3 1/2] memory: export migration page size

[Laszlo Ersek <lersek@redhat.com>]

On 08/13/13 00:43, Michael S. Tsirkin wrote:
> Migration code assumes that each RAM block is a multiple of target page
> size.

Isn't that a valid assumption, considering the TARGET_PAGE_ALIGN() macro
call in qemu_ram_alloc_from_ptr() [exec.c]?

> We can fix this in a variety of ways, the simplest way is
> exporting the required page size so callers can make regions
> large enough.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  arch_init.c           | 6 ++++++
>  include/exec/memory.h | 1 +
>  2 files changed, 7 insertions(+)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 68a7ab7..c62778f 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -150,6 +150,12 @@ int qemu_read_default_config_files(bool userconfig)
>      return 0;
>  }
>  
> +/* Smallest page size for migrated RAM. */
> +uint64_t qemu_migration_page_size(void)
> +{
> +    return TARGET_PAGE_SIZE;
> +}
> +
>  static inline bool is_zero_page(uint8_t *p)
>  {
>      return buffer_find_nonzero_offset(p, TARGET_PAGE_SIZE) ==
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index ebe0d24..6ffffa2 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -1055,6 +1055,7 @@ void *address_space_map(AddressSpace *as, hwaddr addr,
>  void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
>                           int is_write, hwaddr access_len);
>  
> +extern uint64_t qemu_migration_page_size(void);
>  
>  #endif

External linkage functions that are defined in "arch_init.c", and relate
to migration -- for example, skipped_mig_bytes_transferred() -- are
declared in "include/migration/migration.h". They seem to use
TARGET_PAGE_SIZE too.

What justifies declaring this new function in "include/exec/memory.h"?

Thanks,
Laszlo