Re: [Qemu-devel] [PATCH 05/15] util: add a helper to mmap private anonymous memory

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

On Tue, Jun 28, 2016 at 11:01:29AM +0200, Peter Lieven wrote:
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  include/qemu/mmap-alloc.h |  6 ++++++
>  util/mmap-alloc.c         | 17 +++++++++++++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index 0899b2f..a457721 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -9,4 +9,10 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared);
>  
>  void qemu_ram_munmap(void *ptr, size_t size);
>  
> +/* qemu_anon_ram_mmap maps private anonymous memory using mmap and
> + * aborts if the allocation fails. its meant to act as an replacement
> + * for g_malloc0 and friends. */

This needs better docs. When should one use g_malloc0 and when
qemu_anon_ram_munmap?



> +void *qemu_anon_ram_mmap(size_t size);
> +void qemu_anon_ram_munmap(void *ptr, size_t size);
> +

The names are confusing - this isn't guest RAM, this is
just internal QEMU memory, isn't it?

Just rename it qemu_malloc0 then ...

>  #endif
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 629d97a..c099858 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -107,3 +107,20 @@ void qemu_ram_munmap(void *ptr, size_t size)
>          munmap(ptr, size + getpagesize());
>      }
>  }
> +
> +void *qemu_anon_ram_mmap(size_t size)
> +{
> +    void *ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,
> +                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +    if (ptr == MAP_FAILED) {
> +        abort();
> +    }
> +    return ptr;
> +}
> +
> +void qemu_anon_ram_munmap(void *ptr, size_t size)
> +{
> +    if (ptr) {
> +        munmap(ptr, size);
> +    }
> +}
> -- 
> 1.9.1