Re: [PATCH v1 09/13] util/mmap-alloc: Implement resizable mmaps

[Richard Henderson]

On 2/3/20 6:31 PM, David Hildenbrand wrote:
> +void *qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t 
> new_size,
> +                           bool shared, bool is_pmem)
>  {
>      const size_t pagesize = mmap_pagesize(fd);
>  
>      /* we can only map whole pages */
> -    size = QEMU_ALIGN_UP(size, pagesize);
> +    old_size = QEMU_ALIGN_UP(old_size, pagesize);
> +    new_size = QEMU_ALIGN_UP(new_size, pagesize);
> +
> +    /* we support actually resizable memory regions only on Linux */
> +    if (old_size < new_size) {
> +        /* populate the missing piece into the reserved area */
> +        ptr = mmap_populate(ptr + old_size, new_size - old_size, fd, 
> old_size,
> +                            shared, is_pmem);
> +    } else if (old_size > new_size) {
> +        /* discard this piece, keeping the area reserved (should never fail) 
> */
> +        ptr = mmap_reserve(ptr + new_size, old_size - new_size, fd);
> +    }
> +    return ptr;
> +}

What does the return value indicate?
Is it just for != MAP_FAILED?

Would we be better off with an assert?  There's the comment re mmap_reserve,
but I can't see why mmap_populate should fail either.

Assuming an assert isn't viable, are we better off with a boolean return?  With
an Error **ptr?


r~