Re: [PATCH v4 1/5] xen/domctl, tools: Introduce a new domctl to get guest memory map

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.04.2024 06:53, Henry Wang wrote:
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -697,6 +697,43 @@ int xc_domain_setmaxmem(xc_interface *xch,
>      return do_domctl(xch, &domctl);
>  }
>  
> +int xc_get_domain_mem_map(xc_interface *xch, uint32_t domid,
> +                          struct xen_mem_region mem_regions[],
> +                          uint32_t *nr_regions)
> +{
> +    int rc;
> +    uint32_t nr = *nr_regions;
> +    struct xen_domctl domctl = {
> +        .cmd         = XEN_DOMCTL_get_mem_map,
> +        .domain      = domid,
> +        .u.mem_map = {
> +            .nr_mem_regions = nr,
> +        },
> +    };
> +
> +    DECLARE_HYPERCALL_BOUNCE(mem_regions, sizeof(xen_mem_region_t) * nr,
> +                             XC_HYPERCALL_BUFFER_BOUNCE_OUT);
> +
> +    if ( !mem_regions || xc_hypercall_bounce_pre(xch, mem_regions) || nr < 1 
> )

Why the nr < 1 part? For a caller to size the necessary buffer, it may want
to pass in 0 (and a NULL buffer pointer) first.

> @@ -176,6 +175,33 @@ long arch_do_domctl(struct xen_domctl *domctl, struct 
> domain *d,
>  
>          return rc;
>      }
> +    case XEN_DOMCTL_get_mem_map:
> +    {
> +        int rc = 0;
> +        uint32_t nr_regions;

unsigned int (see ./CODING_STYLE)?

> --- a/xen/include/public/arch-arm.h
> +++ b/xen/include/public/arch-arm.h
> @@ -223,6 +223,13 @@ typedef uint64_t xen_pfn_t;
>   */
>  #define XEN_LEGACY_MAX_VCPUS 1
>  
> +/*
> + * Maximum number of memory map regions for guest memory layout.
> + * Used by XEN_DOMCTL_get_mem_map, currently there is only one region
> + * for the guest magic pages.
> + */
> +#define XEN_MAX_MEM_REGIONS 1

Why is this in the public header? I can only find Xen-internal uses.

> --- a/xen/include/public/domctl.h
> +++ b/xen/include/public/domctl.h
> @@ -946,6 +946,33 @@ struct xen_domctl_paging_mempool {
>      uint64_aligned_t size; /* Size in bytes. */
>  };
>  
> +#ifndef XEN_MAX_MEM_REGIONS
> +#define XEN_MAX_MEM_REGIONS 1
> +#endif
> +
> +struct xen_mem_region {
> +    uint64_aligned_t start;
> +    uint64_aligned_t size;
> +#define XEN_MEM_REGION_DEFAULT    0

I can't spot any use of this. What's its purpose?

> +#define XEN_MEM_REGION_MAGIC      1
> +    uint32_t         type;
> +    /* Must be zero */
> +    uint32_t         pad;

This being OUT only, I don't think the comment makes sense. I'd omit it
completely; if you absolutely want one, please say "will" instead of "must".

Jan