Re: [PATCH v3] xen/domain: introduce DOMID_ANY

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 23 Sep 2025, dmukhin@xxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> Add a new symbol DOMID_ANY aliasing DOMID_INVALID to improve the readability
> of the code.
> 
> Update all relevant domid_alloc() call sites.
> 
> Amends: 2d5065060710 ("xen/domain: unify domain ID allocation")
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
> Changes since v2:
> - move DOMID_ANY back to the public header; add proper guards
> - CI: https://gitlab.com/xen-project/people/dmukhin/xen/-/pipelines/2056319227
> - Link to v2: 
> https://lore.kernel.org/xen-devel/20250920174732.1207847-2-dmukhin@xxxxxxxx/
> ---
>  tools/tests/domid/harness.h             |  1 +
>  tools/tests/domid/test-domid.c          | 12 ++++++------
>  xen/common/device-tree/dom0less-build.c |  2 +-
>  xen/common/domctl.c                     |  2 +-
>  xen/common/domid.c                      |  2 +-
>  xen/include/public/xen.h                |  5 +++++
>  6 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/tests/domid/harness.h b/tools/tests/domid/harness.h
> index 17eb22a9a854..610b564d4061 100644
> --- a/tools/tests/domid/harness.h
> +++ b/tools/tests/domid/harness.h
> @@ -41,6 +41,7 @@ extern unsigned long find_next_zero_bit(const unsigned long 
> *addr,
>  
>  #define DOMID_FIRST_RESERVED            (100)
>  #define DOMID_INVALID                   (101)
> +#define DOMID_ANY                       DOMID_INVALID
>  
>  #endif /* _TEST_HARNESS_ */
>  
> diff --git a/tools/tests/domid/test-domid.c b/tools/tests/domid/test-domid.c
> index 5915c4699a5c..71cc4e7fd86d 100644
> --- a/tools/tests/domid/test-domid.c
> +++ b/tools/tests/domid/test-domid.c
> @@ -41,20 +41,20 @@ int main(int argc, char **argv)
>          domid_free(expected);
>  
>      /*
> -     * Test that that two consecutive calls of domid_alloc(DOMID_INVALID)
> +     * Test that that two consecutive calls of domid_alloc(DOMID_ANY)
>       * will never return the same ID.
>       * NB: ID#0 is reserved and shall not be allocated by
> -     * domid_alloc(DOMID_INVALID).
> +     * domid_alloc(DOMID_ANY).
>       */
>      for ( expected = 1; expected < DOMID_FIRST_RESERVED; expected++ )
>      {
> -        allocated = domid_alloc(DOMID_INVALID);
> +        allocated = domid_alloc(DOMID_ANY);
>          verify(allocated == expected,
>                 "TEST 3: expected %u allocated %u\n", expected, allocated);
>      }
>      for ( expected = 1; expected < DOMID_FIRST_RESERVED; expected++ )
>      {
> -        allocated = domid_alloc(DOMID_INVALID);
> +        allocated = domid_alloc(DOMID_ANY);
>          verify(allocated == DOMID_INVALID,
>                 "TEST 4: expected %u allocated %u\n", DOMID_INVALID, 
> allocated);
>      }
> @@ -64,7 +64,7 @@ int main(int argc, char **argv)
>          domid_free(expected);
>      for ( expected = 1; expected < DOMID_FIRST_RESERVED / 2; expected++ )
>      {
> -        allocated = domid_alloc(DOMID_INVALID);
> +        allocated = domid_alloc(DOMID_ANY);
>          verify(allocated == expected,
>                 "TEST 5: expected %u allocated %u\n", expected, allocated);
>      }
> @@ -72,7 +72,7 @@ int main(int argc, char **argv)
>      /* Re-allocate last ID from [1..DOMID_FIRST_RESERVED - 1]. */
>      expected = DOMID_FIRST_RESERVED - 1;
>      domid_free(DOMID_FIRST_RESERVED - 1);
> -    allocated = domid_alloc(DOMID_INVALID);
> +    allocated = domid_alloc(DOMID_ANY);
>      verify(allocated == expected,
>             "TEST 6: expected %u allocated %u\n", expected, allocated);
>  
> diff --git a/xen/common/device-tree/dom0less-build.c 
> b/xen/common/device-tree/dom0less-build.c
> index 9fd004c42af7..e2764768c983 100644
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -848,7 +848,7 @@ void __init create_domUs(void)
>          if ( (max_init_domid + 1) >= DOMID_FIRST_RESERVED )
>              panic("No more domain IDs available\n");
>  
> -        domid = domid_alloc(DOMID_INVALID);
> +        domid = domid_alloc(DOMID_ANY);
>          if ( domid == DOMID_INVALID )
>              panic("Error allocating ID for domain %s\n", dt_node_name(node));
>  
> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 954d79022645..ca91686a03d8 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -410,7 +410,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
> u_domctl)
>      case XEN_DOMCTL_createdomain:
>      {
>          /* NB: ID#0 is reserved, find the first suitable ID instead. */
> -        domid_t domid = domid_alloc(op->domain ?: DOMID_INVALID);
> +        domid_t domid = domid_alloc(op->domain ?: DOMID_ANY);
>  
>          if ( domid == DOMID_INVALID )
>          {
> diff --git a/xen/common/domid.c b/xen/common/domid.c
> index 2387ddb08300..76b7f3e7ae6e 100644
> --- a/xen/common/domid.c
> +++ b/xen/common/domid.c
> @@ -19,7 +19,7 @@ static DECLARE_BITMAP(domid_bitmap, DOMID_FIRST_RESERVED);
>   * @param domid Domain ID hint:
>   * - If an explicit domain ID is provided, verify its availability and use it
>   *   if ID is not used;
> - * - If DOMID_INVALID is provided, search [1..DOMID_FIRST_RESERVED-1] range,
> + * - If DOMID_ANY is provided, search [1..DOMID_FIRST_RESERVED-1] range,
>   *   starting from the last used ID. Implementation guarantees that two
>   *   consecutive calls will never return the same ID. ID#0 is reserved for
>   *   the first boot domain (currently, dom0) and excluded from the allocation
> diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
> index 82b9c05a76b7..29b7c81ba1bb 100644
> --- a/xen/include/public/xen.h
> +++ b/xen/include/public/xen.h
> @@ -608,6 +608,11 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
>  /* DOMID_INVALID is used to identify pages with unknown owner. */
>  #define DOMID_INVALID        xen_mk_uint(0x7FF4)
>  
> +#if defined(__XEN__) || defined(__XEN_TOOLS__)
> +/* Domain ID allocator: search [1..DOMID_FIRST_RESERVED-1] range. */
> +#define DOMID_ANY            DOMID_INVALID
> +#endif
> +
>  /* Idle domain. */
>  #define DOMID_IDLE           xen_mk_uint(0x7FFF)
>  
> -- 
> 2.51.0
>