On 09.08.2025 19:08, dm...@proton.me wrote:
> --- /dev/null
> +++ b/xen/common/domid.c
> @@ -0,0 +1,95 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Domain ID allocator.
> + *
> + * Covers dom0 or late hwdom, predefined domains, post-boot domains.
> + * Excludes system domains (ID >= DOMID_FIRST_RESERVED).
> + *
> + * Copyright 2025 Ford Motor Company
> + */
> +
> +#include <xen/domain.h>
> +
> +static DEFINE_SPINLOCK(domid_lock);
> +static DECLARE_BITMAP(domid_bitmap, DOMID_FIRST_RESERVED);
> +
> +/*
> + * Allocate domain ID.
> + *
> + * @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,
> + * 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
> + * range.
> + * @return Valid domain ID in case of successful allocation,
> + * DOMID_INVALID - otherwise.
> + */
> +domid_t domid_alloc(domid_t domid)
> +{
> + static domid_t domid_last;
> +
> + spin_lock(&domid_lock);
> +
> + /* Exact match. */
> + if ( domid < DOMID_FIRST_RESERVED )
> + {
> + if ( __test_and_set_bit(domid, domid_bitmap) )
> + domid = DOMID_INVALID;
> + }
> + /*
> + * Exhaustive search.
> + *
> + * Domain ID#0 is reserved for the first boot domain (e.g. control
> domain)
> + * and excluded from allocation.
> + */
> + else
> + {
> + domid_t num = DOMID_FIRST_RESERVED;
> +
> + domid = find_next_zero_bit(domid_bitmap, num, domid_last + 1);
> + if ( domid == num && domid_last != 0 )
I'm pretty sure I commented on this before, yet then maybe it was in the context
of another patch: Using == here isn't sufficient; it needs to be >=. See e.g.
cpumask_next().
Jan
