bpf: Add bpf_cpumask_weight() kfunc

It can be useful to query how many bits are set in a cpumask. For
example, if you want to perform special logic for the last remaining
core that's set in a mask. Let's therefore add a new
bpf_cpumask_weight() kfunc which checks how many bits are set in a mask.

Signed-off-by: David Vernet <void@manifault.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231207210843.168466-2-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/Documentation/bpf/cpumasks.rst b/Documentation/bpf/cpumasks.rst
index a22b6ad105fbb5880c3295d7e72f262fb5cc7f70..b5d47a04da5d8d5c1754f15417468350c90e6ff1 100644 (file)
--- a/Documentation/bpf/cpumasks.rst
+++ b/Documentation/bpf/cpumasks.rst
@@ -352,7 +352,7 @@ can be used to query the contents of cpumasks.
 
 .. kernel-doc:: kernel/bpf/cpumask.c
    :identifiers: bpf_cpumask_first bpf_cpumask_first_zero bpf_cpumask_first_and
-                 bpf_cpumask_test_cpu
+                 bpf_cpumask_test_cpu bpf_cpumask_weight
 
 .. kernel-doc:: kernel/bpf/cpumask.c
    :identifiers: bpf_cpumask_equal bpf_cpumask_intersects bpf_cpumask_subset

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index e01c741e54e7b8dcf7ebb60b65955fafc55639c8..7499b7d8c06fe34c09a870bffb64123e212b9089 100644 (file)
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -405,6 +405,17 @@ __bpf_kfunc u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1,
        return cpumask_any_and_distribute(src1, src2);
 }
 
+/**
+ * bpf_cpumask_weight() - Return the number of bits in @cpumask.
+ * @cpumask: The cpumask being queried.
+ *
+ * Count the number of set bits in the given cpumask.
+ */
+__bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
+{
+       return cpumask_weight(cpumask);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_SET8_START(cpumask_kfunc_btf_ids)
@@ -432,6 +443,7 @@ BTF_ID_FLAGS(func, bpf_cpumask_full, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU)
 BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU)
+BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU)
 BTF_SET8_END(cpumask_kfunc_btf_ids)
 
 static const struct btf_kfunc_id_set cpumask_kfunc_set = {