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From:   David Vernet <void@manifault.com>
To:     bpf@vger.kernel.org
Cc:     ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev,
        john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
        haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com
Subject: [PATCH bpf-next 1/2] bpf: Add bpf_cpumask_weight() kfunc
Date:   Thu,  7 Dec 2023 15:08:42 -0600
Message-ID: <20231207210843.168466-2-void@manifault.com>
In-Reply-To: <20231207210843.168466-1-void@manifault.com>
References: <20231207210843.168466-1-void@manifault.com>
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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>
---
 Documentation/bpf/cpumasks.rst |  2 +-
 kernel/bpf/cpumask.c           | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/bpf/cpumasks.rst b/Documentation/bpf/cpumasks.rst
index a22b6ad105fb..b5d47a04da5d 100644
--- 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 e01c741e54e7..7499b7d8c06f 100644
--- 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 = {
-- 
2.42.1