netdev - [PATCH v2 bpf-next 4/9] libbpf: extract generic string hashing function for reuse

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Date:   Fri, 25 Sep 2020 18:13:52 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: [PATCH v2 bpf-next 4/9] libbpf: extract generic string hashing function for reuse

Calculating a hash of zero-terminated string is a common need when using
hashmap, so extract it for reuse.

Acked-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/btf_dump.c |  9 +--------
 tools/lib/bpf/hashmap.h  | 12 ++++++++++++
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 6c079b3c8679..91310e528a3a 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -90,14 +90,7 @@ struct btf_dump {
 
 static size_t str_hash_fn(const void *key, void *ctx)
 {
-	const char *s = key;
-	size_t h = 0;
-
-	while (*s) {
-		h = h * 31 + *s;
-		s++;
-	}
-	return h;
+	return str_hash(key);
 }
 
 static bool str_equal_fn(const void *a, const void *b, void *ctx)
diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
index e0af36b0e5d8..d9b385fe808c 100644
--- a/tools/lib/bpf/hashmap.h
+++ b/tools/lib/bpf/hashmap.h
@@ -25,6 +25,18 @@ static inline size_t hash_bits(size_t h, int bits)
 #endif
 }
 
+/* generic C-string hashing function */
+static inline size_t str_hash(const char *s)
+{
+	size_t h = 0;
+
+	while (*s) {
+		h = h * 31 + *s;
+		s++;
+	}
+	return h;
+}
+
 typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);
 typedef bool (*hashmap_equal_fn)(const void *key1, const void *key2, void *ctx);
 
-- 
2.24.1