[PATCH bpf v1 2/7] selftests/bpf: Add strscpy_cat()

[Ihor Solodrai <ihor.solodrai@linux.dev>]

Add sized_strscpy_cat() to bpf_util.h, which concatenates multiple
strings into a destination buffer with strscpy().

Add strscpy_cat() macro with varargs.

This is a convenient helper that provides the same guarantees as
strscpy(), but for a case when multiple strings need to be
concatenated into destination.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 tools/testing/selftests/bpf/bpf_util.h | 28 ++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_util.h b/tools/testing/selftests/bpf/bpf_util.h
index 8c95ef7ed7c0..61bb22c3e517 100644
--- a/tools/testing/selftests/bpf/bpf_util.h
+++ b/tools/testing/selftests/bpf/bpf_util.h
@@ -52,6 +52,34 @@ static inline ssize_t sized_strscpy(char *dest, const char *src, size_t count)
 #undef strscpy /* Redefine the placeholder from tools/include/linux/string.h */
 #define strscpy sized_strscpy
 
+/*
+ * strscpy() analogue that concatenates multiple strings into a buffer
+ */
+static inline ssize_t sized_strscpy_cat(char *dest, size_t dest_sz,
+					const char * const *srcs, size_t n)
+{
+	ssize_t pos = 0;
+
+	if (dest_sz == 0)
+		return -E2BIG;
+
+	for (size_t i = 0; i < n; i++) {
+		ssize_t res = strscpy(dest + pos, srcs[i], dest_sz - pos);
+
+		if (res < 0)
+			return res;
+		pos += res;
+	}
+
+	return pos;
+}
+
+#define strscpy_cat(dest, count, ...)					\
+	sized_strscpy_cat(dest, count,					\
+			  (const char * const[]){ __VA_ARGS__ },	\
+			  ARRAY_SIZE(((const char * const[]){ __VA_ARGS__ })))
+
+
 #define __bpf_percpu_val_align	__attribute__((__aligned__(8)))
 
 #define BPF_DECLARE_PERCPU(type, name)				\
-- 
2.53.0