lib: add `%pVA` recursive printfrr

Analogous to Linux kernel `%pV` (but our mechanism expects 2 specifier
chars and `%pVA` is clearer anyway.)

Signed-off-by: David Lamparter <equinox@diac24.net>

4 files changed, 48 insertions, 0 deletions

diff --git a/doc/developer/logging.rst b/doc/developer/logging.rst
index a35e60619c..5e8cb79cc2 100644
--- a/doc/developer/logging.rst
+++ b/doc/developer/logging.rst
@@ -65,6 +65,8 @@ Extensions
 +-----------+--------------------------+----------------------------------------------+
 | ``%Ld``   | ``int64_t``              | ``-12345``                                   |
 +-----------+--------------------------+----------------------------------------------+
+| ``%pVA``  | ``struct va_format *``   | (recursive printfrr)                         |
++-----------+--------------------------+----------------------------------------------+
 | ``%pI4``  | ``struct in_addr *``     | ``1.2.3.4``                                  |
 |           |                          |                                              |
 |           | ``in_addr_t *``          |                                              |
diff --git a/lib/printf/glue.c b/lib/printf/glue.c
index 389f503c33..2c97dd639e 100644
--- a/lib/printf/glue.c
+++ b/lib/printf/glue.c
@@ -255,3 +255,21 @@ ssize_t printfrr_exti(struct fbuf *buf, struct printfrr_eargs *ea,
 	}
 	return -1;
 }
+
+printfrr_ext_autoreg_p("VA", printfrr_va)
+static ssize_t printfrr_va(struct fbuf *buf, struct printfrr_eargs *ea,
+			   const void *ptr)
+{
+	const struct va_format *vaf = ptr;
+	va_list ap;
+
+	if (!vaf || !vaf->fmt || !vaf->va)
+		return bputs(buf, "NULL");
+
+	/* make sure we don't alter the data passed in - especially since
+	 * bprintfrr (and thus this) might be called on the same format twice,
+	 * when allocating a larger buffer in asnprintfrr()
+	 */
+	va_copy(ap, *vaf->va);
+	return vbprintfrr(buf, vaf->fmt, ap);
+}
diff --git a/lib/printfrr.h b/lib/printfrr.h
index 8245a664b3..6ca4d963c4 100644
--- a/lib/printfrr.h
+++ b/lib/printfrr.h
@@ -251,6 +251,17 @@ static inline ssize_t bputch(struct fbuf *buf, char ch)
 	return 1;
 }
 
+/* %pVA extension, equivalent to Linux kernel %pV */
+
+struct va_format {
+	const char *fmt;
+	va_list *va;
+};
+
+#ifdef _FRR_ATTRIBUTE_PRINTFRR
+#pragma FRR printfrr_ext "%pVA" (struct va_format *)
+#endif
+
 /* when using non-ISO-C compatible extension specifiers... */
 
 #ifdef _FRR_ATTRIBUTE_PRINTFRR
diff --git a/tests/lib/test_printfrr.c b/tests/lib/test_printfrr.c
index 5a8d10e9b7..8fa8bfcc23 100644
--- a/tests/lib/test_printfrr.c
+++ b/tests/lib/test_printfrr.c
@@ -128,6 +128,21 @@ static int printchk(const char *ref, const char *fmt, ...)
 	return 0;
 }
 
+static void test_va(const char *ref, const char *fmt, ...) PRINTFRR(2, 3);
+static void test_va(const char *ref, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list ap;
+
+	va_start(ap, fmt);
+	vaf.fmt = fmt;
+	vaf.va = ≈
+
+	printchk(ref, "VA [%pVA] %s", &vaf, "--");
+
+	va_end(ap);
+}
+
 int main(int argc, char **argv)
 {
 	size_t i;
@@ -168,6 +183,8 @@ int main(int argc, char **argv)
 
 	printcmp("%p", &ip);
 
+	test_va("VA [192.168.1.2 1234] --", "%pI4 %u", &ip, 1234);
+
 	snprintfrr(buf, sizeof(buf), "test%s", "#1");
 	csnprintfrr(buf, sizeof(buf), "test%s", "#2");
 	assert(strcmp(buf, "test#1test#2") == 0);