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[bpf-next,3/5] libbpf: Add bpf_vprintk convenience macro

Message ID 20210821025837.1614098-4-davemarchevsky@fb.com
State New
Headers show
Series None | expand

Commit Message

Dave Marchevsky Aug. 21, 2021, 2:58 a.m. UTC
bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF
macros elsewhere in the file - it allows use of bpf_trace_vprintk
without manual conversion of varargs to u64 array.

Like the bpf_printk macro, bpf_vprintk is meant to be the main interface
to the bpf_trace_vprintk helper and thus is uncapitalized.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
 tools/lib/bpf/bpf_helpers.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Comments

Andrii Nakryiko Aug. 24, 2021, 4:54 a.m. UTC | #1
On Fri, Aug 20, 2021 at 7:59 PM Dave Marchevsky <davemarchevsky@fb.com> wrote:
>

> bpf_vprintk functions similarly to BPF_SEQ_PRINTF and BPF_SNPRINTF

> macros elsewhere in the file - it allows use of bpf_trace_vprintk

> without manual conversion of varargs to u64 array.

>

> Like the bpf_printk macro, bpf_vprintk is meant to be the main interface

> to the bpf_trace_vprintk helper and thus is uncapitalized.

>

> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>

> ---

>  tools/lib/bpf/bpf_helpers.h | 18 ++++++++++++++++++

>  1 file changed, 18 insertions(+)

>

> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h

> index b9987c3efa3c..43c8115956c3 100644

> --- a/tools/lib/bpf/bpf_helpers.h

> +++ b/tools/lib/bpf/bpf_helpers.h

> @@ -224,4 +224,22 @@ enum libbpf_tristate {

>                      ___param, sizeof(___param));               \

>  })

>

> +/*

> + * bpf_vprintk wraps the bpf_trace_printk helper with variadic arguments

> + * instead of an array of u64.

> + */

> +#define bpf_vprintk(fmt, args...)                              \


Given BPF_SNPRINTF and BPF_SEQ_PRINTF, should we call this one in
all-caps as well?

> +({                                                             \

> +       static const char ___fmt[] = fmt;                       \

> +       unsigned long long ___param[___bpf_narg(args)];         \


I wonder how hard would it be to still use bpf_trace_printk() if the
number of input arguments is less than 3? That way you could use
BPF_PRINTF() everywhere, even on old kernels (you just need to
remember to use < 3 arguments). WDYT? It might be more challenging
than it seems, given it's hard to do conditionals inside #defines :(

> +                                                               \

> +       _Pragma("GCC diagnostic push")                          \

> +       _Pragma("GCC diagnostic ignored \"-Wint-conversion\"")  \

> +       ___bpf_fill(___param, args);                            \

> +       _Pragma("GCC diagnostic pop")                           \

> +                                                               \

> +       bpf_trace_vprintk(___fmt, sizeof(___fmt),               \

> +                    ___param, sizeof(___param));               \

> +})

> +

>  #endif

> --

> 2.30.2

>
diff mbox series

Patch

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index b9987c3efa3c..43c8115956c3 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -224,4 +224,22 @@  enum libbpf_tristate {
 		     ___param, sizeof(___param));		\
 })
 
+/*
+ * bpf_vprintk wraps the bpf_trace_printk helper with variadic arguments
+ * instead of an array of u64.
+ */
+#define bpf_vprintk(fmt, args...)				\
+({								\
+	static const char ___fmt[] = fmt;			\
+	unsigned long long ___param[___bpf_narg(args)];		\
+								\
+	_Pragma("GCC diagnostic push")				\
+	_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")	\
+	___bpf_fill(___param, args);				\
+	_Pragma("GCC diagnostic pop")				\
+								\
+	bpf_trace_vprintk(___fmt, sizeof(___fmt),		\
+		     ___param, sizeof(___param));		\
+})
+
 #endif