[PATCH v2] libtraceevent kbuffer: Add SAME_AS_HOST for endian and size

[PATCH v2] libtraceevent kbuffer: Add SAME_AS_HOST for endian and size

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Add a SAME_AS_HOST to the endian and size parameters of kbuffer_alloc()
that makes it easier for the applications that simply read the ring
buffer.

If the host has 4 byte word, it will call uname() and check the machine
value. If machine contains the string "64", it will assume that the kernel
is 64 bit and that is what the host will be considered.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v1 https://lore.kernel.org/all/20221208152422.2d0a62cc@gandalf.local.home/
 - Accidentally deleted the "break" statement. Add it back.

 include/traceevent/kbuffer.h |  2 ++
 src/kbuffer-parse.c          | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/include/traceevent/kbuffer.h b/include/traceevent/kbuffer.h
index c8983a000585..abfd83e6fe9f 100644
--- a/include/traceevent/kbuffer.h
+++ b/include/traceevent/kbuffer.h
@@ -13,11 +13,13 @@
 enum kbuffer_endian {
 	KBUFFER_ENDIAN_BIG,
 	KBUFFER_ENDIAN_LITTLE,
+	KBUFFER_ENDIAN_SAME_AS_HOST,
 };
 
 enum kbuffer_long_size {
 	KBUFFER_LSIZE_4,
 	KBUFFER_LSIZE_8,
+	KBUFFER_LSIZE_SAME_AS_HOST,
 };
 
 enum {
diff --git a/src/kbuffer-parse.c b/src/kbuffer-parse.c
index d174e7276df2..390a789b20fb 100644
--- a/src/kbuffer-parse.c
+++ b/src/kbuffer-parse.c
@@ -6,6 +6,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdbool.h>
+
+#include <sys/utsname.h>
 
 #include "kbuffer.h"
 
@@ -159,6 +162,24 @@ static int calc_index(struct kbuffer *kbuf, void *ptr)
 
 static int __next_event(struct kbuffer *kbuf);
 
+/*
+ * Just because sizeof(long) is 4 bytes, doesn't mean the OS isn't
+ * 64bits
+ */
+static bool host_is_32bit(void)
+{
+	struct utsname buf;
+	int ret;
+
+	ret = uname(&buf);
+	if (ret < 0) {
+		/* Oh well, just assume it is 32 bit */
+		return true;
+	}
+	/* If the uname machine value contains 64, assume the kernel is 64 bit */
+	return strstr(buf.machine, "64") == NULL;
+}
+
 /**
  * kbuffer_alloc - allocat a new kbuffer
  * @size;	enum to denote size of word
@@ -175,6 +196,10 @@ kbuffer_alloc(enum kbuffer_long_size size, enum kbuffer_endian endian)
 	switch (size) {
 	case KBUFFER_LSIZE_4:
 		break;
+	case KBUFFER_LSIZE_SAME_AS_HOST:
+		if (sizeof(long) != 8 && host_is_32bit())
+			break;
+		/* fallthrough */
 	case KBUFFER_LSIZE_8:
 		flags |= KBUFFER_FL_LONG_8;
 		break;
@@ -184,6 +209,7 @@ kbuffer_alloc(enum kbuffer_long_size size, enum kbuffer_endian endian)
 
 	switch (endian) {
 	case KBUFFER_ENDIAN_LITTLE:
+	case KBUFFER_ENDIAN_SAME_AS_HOST:
 		break;
 	case KBUFFER_ENDIAN_BIG:
 		flags |= KBUFFER_FL_BIG_ENDIAN;
@@ -198,8 +224,11 @@ kbuffer_alloc(enum kbuffer_long_size size, enum kbuffer_endian endian)
 
 	kbuf->flags = flags;
 
-	if (host_is_bigendian())
+	if (host_is_bigendian()) {
+		if (endian == KBUFFER_ENDIAN_SAME_AS_HOST)
+			flags |= KBUFFER_FL_BIG_ENDIAN;
 		kbuf->flags |= KBUFFER_FL_HOST_BIG_ENDIAN;
+	}
 
 	if (do_swap(kbuf)) {
 		kbuf->read_8 = __read_8_sw;
-- 
2.35.1