[tip:perf/urgent] perf tools: Add gzip_is_compressed function

[tip-bot for Jiri Olsa]

Commit-ID:  88c74dc76a30b9242c2df687deb44788d93fee6b
Gitweb:     https://git.kernel.org/tip/88c74dc76a30b9242c2df687deb44788d93fee6b
Author:     Jiri Olsa <jolsa@xxxxxxxxxx>
AuthorDate: Fri, 17 Aug 2018 11:48:12 +0200
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Mon, 20 Aug 2018 08:54:59 -0300

perf tools: Add gzip_is_compressed function

Add implementation of the is_compressed callback for gzip.

Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Michael Petlan <mpetlan@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20180817094813.15086-13-jolsa@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/zlib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/zlib.c b/tools/perf/util/zlib.c
index e68317214679..902ce6384f57 100644
--- a/tools/perf/util/zlib.c
+++ b/tools/perf/util/zlib.c
@@ -6,6 +6,7 @@
 #include <sys/mman.h>
 #include <zlib.h>
 #include <linux/compiler.h>
+#include <unistd.h>
 
 #include "util/compress.h"
 #include "util/util.h"
@@ -81,7 +82,18 @@ out_close:
 	return ret == Z_STREAM_END ? 0 : -1;
 }
 
-bool gzip_is_compressed(const char *input __maybe_unused)
+bool gzip_is_compressed(const char *input)
 {
-	return true;
+	int fd = open(input, O_RDONLY);
+	const uint8_t magic[2] = { 0x1f, 0x8b };
+	char buf[2] = { 0 };
+	ssize_t rc;
+
+	if (fd < 0)
+		return -1;
+
+	rc = read(fd, buf, sizeof(buf));
+	close(fd);
+	return rc == sizeof(buf) ?
+	       memcmp(buf, magic, sizeof(buf)) == 0 : false;
 }