perf tools: Add lzma_is_compressed function

Add implementation of the is_compressed callback for lzma.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180817094813.15086-12-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/lzma.c

@@ -3,9 +3,13 @@
 #include <lzma.h>
 #include <stdio.h>
 #include <linux/compiler.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include "compress.h"
 #include "util.h"
 #include "debug.h"
+#include <unistd.h>
 
 #define BUFSIZE 8192
 
@@ -100,7 +104,18 @@ err_fclose:
 	return err;
 }
 
-bool lzma_is_compressed(const char *input __maybe_unused)
+bool lzma_is_compressed(const char *input)
 {
-	return true;
+	int fd = open(input, O_RDONLY);
+	const uint8_t magic[6] = { 0xFD, '7', 'z', 'X', 'Z', 0x00 };
+	char buf[6] = { 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;
 }