perf tools: Add is_compressed callback to compressions array

Add is_compressed callback to the compressions array, that returns 0 if
the file is compressed or != 0 if not.

The new callback is used to recognize the situation when we have a
'compressed' object, like:

  /lib/modules/.../drivers/net/ethernet/intel/igb/igb.ko.xz

but we need to read its debug data from debuginfo files, which might not
be compressed, like:

  /root/.debug/.build-id/d6/...c4b301f/debug

So even for a 'compressed' object we read debug data from a plain
uncompressed object. To keep this transparent, we detect this in
decompress_kmodule() and return the file descriptor to the uncompressed
file.

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/20180817094813.15086-11-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/compress.h

@@ -4,10 +4,12 @@
 
 #ifdef HAVE_ZLIB_SUPPORT
 int gzip_decompress_to_file(const char *input, int output_fd);
+bool gzip_is_compressed(const char *input);
 #endif
 
 #ifdef HAVE_LZMA_SUPPORT
 int lzma_decompress_to_file(const char *input, int output_fd);
+bool lzma_is_compressed(const char *input);
 #endif
 
 #endif /* PERF_COMPRESS_H */

tools/perf/util/dso.c

@@ -196,15 +196,16 @@ enum {
 static const struct {
 	const char *fmt;
 	int (*decompress)(const char *input, int output);
+	bool (*is_compressed)(const char *input);
 } compressions[] = {
 	[COMP_ID__NONE] = { .fmt = NULL, },
 #ifdef HAVE_ZLIB_SUPPORT
-	{ "gz", gzip_decompress_to_file },
+	{ "gz", gzip_decompress_to_file, gzip_is_compressed },
 #endif
 #ifdef HAVE_LZMA_SUPPORT
-	{ "xz", lzma_decompress_to_file },
+	{ "xz", lzma_decompress_to_file, lzma_is_compressed },
 #endif
-	{ NULL, NULL },
+	{ NULL, NULL, NULL },
 };
 
 static int is_supported_compression(const char *ext)
@@ -262,6 +263,22 @@ static int decompress_kmodule(struct dso *dso, const char *name,
 	if (dso->comp == COMP_ID__NONE)
 		return -1;
 
+	/*
+	 * We have proper compression id for DSO and yet the file
+	 * behind the 'name' can still be plain uncompressed object.
+	 *
+	 * The reason is behind the logic we open the DSO object files,
+	 * when we try all possible 'debug' objects until we find the
+	 * data. So even if the DSO is represented by 'krava.xz' module,
+	 * we can end up here opening ~/.debug/....23432432/debug' file
+	 * which is not compressed.
+	 *
+	 * To keep this transparent, we detect this and return the file
+	 * descriptor to the uncompressed file.
+	 */
+	if (!compressions[dso->comp].is_compressed(name))
+		return open(name, O_RDONLY);
+
 	fd = mkstemp(tmpbuf);
 	if (fd < 0) {
 		dso->load_errno = errno;

tools/perf/util/lzma.c

@@ -99,3 +99,8 @@ err_fclose:
 	fclose(infile);
 	return err;
 }
+
+bool lzma_is_compressed(const char *input __maybe_unused)
+{
+	return true;
+}

tools/perf/util/zlib.c

@@ -5,6 +5,7 @@
 #include <sys/stat.h>
 #include <sys/mman.h>
 #include <zlib.h>
+#include <linux/compiler.h>
 
 #include "util/compress.h"
 #include "util/util.h"
@@ -79,3 +80,8 @@ out_close:
 
 	return ret == Z_STREAM_END ? 0 : -1;
 }
+
+bool gzip_is_compressed(const char *input __maybe_unused)
+{
+	return true;
+}