perf tools: Introduce perf_session class

That does all the initialization boilerplate, opening the file,
reading the header, checking if it is valid, etc.

And that will as well have the threads list, kmap (now) global
variable, etc, so that we can handle two (or more) perf.data files
describing sessions to compare.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1260573842-19720-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/util/session.c

@@ -0,0 +1,80 @@
+#include <linux/kernel.h>
+
+#include <unistd.h>
+#include <sys/types.h>
+
+#include "session.h"
+#include "util.h"
+
+static int perf_session__open(struct perf_session *self, bool force)
+{
+	struct stat input_stat;
+
+	self->fd = open(self->filename, O_RDONLY);
+	if (self->fd < 0) {
+		pr_err("failed to open file: %s", self->filename);
+		if (!strcmp(self->filename, "perf.data"))
+			pr_err("  (try 'perf record' first)");
+		pr_err("\n");
+		return -errno;
+	}
+
+	if (fstat(self->fd, &input_stat) < 0)
+		goto out_close;
+
+	if (!force && input_stat.st_uid && (input_stat.st_uid != geteuid())) {
+		pr_err("file %s not owned by current user or root\n",
+		       self->filename);
+		goto out_close;
+	}
+
+	if (!input_stat.st_size) {
+		pr_info("zero-sized file (%s), nothing to do!\n",
+			self->filename);
+		goto out_close;
+	}
+
+	if (perf_header__read(&self->header, self->fd) < 0) {
+		pr_err("incompatible file format");
+		goto out_close;
+	}
+
+	self->size = input_stat.st_size;
+	return 0;
+
+out_close:
+	close(self->fd);
+	self->fd = -1;
+	return -1;
+}
+
+struct perf_session *perf_session__new(const char *filename, int mode, bool force)
+{
+	size_t len = strlen(filename) + 1;
+	struct perf_session *self = zalloc(sizeof(*self) + len);
+
+	if (self == NULL)
+		goto out;
+
+	if (perf_header__init(&self->header) < 0)
+		goto out_delete;
+
+	memcpy(self->filename, filename, len);
+
+	if (mode == O_RDONLY && perf_session__open(self, force) < 0) {
+		perf_session__delete(self);
+		self = NULL;
+	}
+out:
+	return self;
+out_delete:
+	free(self);
+	return NULL;
+}
+
+void perf_session__delete(struct perf_session *self)
+{
+	perf_header__exit(&self->header);
+	close(self->fd);
+	free(self);
+}