perf namespaces: Avoid get_current_dir_name dependency

get_current_dir_name is a GNU extension not supported on, for example,
Android. There is only one use of it so let's just switch to getcwd to
avoid build and other complexity.

Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Makefile.config

···
   CFLAGS += -DHAVE_EVENTFD_SUPPORT
 endif
 
-ifeq ($(feature-get_current_dir_name), 1)
-  CFLAGS += -DHAVE_GET_CURRENT_DIR_NAME
-endif
-
 ifeq ($(feature-gettid), 1)
   CFLAGS += -DHAVE_GETTID
 endif

tools/perf/util/Build

···
 perf-util-y += perf_event_attr_fprintf.o
 perf-util-y += evswitch.o
 perf-util-y += find_bit.o
-perf-util-y += get_current_dir_name.o
 perf-util-y += levenshtein.o
 perf-util-$(CONFIG_LIBBFD) += libbfd.o
 perf-util-y += llvm.o

tools/perf/util/get_current_dir_name.c

···
-// SPDX-License-Identifier: LGPL-2.1
-// Copyright (C) 2018, 2019 Red Hat Inc, Arnaldo Carvalho de Melo <[e-mail]>
-//
-#ifndef HAVE_GET_CURRENT_DIR_NAME
-#include "get_current_dir_name.h"
-#include <limits.h>
-#include <string.h>
-#include <unistd.h>
-
-/* Android's 'bionic' library, for one, doesn't have this */
-
-char *get_current_dir_name(void)
-{
-	char pwd[PATH_MAX];
-
-	return getcwd(pwd, sizeof(pwd)) == NULL ? NULL : strdup(pwd);
-}
-#endif // HAVE_GET_CURRENT_DIR_NAME

tools/perf/util/get_current_dir_name.h

···
-// SPDX-License-Identifier: LGPL-2.1
-// Copyright (C) 2018, 2019 Red Hat Inc, Arnaldo Carvalho de Melo <[e-mail]>
-//
-#ifndef __PERF_GET_CURRENT_DIR_NAME_H
-#ifndef HAVE_GET_CURRENT_DIR_NAME
-char *get_current_dir_name(void);
-#endif // HAVE_GET_CURRENT_DIR_NAME
-#endif // __PERF_GET_CURRENT_DIR_NAME_H

tools/perf/util/namespaces.c

···
 
 #include "namespaces.h"
 #include "event.h"
-#include "get_current_dir_name.h"
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
···
 	if (!nsi || !nsinfo__need_setns(nsi))
 		return;
 
-	if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+	if (!getcwd(curpath, sizeof(curpath)))
 		return;
 
-	oldcwd = get_current_dir_name();
+	oldcwd = strdup(curpath);
 	if (!oldcwd)
 		return;
 
-	oldns = open(curpath, O_RDONLY);
+	oldns = open("/proc/self/ns/mnt", O_RDONLY);
 	if (oldns < 0)
 		goto errout;