linux-kernel - [PATCH v1 1/2] perf namespaces: Avoid get_current_dir

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Message-ID: <20251003004102.2369463-1-irogers@google.com>
Date: Thu,  2 Oct 2025 17:41:01 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: [PATCH v1 1/2] 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.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/Makefile.config             |  4 ----
 tools/perf/util/Build                  |  1 -
 tools/perf/util/get_current_dir_name.c | 18 ------------------
 tools/perf/util/get_current_dir_name.h |  8 --------
 tools/perf/util/namespaces.c           | 14 +++++---------
 5 files changed, 5 insertions(+), 40 deletions(-)
 delete mode 100644 tools/perf/util/get_current_dir_name.c
 delete mode 100644 tools/perf/util/get_current_dir_name.h

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 0f4b297fbacc..6cdb96576cb8 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -417,10 +417,6 @@ ifeq ($(feature-eventfd), 1)
   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
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 5ead46dc98e7..9464eceb764b 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -23,7 +23,6 @@ perf-util-y += evsel_fprintf.o
 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-y += mmap.o
 perf-util-y += memswap.o
diff --git a/tools/perf/util/get_current_dir_name.c b/tools/perf/util/get_current_dir_name.c
deleted file mode 100644
index e68935e9ac8c..000000000000
--- a/tools/perf/util/get_current_dir_name.c
+++ /dev/null
@@ -1,18 +0,0 @@
-// SPDX-License-Identifier: LGPL-2.1
-// Copyright (C) 2018, 2019 Red Hat Inc, Arnaldo Carvalho de Melo <acme@...hat.com>
-//
-#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
diff --git a/tools/perf/util/get_current_dir_name.h b/tools/perf/util/get_current_dir_name.h
deleted file mode 100644
index 69f7d5537d32..000000000000
--- a/tools/perf/util/get_current_dir_name.h
+++ /dev/null
@@ -1,8 +0,0 @@
-// SPDX-License-Identifier: LGPL-2.1
-// Copyright (C) 2018, 2019 Red Hat Inc, Arnaldo Carvalho de Melo <acme@...hat.com>
-//
-#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
diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
index 68f5de2d79c7..d1475b79a4a7 100644
--- a/tools/perf/util/namespaces.c
+++ b/tools/perf/util/namespaces.c
@@ -6,7 +6,6 @@
 
 #include "namespaces.h"
 #include "event.h"
-#include "get_current_dir_name.h"
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -279,10 +278,9 @@ void nsinfo__set_in_pidns(struct nsinfo *nsi)
 void nsinfo__mountns_enter(struct nsinfo *nsi,
 				  struct nscookie *nc)
 {
-	char curpath[PATH_MAX];
+	char oldcwd[PATH_MAX];
 	int oldns = -1;
 	int newns = -1;
-	char *oldcwd = NULL;
 
 	if (nc == NULL)
 		return;
@@ -293,14 +291,14 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
 	if (!nsi || !nsinfo__need_setns(nsi))
 		return;
 
-	if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+	if (!getcwd(oldcwd, sizeof(oldcwd)))
 		return;
 
-	oldcwd = get_current_dir_name();
-	if (!oldcwd)
+	nc->oldcwd = strdup(oldcwd);
+	if (!nc->oldcwd)
 		return;
 
-	oldns = open(curpath, O_RDONLY);
+	oldns = open("/proc/self/ns/mnt", O_RDONLY);
 	if (oldns < 0)
 		goto errout;
 
@@ -311,13 +309,11 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
 	if (setns(newns, CLONE_NEWNS) < 0)
 		goto errout;
 
-	nc->oldcwd = oldcwd;
 	nc->oldns = oldns;
 	nc->newns = newns;
 	return;
 
 errout:
-	free(oldcwd);
 	if (oldns > -1)
 		close(oldns);
 	if (newns > -1)
-- 
2.51.0.618.g983fd99d29-goog