From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8C313F7ABC for ; Sat, 8 Aug 2026 14:08:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786198136; cv=none; b=l+nh5sMA0+bLlyUC4yRg112CMSEaGN+X55ku6tSu53+XE9UBAFUmtUcdJKIlYomUCLAZ0l7vRRmRWkxidoxOPjO/hX6mm5/f0Wm7tSMmHDU9IyWaLe/jVcrwvLozQ68aB08NyRhRY/DbfJiCVbvoeP5wwAX/4aLWcRJ3e8Rh4pg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786198136; c=relaxed/simple; bh=FP5V+/ygynVfbTL23lPPyV9rBlyavXD/fkc1dieAk/c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=na55z0UTvyIH4luuUq+6eJud0Ycjzd1QTsVXgX6lEnxdj5aiI5pW79HBdLxfAWycelKbkMKf8FkGUhZx13AKkLA/onX35iJwpHzphEx3FXdDXpoY4uIRaNhsQ6EaUdgZbDQWFhXAhSsw0lXo2gSh2bb8MnIKiFnEoBNoOMrT/wk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=f7wT/VD8; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="f7wT/VD8" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1786198132; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aP+xZvCeYjCPMovU6nFO+tDWTQv8q8MytFmDoJ6Dhdo=; b=f7wT/VD88t6Or8sm4k3jWxjdEBCUEmo8imX/yDihc5asv7eVH2eTvwjF2o3SsQfOnrvoic 8E+x2aNY96JZwalym86vRZaz2GPbBhccdfYajiGP8NbFGs63jza41YPAQrqHOW+globGih HxsFHpTG6CEMivzfXOVdlrO+UJO84y4= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , John Fastabend , Shuah Khan , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: [PATCH bpf-next v3 3/4] selftests/bpf: Add read_cgroup_file() to cgroup_helpers Date: Sat, 8 Aug 2026 22:05:55 +0800 Message-ID: <20260808140720.293604-4-jiayuan.chen@linux.dev> In-Reply-To: <20260808140720.293604-1-jiayuan.chen@linux.dev> References: <20260808140720.293604-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT cgroup_helpers has write_cgroup_file()/write_cgroup_file_parent() but no read counterpart. Add read_cgroup_file() and read_cgroup_file_parent() so a forked child can read a cgroup file (e.g. memory.current) from the work dir owned by the parent that set the environment up, without hand-building the /mnt/... path. Signed-off-by: Jiayuan Chen --- tools/testing/selftests/bpf/cgroup_helpers.c | 67 ++++++++++++++++++++ tools/testing/selftests/bpf/cgroup_helpers.h | 4 ++ 2 files changed, 71 insertions(+) diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c index 45cd0b479fe3..4183ff6150c2 100644 --- a/tools/testing/selftests/bpf/cgroup_helpers.c +++ b/tools/testing/selftests/bpf/cgroup_helpers.c @@ -188,6 +188,73 @@ int write_cgroup_file_parent(const char *relative_path, const char *file, return __write_cgroup_file(cgroup_path, file, buf); } +static int __read_cgroup_file(const char *cgroup_path, const char *file, + char *buf, size_t len) +{ + char file_path[PATH_MAX + 1]; + ssize_t got; + int fd; + + snprintf(file_path, sizeof(file_path), "%s/%s", cgroup_path, file); + fd = open(file_path, O_RDONLY); + if (fd < 0) { + log_err("Opening %s", file_path); + return 1; + } + + got = read(fd, buf, len - 1); + if (got < 0) { + log_err("Reading %s", file_path); + close(fd); + return 1; + } + buf[got] = '\0'; + close(fd); + return 0; +} + +/** + * read_cgroup_file() - Read from a cgroup file + * @relative_path: The cgroup path, relative to the workdir + * @file: The name of the file in cgroupfs to read from + * @buf: Buffer to read into, NUL-terminated on success + * @len: Size of @buf + * + * Read from a file in the given cgroup's directory. + * + * If successful, 0 is returned. + */ +int read_cgroup_file(const char *relative_path, const char *file, + char *buf, size_t len) +{ + char cgroup_path[PATH_MAX - 24]; + + format_cgroup_path(cgroup_path, relative_path); + return __read_cgroup_file(cgroup_path, file, buf, len); +} + +/** + * read_cgroup_file_parent() - Read from a cgroup file in the parent process + * workdir + * @relative_path: The cgroup path, relative to the parent process workdir + * @file: The name of the file in cgroupfs to read from + * @buf: Buffer to read into, NUL-terminated on success + * @len: Size of @buf + * + * Read from a file in the given cgroup's directory under the parent process + * workdir. + * + * If successful, 0 is returned. + */ +int read_cgroup_file_parent(const char *relative_path, const char *file, + char *buf, size_t len) +{ + char cgroup_path[PATH_MAX - 24]; + + format_parent_cgroup_path(cgroup_path, relative_path); + return __read_cgroup_file(cgroup_path, file, buf, len); +} + /** * setup_cgroup_environment() - Setup the cgroup environment * diff --git a/tools/testing/selftests/bpf/cgroup_helpers.h b/tools/testing/selftests/bpf/cgroup_helpers.h index 3857304be874..d42d2e13044e 100644 --- a/tools/testing/selftests/bpf/cgroup_helpers.h +++ b/tools/testing/selftests/bpf/cgroup_helpers.h @@ -15,6 +15,10 @@ int write_cgroup_file(const char *relative_path, const char *file, const char *buf); int write_cgroup_file_parent(const char *relative_path, const char *file, const char *buf); +int read_cgroup_file(const char *relative_path, const char *file, + char *buf, size_t len); +int read_cgroup_file_parent(const char *relative_path, const char *file, + char *buf, size_t len); int cgroup_setup_and_join(const char *relative_path); int get_root_cgroup(void); int create_and_get_cgroup(const char *relative_path); -- 2.43.0