From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-35.mta0.migadu.com [91.218.175.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 259055328B7 for ; Tue, 22 Sep 2026 10:19:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.35 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790072380; cv=none; b=NFuyFX/H888HJAZW2FRHKPy8GVJmIuf1HnLh3GoJ/krSPY/m0TFPZF5BzXZMTPbwmAwhBTREOJX0AxT+6w3D8kRo/jbBkAoIOUHNFr7znughrkhNqRc1c/m/PbyP8zJgQt0l8+l405JlnHC9QqQI8Qls7AdnYJ/8Ok6ErEUsGpk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790072380; c=relaxed/simple; bh=4ZMgtbSq1fLEo9A153G8EUdhTbvG1BhTa+Q06muy2Bc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WPIhKWit/uB6mViIo/OASKb3YPRN5fgwI6osRDM3JFAgBPqHAqYcWlG470Zk6gAedEfjcTHTGSre8odeOtoP+rUI6RmLpl+brOO9SQ4Tf484zcJ2l4FwZJNmpeoB3H0ii09pZmSMwj3aATzkK4aZ0VALH20rwP457v+eabPpWMk= 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=wzxTifWS; arc=none smtp.client-ip=91.218.175.35 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="wzxTifWS" X-Envelope-To: linux-kselftest@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=4ZMgtbSq1fLEo9A153G8EUdhTbvG1BhTa+Q06muy2Bc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790072375; v=1; x=1790677175; b=wzxTifWSgi+8YpXa30hSTn5d7kCLH/U2UrLUH4LgP7OwhZzYLd2Y4d9s0lNNBpUov0qErY0q a3u1qe6Exlib+BMMTQEU7BKcQbcsTbSQiqAxQouuK9kNnUArE3JlfwrEVJLHIM1KfJeLDqQ9ewB BtsS6z0Hi1o4L4gmEDaXE4Do= X-Envelope-To: linux-kselftest@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 228bac855f9d92f3; Tue, 22 Sep 2026 10:19:34 +0000 X-Mizu-Trace-ID: 228bac855f9d92f3 X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Emil Tsalapatis , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Ihor Solodrai , Shuah Khan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf-next v9 2/3] selftests/bpf: Add read_cgroup_file() to cgroup_helpers Date: Tue, 22 Sep 2026 18:17:34 +0800 Message-ID: <20260922101831.192102-3-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260922101831.192102-1-jiayuan.chen@linux.dev> References: <20260922101831.192102-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Reviewed-by: Emil Tsalapatis 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 45cd0b479fe35..4183ff6150c28 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 3857304be8741..d42d2e13044e5 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