From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-155.mta0.migadu.com [91.218.175.155]) (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 B029E48B385 for ; Fri, 18 Sep 2026 08:42:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.155 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789720947; cv=none; b=VWdQ+D+8PwIkeYCDG29vmmTJCJMpUo+b17ti4ijMDGXBqI/0zaRntr4pK6wYIs9prixW8lpKwuSOmYRFgN/+g2VdzIU7ERzCmvkxxm33PW2yV5xL+8Eao2rppqm9lGGf2gk2uHlmo12gG2imTCBPywqlRiOnrhIQqQ2CPuDiGVw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789720947; c=relaxed/simple; bh=4ZMgtbSq1fLEo9A153G8EUdhTbvG1BhTa+Q06muy2Bc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=f4QbtXPLCGXtKpSltaiggnRdwYn9wyyuDp+QRl10GML3UY5eVyRPMOGcKyq3tG+hoMuWnwv7Ax5wmZgUcMZF8ljDk8PGbfZl3olPbWZSPljfoCso0JgjVhYWSmepedd+gSjIyn5MwTVaotR4p/I5E5/BTlTB2rc92EU8IKrwhTY= 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=O8U6Qrrs; arc=none smtp.client-ip=91.218.175.155 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="O8U6Qrrs" X-Envelope-To: linux-kernel@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=1789720943; v=1; x=1790325743; b=O8U6Qrrs6H1FKwqrnosTBet68oPZ/X9pLpqDy8MJOSkzShLu9QJuimrPnpbG1Y7OXFIaTbp2 snCJ4RX38Fi8xxPzmtYUhFobmkuO+sb5UvolKhyojIiMrDrCAkzVbu1YwOhS6Y5dPzaqYizxPdL EzcCRxkrdFWSgCQkpAC9NHoI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 89df3aa9709f030b; Fri, 18 Sep 2026 08:42:23 +0000 X-Mizu-Trace-ID: 89df3aa9709f030b 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 v8 2/3] selftests/bpf: Add read_cgroup_file() to cgroup_helpers Date: Fri, 18 Sep 2026 16:40:26 +0800 Message-ID: <20260918084123.39477-3-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260918084123.39477-1-jiayuan.chen@linux.dev> References: <20260918084123.39477-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@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