linux-kernel - [PATCH v2 2/4] selftests: cgroup: return the errno of write() in cg

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Date:   Thu,  7 Apr 2022 22:42:42 +0000
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     David Rientjes <rientjes@...gle.com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Chen Wandun <chenwandun@...wei.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>, Huang@...gle.com,
        Ying <ying.huang@...el.com>,
        "Michal Koutný" <mkoutny@...e.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: [PATCH v2 2/4] selftests: cgroup: return the errno of write() in
 cg_write() on failure

Currently, cg_write() returns 0 on success and -1 on failure. Modify it
to return the errno of write() syscall on failure.

Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
---
 tools/testing/selftests/cgroup/cgroup_util.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index dbaa7aabbb4a..ef76db6026aa 100644
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -48,6 +48,8 @@ static ssize_t write_text(const char *path, char *buf, ssize_t len)
 
 	len = write(fd, buf, len);
 	if (len < 0) {
+		/* preserve the errno of write() */
+		len = errno;
 		close(fd);
 		return len;
 	}
@@ -177,17 +179,16 @@ long cg_read_lc(const char *cgroup, const char *control)
 	return cnt;
 }
 
+/* Returns 0 on success, or the errno of write() on failure. */
 int cg_write(const char *cgroup, const char *control, char *buf)
 {
 	char path[PATH_MAX];
-	ssize_t len = strlen(buf);
+	ssize_t len = strlen(buf), ret;
 
 	snprintf(path, sizeof(path), "%s/%s", cgroup, control);
 
-	if (write_text(path, buf, len) == len)
-		return 0;
-
-	return -1;
+	ret = write_text(path, buf, len);
+	return ret == len ? 0 : ret;
 }
 
 int cg_find_unified_root(char *root, size_t len)
-- 
2.35.1.1178.g4f1659d476-goog