tools/bpf: add a selftest for bpf_get_current_cgroup_id() helper

Syscall name_to_handle_at() can be used to get cgroup id
for a particular cgroup path in user space. The selftest
got cgroup id from both user and kernel, and compare to
ensure they are equal to each other.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 57 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
index f3bca3ade0f3..c87b4e052ce9 100644
--- a/tools/testing/selftests/bpf/cgroup_helpers.c
+++ b/tools/testing/selftests/bpf/cgroup_helpers.c
@@ -6,6 +6,7 @@
 #include <sys/types.h>
 #include <linux/limits.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <linux/sched.h>
 #include <fcntl.h>
 #include <unistd.h>
@@ -176,3 +177,59 @@ int create_and_get_cgroup(char *path)
 
 	return fd;
 }
+
+/**
+ * get_cgroup_id() - Get cgroup id for a particular cgroup path
+ * @path: The cgroup path, relative to the workdir, to join
+ *
+ * On success, it returns the cgroup id. On failure it returns 0,
+ * which is an invalid cgroup id.
+ * If there is a failure, it prints the error to stderr.
+ */
+unsigned long long get_cgroup_id(char *path)
+{
+	int dirfd, err, flags, mount_id, fhsize;
+	union {
+		unsigned long long cgid;
+		unsigned char raw_bytes[8];
+	} id;
+	char cgroup_workdir[PATH_MAX + 1];
+	struct file_handle *fhp, *fhp2;
+	unsigned long long ret = 0;
+
+	format_cgroup_path(cgroup_workdir, path);
+
+	dirfd = AT_FDCWD;
+	flags = 0;
+	fhsize = sizeof(*fhp);
+	fhp = calloc(1, fhsize);
+	if (!fhp) {
+		log_err("calloc");
+		return 0;
+	}
+	err = name_to_handle_at(dirfd, cgroup_workdir, fhp, &mount_id, flags);
+	if (err >= 0 || fhp->handle_bytes != 8) {
+		log_err("name_to_handle_at");
+		goto free_mem;
+	}
+
+	fhsize = sizeof(struct file_handle) + fhp->handle_bytes;
+	fhp2 = realloc(fhp, fhsize);
+	if (!fhp2) {
+		log_err("realloc");
+		goto free_mem;
+	}
+	err = name_to_handle_at(dirfd, cgroup_workdir, fhp2, &mount_id, flags);
+	fhp = fhp2;
+	if (err < 0) {
+		log_err("name_to_handle_at");
+		goto free_mem;
+	}
+
+	memcpy(id.raw_bytes, fhp->f_handle, 8);
+	ret = id.cgid;
+
+free_mem:
+	free(fhp);
+	return ret;
+}