This commit adds a function, cgroupv2_get_subtree_control(), that
will verify if a controller is enabled in the subtree control
file or not.
This function will be used in the next commit - "api.c: Add function to
check if a controller is enabled for a cgroup v2 cgroup" - to determine
if the requested cgroup v2 controller is enabled for a cgroup. This is a
required check to ensure that the cgclassify/cgexec operation will
succeed.
Signed-off-by: Tom Hromatka <tom.hroma...@oracle.com>
---
src/api.c | 66 ++++++++++++++++++++++++++++++++++++++++
src/libcgroup-internal.h | 3 ++
2 files changed, 69 insertions(+)
diff --git a/src/api.c b/src/api.c
index 274718bbe8f4..88042f95a51c 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1884,6 +1884,72 @@ err:
return error;
}
+/**
+ * Check if the requested cgroup controller is enabled on this subtree
+ *
+ * @param path Cgroup directory
+ * @param ctrl_name Name of the controller to check
+ * @param output parameter that indicates whether the controller is enabled\
+ */
+STATIC int cgroupv2_get_subtree_control(const char *path,
+ const char *ctrl_name,
+ bool * const enabled)
+{
+ char *path_copy = NULL, *saveptr = NULL, *token, *ret_c;
+ int ret, error = ECGROUPNOTMOUNTED;
+ char buffer[FILENAME_MAX];
+ FILE *fp = NULL;
+
+ if (!path || !ctrl_name || !enabled)
+ return ECGOTHER;
+
+ *enabled = false;
+
+ path_copy = (char *)malloc(FILENAME_MAX);
+ if (!path_copy)
+ goto out;
+
+ ret = snprintf(path_copy, FILENAME_MAX, "%s/%s", path,
+ CGV2_SUBTREE_CTRL_FILE);
+ if (ret < 0)
+ goto out;
+
+ fp = fopen(path_copy, "re");
+ if (!fp) {
+ cgroup_warn("Warning: fopen failed\n");
+ last_errno = errno;
+ goto out;
+ }
+
+ ret_c = fgets(buffer, sizeof(buffer), fp);
+ if (ret_c == NULL)
+ /* The subtree control file is empty */
+ goto out;
+
+ /* remove the trailing newline */
+ ret_c[strlen(ret_c) - 1] = '\0';
+
+ /* Split the enabled controllers by " " and evaluate if the requested
+ * controller is enabled.
+ */
+ token = strtok_r(buffer, " ", &saveptr);
+ do {
+ if (strncmp(ctrl_name, token, FILENAME_MAX) == 0) {
+ error = 0;
+ *enabled = true;
+ break;
+ }
+ } while ((token = strtok_r(NULL, " ", &saveptr)));
+
+out:
+ if (path_copy)
+ free(path_copy);
+ if (fp)
+ fclose(fp);
+
+ return error;
+}
+
/**
* Enable/Disable a controller in the cgroup v2 subtree_control file
*
diff --git a/src/libcgroup-internal.h b/src/libcgroup-internal.h
index 72ddc19ea6e5..b834202dcf6b 100644
--- a/src/libcgroup-internal.h
+++ b/src/libcgroup-internal.h
@@ -347,6 +347,9 @@ int cgroup_build_tasks_procs_path(char * const path,
size_t path_sz, const char * const cg_name,
const char * const ctrl_name);
+int cgroupv2_get_subtree_control(const char *path,
+ const char *ctrl_name,
+ bool * const enabled);
#endif /* UNIT_TEST */
__END_DECLS
--
2.25.4
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