util: introduce container_of() macro

[elogind.git] / src / shared / util.h

diff --git a/src/shared/util.h b/src/shared/util.h
index a26c1d9d0613e1f100c8c1bfe17548cd8074a338..0246dfd826c40d417e95ac4d1630db61a09f1e31 100644 (file)
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -59,6 +59,17 @@ typedef struct dual_timestamp {
 #define USEC_PER_MONTH (2629800ULL*USEC_PER_SEC)
 #define USEC_PER_YEAR (31557600ULL*USEC_PER_SEC)
 
+/*
+ * container_of - cast a member of a structure out to the containing structure
+ * @ptr: the pointer to the member.
+ * @type: the type of the container struct this is embedded in.
+ * @member: the name of the member within the struct.
+ *
+ */
+#define container_of(ptr, type, member) ({ \
+        const typeof( ((type *)0)->member ) *__mptr = (ptr); \
+        (type *)( (char *)__mptr - offsetof(type,member) );})
+
 /* What is interpreted as whitespace? */
 #define WHITESPACE " \t\n\r"
 #define NEWLINE "\n\r"
@@ -540,4 +551,6 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
 
 int setrlimit_closest(int resource, const struct rlimit *rlim);
 
+int getenv_for_pid(pid_t pid, const char *field, char **_value);
+
 #endif