Recently, I'm tracing source code about kthread-family. And I found something confused me.
#define kthread_run(threadfn, data, namefmt, ...) \
({ \
struct task_struct *__k \
= kthread_create(threadfn, data, namefmt, ## __VA_ARGS__); \
if (!IS_ERR(__k)) \
wake_up_process(__k); \
__k; \
})
If I replace above macro into real case ( call it ) will be:
// the type of `task_id` is struct task_struct
qinfo->task_id = ({ \
struct task_struct *__k = kthread_create(threadfn, data, namefmt, ## __VA_ARGS__); \
if (!IS_ERR(__k))wake_up_process(__k);\
__k;
})
Follow by document, this macro can do kthread_create() followed by wake_up_process(). Also, returns the kthread. First two thing I can understand, but last I can't.
Following is my question:
1.
Why __k can used as return value like this?
qinfo->task_id = ({statement1; statement2; __k});
2. What is the purpose or function of using curly braces '{....}'?
