33 /* 34  * Do not touch the structure directly, use the access functions 35  * poll_does_not_wait() and poll_requested_events() instead. 36  */ 37 typedef struct poll_table_struct { 38         poll_queue_proc _qproc; 39         unsigned long _key; 40 } poll_table; 41  42 static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p) 43 { 44         if (p && p->_qproc && wait_address) 45                 p->_qproc(filp, wait_address, p); 46 } 47  48 /* 49  * Return true if it is guaranteed that poll will not wait. This is the case 50  * if the poll() of another file descriptor in the set got an event, so there 51  * is no need for waiting. 52  */ 53 static inline bool poll_does_not_wait(const poll_table *p) 54 { 55         return p == NULL || p->_qproc == NULL; 56 } 57  58 /* 59  * Return the set of events that the application wants to poll for. 60  * This is useful for drivers that need to know whether a DMA transfer has 61  * to be started implicitly on poll(). You typically only want to do that 62  * if the application is actually polling for POLLIN and/or POLLOUT. 63  */ 64 static inline unsigned long poll_requested_events(const poll_table *p) 65 { 66         return p ? p->_key : ~0UL; 67 } 68  69 static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc) 70 { 71         pt->_qproc = qproc; 72         pt->_key   = ~0UL; /* all events enabled */ 73 } 74  75 struct poll_table_entry { 76         struct file *filp; 77         unsigned long key; 78         wait_queue_t wait; 79         wait_queue_head_t *wait_address; 80 }; 81  82 /* 83  * Structures and helpers for select/poll syscall 84  */ 85 struct poll_wqueues { 86         poll_table pt; 87         struct poll_table_page *table; 88         struct task_struct *polling_task; 89         int triggered; 90         int error; 91         int inline_index; 92         struct poll_table_entry inline_entries[N_INLINE_POLL_ENTRIES]; 93 }; 94 

395 int do_select(int n, fd_set_bits *fds, struct timespec *end_time)396 {397         ktime_t expire, *to = NULL;398         struct poll_wqueues table;399         poll_table *wait;400         int retval, i, timed_out = 0;401         unsigned long slack = 0;402 403         rcu_read_lock();404         retval = max_select_fd(n, fds);405         rcu_read_unlock();406 407         if (retval < 0)408                 return retval;409         n = retval;410 411         poll_initwait(&table); //初始化poll_wqueues结构412         wait = &table.pt;

116 void poll_initwait(struct poll_wqueues *pwq)117 {118         init_poll_funcptr(&pwq->pt, __pollwait);119         pwq->polling_task = current;120         pwq->triggered = 0;121         pwq->error = 0;122         pwq->table = NULL;123         pwq->inline_index = 0;124 }

215 /* Add a new entry */216 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,217                                 poll_table *p)218 {219         struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);220         struct poll_table_entry *entry = poll_get_entry(pwq);221         if (!entry)222                 return;223         entry->filp = get_file(filp);224         entry->wait_address = wait_address;225         entry->key = p->_key;226         init_waitqueue_func_entry(&entry->wait, pollwake);227         entry->wait.private = pwq;228         add_wait_queue(wait_address, &entry->wait); //list_add(&entry->wait.task_list, &wait_address->task_list);229 }