wrapper/poll.c

   1 /*
   2  * Copyright (C) 2011 Mathieu Desnoyers (mathieu.desnoyers@efficios.com)
   3  *
   4  * wrapper around poll_get_entry, implementing __pollwait with exclusive
   5  * wakeups. Using KALLSYMS to get poll_get_entry address when available,
   6  * else we need to have a kernel that exports this function to GPL
   7  * modules.
   8  *
   9  * GPL v2 license.
  10  */
  11
  12 #ifdef CONFIG_KALLSYMS
  13
  14 #include <linux/kallsyms.h>
  15 #include <linux/poll.h>
  16 #include <linux/wait.h>
  17
  18 struct poll_table_entry;
  19 struct splice_pipe_desc;
  20
  21 static
  22 int (*pollwake_sym)(wait_queue_t *wait, unsigned mode, int sync, void *key);
  23 static
  24 struct poll_table_entry *(*poll_get_entry_sym)(struct poll_wqueues *p);
  25
  26 /* Add a new entry */
  27 static void __pollwait_exclusive(struct file *filp,
  28                                  wait_queue_head_t *wait_address,
  29                                  poll_table *p)
  30 {
  31         struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
  32         struct poll_table_entry *entry;
  33
  34         if (!poll_get_entry_sym)
  35                 poll_get_entry_sym = (void *) kallsyms_lookup_name("poll_get_entry");
  36         if (!poll_get_entry_sym) {
  37                 printk(KERN_WARNING "LTTng: poll_get_entry_sym symbol lookup failed.\n");
  38                 return;
  39         }
  40
  41         if (!pollwake_sym)
  42                 pollwake_sym = (void *) kallsyms_lookup_name("pollwake");
  43         if (!pollwake_sym) {
  44                 printk(KERN_WARNING "LTTng: pollwake_sym symbol lookup failed.\n");
  45                 return;
  46         }
  47
  48         entry = poll_get_entry_sym(pwq);
  49
  50         if (!entry)
  51                 return;
  52         get_file(filp);
  53         entry->filp = filp;
  54         entry->wait_address = wait_address;
  55         entry->key = p->key;
  56         init_waitqueue_func_entry(&entry->wait, pollwake_sym);
  57         entry->wait.private = pwq;
  58         add_wait_queue_exclusive(wait_address, &entry->wait);
  59 }
  60
  61 void wrapper_pollwait_exclusive(struct file *filp,
  62                          wait_queue_head_t *wait_address,
  63                          poll_table *p)
  64
  65 {
  66         __pollwait_exclusive(filp, wait_address, p);
  67 }
  68
  69 #else
  70
  71 #include <linux/poll.h>
  72
  73 ssize_t wrapper_pollwait_exclusive(struct file *filp,
  74                         wait_queue_head_t *wait_address,
  75                         poll_table *p)
  76 {
  77         return pollwait_exclusive(filp, wait_address, p);
  78 }
  79
  80 #endif