net/dccp/ccid.c

   1 /*
   2  *  net/dccp/ccid.c
   3  *
   4  *  An implementation of the DCCP protocol
   5  *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   6  *
   7  *  CCID infrastructure
   8  *
   9  *      This program is free software; you can redistribute it and/or modify it
  10  *      under the terms of the GNU General Public License version 2 as
  11  *      published by the Free Software Foundation.
  12  */
  13
  14 #include "ccid.h"
  15
  16 static struct ccid *ccids[CCID_MAX];
  17 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
  18 static atomic_t ccids_lockct = ATOMIC_INIT(0);
  19 static DEFINE_SPINLOCK(ccids_lock);
  20
  21 /*
  22  * The strategy is: modifications ccids vector are short, do not sleep and
  23  * veeery rare, but read access should be free of any exclusive locks.
  24  */
  25 static void ccids_write_lock(void)
  26 {
  27         spin_lock(&ccids_lock);
  28         while (atomic_read(&ccids_lockct) != 0) {
  29                 spin_unlock(&ccids_lock);
  30                 yield();
  31                 spin_lock(&ccids_lock);
  32         }
  33 }
  34
  35 static inline void ccids_write_unlock(void)
  36 {
  37         spin_unlock(&ccids_lock);
  38 }
  39
  40 static inline void ccids_read_lock(void)
  41 {
  42         atomic_inc(&ccids_lockct);
  43         spin_unlock_wait(&ccids_lock);
  44 }
  45
  46 static inline void ccids_read_unlock(void)
  47 {
  48         atomic_dec(&ccids_lockct);
  49 }
  50
  51 #else
  52 #define ccids_write_lock() do { } while(0)
  53 #define ccids_write_unlock() do { } while(0)
  54 #define ccids_read_lock() do { } while(0)
  55 #define ccids_read_unlock() do { } while(0)
  56 #endif
  57
  58 int ccid_register(struct ccid *ccid)
  59 {
  60         int err;
  61
  62         if (ccid->ccid_init == NULL)
  63                 return -1;
  64
  65         ccids_write_lock();
  66         err = -EEXIST;
  67         if (ccids[ccid->ccid_id] == NULL) {
  68                 ccids[ccid->ccid_id] = ccid;
  69                 err = 0;
  70         }
  71         ccids_write_unlock();
  72         if (err == 0)
  73                 pr_info("CCID: Registered CCID %d (%s)\n",
  74                         ccid->ccid_id, ccid->ccid_name);
  75         return err;
  76 }
  77
  78 EXPORT_SYMBOL_GPL(ccid_register);
  79
  80 int ccid_unregister(struct ccid *ccid)
  81 {
  82         ccids_write_lock();
  83         ccids[ccid->ccid_id] = NULL;
  84         ccids_write_unlock();
  85         pr_info("CCID: Unregistered CCID %d (%s)\n",
  86                 ccid->ccid_id, ccid->ccid_name);
  87         return 0;
  88 }
  89
  90 EXPORT_SYMBOL_GPL(ccid_unregister);
  91
  92 struct ccid *ccid_init(unsigned char id, struct sock *sk)
  93 {
  94         struct ccid *ccid;
  95
  96 #ifdef CONFIG_KMOD
  97         if (ccids[id] == NULL)
  98                 request_module("net-dccp-ccid-%d", id);
  99 #endif
 100         ccids_read_lock();
 101
 102         ccid = ccids[id];
 103         if (ccid == NULL)
 104                 goto out;
 105
 106         if (!try_module_get(ccid->ccid_owner))
 107                 goto out_err;
 108
 109         if (ccid->ccid_init(sk) != 0)
 110                 goto out_module_put;
 111 out:
 112         ccids_read_unlock();
 113         return ccid;
 114 out_module_put:
 115         module_put(ccid->ccid_owner);
 116 out_err:
 117         ccid = NULL;
 118         goto out;
 119 }
 120
 121 EXPORT_SYMBOL_GPL(ccid_init);
 122
 123 void ccid_exit(struct ccid *ccid, struct sock *sk)
 124 {
 125         if (ccid == NULL)
 126                 return;
 127
 128         ccids_read_lock();
 129
 130         if (ccids[ccid->ccid_id] != NULL) {
 131                 if (ccid->ccid_exit != NULL)
 132                         ccid->ccid_exit(sk);
 133                 module_put(ccid->ccid_owner);
 134         }
 135
 136         ccids_read_unlock();
 137 }
 138
 139 EXPORT_SYMBOL_GPL(ccid_exit);