drivers/md/dm-path-selector.c

   1 /*
   2  * Copyright (C) 2003 Sistina Software.
   3  * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
   4  *
   5  * Module Author: Heinz Mauelshagen
   6  *
   7  * This file is released under the GPL.
   8  *
   9  * Path selector registration.
  10  */
  11
  12 #include "dm.h"
  13 #include "dm-path-selector.h"
  14
  15 #include <linux/slab.h>
  16
  17 struct ps_internal {
  18         struct path_selector_type pst;
  19
  20         struct list_head list;
  21         long use;
  22 };
  23
  24 #define pst_to_psi(__pst) container_of((__pst), struct ps_internal, pst)
  25
  26 static LIST_HEAD(_path_selectors);
  27 static DECLARE_RWSEM(_ps_lock);
  28
  29 struct ps_internal *__find_path_selector_type(const char *name)
  30 {
  31         struct ps_internal *psi;
  32
  33         list_for_each_entry(psi, &_path_selectors, list) {
  34                 if (!strcmp(name, psi->pst.name))
  35                         return psi;
  36         }
  37
  38         return NULL;
  39 }
  40
  41 static struct ps_internal *get_path_selector(const char *name)
  42 {
  43         struct ps_internal *psi;
  44
  45         down_read(&_ps_lock);
  46         psi = __find_path_selector_type(name);
  47         if (psi) {
  48                 if ((psi->use == 0) && !try_module_get(psi->pst.module))
  49                         psi = NULL;
  50                 else
  51                         psi->use++;
  52         }
  53         up_read(&_ps_lock);
  54
  55         return psi;
  56 }
  57
  58 struct path_selector_type *dm_get_path_selector(const char *name)
  59 {
  60         struct ps_internal *psi;
  61
  62         if (!name)
  63                 return NULL;
  64
  65         psi = get_path_selector(name);
  66         if (!psi) {
  67                 request_module("dm-%s", name);
  68                 psi = get_path_selector(name);
  69         }
  70
  71         return psi ? &psi->pst : NULL;
  72 }
  73
  74 void dm_put_path_selector(struct path_selector_type *pst)
  75 {
  76         struct ps_internal *psi;
  77
  78         if (!pst)
  79                 return;
  80
  81         down_read(&_ps_lock);
  82         psi = __find_path_selector_type(pst->name);
  83         if (!psi)
  84                 goto out;
  85
  86         if (--psi->use == 0)
  87                 module_put(psi->pst.module);
  88
  89         if (psi->use < 0)
  90                 BUG();
  91
  92 out:
  93         up_read(&_ps_lock);
  94 }
  95
  96 static struct ps_internal *_alloc_path_selector(struct path_selector_type *pst)
  97 {
  98         struct ps_internal *psi = kmalloc(sizeof(*psi), GFP_KERNEL);
  99
 100         if (psi) {
 101                 memset(psi, 0, sizeof(*psi));
 102                 psi->pst = *pst;
 103         }
 104
 105         return psi;
 106 }
 107
 108 int dm_register_path_selector(struct path_selector_type *pst)
 109 {
 110         int r = 0;
 111         struct ps_internal *psi = _alloc_path_selector(pst);
 112
 113         if (!psi)
 114                 return -ENOMEM;
 115
 116         down_write(&_ps_lock);
 117
 118         if (__find_path_selector_type(pst->name)) {
 119                 kfree(psi);
 120                 r = -EEXIST;
 121         } else
 122                 list_add(&psi->list, &_path_selectors);
 123
 124         up_write(&_ps_lock);
 125
 126         return r;
 127 }
 128
 129 int dm_unregister_path_selector(struct path_selector_type *pst)
 130 {
 131         struct ps_internal *psi;
 132
 133         down_write(&_ps_lock);
 134
 135         psi = __find_path_selector_type(pst->name);
 136         if (!psi) {
 137                 up_write(&_ps_lock);
 138                 return -EINVAL;
 139         }
 140
 141         if (psi->use) {
 142                 up_write(&_ps_lock);
 143                 return -ETXTBSY;
 144         }
 145
 146         list_del(&psi->list);
 147
 148         up_write(&_ps_lock);
 149
 150         kfree(psi);
 151
 152         return 0;
 153 }
 154
 155 EXPORT_SYMBOL_GPL(dm_register_path_selector);
 156 EXPORT_SYMBOL_GPL(dm_unregister_path_selector);