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