lib/util/talloc_stack.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Implement a stack of talloc contexts
   4    Copyright (C) Volker Lendecke 2007
   5    Copyright (C) Jeremy Allison 2009 - made thread safe.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22 /*
  23  * Implement a stack of talloc frames.
  24  *
  25  * When a new talloc stackframe is allocated with talloc_stackframe(), then
  26  * the TALLOC_CTX returned with talloc_tos() is reset to that new
  27  * frame. Whenever that stack frame is TALLOC_FREE()'ed, then the reverse
  28  * happens: The previous talloc_tos() is restored.
  29  *
  30  * This API is designed to be robust in the sense that if someone forgets to
  31  * TALLOC_FREE() a stackframe, then the next outer one correctly cleans up and
  32  * resets the talloc_tos().
  33  *
  34  * This robustness feature means that we can't rely on a linked list with
  35  * talloc destructors because in a hierarchy of talloc destructors the parent
  36  * destructor is called before its children destructors. The child destructor
  37  * called after the parent would set the talloc_tos() to the wrong value.
  38  */
  39
  40 #include "includes.h"
  41
  42 struct talloc_stackframe {
  43         int talloc_stacksize;
  44         int talloc_stack_arraysize;
  45         TALLOC_CTX **talloc_stack;
  46 };
  47
  48 /*
  49  * In the single threaded case this is a pointer
  50  * to the global talloc_stackframe. In the MT-case
  51  * this is the pointer to the thread-specific key
  52  * used to look up the per-thread talloc_stackframe
  53  * pointer.
  54  */
  55
  56 static void *global_ts;
  57
  58 /* Variable to ensure TLS value is only initialized once. */
  59 static smb_thread_once_t ts_initialized = SMB_THREAD_ONCE_INIT;
  60
  61 static void talloc_stackframe_init(void)
  62 {
  63         if (!global_tfp) {
  64                 /* Non-thread safe init case. */
  65                 if (SMB_THREAD_ONCE_IS_INITIALIZED(ts_initialized)) {
  66                         return;
  67                 }
  68                 SMB_THREAD_ONCE_INITIALIZE(ts_initialized);
  69         }
  70
  71         if (SMB_THREAD_CREATE_TLS("talloc_stackframe", global_ts)) {
  72                 smb_panic("talloc_stackframe_init create_tls failed");
  73         }
  74 }
  75
  76 static struct talloc_stackframe *talloc_stackframe_create(void)
  77 {
  78 #if defined(PARANOID_MALLOC_CHECKER)
  79 #ifdef malloc
  80 #undef malloc
  81 #endif
  82 #endif
  83         struct talloc_stackframe *ts =
  84                 (struct talloc_stackframe *)malloc(sizeof(struct talloc_stackframe));
  85 #if defined(PARANOID_MALLOC_CHECKER)
  86 #define malloc(s) __ERROR_DONT_USE_MALLOC_DIRECTLY
  87 #endif
  88
  89         if (!ts) {
  90                 smb_panic("talloc_stackframe_init malloc failed");
  91         }
  92
  93         ZERO_STRUCTP(ts);
  94
  95         SMB_THREAD_ONCE(&ts_initialized, talloc_stackframe_init);
  96
  97         if (SMB_THREAD_SET_TLS(global_ts, ts)) {
  98                 smb_panic("talloc_stackframe_init set_tls failed");
  99         }
 100         return ts;
 101 }
 102
 103 static int talloc_pop(TALLOC_CTX *frame)
 104 {
 105         struct talloc_stackframe *ts =
 106                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 107         int i;
 108
 109         for (i=ts->talloc_stacksize-1; i>0; i--) {
 110                 if (frame == ts->talloc_stack[i]) {
 111                         break;
 112                 }
 113                 talloc_free(ts->talloc_stack[i]);
 114         }
 115
 116         ts->talloc_stacksize = i;
 117         return 0;
 118 }
 119
 120 /*
 121  * Create a new talloc stack frame.
 122  *
 123  * When free'd, it frees all stack frames that were created after this one and
 124  * not explicitly freed.
 125  */
 126
 127 static TALLOC_CTX *talloc_stackframe_internal(size_t poolsize)
 128 {
 129         TALLOC_CTX **tmp, *top, *parent;
 130         struct talloc_stackframe *ts =
 131                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 132
 133         if (ts == NULL) {
 134                 ts = talloc_stackframe_create();
 135         }
 136
 137         if (ts->talloc_stack_arraysize < ts->talloc_stacksize + 1) {
 138                 tmp = talloc_realloc(NULL, ts->talloc_stack, TALLOC_CTX *,
 139                                            ts->talloc_stacksize + 1);
 140                 if (tmp == NULL) {
 141                         goto fail;
 142                 }
 143                 ts->talloc_stack = tmp;
 144                 ts->talloc_stack_arraysize = ts->talloc_stacksize + 1;
 145         }
 146
 147         if (ts->talloc_stacksize == 0) {
 148                 parent = ts->talloc_stack;
 149         } else {
 150                 parent = ts->talloc_stack[ts->talloc_stacksize-1];
 151         }
 152
 153         if (poolsize) {
 154                 top = talloc_pool(parent, poolsize);
 155         } else {
 156                 top = talloc_new(parent);
 157         }
 158
 159         if (top == NULL) {
 160                 goto fail;
 161         }
 162
 163         talloc_set_destructor(top, talloc_pop);
 164
 165         ts->talloc_stack[ts->talloc_stacksize++] = top;
 166         return top;
 167
 168  fail:
 169         smb_panic("talloc_stackframe failed");
 170         return NULL;
 171 }
 172
 173 TALLOC_CTX *talloc_stackframe(void)
 174 {
 175         return talloc_stackframe_internal(0);
 176 }
 177
 178 TALLOC_CTX *talloc_stackframe_pool(size_t poolsize)
 179 {
 180         return talloc_stackframe_internal(poolsize);
 181 }
 182
 183 /*
 184  * Get us the current top of the talloc stack.
 185  */
 186
 187 TALLOC_CTX *talloc_tos(void)
 188 {
 189         struct talloc_stackframe *ts =
 190                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 191
 192         if (ts == NULL) {
 193                 talloc_stackframe();
 194                 ts = (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 195                 DEBUG(0, ("no talloc stackframe around, leaking memory\n"));
 196         }
 197
 198         return ts->talloc_stack[ts->talloc_stacksize-1];
 199 }