lttng-probes.c

   1 /*
   2  * lttng-probes.c
   3  *
   4  * Holds LTTng probes registry.
   5  *
   6  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; only
  11  * version 2.1 of the License.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/list.h>
  25 #include <linux/mutex.h>
  26 #include <linux/seq_file.h>
  27
  28 #include "lttng-events.h"
  29
  30 /*
  31  * probe list is protected by sessions lock.
  32  */
  33 static LIST_HEAD(_probe_list);
  34
  35 /*
  36  * List of probes registered by not yet processed.
  37  */
  38 static LIST_HEAD(lazy_probe_init);
  39
  40 /*
  41  * lazy_nesting counter ensures we don't trigger lazy probe registration
  42  * fixup while we are performing the fixup. It is protected by the
  43  * sessions lock.
  44  */
  45 static int lazy_nesting;
  46
  47 /*
  48  * Called under sessions lock.
  49  */
  50 static
  51 int check_event_provider(struct lttng_probe_desc *desc)
  52 {
  53         int i;
  54         size_t provider_name_len;
  55
  56         provider_name_len = strnlen(desc->provider,
  57                                 LTTNG_KERNEL_SYM_NAME_LEN - 1);
  58         for (i = 0; i < desc->nr_events; i++) {
  59                 if (strncmp(desc->event_desc[i]->name,
  60                                 desc->provider,
  61                                 provider_name_len))
  62                         return 0;       /* provider mismatch */
  63                 /*
  64                  * The event needs to contain at least provider name + _ +
  65                  * one or more letter.
  66                  */
  67                 if (strlen(desc->event_desc[i]->name) <= provider_name_len + 1)
  68                         return 0;       /* provider mismatch */
  69                 if (desc->event_desc[i]->name[provider_name_len] != '_')
  70                         return 0;       /* provider mismatch */
  71         }
  72         return 1;
  73 }
  74
  75 /*
  76  * Called under sessions lock.
  77  */
  78 static
  79 void lttng_lazy_probe_register(struct lttng_probe_desc *desc)
  80 {
  81         struct lttng_probe_desc *iter;
  82         struct list_head *probe_list;
  83
  84         /*
  85          * Each provider enforce that every event name begins with the
  86          * provider name. Check this in an assertion for extra
  87          * carefulness. This ensures we cannot have duplicate event
  88          * names across providers.
  89          */
  90         WARN_ON_ONCE(!check_event_provider(desc));
  91
  92         /*
  93          * The provider ensures there are no duplicate event names.
  94          * Duplicated TRACEPOINT_EVENT event names would generate a
  95          * compile-time error due to duplicated symbol names.
  96          */
  97
  98         /*
  99          * We sort the providers by struct lttng_probe_desc pointer
 100          * address.
 101          */
 102         probe_list = &_probe_list;
 103         list_for_each_entry_reverse(iter, probe_list, head) {
 104                 BUG_ON(iter == desc); /* Should never be in the list twice */
 105                 if (iter < desc) {
 106                         /* We belong to the location right after iter. */
 107                         list_add(&desc->head, &iter->head);
 108                         goto desc_added;
 109                 }
 110         }
 111         /* We should be added at the head of the list */
 112         list_add(&desc->head, probe_list);
 113 desc_added:
 114         pr_debug("LTTng: just registered probe %s containing %u events\n",
 115                 desc->provider, desc->nr_events);
 116 }
 117
 118 /*
 119  * Called under sessions lock.
 120  */
 121 static
 122 void fixup_lazy_probes(void)
 123 {
 124         struct lttng_probe_desc *iter, *tmp;
 125         int ret;
 126
 127         lazy_nesting++;
 128         list_for_each_entry_safe(iter, tmp,
 129                         &lazy_probe_init, lazy_init_head) {
 130                 lttng_lazy_probe_register(iter);
 131                 iter->lazy = 0;
 132                 list_del(&iter->lazy_init_head);
 133         }
 134         ret = lttng_fix_pending_events();
 135         WARN_ON_ONCE(ret);
 136         lazy_nesting--;
 137 }
 138
 139 /*
 140  * Called under sessions lock.
 141  */
 142 struct list_head *lttng_get_probe_list_head(void)
 143 {
 144         if (!lazy_nesting && !list_empty(&lazy_probe_init))
 145                 fixup_lazy_probes();
 146         return &_probe_list;
 147 }
 148
 149 static
 150 const struct lttng_probe_desc *find_provider(const char *provider)
 151 {
 152         struct lttng_probe_desc *iter;
 153         struct list_head *probe_list;
 154
 155         probe_list = lttng_get_probe_list_head();
 156         list_for_each_entry(iter, probe_list, head) {
 157                 if (!strcmp(iter->provider, provider))
 158                         return iter;
 159         }
 160         return NULL;
 161 }
 162
 163 int lttng_probe_register(struct lttng_probe_desc *desc)
 164 {
 165         int ret = 0;
 166
 167         lttng_lock_sessions();
 168
 169         /*
 170          * Check if the provider has already been registered.
 171          */
 172         if (find_provider(desc->provider)) {
 173                 ret = -EEXIST;
 174                 goto end;
 175         }
 176         list_add(&desc->lazy_init_head, &lazy_probe_init);
 177         desc->lazy = 1;
 178         pr_debug("LTTng: adding probe %s containing %u events to lazy registration list\n",
 179                 desc->provider, desc->nr_events);
 180         /*
 181          * If there is at least one active session, we need to register
 182          * the probe immediately, since we cannot delay event
 183          * registration because they are needed ASAP.
 184          */
 185         if (lttng_session_active())
 186                 fixup_lazy_probes();
 187 end:
 188         lttng_unlock_sessions();
 189         return ret;
 190 }
 191 EXPORT_SYMBOL_GPL(lttng_probe_register);
 192
 193 void lttng_probe_unregister(struct lttng_probe_desc *desc)
 194 {
 195         lttng_lock_sessions();
 196         if (!desc->lazy)
 197                 list_del(&desc->head);
 198         else
 199                 list_del(&desc->lazy_init_head);
 200         pr_debug("LTTng: just unregistered probe %s\n", desc->provider);
 201         lttng_unlock_sessions();
 202 }
 203 EXPORT_SYMBOL_GPL(lttng_probe_unregister);
 204
 205 /*
 206  * TODO: this is O(nr_probes * nb_events), could be faster.
 207  * Called with sessions lock held.
 208  */
 209 static
 210 const struct lttng_event_desc *find_event(const char *name)
 211 {
 212         struct lttng_probe_desc *probe_desc;
 213         int i;
 214
 215         list_for_each_entry(probe_desc, &_probe_list, head) {
 216                 for (i = 0; i < probe_desc->nr_events; i++) {
 217                         if (!strcmp(probe_desc->event_desc[i]->name, name))
 218                                 return probe_desc->event_desc[i];
 219                         }
 220         }
 221         return NULL;
 222 }
 223
 224 /*
 225  * Called with sessions lock held.
 226  */
 227 const struct lttng_event_desc *lttng_event_get(const char *name)
 228 {
 229         const struct lttng_event_desc *event;
 230         int ret;
 231
 232         event = find_event(name);
 233         if (!event)
 234                 return NULL;
 235         ret = try_module_get(event->owner);
 236         WARN_ON_ONCE(!ret);
 237         return event;
 238 }
 239 EXPORT_SYMBOL_GPL(lttng_event_get);
 240
 241 /*
 242  * Called with sessions lock held.
 243  */
 244 void lttng_event_put(const struct lttng_event_desc *event)
 245 {
 246         module_put(event->owner);
 247 }
 248 EXPORT_SYMBOL_GPL(lttng_event_put);
 249
 250 static
 251 void *tp_list_start(struct seq_file *m, loff_t *pos)
 252 {
 253         struct lttng_probe_desc *probe_desc;
 254         struct list_head *probe_list;
 255         int iter = 0, i;
 256
 257         lttng_lock_sessions();
 258         probe_list = lttng_get_probe_list_head();
 259         list_for_each_entry(probe_desc, probe_list, head) {
 260                 for (i = 0; i < probe_desc->nr_events; i++) {
 261                         if (iter++ >= *pos)
 262                                 return (void *) probe_desc->event_desc[i];
 263                 }
 264         }
 265         /* End of list */
 266         return NULL;
 267 }
 268
 269 static
 270 void *tp_list_next(struct seq_file *m, void *p, loff_t *ppos)
 271 {
 272         struct lttng_probe_desc *probe_desc;
 273         struct list_head *probe_list;
 274         int iter = 0, i;
 275
 276         (*ppos)++;
 277         probe_list = lttng_get_probe_list_head();
 278         list_for_each_entry(probe_desc, probe_list, head) {
 279                 for (i = 0; i < probe_desc->nr_events; i++) {
 280                         if (iter++ >= *ppos)
 281                                 return (void *) probe_desc->event_desc[i];
 282                 }
 283         }
 284         /* End of list */
 285         return NULL;
 286 }
 287
 288 static
 289 void tp_list_stop(struct seq_file *m, void *p)
 290 {
 291         lttng_unlock_sessions();
 292 }
 293
 294 static
 295 int tp_list_show(struct seq_file *m, void *p)
 296 {
 297         const struct lttng_event_desc *probe_desc = p;
 298
 299         seq_printf(m,   "event { name = %s; };\n",
 300                    probe_desc->name);
 301         return 0;
 302 }
 303
 304 static
 305 const struct seq_operations lttng_tracepoint_list_seq_ops = {
 306         .start = tp_list_start,
 307         .next = tp_list_next,
 308         .stop = tp_list_stop,
 309         .show = tp_list_show,
 310 };
 311
 312 static
 313 int lttng_tracepoint_list_open(struct inode *inode, struct file *file)
 314 {
 315         return seq_open(file, &lttng_tracepoint_list_seq_ops);
 316 }
 317
 318 const struct file_operations lttng_tracepoint_list_fops = {
 319         .owner = THIS_MODULE,
 320         .open = lttng_tracepoint_list_open,
 321         .read = seq_read,
 322         .llseek = seq_lseek,
 323         .release = seq_release,
 324 };