liblttng-ust/lttng-context-provider.c

   1 /*
   2  * lttng-context-provider.c
   3  *
   4  * LTTng UST application context provider.
   5  *
   6  * Copyright (C) 2016 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 #define _LGPL_SOURCE
  24 #include <sys/types.h>
  25 #include <unistd.h>
  26 #include <lttng/ust-context-provider.h>
  27 #include "lttng-tracer-core.h"
  28 #include "jhash.h"
  29 #include <helper.h>
  30
  31 #define CONTEXT_PROVIDER_HT_BITS        12
  32 #define CONTEXT_PROVIDER_HT_SIZE        (1U << CONTEXT_PROVIDER_HT_BITS)
  33 struct context_provider_ht {
  34         struct cds_hlist_head table[CONTEXT_PROVIDER_HT_SIZE];
  35 };
  36
  37 static struct context_provider_ht context_provider_ht;
  38
  39 static struct lttng_ust_context_provider *
  40                 lookup_provider_by_name(const char *name)
  41 {
  42         struct cds_hlist_head *head;
  43         struct cds_hlist_node *node;
  44         struct lttng_ust_context_provider *provider;
  45         uint32_t hash;
  46         const char *end;
  47         size_t len;
  48
  49         /* Lookup using everything before first ':' as key. */
  50         end = strchr(name, ':');
  51         if (end)
  52                 len = end - name;
  53         else
  54                 len = strlen(name);
  55         hash = jhash(name, len, 0);
  56         head = &context_provider_ht.table[hash & (CONTEXT_PROVIDER_HT_SIZE - 1)];
  57         cds_hlist_for_each_entry(provider, node, head, node) {
  58                 if (!strncmp(provider->name, name, len))
  59                         return provider;
  60         }
  61         return NULL;
  62 }
  63
  64 int lttng_ust_context_provider_register(struct lttng_ust_context_provider *provider)
  65 {
  66         struct cds_hlist_head *head;
  67         size_t name_len = strlen(provider->name);
  68         uint32_t hash;
  69         int ret = 0;
  70
  71         /* Provider name starts with "$app.". */
  72         if (strncmp("$app.", provider->name, strlen("$app.") != 0))
  73                 return -EINVAL;
  74         /* Provider name cannot contain a column character. */
  75         if (strchr(provider->name, ':'))
  76                 return -EINVAL;
  77         if (ust_lock()) {
  78                 ret = -EBUSY;
  79                 goto end;
  80         }
  81         if (lookup_provider_by_name(provider->name)) {
  82                 ret = -EBUSY;
  83                 goto end;
  84         }
  85         hash = jhash(provider->name, name_len, 0);
  86         head = &context_provider_ht.table[hash & (CONTEXT_PROVIDER_HT_SIZE - 1)];
  87         cds_hlist_add_head(&provider->node, head);
  88         lttng_ust_context_set_session_provider(provider->name,
  89                 provider->get_size, provider->record,
  90                 provider->get_value);
  91 end:
  92         ust_unlock();
  93         return ret;
  94 }
  95
  96 void lttng_ust_context_provider_unregister(struct lttng_ust_context_provider *provider)
  97 {
  98         if (ust_lock())
  99                 goto end;
 100         lttng_ust_context_set_session_provider(provider->name,
 101                 lttng_ust_dummy_get_size, lttng_ust_dummy_record,
 102                 lttng_ust_dummy_get_value);
 103         cds_hlist_del(&provider->node);
 104 end:
 105         ust_unlock();
 106 }
 107
 108 /*
 109  * Called with ust mutex held.
 110  * Add application context to array of context, even if the application
 111  * context is not currently loaded by application. It will then use the
 112  * dummy callbacks in that case.
 113  * Always performed before tracing is started, since it modifies
 114  * metadata describing the context.
 115  */
 116 int lttng_ust_add_app_context_to_ctx_rcu(const char *name,
 117                 struct lttng_ctx **ctx)
 118 {
 119         struct lttng_ust_context_provider *provider;
 120         struct lttng_ctx_field new_field;
 121         int ret;
 122
 123         if (*ctx && lttng_find_context(*ctx, name))
 124                 return -EEXIST;
 125         /*
 126          * For application context, add it by expanding
 127          * ctx array.
 128          */
 129         memset(&new_field, 0, sizeof(new_field));
 130         new_field.field_name = strdup(name);
 131         if (!new_field.field_name)
 132                 return -ENOMEM;
 133         new_field.event_field.name = new_field.field_name;
 134         new_field.event_field.type.atype = atype_dynamic;
 135         /*
 136          * If provider is not found, we add the context anyway, but
 137          * it will provide a dummy context.
 138          */
 139         provider = lookup_provider_by_name(name);
 140         if (provider) {
 141                 new_field.get_size = provider->get_size;
 142                 new_field.record = provider->record;
 143                 new_field.get_value = provider->get_value;
 144         } else {
 145                 new_field.get_size = lttng_ust_dummy_get_size;
 146                 new_field.record = lttng_ust_dummy_record;
 147                 new_field.get_value = lttng_ust_dummy_get_value;
 148         }
 149         ret = lttng_context_add_rcu(ctx, &new_field);
 150         if (ret) {
 151                 free(new_field.field_name);
 152                 return ret;
 153         }
 154         return 0;
 155 }