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 #include <sys/types.h>
  24 #include <unistd.h>
  25 #include <lttng/ust-context-provider.h>
  26 #include "lttng-tracer-core.h"
  27 #include "jhash.h"
  28 #include <helper.h>
  29
  30 #define CONTEXT_PROVIDER_HT_BITS        12
  31 #define CONTEXT_PROVIDER_HT_SIZE        (1U << CONTEXT_PROVIDER_HT_BITS)
  32 struct context_provider_ht {
  33         struct cds_hlist_head table[CONTEXT_PROVIDER_HT_SIZE];
  34 };
  35
  36 static struct context_provider_ht context_provider_ht;
  37
  38 static struct lttng_ust_context_provider *
  39                 lookup_provider_by_name(const char *name)
  40 {
  41         struct cds_hlist_head *head;
  42         struct cds_hlist_node *node;
  43         struct lttng_ust_context_provider *provider;
  44         uint32_t hash;
  45         const char *end;
  46         size_t len;
  47
  48         /* Lookup using everything before first ':' as key. */
  49         end = strchr(name, ':');
  50         if (end)
  51                 len = end - name;
  52         else
  53                 len = strlen(name);
  54         hash = jhash(name, len, 0);
  55         head = &context_provider_ht.table[hash & (CONTEXT_PROVIDER_HT_SIZE - 1)];
  56         cds_hlist_for_each_entry(provider, node, head, node) {
  57                 if (!strncmp(provider->name, name, len))
  58                         return provider;
  59         }
  60         return NULL;
  61 }
  62
  63 int lttng_ust_context_provider_register(struct lttng_ust_context_provider *provider)
  64 {
  65         struct cds_hlist_head *head;
  66         size_t name_len = strlen(provider->name);
  67         uint32_t hash;
  68         int ret = 0;
  69
  70         /* Provider name starts with "$app.". */
  71         if (strncmp("$app.", provider->name, strlen("$app.") != 0))
  72                 return -EINVAL;
  73         /* Provider name cannot contain a column character. */
  74         if (strchr(provider->name, ':'))
  75                 return -EINVAL;
  76         if (ust_lock()) {
  77                 ret = -EBUSY;
  78                 goto end;
  79         }
  80         if (lookup_provider_by_name(provider->name)) {
  81                 ret = -EBUSY;
  82                 goto end;
  83         }
  84         hash = jhash(provider->name, name_len, 0);
  85         head = &context_provider_ht.table[hash & (CONTEXT_PROVIDER_HT_SIZE - 1)];
  86         cds_hlist_add_head(&provider->node, head);
  87         lttng_ust_context_set_session_provider(provider->name,
  88                 provider->get_size, provider->record,
  89                 provider->get_value);
  90 end:
  91         ust_unlock();
  92         return ret;
  93 }
  94
  95 size_t lttng_ust_dummy_get_size(struct lttng_ctx_field *field, size_t offset)
  96 {
  97         size_t size = 0;
  98
  99         size += lib_ring_buffer_align(offset, lttng_alignof(char));
 100         size += sizeof(char);           /* tag */
 101         return size;
 102 }
 103
 104 void lttng_ust_dummy_record(struct lttng_ctx_field *field,
 105                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 106                  struct lttng_channel *chan)
 107 {
 108         char sel_char = (char) LTTNG_UST_DYNAMIC_TYPE_NONE;
 109
 110         lib_ring_buffer_align_ctx(ctx, lttng_alignof(sel_char));
 111         chan->ops->event_write(ctx, &sel_char, sizeof(sel_char));
 112 }
 113
 114 void lttng_ust_dummy_get_value(struct lttng_ctx_field *field,
 115                 struct lttng_ctx_value *value)
 116 {
 117         value->sel = LTTNG_UST_DYNAMIC_TYPE_NONE;
 118 }
 119
 120 void lttng_ust_context_provider_unregister(struct lttng_ust_context_provider *provider)
 121 {
 122         if (ust_lock())
 123                 goto end;
 124         lttng_ust_context_set_session_provider(provider->name,
 125                 lttng_ust_dummy_get_size, lttng_ust_dummy_record,
 126                 lttng_ust_dummy_get_value);
 127         cds_hlist_del(&provider->node);
 128 end:
 129         ust_unlock();
 130 }
 131
 132 /*
 133  * Called with ust mutex held.
 134  * Add application context to array of context, even if the application
 135  * context is not currently loaded by application. It will then use the
 136  * dummy callbacks in that case.
 137  * Always performed before tracing is started, since it modifies
 138  * metadata describing the context.
 139  */
 140 int lttng_ust_add_app_context_to_ctx_rcu(const char *name,
 141                 struct lttng_ctx **ctx)
 142 {
 143         struct lttng_ust_context_provider *provider;
 144         struct lttng_ctx_field new_field;
 145         int ret;
 146
 147         if (*ctx && lttng_find_context(*ctx, name))
 148                 return -EEXIST;
 149         /*
 150          * For application context, add it by expanding
 151          * ctx array.
 152          */
 153         memset(&new_field, 0, sizeof(new_field));
 154         new_field.field_name = strdup(name);
 155         if (!new_field.field_name)
 156                 return -ENOMEM;
 157         new_field.event_field.name = new_field.field_name;
 158         new_field.event_field.type.atype = atype_dynamic;
 159         /*
 160          * If provider is not found, we add the context anyway, but
 161          * it will provide a dummy context.
 162          */
 163         provider = lookup_provider_by_name(name);
 164         if (provider) {
 165                 new_field.get_size = provider->get_size;
 166                 new_field.record = provider->record;
 167                 new_field.get_value = provider->get_value;
 168         } else {
 169                 new_field.get_size = lttng_ust_dummy_get_size;
 170                 new_field.record = lttng_ust_dummy_record;
 171                 new_field.get_value = lttng_ust_dummy_get_value;
 172         }
 173         ret = lttng_context_add_rcu(ctx, &new_field);
 174         if (ret) {
 175                 free(new_field.field_name);
 176                 return ret;
 177         }
 178         return 0;
 179 }