libringbuffer/shm.h

   1 #ifndef _LIBRINGBUFFER_SHM_H
   2 #define _LIBRINGBUFFER_SHM_H
   3
   4 /*
   5  * libringbuffer/shm.h
   6  *
   7  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; only
  12  * version 2.1 of the License.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #include <stdint.h>
  25 #include <usterr-signal-safe.h>
  26 #include <urcu/compiler.h>
  27 #include "shm_types.h"
  28
  29 /*
  30  * Pointer dereferencing. We don't trust the shm_ref, so we validate
  31  * both the index and offset with known boundaries.
  32  *
  33  * "shmp" and "shmp_index" guarantee that it's safe to use the pointer
  34  * target type, even in the occurrence of shm_ref modification by an
  35  * untrusted process having write access to the shm_ref. We return a
  36  * NULL pointer if the ranges are invalid.
  37  */
  38 static inline
  39 char *_shmp_offset(struct shm_object_table *table, struct shm_ref *ref,
  40                    size_t idx, size_t elem_size)
  41 {
  42         struct shm_object *obj;
  43         size_t objindex, ref_offset;
  44
  45         objindex = (size_t) ref->index;
  46         if (caa_unlikely(objindex >= table->allocated_len))
  47                 return NULL;
  48         obj = &table->objects[objindex];
  49         ref_offset = (size_t) ref->offset;
  50         ref_offset += idx * elem_size;
  51         /* Check if part of the element returned would exceed the limits. */
  52         if (caa_unlikely(ref_offset + elem_size > obj->memory_map_size))
  53                 return NULL;
  54         return &obj->memory_map[ref_offset];
  55 }
  56
  57 #define shmp_index(handle, ref, index)                                  \
  58         ({                                                              \
  59                 __typeof__((ref)._type) ____ptr_ret;                    \
  60                 ____ptr_ret = (__typeof__(____ptr_ret)) _shmp_offset((handle)->table, &(ref)._ref, index, sizeof(*____ptr_ret));        \
  61                 ____ptr_ret;                                            \
  62         })
  63
  64 #define shmp(handle, ref)       shmp_index(handle, ref, 0)
  65
  66 static inline
  67 void _set_shmp(struct shm_ref *ref, struct shm_ref src)
  68 {
  69         *ref = src;
  70 }
  71
  72 #define set_shmp(ref, src)      _set_shmp(&(ref)._ref, src)
  73
  74 struct shm_object_table *shm_object_table_create(size_t max_nb_obj);
  75 struct shm_object *shm_object_table_append_shadow(struct shm_object_table *table,
  76                         int shm_fd, int wait_fd, size_t memory_map_size);
  77 void shm_object_table_destroy(struct shm_object_table *table);
  78 struct shm_object *shm_object_table_append(struct shm_object_table *table,
  79                                            size_t memory_map_size);
  80
  81 /*
  82  * zalloc_shm - allocate memory within a shm object.
  83  *
  84  * Shared memory is already zeroed by shmget.
  85  * *NOT* multithread-safe (should be protected by mutex).
  86  * Returns a -1, -1 tuple on error.
  87  */
  88 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len);
  89 void align_shm(struct shm_object *obj, size_t align);
  90
  91 static inline
  92 int shm_get_wakeup_fd(struct lttng_ust_shm_handle *handle, struct shm_ref *ref)
  93 {
  94         struct shm_object_table *table = handle->table;
  95         struct shm_object *obj;
  96         size_t index;
  97
  98         index = (size_t) ref->index;
  99         if (caa_unlikely(index >= table->allocated_len))
 100                 return -EPERM;
 101         obj = &table->objects[index];
 102         return obj->wait_fd[1];
 103
 104 }
 105
 106 static inline
 107 int shm_get_wait_fd(struct lttng_ust_shm_handle *handle, struct shm_ref *ref)
 108 {
 109         struct shm_object_table *table = handle->table;
 110         struct shm_object *obj;
 111         size_t index;
 112
 113         index = (size_t) ref->index;
 114         if (caa_unlikely(index >= table->allocated_len))
 115                 return -EPERM;
 116         obj = &table->objects[index];
 117         return obj->wait_fd[0];
 118 }
 119
 120 static inline
 121 int shm_get_object_data(struct lttng_ust_shm_handle *handle, struct shm_ref *ref,
 122                 int **shm_fd, int **wait_fd, uint64_t **memory_map_size)
 123 {
 124         struct shm_object_table *table = handle->table;
 125         struct shm_object *obj;
 126         size_t index;
 127
 128         index = (size_t) ref->index;
 129         if (caa_unlikely(index >= table->allocated_len))
 130                 return -EPERM;
 131         obj = &table->objects[index];
 132         *shm_fd = &obj->shm_fd;
 133         *wait_fd = &obj->wait_fd[0];
 134         *memory_map_size = &obj->allocated_len;
 135         return 0;
 136 }
 137
 138 #endif /* _LIBRINGBUFFER_SHM_H */