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 #include <fcntl.h>
  29
  30 /*
  31  * Pointer dereferencing. We don't trust the shm_ref, so we validate
  32  * both the index and offset with known boundaries.
  33  *
  34  * "shmp" and "shmp_index" guarantee that it's safe to use the pointer
  35  * target type, even in the occurrence of shm_ref modification by an
  36  * untrusted process having write access to the shm_ref. We return a
  37  * NULL pointer if the ranges are invalid.
  38  */
  39 static inline
  40 char *_shmp_offset(struct shm_object_table *table, struct shm_ref *ref,
  41                    size_t idx, size_t elem_size)
  42 {
  43         struct shm_object *obj;
  44         size_t objindex, ref_offset;
  45
  46         objindex = (size_t) ref->index;
  47         if (caa_unlikely(objindex >= table->allocated_len))
  48                 return NULL;
  49         obj = &table->objects[objindex];
  50         ref_offset = (size_t) ref->offset;
  51         ref_offset += idx * elem_size;
  52         /* Check if part of the element returned would exceed the limits. */
  53         if (caa_unlikely(ref_offset + elem_size > obj->memory_map_size))
  54                 return NULL;
  55         return &obj->memory_map[ref_offset];
  56 }
  57
  58 #define shmp_index(handle, ref, index)                                  \
  59         ({                                                              \
  60                 __typeof__((ref)._type) ____ptr_ret;                    \
  61                 ____ptr_ret = (__typeof__(____ptr_ret)) _shmp_offset((handle)->table, &(ref)._ref, index, sizeof(*____ptr_ret));        \
  62                 ____ptr_ret;                                            \
  63         })
  64
  65 #define shmp(handle, ref)       shmp_index(handle, ref, 0)
  66
  67 static inline
  68 void _set_shmp(struct shm_ref *ref, struct shm_ref src)
  69 {
  70         *ref = src;
  71 }
  72
  73 #define set_shmp(ref, src)      _set_shmp(&(ref)._ref, src)
  74
  75 struct shm_object_table *shm_object_table_create(size_t max_nb_obj);
  76 struct shm_object *shm_object_table_append_shadow(struct shm_object_table *table,
  77                         int shm_fd, int wait_fd, size_t memory_map_size);
  78 void shm_object_table_destroy(struct shm_object_table *table);
  79 struct shm_object *shm_object_table_append(struct shm_object_table *table,
  80                                            size_t memory_map_size);
  81
  82 /*
  83  * zalloc_shm - allocate memory within a shm object.
  84  *
  85  * Shared memory is already zeroed by shmget.
  86  * *NOT* multithread-safe (should be protected by mutex).
  87  * Returns a -1, -1 tuple on error.
  88  */
  89 struct shm_ref zalloc_shm(struct shm_object *obj, size_t len);
  90 void align_shm(struct shm_object *obj, size_t align);
  91
  92 static inline
  93 int shm_get_wakeup_fd(struct lttng_ust_shm_handle *handle, struct shm_ref *ref)
  94 {
  95         struct shm_object_table *table = handle->table;
  96         struct shm_object *obj;
  97         size_t index;
  98
  99         index = (size_t) ref->index;
 100         if (caa_unlikely(index >= table->allocated_len))
 101                 return -EPERM;
 102         obj = &table->objects[index];
 103
 104         return obj->wait_fd[1];
 105 }
 106
 107 static inline
 108 int shm_open_wakeup_pipe(struct lttng_ust_shm_handle *handle, struct shm_ref *ref)
 109 {
 110         struct shm_object_table *table = handle->table;
 111         struct shm_object *obj;
 112         size_t index;
 113         int fd, ret = -1;
 114
 115         index = (size_t) ref->index;
 116         if (caa_unlikely(index >= table->allocated_len))
 117                 return -EPERM;
 118
 119         obj = &table->objects[index];
 120
 121         if (obj->wait_fd[1] < 0 && obj->wait_pipe_path != NULL) {
 122                 fd = open(obj->wait_pipe_path, O_WRONLY);
 123                 if (fd < 0) {
 124                         ret = -1;
 125                 } else {
 126                         /* FIXME: What if fcntl fail? */
 127                         fcntl(fd, F_SETFD, FD_CLOEXEC);
 128                         obj->wait_fd[1] = fd;
 129                         ret = 0;
 130                 }
 131         }
 132
 133         return ret;
 134 }
 135
 136 static inline
 137 int shm_get_wait_fd(struct lttng_ust_shm_handle *handle, struct shm_ref *ref)
 138 {
 139         struct shm_object_table *table = handle->table;
 140         struct shm_object *obj;
 141         size_t index;
 142
 143         index = (size_t) ref->index;
 144         if (caa_unlikely(index >= table->allocated_len))
 145                 return -EPERM;
 146         obj = &table->objects[index];
 147         return obj->wait_fd[0];
 148 }
 149
 150 static inline
 151 int shm_get_object_data(struct lttng_ust_shm_handle *handle, struct shm_ref *ref,
 152                         int **shm_fd, char **shm_path,
 153                         int **wait_fd, char **wait_pipe_path,
 154                         uint64_t **memory_map_size)
 155 {
 156         struct shm_object_table *table = handle->table;
 157         struct shm_object *obj;
 158         size_t index;
 159
 160         index = (size_t) ref->index;
 161         if (caa_unlikely(index >= table->allocated_len))
 162                 return -EPERM;
 163         obj = &table->objects[index];
 164         *shm_fd   = &obj->shm_fd;
 165         *shm_path = obj->shm_path;
 166         *wait_fd        = &obj->wait_fd[0];
 167         *wait_pipe_path = obj->wait_pipe_path;
 168         *memory_map_size = &obj->allocated_len;
 169         return 0;
 170 }
 171
 172 #endif /* _LIBRINGBUFFER_SHM_H */