Add explanation about lifetime of table description.
[osl.git] / osl.h.in
1 /*
2 * Copyright (C) 2007-2009 Andre Noll <maan@tuebingen.mpg.de>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file osl.h User interface for the object storage layer. */
8
9 #include <sys/mman.h>
10 #include <inttypes.h>
11
12 /** Export all declarations in this file. */
13 #pragma GCC visibility push(default)
14
15 /** Describes an object of the object storage layer (osl) */
16 struct osl_object {
17 /** Pointer to the data of the object. */
18 void *data;
19 /** The object's size. */
20 size_t size;
21 };
22
23 /** Flags that change the internal handling of osl tables. */
24 enum osl_table_flags {
25 /** This table will have many rows. */
26 OSL_LARGE_TABLE = 1
27 };
28
29 /** The three different types of storage for an osl column */
30 enum osl_storage_type {
31 /**
32 * All data for this column is stored in one file which gets mmapped by
33 * osl_open_table(). This is suitable for columns that do not hold much
34 * data.
35 */
36 OSL_MAPPED_STORAGE,
37 /**
38 * Each entry is stored on disk and is loaded on demand by
39 * open_disk_object(). This is the preferable storage type for large
40 * objects that need not be in memory all the time.
41 */
42 OSL_DISK_STORAGE,
43 /**
44 * Objects for columns of this type are volatile: They are only stored
45 * in memory and are discarded when the table is closed.
46 */
47 OSL_NO_STORAGE
48 };
49
50 /**
51 * Additional per-column flags
52 */
53 enum osl_storage_flags {
54 /**
55 * Build an rbtree for this column. This is only possible if the
56 * storage type of the column is either \a OSL_MAPPED_STORAGE or \a
57 * OSL_NO_STORAGE. In order to lookup objects in the table by using \a
58 * osl_get_row(), the lookup column must have an associated rbtree.
59 *
60 * \sa osl_storage_type, osl_get_row()
61 */
62 OSL_RBTREE = 1,
63 /** The data for this column will have constant size. */
64 OSL_FIXED_SIZE = 2,
65 /** All values are different. Must be set if \p OSL_RBTREE is set. */
66 OSL_UNIQUE = 4,
67 /** Do not free the data for this column (\p OSL_NO_STORAGE). */
68 OSL_DONT_FREE = 8
69 };
70
71 /** Opaque osl table structure. */
72 struct osl_table;
73 /** Opaque osl row structure. */
74 struct osl_row;
75
76 /**
77 * In order to build up an rbtree a compare function for the objects must be
78 * provided. This function takes pointers to the two objects to be compared. It
79 * must return -1, zero, or 1, if the first argument is considered to be
80 * respectively less than, equal to, or greater than the second. If two members
81 * compare as equal, their order in the rbtree is undefined.
82 */
83 typedef int osl_compare_func(const struct osl_object *obj1,
84 const struct osl_object *obj2);
85
86 /**
87 * The osl_rbreee_loop functions take a function pointer of this type. For each
88 * node in the rbtree, the given function is called.
89 *
90 * \sa osl_rbtree_loop(), osl_rbtree_loop_reverse().
91 */
92 typedef int osl_rbtree_loop_func(struct osl_row *row, void *data);
93
94 /**
95 * Describes one column of a osl table.
96 */
97 struct osl_column_description {
98 /** One of the three possible types of storage, \sa osl_storage_type. */
99 uint16_t storage_type;
100 /** Specifies further properties of the column, \sa osl_storage_flags. */
101 uint16_t storage_flags;
102 /**
103 * The column name determines the name of the directory where all data
104 * for this column will be stored. Its hash is stored in the table
105 * header. This field is ignored if the storage type is \a NO_STORAGE.
106 */
107 char *name;
108 /**
109 * For columns with an associated rbtree, this must point to a function
110 * that compares the values of two objects, either a built-in function
111 * or a function defined by the application may be supplied. This
112 * field is ignored if the column does not have an associated rbtree.
113 *
114 * \sa osl_storage_flags, osl_compare_func
115 */
116 osl_compare_func *compare_function;
117 /**
118 * If the \a OSL_FIXED_SIZE flag is set for this column, this value
119 * describes the number of bytes of each object of this column. It is
120 * ignored, if \a OSL_FIXED_SIZE is not set.
121 */
122 uint32_t data_size;
123 };
124
125 /**
126 * Describes one osl table.
127 *
128 * A pointer to the table description is passed to \ref osl_create_table() and
129 * \ref osl_open_table(). The osl library calls which operate on an open table
130 * refer to the fields of the table description through this pointer. Hence the
131 * table description must not be modified or freed before the table is closed.
132 */
133 struct osl_table_description {
134 /**
135 * The directory which contains all files of this table. This may be
136 * either relative to the cwd or an absolute path.
137 */
138 const char *dir;
139 /**
140 * The table name. A subdirectory of \a dir called \a name is created
141 * at table creation time. It must be a valid name for a subdirectory.
142 * In particular, no slashes are allowed for \a name.
143 */
144 const char *name;
145 /** The number of columns of this table. */
146 uint16_t num_columns;
147 /** Further table-wide information, \sa osl_table_flags. */
148 uint8_t flags;
149 /** The array describing the individual columns of the table. */
150 struct osl_column_description *column_descriptions;
151 };
152
153 /** Flags to be passed to \a osl_close_table(). */
154 enum osl_close_flags {
155 /**
156 * The table header contains a "dirty" flag which indicates whether the
157 * table is currently held open by another process. The \a
158 * OSL_MARK_CLEAN flag instructs libosl to clear the dirty flag when
159 * the table is closed.
160 */
161 OSL_MARK_CLEAN = 1,
162 /**
163 * If the table contains columns of type \a OSL_NO_STORAGE and this
164 * flag is passed to osl_close_table(), free(3) is called for each
165 * object of each column of type \a OSL_NO_STORAGE.
166 */
167 OSL_FREE_VOLATILE = 2
168 };
169
170 /**
171 * Create a new osl table.
172 *
173 * \param desc Pointer to the table description.
174 *
175 * \return Standard.
176 */
177 int osl_create_table(const struct osl_table_description *desc);
178
179 /**
180 * Open an osl table.
181 *
182 * Each osl table must be opened before its data can be accessed.
183 *
184 * \param desc Describes the table to be opened.
185 * \param result Contains a pointer to the open table on success.
186 *
187 * The table description given by \a desc should coincide with the
188 * description used at creation time.
189 *
190 * \return Standard.
191 */
192 int osl_open_table(const struct osl_table_description *desc,
193 struct osl_table **result);
194
195 /**
196 * Close an osl table.
197 *
198 * \param t Pointer to the table to be closed.
199 * \param flags Options for what should be cleaned up.
200 *
201 * If osl_open_table() succeeds, the resulting table pointer must later be
202 * passed to this function in order to flush all changes to the file system and
203 * to free the resources that were allocated by osl_open_table().
204 *
205 * \return Standard.
206 *
207 * \sa osl_open_table(), unmap_table().
208 */
209 int osl_close_table(struct osl_table *t, enum osl_close_flags flags);
210
211 /**
212 * Get the row that contains the given object.
213 *
214 * \param t Pointer to an open osl table.
215 * \param col_num The number of the column to be searched.
216 * \param obj The object to be looked up.
217 * \param result Points to the row containing \a obj.
218 *
219 * Lookup \a obj in \a t and return the row containing \a obj. The column
220 * specified by \a col_num must have an associated rbtree.
221 *
222 * \return Standard. \a result is set to \p NULL if and only if the function
223 * returns negative.
224 *
225 * \sa osl_storage_flags
226 */
227 int osl_get_row(const struct osl_table *t, unsigned col_num,
228 const struct osl_object *obj, struct osl_row **result);
229
230 /**
231 * Retrieve an object identified by row and column.
232 *
233 * \param t Pointer to an open osl table.
234 * \param row Pointer to the row.
235 * \param col_num The column number.
236 * \param object The result pointer.
237 *
238 * The column determined by \a col_num must be of type \p OSL_MAPPED_STORAGE
239 * or \p OSL_NO_STORAGE, i.e. no disk storage objects may be retrieved by this
240 * function.
241 *
242 * \return Standard.
243 *
244 * \sa osl_storage_type, osl_open_disk_object().
245 */
246 int osl_get_object(const struct osl_table *t, const struct osl_row *row,
247 unsigned col_num, struct osl_object *object);
248
249 /**
250 * Retrieve an object of type \p OSL_DISK_STORAGE by row and column.
251 *
252 * \param t Pointer to an open osl table.
253 * \param r Pointer to the row containing the object.
254 * \param col_num The column number.
255 * \param obj Points to the result upon successful return.
256 *
257 * For columns of type \p OSL_DISK_STORAGE, this function must be used to
258 * retrieve one of its containing objects. Afterwards, osl_close_disk_object()
259 * must be called in order to deallocate the resources.
260 *
261 * \return Standard.
262 *
263 * \sa osl_get_object(), osl_storage_type, osl_close_disk_object().
264 */
265 int osl_open_disk_object(const struct osl_table *t,
266 const struct osl_row *r, unsigned col_num, struct osl_object *obj);
267
268 /**
269 * Free resources that were allocated during osl_open_disk_object().
270 *
271 * \param obj Pointer to the object previously returned by open_disk_object().
272 *
273 * \return The return value of the underlying call to munmap().
274 *
275 * \sa munmap(2).
276 */
277 int osl_close_disk_object(struct osl_object *obj);
278
279 /**
280 * Add a new row to an osl table and retrieve this row.
281 *
282 * \param t Pointer to an open osl table.
283 * \param objects Array of objects to be added.
284 * \param row Result pointer.
285 *
286 * The \a objects parameter must point to an array containing one object per
287 * column. The order of the objects in the array is given by the table
288 * description of \a table. Several sanity checks are performed during object
289 * insertion and the function returns without modifying the table if any of
290 * these tests fail. In fact, it is atomic in the sense that it either
291 * succeeds or leaves the table unchanged (i.e. either all or none of the
292 * objects are added to the table).
293 *
294 * It is considered an error if an object is added to a column with associated
295 * rbtree if this object is equal to an object already contained in that column
296 * (i.e. the compare function for the column's rbtree returns zero).
297 *
298 * \return Standard.
299 *
300 * \sa struct osl_table_description, osl_compare_func, osl_add_row().
301 */
302 int osl_add_and_get_row(struct osl_table *t, struct osl_object *objects,
303 struct osl_row **row);
304
305
306 /**
307 * Add a new row to an osl table.
308 *
309 * \param t Same meaning as osl_add_and_get_row().
310 * \param objects Same meaning as osl_add_and_get_row().
311 *
312 * \return The return value of the underlying call to osl_add_and_get_row().
313 *
314 * This is equivalent to osl_add_and_get_row(t, objects, NULL).
315 */
316 int osl_add_row(struct osl_table *t, struct osl_object *objects);
317
318 /**
319 * Delete a row from an osl table.
320 *
321 * \param t Pointer to an open osl table.
322 * \param row Pointer to the row to delete.
323 *
324 * This removes all disk storage objects, removes all rbtree nodes, and frees
325 * all volatile objects belonging to the given row. For mapped columns, the
326 * data is merely marked invalid and may be pruned from time to time by
327 * osl_fsck.
328 *
329 * \return Standard.
330 */
331 int osl_del_row(struct osl_table *t, struct osl_row *row);
332
333 /**
334 * Loop over all nodes in an rbtree.
335 *
336 * \param t Pointer to an open osl table.
337 * \param col_num The column to use for iterating over the elements.
338 * \param private_data Pointer that gets passed to \a func.
339 * \param func The function to be called for each node in the rbtree.
340 *
341 * This function does an in-order walk of the rbtree associated with \a
342 * col_num. It is an error if the \p OSL_RBTREE flag is not set for this
343 * column. For each node in the rbtree, the given function \a func is called
344 * with two pointers as arguments: The first osl_row* argument points to the
345 * row that contains the object corresponding to the rbtree node currently
346 * traversed, and the \a private_data pointer is passed verbatim to \a func as the
347 * second argument. The loop terminates either if \a func returns a negative
348 * value, or if all nodes of the tree have been visited.
349 *
350 *
351 * \return Standard. If the termination of the loop was caused by \a func
352 * returning a negative value, \p -E_OSL_LOOP is returned.
353 *
354 * \sa osl_storage_flags, osl_rbtree_loop_reverse(), osl_compare_func.
355 */
356 int osl_rbtree_loop(const struct osl_table *t, unsigned col_num,
357 void *private_data, osl_rbtree_loop_func *func);
358
359 /**
360 * Loop over all nodes in an rbtree in reverse order.
361 *
362 * \param t Identical meaning as in \p osl_rbtree_loop().
363 * \param col_num Identical meaning as in \p osl_rbtree_loop().
364 * \param private_data Identical meaning as in \p osl_rbtree_loop().
365 * \param func Identical meaning as in \p osl_rbtree_loop().
366 *
367 * This function is identical to \p osl_rbtree_loop(), the only difference
368 * is that the tree is walked in reverse order.
369 *
370 * \return The same return value as \p osl_rbtree_loop().
371 *
372 * \sa osl_rbtree_loop().
373 */
374 int osl_rbtree_loop_reverse(const struct osl_table *t, unsigned col_num,
375 void *private_data, osl_rbtree_loop_func *func);
376
377 /**
378 * Change an object in an osl table.
379 *
380 * \param t Pointer to an open osl table.
381 * \param r Pointer to the row containing the object to be updated.
382 * \param col_num Number of the column containing the object to be updated.
383 * \param obj Pointer to the replacement object.
384 *
385 * This function gets rid of all references to the old object. This includes
386 * removal of the rbtree node in case there is an rbtree associated with \a
387 * col_num. It then inserts \a obj into the table and the rbtree if necessary.
388 *
389 * If the \p OSL_RBTREE flag is set for \a col_num, you \b MUST call this
390 * function in order to change the contents of an object, even for volatile or
391 * mapped columns of constant size (which may be updated directly if \p
392 * OSL_RBTREE is not set). Otherwise the rbtree might become corrupt.
393 *
394 * \return Standard
395 */
396 int osl_update_object(struct osl_table *t, const struct osl_row *r,
397 unsigned col_num, struct osl_object *obj);
398
399 /**
400 * Get the number of rows of the given table.
401 *
402 * \param t Pointer to an open osl table.
403 * \param num_rows Result is returned here.
404 *
405 * The number of rows returned via \a num_rows excluding any invalid rows.
406 *
407 * \return Positive on success, \p -E_OSL_BAD_TABLE if \a t is \p NULL.
408 */
409 int osl_get_num_rows(const struct osl_table *t, unsigned *num_rows);
410
411
412 /**
413 * Get the row corresponding to the smallest rbtree node of a column.
414 *
415 * \param t An open rbtree table.
416 * \param col_num The number of the rbtree column.
417 * \param result A pointer to the first row is returned here.
418 *
419 * The rbtree node of the smallest object (with respect to the corresponding
420 * compare function) is selected and the row containing this object is
421 * returned. It is an error if \a col_num refers to a column without an
422 * associated rbtree.
423 *
424 * \return Standard.
425 *
426 * \sa osl_get_nth_row(), osl_rbtree_last_row().
427 */
428 int osl_rbtree_first_row(const struct osl_table *t, unsigned col_num,
429 struct osl_row **result);
430
431 /**
432 * Get the row corresponding to the greatest rbtree node of a column.
433 *
434 * \param t The same meaning as in \p osl_rbtree_first_row().
435 * \param col_num The same meaning as in \p osl_rbtree_first_row().
436 * \param result The same meaning as in \p osl_rbtree_first_row().
437 *
438 * This function works just like osl_rbtree_first_row(), the only difference
439 * is that the row containing the greatest rather than the smallest object is
440 * returned.
441 *
442 * \return Standard.
443 *
444 * \sa osl_get_nth_row(), osl_rbtree_first_row().
445 */
446 int osl_rbtree_last_row(const struct osl_table *t, unsigned col_num,
447 struct osl_row **result);
448
449 /**
450 * Get the row with n-th greatest value.
451 *
452 * \param t Pointer to an open osl table.
453 * \param col_num The column number.
454 * \param n The rank of the desired row.
455 * \param result Row is returned here.
456 *
457 * Retrieve the n-th order statistic with respect to the compare function
458 * of the rbtree column \a col_num. In other words, get the row with
459 * \a n th greatest value in column \a col_num. It is an error if
460 * \a col_num is not a rbtree column, or if \a n is larger than the
461 * number of rows in the table.
462 *
463 * \return Standard.
464 *
465 * \sa osl_storage_flags, osl_compare_func, osl_get_row(),
466 * osl_rbtree_last_row(), osl_rbtree_first_row(), osl_get_rank().
467 */
468 int osl_get_nth_row(const struct osl_table *t, unsigned col_num,
469 unsigned n, struct osl_row **result);
470
471 /**
472 * Get the rank of a row.
473 *
474 * \param t An open osl table.
475 * \param r The row to get the rank of.
476 * \param col_num The number of an rbtree column.
477 * \param rank Result pointer.
478 *
479 * The rank is, by definition, the position of the row in the linear order
480 * determined by an in-order tree walk of the rbtree associated with column
481 * number \a col_num of \a table.
482 *
483 * \return Standard.
484 *
485 * \sa osl_get_nth_row().
486 */
487 int osl_get_rank(const struct osl_table *t, struct osl_row *r,
488 unsigned col_num, unsigned *rank);
489
490 /**
491 * Get a string describing the error code passed in the argument.
492 *
493 * \param num The error code.
494 *
495 * This works just like strerror(3). The given number must be an osl error
496 * code. The result must not be freed by the caller.
497 *
498 * \return The error text corresponding to an osl error code.
499 */
500 const char *osl_strerror(int num);
501
502 #pragma GCC visibility pop