1/*
2 * zpool memory storage api
3 *
4 * Copyright (C) 2014 Dan Streetman
5 *
6 * This is a common frontend for memory storage pool implementations.
7 * Typically, this is used to store compressed memory.
8 */
9
10#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11
12#include <linux/list.h>
13#include <linux/types.h>
14#include <linux/mm.h>
15#include <linux/slab.h>
16#include <linux/spinlock.h>
17#include <linux/module.h>
18#include <linux/zpool.h>
19
20struct zpool {
21 struct zpool_driver *driver;
22 void *pool;
23 const struct zpool_ops *ops;
24 bool evictable;
25
26 struct list_head list;
27};
28
29static LIST_HEAD(drivers_head);
30static DEFINE_SPINLOCK(drivers_lock);
31
32static LIST_HEAD(pools_head);
33static DEFINE_SPINLOCK(pools_lock);
34
35/**
36 * zpool_register_driver() - register a zpool implementation.
37 * @driver: driver to register
38 */
39void zpool_register_driver(struct zpool_driver *driver)
40{
41 spin_lock(&drivers_lock);
42 atomic_set(&driver->refcount, 0);
43 list_add(&driver->list, &drivers_head);
44 spin_unlock(&drivers_lock);
45}
46EXPORT_SYMBOL(zpool_register_driver);
47
48/**
49 * zpool_unregister_driver() - unregister a zpool implementation.
50 * @driver: driver to unregister.
51 *
52 * Module usage counting is used to prevent using a driver
53 * while/after unloading, so if this is called from module
54 * exit function, this should never fail; if called from
55 * other than the module exit function, and this returns
56 * failure, the driver is in use and must remain available.
57 */
58int zpool_unregister_driver(struct zpool_driver *driver)
59{
60 int ret = 0, refcount;
61
62 spin_lock(&drivers_lock);
63 refcount = atomic_read(&driver->refcount);
64 WARN_ON(refcount < 0);
65 if (refcount > 0)
66 ret = -EBUSY;
67 else
68 list_del(&driver->list);
69 spin_unlock(&drivers_lock);
70
71 return ret;
72}
73EXPORT_SYMBOL(zpool_unregister_driver);
74
75/* this assumes @type is null-terminated. */
76static struct zpool_driver *zpool_get_driver(const char *type)
77{
78 struct zpool_driver *driver;
79
80 spin_lock(&drivers_lock);
81 list_for_each_entry(driver, &drivers_head, list) {
82 if (!strcmp(driver->type, type)) {
83 bool got = try_module_get(driver->owner);
84
85 if (got)
86 atomic_inc(&driver->refcount);
87 spin_unlock(&drivers_lock);
88 return got ? driver : NULL;
89 }
90 }
91
92 spin_unlock(&drivers_lock);
93 return NULL;
94}
95
96static void zpool_put_driver(struct zpool_driver *driver)
97{
98 atomic_dec(&driver->refcount);
99 module_put(driver->owner);
100}
101
102/**
103 * zpool_has_pool() - Check if the pool driver is available
104 * @type: The type of the zpool to check (e.g. zbud, zsmalloc)
105 *
106 * This checks if the @type pool driver is available. This will try to load
107 * the requested module, if needed, but there is no guarantee the module will
108 * still be loaded and available immediately after calling. If this returns
109 * true, the caller should assume the pool is available, but must be prepared
110 * to handle the @zpool_create_pool() returning failure. However if this
111 * returns false, the caller should assume the requested pool type is not
112 * available; either the requested pool type module does not exist, or could
113 * not be loaded, and calling @zpool_create_pool() with the pool type will
114 * fail.
115 *
116 * The @type string must be null-terminated.
117 *
118 * Returns: true if @type pool is available, false if not
119 */
120bool zpool_has_pool(char *type)
121{
122 struct zpool_driver *driver = zpool_get_driver(type);
123
124 if (!driver) {
125 request_module("zpool-%s", type);
126 driver = zpool_get_driver(type);
127 }
128
129 if (!driver)
130 return false;
131
132 zpool_put_driver(driver);
133 return true;
134}
135EXPORT_SYMBOL(zpool_has_pool);
136
137/**
138 * zpool_create_pool() - Create a new zpool
139 * @type: The type of the zpool to create (e.g. zbud, zsmalloc)
140 * @name: The name of the zpool (e.g. zram0, zswap)
141 * @gfp: The GFP flags to use when allocating the pool.
142 * @ops: The optional ops callback.
143 *
144 * This creates a new zpool of the specified type. The gfp flags will be
145 * used when allocating memory, if the implementation supports it. If the
146 * ops param is NULL, then the created zpool will not be evictable.
147 *
148 * Implementations must guarantee this to be thread-safe.
149 *
150 * The @type and @name strings must be null-terminated.
151 *
152 * Returns: New zpool on success, NULL on failure.
153 */
154struct zpool *zpool_create_pool(const char *type, const char *name, gfp_t gfp,
155 const struct zpool_ops *ops)
156{
157 struct zpool_driver *driver;
158 struct zpool *zpool;
159
160 pr_debug("creating pool type %s\n", type);
161
162 driver = zpool_get_driver(type);
163
164 if (!driver) {
165 request_module("zpool-%s", type);
166 driver = zpool_get_driver(type);
167 }
168
169 if (!driver) {
170 pr_err("no driver for type %s\n", type);
171 return NULL;
172 }
173
174 zpool = kmalloc(sizeof(*zpool), gfp);
175 if (!zpool) {
176 pr_err("couldn't create zpool - out of memory\n");
177 zpool_put_driver(driver);
178 return NULL;
179 }
180
181 zpool->driver = driver;
182 zpool->pool = driver->create(name, gfp, ops, zpool);
183 zpool->ops = ops;
184 zpool->evictable = driver->shrink && ops && ops->evict;
185
186 if (!zpool->pool) {
187 pr_err("couldn't create %s pool\n", type);
188 zpool_put_driver(driver);
189 kfree(zpool);
190 return NULL;
191 }
192
193 pr_debug("created pool type %s\n", type);
194
195 spin_lock(&pools_lock);
196 list_add(&zpool->list, &pools_head);
197 spin_unlock(&pools_lock);
198
199 return zpool;
200}
201
202/**
203 * zpool_destroy_pool() - Destroy a zpool
204 * @zpool: The zpool to destroy.
205 *
206 * Implementations must guarantee this to be thread-safe,
207 * however only when destroying different pools. The same
208 * pool should only be destroyed once, and should not be used
209 * after it is destroyed.
210 *
211 * This destroys an existing zpool. The zpool should not be in use.
212 */
213void zpool_destroy_pool(struct zpool *zpool)
214{
215 pr_debug("destroying pool type %s\n", zpool->driver->type);
216
217 spin_lock(&pools_lock);
218 list_del(&zpool->list);
219 spin_unlock(&pools_lock);
220 zpool->driver->destroy(zpool->pool);
221 zpool_put_driver(zpool->driver);
222 kfree(zpool);
223}
224
225/**
226 * zpool_get_type() - Get the type of the zpool
227 * @zpool: The zpool to check
228 *
229 * This returns the type of the pool.
230 *
231 * Implementations must guarantee this to be thread-safe.
232 *
233 * Returns: The type of zpool.
234 */
235const char *zpool_get_type(struct zpool *zpool)
236{
237 return zpool->driver->type;
238}
239
240/**
241 * zpool_malloc() - Allocate memory
242 * @zpool: The zpool to allocate from.
243 * @size: The amount of memory to allocate.
244 * @gfp: The GFP flags to use when allocating memory.
245 * @handle: Pointer to the handle to set
246 *
247 * This allocates the requested amount of memory from the pool.
248 * The gfp flags will be used when allocating memory, if the
249 * implementation supports it. The provided @handle will be
250 * set to the allocated object handle.
251 *
252 * Implementations must guarantee this to be thread-safe.
253 *
254 * Returns: 0 on success, negative value on error.
255 */
256int zpool_malloc(struct zpool *zpool, size_t size, gfp_t gfp,
257 unsigned long *handle)
258{
259 return zpool->driver->malloc(zpool->pool, size, gfp, handle);
260}
261
262/**
263 * zpool_free() - Free previously allocated memory
264 * @zpool: The zpool that allocated the memory.
265 * @handle: The handle to the memory to free.
266 *
267 * This frees previously allocated memory. This does not guarantee
268 * that the pool will actually free memory, only that the memory
269 * in the pool will become available for use by the pool.
270 *
271 * Implementations must guarantee this to be thread-safe,
272 * however only when freeing different handles. The same
273 * handle should only be freed once, and should not be used
274 * after freeing.
275 */
276void zpool_free(struct zpool *zpool, unsigned long handle)
277{
278 zpool->driver->free(zpool->pool, handle);
279}
280
281/**
282 * zpool_shrink() - Shrink the pool size
283 * @zpool: The zpool to shrink.
284 * @pages: The number of pages to shrink the pool.
285 * @reclaimed: The number of pages successfully evicted.
286 *
287 * This attempts to shrink the actual memory size of the pool
288 * by evicting currently used handle(s). If the pool was
289 * created with no zpool_ops, or the evict call fails for any
290 * of the handles, this will fail. If non-NULL, the @reclaimed
291 * parameter will be set to the number of pages reclaimed,
292 * which may be more than the number of pages requested.
293 *
294 * Implementations must guarantee this to be thread-safe.
295 *
296 * Returns: 0 on success, negative value on error/failure.
297 */
298int zpool_shrink(struct zpool *zpool, unsigned int pages,
299 unsigned int *reclaimed)
300{
301 return zpool->driver->shrink ?
302 zpool->driver->shrink(zpool->pool, pages, reclaimed) : -EINVAL;
303}
304
305/**
306 * zpool_map_handle() - Map a previously allocated handle into memory
307 * @zpool: The zpool that the handle was allocated from
308 * @handle: The handle to map
309 * @mapmode: How the memory should be mapped
310 *
311 * This maps a previously allocated handle into memory. The @mapmode
312 * param indicates to the implementation how the memory will be
313 * used, i.e. read-only, write-only, read-write. If the
314 * implementation does not support it, the memory will be treated
315 * as read-write.
316 *
317 * This may hold locks, disable interrupts, and/or preemption,
318 * and the zpool_unmap_handle() must be called to undo those
319 * actions. The code that uses the mapped handle should complete
320 * its operatons on the mapped handle memory quickly and unmap
321 * as soon as possible. As the implementation may use per-cpu
322 * data, multiple handles should not be mapped concurrently on
323 * any cpu.
324 *
325 * Returns: A pointer to the handle's mapped memory area.
326 */
327void *zpool_map_handle(struct zpool *zpool, unsigned long handle,
328 enum zpool_mapmode mapmode)
329{
330 return zpool->driver->map(zpool->pool, handle, mapmode);
331}
332
333/**
334 * zpool_unmap_handle() - Unmap a previously mapped handle
335 * @zpool: The zpool that the handle was allocated from
336 * @handle: The handle to unmap
337 *
338 * This unmaps a previously mapped handle. Any locks or other
339 * actions that the implementation took in zpool_map_handle()
340 * will be undone here. The memory area returned from
341 * zpool_map_handle() should no longer be used after this.
342 */
343void zpool_unmap_handle(struct zpool *zpool, unsigned long handle)
344{
345 zpool->driver->unmap(zpool->pool, handle);
346}
347
348/**
349 * zpool_get_total_size() - The total size of the pool
350 * @zpool: The zpool to check
351 *
352 * This returns the total size in bytes of the pool.
353 *
354 * Returns: Total size of the zpool in bytes.
355 */
356u64 zpool_get_total_size(struct zpool *zpool)
357{
358 return zpool->driver->total_size(zpool->pool);
359}
360
361/**
362 * zpool_evictable() - Test if zpool is potentially evictable
363 * @zpool: The zpool to test
364 *
365 * Zpool is only potentially evictable when it's created with struct
366 * zpool_ops.evict and its driver implements struct zpool_driver.shrink.
367 *
368 * However, it doesn't necessarily mean driver will use zpool_ops.evict
369 * in its implementation of zpool_driver.shrink. It could do internal
370 * defragmentation instead.
371 *
372 * Returns: true if potentially evictable; false otherwise.
373 */
374bool zpool_evictable(struct zpool *zpool)
375{
376 return zpool->evictable;
377}
378
379MODULE_LICENSE("GPL");
380MODULE_AUTHOR("Dan Streetman <ddstreet@ieee.org>");
381MODULE_DESCRIPTION("Common API for compressed memory storage");
382