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Linux/mm/cleancache.c

  1 /*
  2  * Cleancache frontend
  3  *
  4  * This code provides the generic "frontend" layer to call a matching
  5  * "backend" driver implementation of cleancache.  See
  6  * Documentation/vm/cleancache.txt for more information.
  7  *
  8  * Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
  9  * Author: Dan Magenheimer
 10  *
 11  * This work is licensed under the terms of the GNU GPL, version 2.
 12  */
 13 
 14 #include <linux/module.h>
 15 #include <linux/fs.h>
 16 #include <linux/exportfs.h>
 17 #include <linux/mm.h>
 18 #include <linux/debugfs.h>
 19 #include <linux/cleancache.h>
 20 
 21 /*
 22  * cleancache_ops is set by cleancache_register_ops to contain the pointers
 23  * to the cleancache "backend" implementation functions.
 24  */
 25 static const struct cleancache_ops *cleancache_ops __read_mostly;
 26 
 27 /*
 28  * Counters available via /sys/kernel/debug/cleancache (if debugfs is
 29  * properly configured.  These are for information only so are not protected
 30  * against increment races.
 31  */
 32 static u64 cleancache_succ_gets;
 33 static u64 cleancache_failed_gets;
 34 static u64 cleancache_puts;
 35 static u64 cleancache_invalidates;
 36 
 37 static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
 38 {
 39         switch (sb->cleancache_poolid) {
 40         case CLEANCACHE_NO_BACKEND:
 41                 __cleancache_init_fs(sb);
 42                 break;
 43         case CLEANCACHE_NO_BACKEND_SHARED:
 44                 __cleancache_init_shared_fs(sb);
 45                 break;
 46         }
 47 }
 48 
 49 /*
 50  * Register operations for cleancache. Returns 0 on success.
 51  */
 52 int cleancache_register_ops(const struct cleancache_ops *ops)
 53 {
 54         if (cmpxchg(&cleancache_ops, NULL, ops))
 55                 return -EBUSY;
 56 
 57         /*
 58          * A cleancache backend can be built as a module and hence loaded after
 59          * a cleancache enabled filesystem has called cleancache_init_fs. To
 60          * handle such a scenario, here we call ->init_fs or ->init_shared_fs
 61          * for each active super block. To differentiate between local and
 62          * shared filesystems, we temporarily initialize sb->cleancache_poolid
 63          * to CLEANCACHE_NO_BACKEND or CLEANCACHE_NO_BACKEND_SHARED
 64          * respectively in case there is no backend registered at the time
 65          * cleancache_init_fs or cleancache_init_shared_fs is called.
 66          *
 67          * Since filesystems can be mounted concurrently with cleancache
 68          * backend registration, we have to be careful to guarantee that all
 69          * cleancache enabled filesystems that has been mounted by the time
 70          * cleancache_register_ops is called has got and all mounted later will
 71          * get cleancache_poolid. This is assured by the following statements
 72          * tied together:
 73          *
 74          * a) iterate_supers skips only those super blocks that has started
 75          *    ->kill_sb
 76          *
 77          * b) if iterate_supers encounters a super block that has not finished
 78          *    ->mount yet, it waits until it is finished
 79          *
 80          * c) cleancache_init_fs is called from ->mount and
 81          *    cleancache_invalidate_fs is called from ->kill_sb
 82          *
 83          * d) we call iterate_supers after cleancache_ops has been set
 84          *
 85          * From a) it follows that if iterate_supers skips a super block, then
 86          * either the super block is already dead, in which case we do not need
 87          * to bother initializing cleancache for it, or it was mounted after we
 88          * initiated iterate_supers. In the latter case, it must have seen
 89          * cleancache_ops set according to d) and initialized cleancache from
 90          * ->mount by itself according to c). This proves that we call
 91          * ->init_fs at least once for each active super block.
 92          *
 93          * From b) and c) it follows that if iterate_supers encounters a super
 94          * block that has already started ->init_fs, it will wait until ->mount
 95          * and hence ->init_fs has finished, then check cleancache_poolid, see
 96          * that it has already been set and therefore do nothing. This proves
 97          * that we call ->init_fs no more than once for each super block.
 98          *
 99          * Combined together, the last two paragraphs prove the function
100          * correctness.
101          *
102          * Note that various cleancache callbacks may proceed before this
103          * function is called or even concurrently with it, but since
104          * CLEANCACHE_NO_BACKEND is negative, they will all result in a noop
105          * until the corresponding ->init_fs has been actually called and
106          * cleancache_ops has been set.
107          */
108         iterate_supers(cleancache_register_ops_sb, NULL);
109         return 0;
110 }
111 EXPORT_SYMBOL(cleancache_register_ops);
112 
113 /* Called by a cleancache-enabled filesystem at time of mount */
114 void __cleancache_init_fs(struct super_block *sb)
115 {
116         int pool_id = CLEANCACHE_NO_BACKEND;
117 
118         if (cleancache_ops) {
119                 pool_id = cleancache_ops->init_fs(PAGE_SIZE);
120                 if (pool_id < 0)
121                         pool_id = CLEANCACHE_NO_POOL;
122         }
123         sb->cleancache_poolid = pool_id;
124 }
125 EXPORT_SYMBOL(__cleancache_init_fs);
126 
127 /* Called by a cleancache-enabled clustered filesystem at time of mount */
128 void __cleancache_init_shared_fs(struct super_block *sb)
129 {
130         int pool_id = CLEANCACHE_NO_BACKEND_SHARED;
131 
132         if (cleancache_ops) {
133                 pool_id = cleancache_ops->init_shared_fs(sb->s_uuid, PAGE_SIZE);
134                 if (pool_id < 0)
135                         pool_id = CLEANCACHE_NO_POOL;
136         }
137         sb->cleancache_poolid = pool_id;
138 }
139 EXPORT_SYMBOL(__cleancache_init_shared_fs);
140 
141 /*
142  * If the filesystem uses exportable filehandles, use the filehandle as
143  * the key, else use the inode number.
144  */
145 static int cleancache_get_key(struct inode *inode,
146                               struct cleancache_filekey *key)
147 {
148         int (*fhfn)(struct inode *, __u32 *fh, int *, struct inode *);
149         int len = 0, maxlen = CLEANCACHE_KEY_MAX;
150         struct super_block *sb = inode->i_sb;
151 
152         key->u.ino = inode->i_ino;
153         if (sb->s_export_op != NULL) {
154                 fhfn = sb->s_export_op->encode_fh;
155                 if  (fhfn) {
156                         len = (*fhfn)(inode, &key->u.fh[0], &maxlen, NULL);
157                         if (len <= FILEID_ROOT || len == FILEID_INVALID)
158                                 return -1;
159                         if (maxlen > CLEANCACHE_KEY_MAX)
160                                 return -1;
161                 }
162         }
163         return 0;
164 }
165 
166 /*
167  * "Get" data from cleancache associated with the poolid/inode/index
168  * that were specified when the data was put to cleanache and, if
169  * successful, use it to fill the specified page with data and return 0.
170  * The pageframe is unchanged and returns -1 if the get fails.
171  * Page must be locked by caller.
172  *
173  * The function has two checks before any action is taken - whether
174  * a backend is registered and whether the sb->cleancache_poolid
175  * is correct.
176  */
177 int __cleancache_get_page(struct page *page)
178 {
179         int ret = -1;
180         int pool_id;
181         struct cleancache_filekey key = { .u.key = { 0 } };
182 
183         if (!cleancache_ops) {
184                 cleancache_failed_gets++;
185                 goto out;
186         }
187 
188         VM_BUG_ON_PAGE(!PageLocked(page), page);
189         pool_id = page->mapping->host->i_sb->cleancache_poolid;
190         if (pool_id < 0)
191                 goto out;
192 
193         if (cleancache_get_key(page->mapping->host, &key) < 0)
194                 goto out;
195 
196         ret = cleancache_ops->get_page(pool_id, key, page->index, page);
197         if (ret == 0)
198                 cleancache_succ_gets++;
199         else
200                 cleancache_failed_gets++;
201 out:
202         return ret;
203 }
204 EXPORT_SYMBOL(__cleancache_get_page);
205 
206 /*
207  * "Put" data from a page to cleancache and associate it with the
208  * (previously-obtained per-filesystem) poolid and the page's,
209  * inode and page index.  Page must be locked.  Note that a put_page
210  * always "succeeds", though a subsequent get_page may succeed or fail.
211  *
212  * The function has two checks before any action is taken - whether
213  * a backend is registered and whether the sb->cleancache_poolid
214  * is correct.
215  */
216 void __cleancache_put_page(struct page *page)
217 {
218         int pool_id;
219         struct cleancache_filekey key = { .u.key = { 0 } };
220 
221         if (!cleancache_ops) {
222                 cleancache_puts++;
223                 return;
224         }
225 
226         VM_BUG_ON_PAGE(!PageLocked(page), page);
227         pool_id = page->mapping->host->i_sb->cleancache_poolid;
228         if (pool_id >= 0 &&
229                 cleancache_get_key(page->mapping->host, &key) >= 0) {
230                 cleancache_ops->put_page(pool_id, key, page->index, page);
231                 cleancache_puts++;
232         }
233 }
234 EXPORT_SYMBOL(__cleancache_put_page);
235 
236 /*
237  * Invalidate any data from cleancache associated with the poolid and the
238  * page's inode and page index so that a subsequent "get" will fail.
239  *
240  * The function has two checks before any action is taken - whether
241  * a backend is registered and whether the sb->cleancache_poolid
242  * is correct.
243  */
244 void __cleancache_invalidate_page(struct address_space *mapping,
245                                         struct page *page)
246 {
247         /* careful... page->mapping is NULL sometimes when this is called */
248         int pool_id = mapping->host->i_sb->cleancache_poolid;
249         struct cleancache_filekey key = { .u.key = { 0 } };
250 
251         if (!cleancache_ops)
252                 return;
253 
254         if (pool_id >= 0) {
255                 VM_BUG_ON_PAGE(!PageLocked(page), page);
256                 if (cleancache_get_key(mapping->host, &key) >= 0) {
257                         cleancache_ops->invalidate_page(pool_id,
258                                         key, page->index);
259                         cleancache_invalidates++;
260                 }
261         }
262 }
263 EXPORT_SYMBOL(__cleancache_invalidate_page);
264 
265 /*
266  * Invalidate all data from cleancache associated with the poolid and the
267  * mappings's inode so that all subsequent gets to this poolid/inode
268  * will fail.
269  *
270  * The function has two checks before any action is taken - whether
271  * a backend is registered and whether the sb->cleancache_poolid
272  * is correct.
273  */
274 void __cleancache_invalidate_inode(struct address_space *mapping)
275 {
276         int pool_id = mapping->host->i_sb->cleancache_poolid;
277         struct cleancache_filekey key = { .u.key = { 0 } };
278 
279         if (!cleancache_ops)
280                 return;
281 
282         if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
283                 cleancache_ops->invalidate_inode(pool_id, key);
284 }
285 EXPORT_SYMBOL(__cleancache_invalidate_inode);
286 
287 /*
288  * Called by any cleancache-enabled filesystem at time of unmount;
289  * note that pool_id is surrendered and may be returned by a subsequent
290  * cleancache_init_fs or cleancache_init_shared_fs.
291  */
292 void __cleancache_invalidate_fs(struct super_block *sb)
293 {
294         int pool_id;
295 
296         pool_id = sb->cleancache_poolid;
297         sb->cleancache_poolid = CLEANCACHE_NO_POOL;
298 
299         if (cleancache_ops && pool_id >= 0)
300                 cleancache_ops->invalidate_fs(pool_id);
301 }
302 EXPORT_SYMBOL(__cleancache_invalidate_fs);
303 
304 static int __init init_cleancache(void)
305 {
306 #ifdef CONFIG_DEBUG_FS
307         struct dentry *root = debugfs_create_dir("cleancache", NULL);
308         if (root == NULL)
309                 return -ENXIO;
310         debugfs_create_u64("succ_gets", S_IRUGO, root, &cleancache_succ_gets);
311         debugfs_create_u64("failed_gets", S_IRUGO,
312                                 root, &cleancache_failed_gets);
313         debugfs_create_u64("puts", S_IRUGO, root, &cleancache_puts);
314         debugfs_create_u64("invalidates", S_IRUGO,
315                                 root, &cleancache_invalidates);
316 #endif
317         return 0;
318 }
319 module_init(init_cleancache)
320 

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