1 ======= 1 =======
2 Locking 2 Locking
3 ======= 3 =======
4 4
5 The text below describes the locking rules for 5 The text below describes the locking rules for VFS-related methods.
6 It is (believed to be) up-to-date. *Please*, i 6 It is (believed to be) up-to-date. *Please*, if you change anything in
7 prototypes or locking protocols - update this 7 prototypes or locking protocols - update this file. And update the relevant
8 instances in the tree, don't leave that to mai 8 instances in the tree, don't leave that to maintainers of filesystems/devices/
9 etc. At the very least, put the list of dubiou 9 etc. At the very least, put the list of dubious cases in the end of this file.
10 Don't turn it into log - maintainers of out-of 10 Don't turn it into log - maintainers of out-of-the-tree code are supposed to
11 be able to use diff(1). 11 be able to use diff(1).
12 12
13 Thing currently missing here: socket operation 13 Thing currently missing here: socket operations. Alexey?
14 14
15 dentry_operations 15 dentry_operations
16 ================= 16 =================
17 17
18 prototypes:: 18 prototypes::
19 19
20 int (*d_revalidate)(struct dentry *, u 20 int (*d_revalidate)(struct dentry *, unsigned int);
21 int (*d_weak_revalidate)(struct dentry 21 int (*d_weak_revalidate)(struct dentry *, unsigned int);
22 int (*d_hash)(const struct dentry *, s 22 int (*d_hash)(const struct dentry *, struct qstr *);
23 int (*d_compare)(const struct dentry * 23 int (*d_compare)(const struct dentry *,
24 unsigned int, const ch 24 unsigned int, const char *, const struct qstr *);
25 int (*d_delete)(struct dentry *); 25 int (*d_delete)(struct dentry *);
26 int (*d_init)(struct dentry *); 26 int (*d_init)(struct dentry *);
27 void (*d_release)(struct dentry *); 27 void (*d_release)(struct dentry *);
28 void (*d_iput)(struct dentry *, struct 28 void (*d_iput)(struct dentry *, struct inode *);
29 char *(*d_dname)((struct dentry *dentr 29 char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
30 struct vfsmount *(*d_automount)(struct 30 struct vfsmount *(*d_automount)(struct path *path);
31 int (*d_manage)(const struct path *, b 31 int (*d_manage)(const struct path *, bool);
32 struct dentry *(*d_real)(struct dentry !! 32 struct dentry *(*d_real)(struct dentry *, const struct inode *);
33 33
34 locking rules: 34 locking rules:
35 35
36 ================== =========== ======== 36 ================== =========== ======== ============== ========
37 ops rename_lock ->d_lock 37 ops rename_lock ->d_lock may block rcu-walk
38 ================== =========== ======== 38 ================== =========== ======== ============== ========
39 d_revalidate: no no 39 d_revalidate: no no yes (ref-walk) maybe
40 d_weak_revalidate: no no 40 d_weak_revalidate: no no yes no
41 d_hash no no 41 d_hash no no no maybe
42 d_compare: yes no 42 d_compare: yes no no maybe
43 d_delete: no yes 43 d_delete: no yes no no
44 d_init: no no 44 d_init: no no yes no
45 d_release: no no 45 d_release: no no yes no
46 d_prune: no yes 46 d_prune: no yes no no
47 d_iput: no no 47 d_iput: no no yes no
48 d_dname: no no 48 d_dname: no no no no
49 d_automount: no no 49 d_automount: no no yes no
50 d_manage: no no 50 d_manage: no no yes (ref-walk) maybe
51 d_real no no 51 d_real no no yes no
52 ================== =========== ======== 52 ================== =========== ======== ============== ========
53 53
54 inode_operations 54 inode_operations
55 ================ 55 ================
56 56
57 prototypes:: 57 prototypes::
58 58
59 int (*create) (struct mnt_idmap *, str !! 59 int (*create) (struct inode *,struct dentry *,umode_t, bool);
60 struct dentry * (*lookup) (struct inod 60 struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
61 int (*link) (struct dentry *,struct in 61 int (*link) (struct dentry *,struct inode *,struct dentry *);
62 int (*unlink) (struct inode *,struct d 62 int (*unlink) (struct inode *,struct dentry *);
63 int (*symlink) (struct mnt_idmap *, st !! 63 int (*symlink) (struct inode *,struct dentry *,const char *);
64 int (*mkdir) (struct mnt_idmap *, stru !! 64 int (*mkdir) (struct inode *,struct dentry *,umode_t);
65 int (*rmdir) (struct inode *,struct de 65 int (*rmdir) (struct inode *,struct dentry *);
66 int (*mknod) (struct mnt_idmap *, stru !! 66 int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
67 int (*rename) (struct mnt_idmap *, str !! 67 int (*rename) (struct inode *, struct dentry *,
68 struct inode *, struct 68 struct inode *, struct dentry *, unsigned int);
69 int (*readlink) (struct dentry *, char 69 int (*readlink) (struct dentry *, char __user *,int);
70 const char *(*get_link) (struct dentry 70 const char *(*get_link) (struct dentry *, struct inode *, struct delayed_call *);
71 void (*truncate) (struct inode *); 71 void (*truncate) (struct inode *);
72 int (*permission) (struct mnt_idmap *, !! 72 int (*permission) (struct inode *, int, unsigned int);
73 struct posix_acl * (*get_inode_acl)(st !! 73 int (*get_acl)(struct inode *, int);
74 int (*setattr) (struct mnt_idmap *, st !! 74 int (*setattr) (struct dentry *, struct iattr *);
75 int (*getattr) (struct mnt_idmap *, co !! 75 int (*getattr) (const struct path *, struct kstat *, u32, unsigned int);
76 ssize_t (*listxattr) (struct dentry *, 76 ssize_t (*listxattr) (struct dentry *, char *, size_t);
77 int (*fiemap)(struct inode *, struct f 77 int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
78 void (*update_time)(struct inode *, st 78 void (*update_time)(struct inode *, struct timespec *, int);
79 int (*atomic_open)(struct inode *, str 79 int (*atomic_open)(struct inode *, struct dentry *,
80 struct file *, 80 struct file *, unsigned open_flag,
81 umode_t create 81 umode_t create_mode);
82 int (*tmpfile) (struct mnt_idmap *, st !! 82 int (*tmpfile) (struct inode *, struct dentry *, umode_t);
83 struct file *, umode_t !! 83 int (*fileattr_set)(struct user_namespace *mnt_userns,
84 int (*fileattr_set)(struct mnt_idmap * <<
85 struct dentry *den 84 struct dentry *dentry, struct fileattr *fa);
86 int (*fileattr_get)(struct dentry *den 85 int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
87 struct posix_acl * (*get_acl)(struct m <<
88 struct offset_ctx *(*get_offset_ctx)(s <<
89 86
90 locking rules: 87 locking rules:
91 all may block 88 all may block
92 89
93 ============== ============================== !! 90 ============= =============================================
94 ops i_rwsem(inode) 91 ops i_rwsem(inode)
95 ============== ============================== !! 92 ============= =============================================
96 lookup: shared 93 lookup: shared
97 create: exclusive 94 create: exclusive
98 link: exclusive (both) 95 link: exclusive (both)
99 mknod: exclusive 96 mknod: exclusive
100 symlink: exclusive 97 symlink: exclusive
101 mkdir: exclusive 98 mkdir: exclusive
102 unlink: exclusive (both) 99 unlink: exclusive (both)
103 rmdir: exclusive (both)(see below) 100 rmdir: exclusive (both)(see below)
104 rename: exclusive (both parents, some !! 101 rename: exclusive (all) (see below)
105 readlink: no 102 readlink: no
106 get_link: no 103 get_link: no
107 setattr: exclusive 104 setattr: exclusive
108 permission: no (may not block if called in 105 permission: no (may not block if called in rcu-walk mode)
109 get_inode_acl: no <<
110 get_acl: no 106 get_acl: no
111 getattr: no 107 getattr: no
112 listxattr: no 108 listxattr: no
113 fiemap: no 109 fiemap: no
114 update_time: no 110 update_time: no
115 atomic_open: shared (exclusive if O_CREAT i 111 atomic_open: shared (exclusive if O_CREAT is set in open flags)
116 tmpfile: no 112 tmpfile: no
117 fileattr_get: no or exclusive 113 fileattr_get: no or exclusive
118 fileattr_set: exclusive 114 fileattr_set: exclusive
119 get_offset_ctx no !! 115 ============= =============================================
120 ============== ============================== <<
121 116
122 117
123 Additionally, ->rmdir(), ->unlink() an 118 Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
124 exclusive on victim. 119 exclusive on victim.
125 cross-directory ->rename() has (per-su 120 cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
126 ->unlink() and ->rename() have ->i_rws <<
127 involved. <<
128 ->rename() has ->i_rwsem exclusive on <<
129 121
130 See Documentation/filesystems/directory-lockin 122 See Documentation/filesystems/directory-locking.rst for more detailed discussion
131 of the locking scheme for directory operations 123 of the locking scheme for directory operations.
132 124
133 xattr_handler operations 125 xattr_handler operations
134 ======================== 126 ========================
135 127
136 prototypes:: 128 prototypes::
137 129
138 bool (*list)(struct dentry *dentry); 130 bool (*list)(struct dentry *dentry);
139 int (*get)(const struct xattr_handler 131 int (*get)(const struct xattr_handler *handler, struct dentry *dentry,
140 struct inode *inode, const 132 struct inode *inode, const char *name, void *buffer,
141 size_t size); 133 size_t size);
142 int (*set)(const struct xattr_handler 134 int (*set)(const struct xattr_handler *handler,
143 struct mnt_idmap *idmap, !! 135 struct user_namespace *mnt_userns,
144 struct dentry *dentry, stru 136 struct dentry *dentry, struct inode *inode, const char *name,
145 const void *buffer, size_t 137 const void *buffer, size_t size, int flags);
146 138
147 locking rules: 139 locking rules:
148 all may block 140 all may block
149 141
150 ===== ============== 142 ===== ==============
151 ops i_rwsem(inode) 143 ops i_rwsem(inode)
152 ===== ============== 144 ===== ==============
153 list: no 145 list: no
154 get: no 146 get: no
155 set: exclusive 147 set: exclusive
156 ===== ============== 148 ===== ==============
157 149
158 super_operations 150 super_operations
159 ================ 151 ================
160 152
161 prototypes:: 153 prototypes::
162 154
163 struct inode *(*alloc_inode)(struct su 155 struct inode *(*alloc_inode)(struct super_block *sb);
164 void (*free_inode)(struct inode *); 156 void (*free_inode)(struct inode *);
165 void (*destroy_inode)(struct inode *); 157 void (*destroy_inode)(struct inode *);
166 void (*dirty_inode) (struct inode *, i 158 void (*dirty_inode) (struct inode *, int flags);
167 int (*write_inode) (struct inode *, st 159 int (*write_inode) (struct inode *, struct writeback_control *wbc);
168 int (*drop_inode) (struct inode *); 160 int (*drop_inode) (struct inode *);
169 void (*evict_inode) (struct inode *); 161 void (*evict_inode) (struct inode *);
170 void (*put_super) (struct super_block 162 void (*put_super) (struct super_block *);
171 int (*sync_fs)(struct super_block *sb, 163 int (*sync_fs)(struct super_block *sb, int wait);
172 int (*freeze_fs) (struct super_block * 164 int (*freeze_fs) (struct super_block *);
173 int (*unfreeze_fs) (struct super_block 165 int (*unfreeze_fs) (struct super_block *);
174 int (*statfs) (struct dentry *, struct 166 int (*statfs) (struct dentry *, struct kstatfs *);
175 int (*remount_fs) (struct super_block 167 int (*remount_fs) (struct super_block *, int *, char *);
176 void (*umount_begin) (struct super_blo 168 void (*umount_begin) (struct super_block *);
177 int (*show_options)(struct seq_file *, 169 int (*show_options)(struct seq_file *, struct dentry *);
178 ssize_t (*quota_read)(struct super_blo 170 ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
179 ssize_t (*quota_write)(struct super_bl 171 ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
>> 172 int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
180 173
181 locking rules: 174 locking rules:
182 All may block [not true, see below] 175 All may block [not true, see below]
183 176
184 ====================== ============ ====== 177 ====================== ============ ========================
185 ops s_umount note 178 ops s_umount note
186 ====================== ============ ====== 179 ====================== ============ ========================
187 alloc_inode: 180 alloc_inode:
188 free_inode: called 181 free_inode: called from RCU callback
189 destroy_inode: 182 destroy_inode:
190 dirty_inode: 183 dirty_inode:
191 write_inode: 184 write_inode:
192 drop_inode: !!!ino 185 drop_inode: !!!inode->i_lock!!!
193 evict_inode: 186 evict_inode:
194 put_super: write 187 put_super: write
195 sync_fs: read 188 sync_fs: read
196 freeze_fs: write 189 freeze_fs: write
197 unfreeze_fs: write 190 unfreeze_fs: write
198 statfs: maybe(read) (see b 191 statfs: maybe(read) (see below)
199 remount_fs: write 192 remount_fs: write
200 umount_begin: no 193 umount_begin: no
201 show_options: no (names 194 show_options: no (namespace_sem)
202 quota_read: no (see b 195 quota_read: no (see below)
203 quota_write: no (see b 196 quota_write: no (see below)
>> 197 bdev_try_to_free_page: no (see below)
204 ====================== ============ ====== 198 ====================== ============ ========================
205 199
206 ->statfs() has s_umount (shared) when called b 200 ->statfs() has s_umount (shared) when called by ustat(2) (native or
207 compat), but that's an accident of bad API; s_ 201 compat), but that's an accident of bad API; s_umount is used to pin
208 the superblock down when we only have dev_t gi 202 the superblock down when we only have dev_t given us by userland to
209 identify the superblock. Everything else (sta 203 identify the superblock. Everything else (statfs(), fstatfs(), etc.)
210 doesn't hold it when calling ->statfs() - supe 204 doesn't hold it when calling ->statfs() - superblock is pinned down
211 by resolving the pathname passed to syscall. 205 by resolving the pathname passed to syscall.
212 206
213 ->quota_read() and ->quota_write() functions a 207 ->quota_read() and ->quota_write() functions are both guaranteed to
214 be the only ones operating on the quota file b 208 be the only ones operating on the quota file by the quota code (via
215 dqio_sem) (unless an admin really wants to scr 209 dqio_sem) (unless an admin really wants to screw up something and
216 writes to quota files with quotas on). For oth 210 writes to quota files with quotas on). For other details about locking
217 see also dquot_operations section. 211 see also dquot_operations section.
218 212
>> 213 ->bdev_try_to_free_page is called from the ->releasepage handler of
>> 214 the block device inode. See there for more details.
>> 215
219 file_system_type 216 file_system_type
220 ================ 217 ================
221 218
222 prototypes:: 219 prototypes::
223 220
224 struct dentry *(*mount) (struct file_s 221 struct dentry *(*mount) (struct file_system_type *, int,
225 const char *, void *); 222 const char *, void *);
226 void (*kill_sb) (struct super_block *) 223 void (*kill_sb) (struct super_block *);
227 224
228 locking rules: 225 locking rules:
229 226
230 ======= ========= 227 ======= =========
231 ops may block 228 ops may block
232 ======= ========= 229 ======= =========
233 mount yes 230 mount yes
234 kill_sb yes 231 kill_sb yes
235 ======= ========= 232 ======= =========
236 233
237 ->mount() returns ERR_PTR or the root dentry; 234 ->mount() returns ERR_PTR or the root dentry; its superblock should be locked
238 on return. 235 on return.
239 236
240 ->kill_sb() takes a write-locked superblock, d 237 ->kill_sb() takes a write-locked superblock, does all shutdown work on it,
241 unlocks and drops the reference. 238 unlocks and drops the reference.
242 239
243 address_space_operations 240 address_space_operations
244 ======================== 241 ========================
245 prototypes:: 242 prototypes::
246 243
247 int (*writepage)(struct page *page, st 244 int (*writepage)(struct page *page, struct writeback_control *wbc);
248 int (*read_folio)(struct file *, struc !! 245 int (*readpage)(struct file *, struct page *);
249 int (*writepages)(struct address_space 246 int (*writepages)(struct address_space *, struct writeback_control *);
250 bool (*dirty_folio)(struct address_spa !! 247 int (*set_page_dirty)(struct page *page);
251 void (*readahead)(struct readahead_con 248 void (*readahead)(struct readahead_control *);
>> 249 int (*readpages)(struct file *filp, struct address_space *mapping,
>> 250 struct list_head *pages, unsigned nr_pages);
252 int (*write_begin)(struct file *, stru 251 int (*write_begin)(struct file *, struct address_space *mapping,
253 loff_t pos, un !! 252 loff_t pos, unsigned len, unsigned flags,
254 struct folio * !! 253 struct page **pagep, void **fsdata);
255 int (*write_end)(struct file *, struct 254 int (*write_end)(struct file *, struct address_space *mapping,
256 loff_t pos, un 255 loff_t pos, unsigned len, unsigned copied,
257 struct folio * !! 256 struct page *page, void *fsdata);
258 sector_t (*bmap)(struct address_space 257 sector_t (*bmap)(struct address_space *, sector_t);
259 void (*invalidate_folio) (struct folio !! 258 void (*invalidatepage) (struct page *, unsigned int, unsigned int);
260 bool (*release_folio)(struct folio *, !! 259 int (*releasepage) (struct page *, int);
261 void (*free_folio)(struct folio *); !! 260 void (*freepage)(struct page *);
262 int (*direct_IO)(struct kiocb *, struc 261 int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
263 int (*migrate_folio)(struct address_sp !! 262 bool (*isolate_page) (struct page *, isolate_mode_t);
264 struct folio *src, enu !! 263 int (*migratepage)(struct address_space *, struct page *, struct page *);
265 int (*launder_folio)(struct folio *); !! 264 void (*putback_page) (struct page *);
266 bool (*is_partially_uptodate)(struct f !! 265 int (*launder_page)(struct page *);
267 int (*error_remove_folio)(struct addre !! 266 int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
268 int (*swap_activate)(struct swap_info_ !! 267 int (*error_remove_page)(struct address_space *, struct page *);
>> 268 int (*swap_activate)(struct file *);
269 int (*swap_deactivate)(struct file *); 269 int (*swap_deactivate)(struct file *);
270 int (*swap_rw)(struct kiocb *iocb, str <<
271 270
272 locking rules: 271 locking rules:
273 All except dirty_folio and free_folio !! 272 All except set_page_dirty and freepage may block
274 273
275 ====================== ====================== !! 274 ====================== ======================== =========
276 ops folio locked !! 275 ops PageLocked(page) i_rwsem
277 ====================== ====================== !! 276 ====================== ======================== =========
278 writepage: yes, unlocks (see belo 277 writepage: yes, unlocks (see below)
279 read_folio: yes, unlocks !! 278 readpage: yes, unlocks
280 writepages: 279 writepages:
281 dirty_folio: maybe !! 280 set_page_dirty no
282 readahead: yes, unlocks !! 281 readahead: yes, unlocks
283 write_begin: locks the folio !! 282 readpages: no
>> 283 write_begin: locks the page exclusive
284 write_end: yes, unlocks 284 write_end: yes, unlocks exclusive
285 bmap: 285 bmap:
286 invalidate_folio: yes !! 286 invalidatepage: yes
287 release_folio: yes !! 287 releasepage: yes
288 free_folio: yes !! 288 freepage: yes
289 direct_IO: 289 direct_IO:
290 migrate_folio: yes (both) !! 290 isolate_page: yes
291 launder_folio: yes !! 291 migratepage: yes (both)
>> 292 putback_page: yes
>> 293 launder_page: yes
292 is_partially_uptodate: yes 294 is_partially_uptodate: yes
293 error_remove_folio: yes !! 295 error_remove_page: yes
294 swap_activate: no 296 swap_activate: no
295 swap_deactivate: no 297 swap_deactivate: no
296 swap_rw: yes, unlocks !! 298 ====================== ======================== =========
297 ====================== ====================== <<
298 299
299 ->write_begin(), ->write_end() and ->read_foli !! 300 ->write_begin(), ->write_end() and ->readpage() may be called from
300 the request handler (/dev/loop). 301 the request handler (/dev/loop).
301 302
302 ->read_folio() unlocks the folio, either synch !! 303 ->readpage() unlocks the page, either synchronously or via I/O
303 completion. 304 completion.
304 305
305 ->readahead() unlocks the folios that I/O is a !! 306 ->readahead() unlocks the pages that I/O is attempted on like ->readpage().
>> 307
>> 308 ->readpages() populates the pagecache with the passed pages and starts
>> 309 I/O against them. They come unlocked upon I/O completion.
306 310
307 ->writepage() is used for two purposes: for "m 311 ->writepage() is used for two purposes: for "memory cleansing" and for
308 "sync". These are quite different operations 312 "sync". These are quite different operations and the behaviour may differ
309 depending upon the mode. 313 depending upon the mode.
310 314
311 If writepage is called for sync (wbc->sync_mod 315 If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
312 it *must* start I/O against the page, even if 316 it *must* start I/O against the page, even if that would involve
313 blocking on in-progress I/O. 317 blocking on in-progress I/O.
314 318
315 If writepage is called for memory cleansing (s 319 If writepage is called for memory cleansing (sync_mode ==
316 WBC_SYNC_NONE) then its role is to get as much 320 WBC_SYNC_NONE) then its role is to get as much writeout underway as
317 possible. So writepage should try to avoid bl 321 possible. So writepage should try to avoid blocking against
318 currently-in-progress I/O. 322 currently-in-progress I/O.
319 323
320 If the filesystem is not called for "sync" and 324 If the filesystem is not called for "sync" and it determines that it
321 would need to block against in-progress I/O to 325 would need to block against in-progress I/O to be able to start new I/O
322 against the page the filesystem should redirty 326 against the page the filesystem should redirty the page with
323 redirty_page_for_writepage(), then unlock the 327 redirty_page_for_writepage(), then unlock the page and return zero.
324 This may also be done to avoid internal deadlo 328 This may also be done to avoid internal deadlocks, but rarely.
325 329
326 If the filesystem is called for sync then it m 330 If the filesystem is called for sync then it must wait on any
327 in-progress I/O and then start new I/O. 331 in-progress I/O and then start new I/O.
328 332
329 The filesystem should unlock the page synchron 333 The filesystem should unlock the page synchronously, before returning to the
330 caller, unless ->writepage() returns special W 334 caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
331 value. WRITEPAGE_ACTIVATE means that page cann 335 value. WRITEPAGE_ACTIVATE means that page cannot really be written out
332 currently, and VM should stop calling ->writep 336 currently, and VM should stop calling ->writepage() on this page for some
333 time. VM does this by moving page to the head 337 time. VM does this by moving page to the head of the active list, hence the
334 name. 338 name.
335 339
336 Unless the filesystem is going to redirty_page 340 Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
337 and return zero, writepage *must* run set_page 341 and return zero, writepage *must* run set_page_writeback() against the page,
338 followed by unlocking it. Once set_page_write 342 followed by unlocking it. Once set_page_writeback() has been run against the
339 page, write I/O can be submitted and the write 343 page, write I/O can be submitted and the write I/O completion handler must run
340 end_page_writeback() once the I/O is complete. 344 end_page_writeback() once the I/O is complete. If no I/O is submitted, the
341 filesystem must run end_page_writeback() again 345 filesystem must run end_page_writeback() against the page before returning from
342 writepage. 346 writepage.
343 347
344 That is: after 2.5.12, pages which are under w 348 That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
345 if the filesystem needs the page to be locked 349 if the filesystem needs the page to be locked during writeout, that is ok, too,
346 the page is allowed to be unlocked at any poin 350 the page is allowed to be unlocked at any point in time between the calls to
347 set_page_writeback() and end_page_writeback(). 351 set_page_writeback() and end_page_writeback().
348 352
349 Note, failure to run either redirty_page_for_w 353 Note, failure to run either redirty_page_for_writepage() or the combination of
350 set_page_writeback()/end_page_writeback() on a 354 set_page_writeback()/end_page_writeback() on a page submitted to writepage
351 will leave the page itself marked clean but it 355 will leave the page itself marked clean but it will be tagged as dirty in the
352 radix tree. This incoherency can lead to all 356 radix tree. This incoherency can lead to all sorts of hard-to-debug problems
353 in the filesystem like having dirty inodes at 357 in the filesystem like having dirty inodes at umount and losing written data.
354 358
355 ->writepages() is used for periodic writeback 359 ->writepages() is used for periodic writeback and for syscall-initiated
356 sync operations. The address_space should sta 360 sync operations. The address_space should start I/O against at least
357 ``*nr_to_write`` pages. ``*nr_to_write`` must 361 ``*nr_to_write`` pages. ``*nr_to_write`` must be decremented for each page
358 which is written. The address_space implement 362 which is written. The address_space implementation may write more (or less)
359 pages than ``*nr_to_write`` asks for, but it s 363 pages than ``*nr_to_write`` asks for, but it should try to be reasonably close.
360 If nr_to_write is NULL, all dirty pages must b 364 If nr_to_write is NULL, all dirty pages must be written.
361 365
362 writepages should _only_ write pages which are 366 writepages should _only_ write pages which are present on
363 mapping->io_pages. 367 mapping->io_pages.
364 368
365 ->dirty_folio() is called from various places !! 369 ->set_page_dirty() is called from various places in the kernel
366 the target folio is marked as needing writebac !! 370 when the target page is marked as needing writeback. It may be called
367 truncated because either the caller holds the !! 371 under spinlock (it cannot block) and is sometimes called with the page
368 has found the folio while holding the page tab !! 372 not locked.
369 truncation. <<
370 373
371 ->bmap() is currently used by legacy ioctl() ( 374 ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
372 filesystems and by the swapper. The latter wil 375 filesystems and by the swapper. The latter will eventually go away. Please,
373 keep it that way and don't breed new callers. 376 keep it that way and don't breed new callers.
374 377
375 ->invalidate_folio() is called when the filesy !! 378 ->invalidatepage() is called when the filesystem must attempt to drop
376 some or all of the buffers from the page when 379 some or all of the buffers from the page when it is being truncated. It
377 returns zero on success. The filesystem must !! 380 returns zero on success. If ->invalidatepage is zero, the kernel uses
378 invalidate_lock before invalidating page cache !! 381 block_invalidatepage() instead.
379 path (and thus calling into ->invalidate_folio <<
380 cache invalidation and page cache filling func <<
381 <<
382 ->release_folio() is called when the MM wants <<
383 folio that would invalidate the filesystem's p <<
384 it may be about to be removed from the address <<
385 is locked and not under writeback. It may be <<
386 is not usually used for allocation, but rather <<
387 filesystem may do to attempt to free the priva <<
388 return false to indicate that the folio's priv <<
389 If it returns true, it should have already rem <<
390 the folio. If a filesystem does not provide a <<
391 the pagecache will assume that private data is <<
392 try_to_free_buffers(). <<
393 382
394 ->free_folio() is called when the kernel has d !! 383 ->releasepage() is called when the kernel is about to try to drop the
>> 384 buffers from the page in preparation for freeing it. It returns zero to
>> 385 indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
>> 386 the kernel assumes that the fs has no private interest in the buffers.
>> 387
>> 388 ->freepage() is called when the kernel is done dropping the page
395 from the page cache. 389 from the page cache.
396 390
397 ->launder_folio() may be called prior to relea !! 391 ->launder_page() may be called prior to releasing a page if
398 it is still found to be dirty. It returns zero !! 392 it is still found to be dirty. It returns zero if the page was successfully
399 cleaned, or an error value if not. Note that i !! 393 cleaned, or an error value if not. Note that in order to prevent the page
400 getting mapped back in and redirtied, it needs 394 getting mapped back in and redirtied, it needs to be kept locked
401 across the entire operation. 395 across the entire operation.
402 396
403 ->swap_activate() will be called to prepare th !! 397 ->swap_activate will be called with a non-zero argument on
404 should perform any validation and preparation !! 398 files backing (non block device backed) swapfiles. A return value
405 writes can be performed with minimal memory al !! 399 of zero indicates success, in which case this file can be used for
406 add_swap_extent(), or the helper iomap_swapfil !! 400 backing swapspace. The swapspace operations will be proxied to the
407 the number of extents added. If IO should be !! 401 address space operations.
408 ->swap_rw(), it should set SWP_FS_OPS, otherwi <<
409 directly to the block device ``sis->bdev``. <<
410 402
411 ->swap_deactivate() will be called in the sys_ 403 ->swap_deactivate() will be called in the sys_swapoff()
412 path after ->swap_activate() returned success. 404 path after ->swap_activate() returned success.
413 405
414 ->swap_rw will be called for swap IO if SWP_FS <<
415 <<
416 file_lock_operations 406 file_lock_operations
417 ==================== 407 ====================
418 408
419 prototypes:: 409 prototypes::
420 410
421 void (*fl_copy_lock)(struct file_lock 411 void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
422 void (*fl_release_private)(struct file 412 void (*fl_release_private)(struct file_lock *);
423 413
424 414
425 locking rules: 415 locking rules:
426 416
427 =================== ============= ====== 417 =================== ============= =========
428 ops inode->i_lock may bl 418 ops inode->i_lock may block
429 =================== ============= ====== 419 =================== ============= =========
430 fl_copy_lock: yes no 420 fl_copy_lock: yes no
431 fl_release_private: maybe maybe[ 421 fl_release_private: maybe maybe[1]_
432 =================== ============= ====== 422 =================== ============= =========
433 423
434 .. [1]: 424 .. [1]:
435 ->fl_release_private for flock or POSIX loc 425 ->fl_release_private for flock or POSIX locks is currently allowed
436 to block. Leases however can still be freed 426 to block. Leases however can still be freed while the i_lock is held and
437 so fl_release_private called on a lease sho 427 so fl_release_private called on a lease should not block.
438 428
439 lock_manager_operations 429 lock_manager_operations
440 ======================= 430 =======================
441 431
442 prototypes:: 432 prototypes::
443 433
444 void (*lm_notify)(struct file_lock *); 434 void (*lm_notify)(struct file_lock *); /* unblock callback */
445 int (*lm_grant)(struct file_lock *, st 435 int (*lm_grant)(struct file_lock *, struct file_lock *, int);
446 void (*lm_break)(struct file_lock *); 436 void (*lm_break)(struct file_lock *); /* break_lease callback */
447 int (*lm_change)(struct file_lock **, 437 int (*lm_change)(struct file_lock **, int);
448 bool (*lm_breaker_owns_lease)(struct f 438 bool (*lm_breaker_owns_lease)(struct file_lock *);
449 bool (*lm_lock_expirable)(struct file_ <<
450 void (*lm_expire_lock)(void); <<
451 439
452 locking rules: 440 locking rules:
453 441
454 ====================== ============= ====== 442 ====================== ============= ================= =========
455 ops flc_lock blocke !! 443 ops inode->i_lock blocked_lock_lock may block
456 ====================== ============= ====== 444 ====================== ============= ================= =========
457 lm_notify: no yes !! 445 lm_notify: yes yes no
458 lm_grant: no no 446 lm_grant: no no no
459 lm_break: yes no 447 lm_break: yes no no
460 lm_change yes no 448 lm_change yes no no
461 lm_breaker_owns_lease: yes no !! 449 lm_breaker_owns_lease: no no no
462 lm_lock_expirable yes no <<
463 lm_expire_lock no no <<
464 ====================== ============= ====== 450 ====================== ============= ================= =========
465 451
466 buffer_head 452 buffer_head
467 =========== 453 ===========
468 454
469 prototypes:: 455 prototypes::
470 456
471 void (*b_end_io)(struct buffer_head *b 457 void (*b_end_io)(struct buffer_head *bh, int uptodate);
472 458
473 locking rules: 459 locking rules:
474 460
475 called from interrupts. In other words, extrem 461 called from interrupts. In other words, extreme care is needed here.
476 bh is locked, but that's all warranties we hav 462 bh is locked, but that's all warranties we have here. Currently only RAID1,
477 highmem, fs/buffer.c, and fs/ntfs/aops.c are p 463 highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
478 call this method upon the IO completion. 464 call this method upon the IO completion.
479 465
480 block_device_operations 466 block_device_operations
481 ======================= 467 =======================
482 prototypes:: 468 prototypes::
483 469
484 int (*open) (struct block_device *, fm 470 int (*open) (struct block_device *, fmode_t);
485 int (*release) (struct gendisk *, fmod 471 int (*release) (struct gendisk *, fmode_t);
486 int (*ioctl) (struct block_device *, f 472 int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
487 int (*compat_ioctl) (struct block_devi 473 int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
488 int (*direct_access) (struct block_dev 474 int (*direct_access) (struct block_device *, sector_t, void **,
489 unsigned long 475 unsigned long *);
490 void (*unlock_native_capacity) (struct 476 void (*unlock_native_capacity) (struct gendisk *);
491 int (*getgeo)(struct block_device *, s 477 int (*getgeo)(struct block_device *, struct hd_geometry *);
492 void (*swap_slot_free_notify) (struct 478 void (*swap_slot_free_notify) (struct block_device *, unsigned long);
493 479
494 locking rules: 480 locking rules:
495 481
496 ======================= =================== 482 ======================= ===================
497 ops open_mutex !! 483 ops bd_mutex
498 ======================= =================== 484 ======================= ===================
499 open: yes 485 open: yes
500 release: yes 486 release: yes
501 ioctl: no 487 ioctl: no
502 compat_ioctl: no 488 compat_ioctl: no
503 direct_access: no 489 direct_access: no
504 unlock_native_capacity: no 490 unlock_native_capacity: no
505 getgeo: no 491 getgeo: no
506 swap_slot_free_notify: no (see below) 492 swap_slot_free_notify: no (see below)
507 ======================= =================== 493 ======================= ===================
508 494
509 swap_slot_free_notify is called with swap_lock 495 swap_slot_free_notify is called with swap_lock and sometimes the page lock
510 held. 496 held.
511 497
512 498
513 file_operations 499 file_operations
514 =============== 500 ===============
515 501
516 prototypes:: 502 prototypes::
517 503
518 loff_t (*llseek) (struct file *, loff_ 504 loff_t (*llseek) (struct file *, loff_t, int);
519 ssize_t (*read) (struct file *, char _ 505 ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
520 ssize_t (*write) (struct file *, const 506 ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
521 ssize_t (*read_iter) (struct kiocb *, 507 ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
522 ssize_t (*write_iter) (struct kiocb *, 508 ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
523 int (*iopoll) (struct kiocb *kiocb, bo !! 509 int (*iterate) (struct file *, struct dir_context *);
524 int (*iterate_shared) (struct file *, 510 int (*iterate_shared) (struct file *, struct dir_context *);
525 __poll_t (*poll) (struct file *, struc 511 __poll_t (*poll) (struct file *, struct poll_table_struct *);
526 long (*unlocked_ioctl) (struct file *, 512 long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
527 long (*compat_ioctl) (struct file *, u 513 long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
528 int (*mmap) (struct file *, struct vm_ 514 int (*mmap) (struct file *, struct vm_area_struct *);
529 int (*open) (struct inode *, struct fi 515 int (*open) (struct inode *, struct file *);
530 int (*flush) (struct file *); 516 int (*flush) (struct file *);
531 int (*release) (struct inode *, struct 517 int (*release) (struct inode *, struct file *);
532 int (*fsync) (struct file *, loff_t st 518 int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
533 int (*fasync) (int, struct file *, int 519 int (*fasync) (int, struct file *, int);
534 int (*lock) (struct file *, int, struc 520 int (*lock) (struct file *, int, struct file_lock *);
>> 521 ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
>> 522 loff_t *);
>> 523 ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
>> 524 loff_t *);
>> 525 ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
>> 526 void __user *);
>> 527 ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
>> 528 loff_t *, int);
535 unsigned long (*get_unmapped_area)(str 529 unsigned long (*get_unmapped_area)(struct file *, unsigned long,
536 unsigned long, unsigne 530 unsigned long, unsigned long, unsigned long);
537 int (*check_flags)(int); 531 int (*check_flags)(int);
538 int (*flock) (struct file *, int, stru 532 int (*flock) (struct file *, int, struct file_lock *);
539 ssize_t (*splice_write)(struct pipe_in 533 ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
540 size_t, unsigned int); 534 size_t, unsigned int);
541 ssize_t (*splice_read)(struct file *, 535 ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
542 size_t, unsigned int); 536 size_t, unsigned int);
543 int (*setlease)(struct file *, long, s 537 int (*setlease)(struct file *, long, struct file_lock **, void **);
544 long (*fallocate)(struct file *, int, 538 long (*fallocate)(struct file *, int, loff_t, loff_t);
545 void (*show_fdinfo)(struct seq_file *m <<
546 unsigned (*mmap_capabilities)(struct f <<
547 ssize_t (*copy_file_range)(struct file <<
548 loff_t, size_t, unsign <<
549 loff_t (*remap_file_range)(struct file <<
550 struct file *file_out, <<
551 loff_t len, unsigned i <<
552 int (*fadvise)(struct file *, loff_t, <<
553 539
554 locking rules: 540 locking rules:
555 All may block. 541 All may block.
556 542
557 ->llseek() locking has moved from llseek to th 543 ->llseek() locking has moved from llseek to the individual llseek
558 implementations. If your fs is not using gene 544 implementations. If your fs is not using generic_file_llseek, you
559 need to acquire and release the appropriate lo 545 need to acquire and release the appropriate locks in your ->llseek().
560 For many filesystems, it is probably safe to a 546 For many filesystems, it is probably safe to acquire the inode
561 mutex or just to use i_size_read() instead. 547 mutex or just to use i_size_read() instead.
562 Note: this does not protect the file->f_pos ag 548 Note: this does not protect the file->f_pos against concurrent modifications
563 since this is something the userspace has to t 549 since this is something the userspace has to take care about.
564 550
565 ->iterate_shared() is called with i_rwsem held !! 551 ->iterate() is called with i_rwsem exclusive.
566 file f_pos_lock held exclusively !! 552
>> 553 ->iterate_shared() is called with i_rwsem at least shared.
567 554
568 ->fasync() is responsible for maintaining the 555 ->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
569 Most instances call fasync_helper(), which doe 556 Most instances call fasync_helper(), which does that maintenance, so it's
570 not normally something one needs to worry abou 557 not normally something one needs to worry about. Return values > 0 will be
571 mapped to zero in the VFS layer. 558 mapped to zero in the VFS layer.
572 559
573 ->readdir() and ->ioctl() on directories must 560 ->readdir() and ->ioctl() on directories must be changed. Ideally we would
574 move ->readdir() to inode_operations and use a 561 move ->readdir() to inode_operations and use a separate method for directory
575 ->ioctl() or kill the latter completely. One o 562 ->ioctl() or kill the latter completely. One of the problems is that for
576 anything that resembles union-mount we won't h 563 anything that resembles union-mount we won't have a struct file for all
577 components. And there are other reasons why th 564 components. And there are other reasons why the current interface is a mess...
578 565
579 ->read on directories probably must go away - 566 ->read on directories probably must go away - we should just enforce -EISDIR
580 in sys_read() and friends. 567 in sys_read() and friends.
581 568
582 ->setlease operations should call generic_setl 569 ->setlease operations should call generic_setlease() before or after setting
583 the lease within the individual filesystem to 570 the lease within the individual filesystem to record the result of the
584 operation 571 operation
585 572
586 ->fallocate implementation must be really care <<
587 consistency when punching holes or performing <<
588 page cache contents. Usually the filesystem ne <<
589 truncate_inode_pages_range() to invalidate rel <<
590 However the filesystem usually also needs to u <<
591 view of file offset -> disk block mapping. Unt <<
592 filesystem needs to block page faults and read <<
593 cache contents from the disk. Since VFS acquir <<
594 shared mode when loading pages from disk (file <<
595 readahead paths), the fallocate implementation <<
596 prevent reloading. <<
597 <<
598 ->copy_file_range and ->remap_file_range imple <<
599 against modifications of file data while the o <<
600 blocking changes through write(2) and similar <<
601 used. To block changes to file contents via a <<
602 operation, the filesystem must take mapping->i <<
603 with ->page_mkwrite. <<
604 <<
605 dquot_operations 573 dquot_operations
606 ================ 574 ================
607 575
608 prototypes:: 576 prototypes::
609 577
610 int (*write_dquot) (struct dquot *); 578 int (*write_dquot) (struct dquot *);
611 int (*acquire_dquot) (struct dquot *); 579 int (*acquire_dquot) (struct dquot *);
612 int (*release_dquot) (struct dquot *); 580 int (*release_dquot) (struct dquot *);
613 int (*mark_dirty) (struct dquot *); 581 int (*mark_dirty) (struct dquot *);
614 int (*write_info) (struct super_block 582 int (*write_info) (struct super_block *, int);
615 583
616 These operations are intended to be more or le 584 These operations are intended to be more or less wrapping functions that ensure
617 a proper locking wrt the filesystem and call t 585 a proper locking wrt the filesystem and call the generic quota operations.
618 586
619 What filesystem should expect from the generic 587 What filesystem should expect from the generic quota functions:
620 588
621 ============== ============ ============== 589 ============== ============ =========================
622 ops FS recursion Held locks whe 590 ops FS recursion Held locks when called
623 ============== ============ ============== 591 ============== ============ =========================
624 write_dquot: yes dqonoff_sem or 592 write_dquot: yes dqonoff_sem or dqptr_sem
625 acquire_dquot: yes dqonoff_sem or 593 acquire_dquot: yes dqonoff_sem or dqptr_sem
626 release_dquot: yes dqonoff_sem or 594 release_dquot: yes dqonoff_sem or dqptr_sem
627 mark_dirty: no - 595 mark_dirty: no -
628 write_info: yes dqonoff_sem 596 write_info: yes dqonoff_sem
629 ============== ============ ============== 597 ============== ============ =========================
630 598
631 FS recursion means calling ->quota_read() and 599 FS recursion means calling ->quota_read() and ->quota_write() from superblock
632 operations. 600 operations.
633 601
634 More details about quota locking can be found 602 More details about quota locking can be found in fs/dquot.c.
635 603
636 vm_operations_struct 604 vm_operations_struct
637 ==================== 605 ====================
638 606
639 prototypes:: 607 prototypes::
640 608
641 void (*open)(struct vm_area_struct *); !! 609 void (*open)(struct vm_area_struct*);
642 void (*close)(struct vm_area_struct *) !! 610 void (*close)(struct vm_area_struct*);
643 vm_fault_t (*fault)(struct vm_fault *) !! 611 vm_fault_t (*fault)(struct vm_area_struct*, struct vm_fault *);
644 vm_fault_t (*huge_fault)(struct vm_fau <<
645 vm_fault_t (*map_pages)(struct vm_faul <<
646 vm_fault_t (*page_mkwrite)(struct vm_a 612 vm_fault_t (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
647 vm_fault_t (*pfn_mkwrite)(struct vm_ar 613 vm_fault_t (*pfn_mkwrite)(struct vm_area_struct *, struct vm_fault *);
648 int (*access)(struct vm_area_struct *, 614 int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
649 615
650 locking rules: 616 locking rules:
651 617
652 ============= ========== ============== !! 618 ============= ========= ===========================
653 ops mmap_lock PageLocked(pag 619 ops mmap_lock PageLocked(page)
654 ============= ========== ============== !! 620 ============= ========= ===========================
655 open: write !! 621 open: yes
656 close: read/write !! 622 close: yes
657 fault: read can return wit !! 623 fault: yes can return with page locked
658 huge_fault: maybe-read !! 624 map_pages: yes
659 map_pages: maybe-read !! 625 page_mkwrite: yes can return with page locked
660 page_mkwrite: read can return wit !! 626 pfn_mkwrite: yes
661 pfn_mkwrite: read !! 627 access: yes
662 access: read !! 628 ============= ========= ===========================
663 ============= ========== ============== !! 629
664 !! 630 ->fault() is called when a previously not present pte is about
665 ->fault() is called when a previously not pres !! 631 to be faulted in. The filesystem must find and return the page associated
666 in. The filesystem must find and return the pa !! 632 with the passed in "pgoff" in the vm_fault structure. If it is possible that
667 "pgoff" in the vm_fault structure. If it is po !! 633 the page may be truncated and/or invalidated, then the filesystem must lock
668 truncated and/or invalidated, then the filesys !! 634 the page, then ensure it is not already truncated (the page lock will block
669 then ensure the page is not already truncated <<
670 subsequent truncate), and then return with VM_ 635 subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
671 locked. The VM will unlock the page. 636 locked. The VM will unlock the page.
672 637
673 ->huge_fault() is called when there is no PUD <<
674 gives the filesystem the opportunity to instal <<
675 Filesystems can also use the ->fault method to <<
676 so implementing this function may not be neces <<
677 filesystems should not call filemap_fault() fr <<
678 The mmap_lock may not be held when this method <<
679 <<
680 ->map_pages() is called when VM asks to map ea 638 ->map_pages() is called when VM asks to map easy accessible pages.
681 Filesystem should find and map pages associate 639 Filesystem should find and map pages associated with offsets from "start_pgoff"
682 till "end_pgoff". ->map_pages() is called with !! 640 till "end_pgoff". ->map_pages() is called with page table locked and must
683 not block. If it's not possible to reach a pa 641 not block. If it's not possible to reach a page without blocking,
684 filesystem should skip it. Filesystem should u !! 642 filesystem should skip it. Filesystem should use do_set_pte() to setup
685 page table entry. Pointer to entry associated 643 page table entry. Pointer to entry associated with the page is passed in
686 "pte" field in vm_fault structure. Pointers to 644 "pte" field in vm_fault structure. Pointers to entries for other offsets
687 should be calculated relative to "pte". 645 should be calculated relative to "pte".
688 646
689 ->page_mkwrite() is called when a previously r !! 647 ->page_mkwrite() is called when a previously read-only pte is
690 writeable. The filesystem again must ensure th !! 648 about to become writeable. The filesystem again must ensure that there are
691 truncate/invalidate races or races with operat !! 649 no truncate/invalidate races, and then return with the page locked. If
692 or ->copy_file_range, and then return with the !! 650 the page has been truncated, the filesystem should not look up a new page
693 mapping->invalidate_lock is suitable for prope !! 651 like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
694 been truncated, the filesystem should not look !! 652 will cause the VM to retry the fault.
695 handler, but simply return with VM_FAULT_NOPAG <<
696 retry the fault. <<
697 653
698 ->pfn_mkwrite() is the same as page_mkwrite bu 654 ->pfn_mkwrite() is the same as page_mkwrite but when the pte is
699 VM_PFNMAP or VM_MIXEDMAP with a page-less entr 655 VM_PFNMAP or VM_MIXEDMAP with a page-less entry. Expected return is
700 VM_FAULT_NOPAGE. Or one of the VM_FAULT_ERROR 656 VM_FAULT_NOPAGE. Or one of the VM_FAULT_ERROR types. The default behavior
701 after this call is to make the pte read-write, 657 after this call is to make the pte read-write, unless pfn_mkwrite returns
702 an error. 658 an error.
703 659
704 ->access() is called when get_user_pages() fai 660 ->access() is called when get_user_pages() fails in
705 access_process_vm(), typically used to debug a 661 access_process_vm(), typically used to debug a process through
706 /proc/pid/mem or ptrace. This function is nee 662 /proc/pid/mem or ptrace. This function is needed only for
707 VM_IO | VM_PFNMAP VMAs. 663 VM_IO | VM_PFNMAP VMAs.
708 664
709 ---------------------------------------------- 665 --------------------------------------------------------------------------------
710 666
711 Dubious stuff 667 Dubious stuff
712 668
713 (if you break something or notice that it is b 669 (if you break something or notice that it is broken and do not fix it yourself
714 - at least put it here) 670 - at least put it here)
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