1==================== 2Changes since 2.5.0: 3==================== 4 5--- 6 7**recommended** 8 9New helpers: sb_bread(), sb_getblk(), sb_find_get_block(), set_bh(), 10sb_set_blocksize() and sb_min_blocksize(). 11 12Use them. 13 14(sb_find_get_block() replaces 2.4's get_hash_table()) 15 16--- 17 18**recommended** 19 20New methods: ->alloc_inode() and ->destroy_inode(). 21 22Remove inode->u.foo_inode_i 23 24Declare:: 25 26 struct foo_inode_info { 27 /* fs-private stuff */ 28 struct inode vfs_inode; 29 }; 30 static inline struct foo_inode_info *FOO_I(struct inode *inode) 31 { 32 return list_entry(inode, struct foo_inode_info, vfs_inode); 33 } 34 35Use FOO_I(inode) instead of &inode->u.foo_inode_i; 36 37Add foo_alloc_inode() and foo_destroy_inode() - the former should allocate 38foo_inode_info and return the address of ->vfs_inode, the latter should free 39FOO_I(inode) (see in-tree filesystems for examples). 40 41Make them ->alloc_inode and ->destroy_inode in your super_operations. 42 43Keep in mind that now you need explicit initialization of private data 44typically between calling iget_locked() and unlocking the inode. 45 46At some point that will become mandatory. 47 48--- 49 50**mandatory** 51 52Change of file_system_type method (->read_super to ->get_sb) 53 54->read_super() is no more. Ditto for DECLARE_FSTYPE and DECLARE_FSTYPE_DEV. 55 56Turn your foo_read_super() into a function that would return 0 in case of 57success and negative number in case of error (-EINVAL unless you have more 58informative error value to report). Call it foo_fill_super(). Now declare:: 59 60 int foo_get_sb(struct file_system_type *fs_type, 61 int flags, const char *dev_name, void *data, struct vfsmount *mnt) 62 { 63 return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super, 64 mnt); 65 } 66 67(or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind of 68filesystem). 69 70Replace DECLARE_FSTYPE... with explicit initializer and have ->get_sb set as 71foo_get_sb. 72 73--- 74 75**mandatory** 76 77Locking change: ->s_vfs_rename_sem is taken only by cross-directory renames. 78Most likely there is no need to change anything, but if you relied on 79global exclusion between renames for some internal purpose - you need to 80change your internal locking. Otherwise exclusion warranties remain the 81same (i.e. parents and victim are locked, etc.). 82 83--- 84 85**informational** 86 87Now we have the exclusion between ->lookup() and directory removal (by 88->rmdir() and ->rename()). If you used to need that exclusion and do 89it by internal locking (most of filesystems couldn't care less) - you 90can relax your locking. 91 92--- 93 94**mandatory** 95 96->lookup(), ->truncate(), ->create(), ->unlink(), ->mknod(), ->mkdir(), 97->rmdir(), ->link(), ->lseek(), ->symlink(), ->rename() 98and ->readdir() are called without BKL now. Grab it on entry, drop upon return 99- that will guarantee the same locking you used to have. If your method or its 100parts do not need BKL - better yet, now you can shift lock_kernel() and 101unlock_kernel() so that they would protect exactly what needs to be 102protected. 103 104--- 105 106**mandatory** 107 108BKL is also moved from around sb operations. BKL should have been shifted into 109individual fs sb_op functions. If you don't need it, remove it. 110 111--- 112 113**informational** 114 115check for ->link() target not being a directory is done by callers. Feel 116free to drop it... 117 118--- 119 120**informational** 121 122->link() callers hold ->i_mutex on the object we are linking to. Some of your 123problems might be over... 124 125--- 126 127**mandatory** 128 129new file_system_type method - kill_sb(superblock). If you are converting 130an existing filesystem, set it according to ->fs_flags:: 131 132 FS_REQUIRES_DEV - kill_block_super 133 FS_LITTER - kill_litter_super 134 neither - kill_anon_super 135 136FS_LITTER is gone - just remove it from fs_flags. 137 138--- 139 140**mandatory** 141 142FS_SINGLE is gone (actually, that had happened back when ->get_sb() 143went in - and hadn't been documented ;-/). Just remove it from fs_flags 144(and see ->get_sb() entry for other actions). 145 146--- 147 148**mandatory** 149 150->setattr() is called without BKL now. Caller _always_ holds ->i_mutex, so 151watch for ->i_mutex-grabbing code that might be used by your ->setattr(). 152Callers of notify_change() need ->i_mutex now. 153 154--- 155 156**recommended** 157 158New super_block field ``struct export_operations *s_export_op`` for 159explicit support for exporting, e.g. via NFS. The structure is fully 160documented at its declaration in include/linux/fs.h, and in 161Documentation/filesystems/nfs/exporting.rst. 162 163Briefly it allows for the definition of decode_fh and encode_fh operations 164to encode and decode filehandles, and allows the filesystem to use 165a standard helper function for decode_fh, and provide file-system specific 166support for this helper, particularly get_parent. 167 168It is planned that this will be required for exporting once the code 169settles down a bit. 170 171**mandatory** 172 173s_export_op is now required for exporting a filesystem. 174isofs, ext2, ext3, resierfs, fat 175can be used as examples of very different filesystems. 176 177--- 178 179**mandatory** 180 181iget4() and the read_inode2 callback have been superseded by iget5_locked() 182which has the following prototype:: 183 184 struct inode *iget5_locked(struct super_block *sb, unsigned long ino, 185 int (*test)(struct inode *, void *), 186 int (*set)(struct inode *, void *), 187 void *data); 188 189'test' is an additional function that can be used when the inode 190number is not sufficient to identify the actual file object. 'set' 191should be a non-blocking function that initializes those parts of a 192newly created inode to allow the test function to succeed. 'data' is 193passed as an opaque value to both test and set functions. 194 195When the inode has been created by iget5_locked(), it will be returned with the 196I_NEW flag set and will still be locked. The filesystem then needs to finalize 197the initialization. Once the inode is initialized it must be unlocked by 198calling unlock_new_inode(). 199 200The filesystem is responsible for setting (and possibly testing) i_ino 201when appropriate. There is also a simpler iget_locked function that 202just takes the superblock and inode number as arguments and does the 203test and set for you. 204 205e.g.:: 206 207 inode = iget_locked(sb, ino); 208 if (inode->i_state & I_NEW) { 209 err = read_inode_from_disk(inode); 210 if (err < 0) { 211 iget_failed(inode); 212 return err; 213 } 214 unlock_new_inode(inode); 215 } 216 217Note that if the process of setting up a new inode fails, then iget_failed() 218should be called on the inode to render it dead, and an appropriate error 219should be passed back to the caller. 220 221--- 222 223**recommended** 224 225->getattr() finally getting used. See instances in nfs, minix, etc. 226 227--- 228 229**mandatory** 230 231->revalidate() is gone. If your filesystem had it - provide ->getattr() 232and let it call whatever you had as ->revlidate() + (for symlinks that 233had ->revalidate()) add calls in ->follow_link()/->readlink(). 234 235--- 236 237**mandatory** 238 239->d_parent changes are not protected by BKL anymore. Read access is safe 240if at least one of the following is true: 241 242 * filesystem has no cross-directory rename() 243 * we know that parent had been locked (e.g. we are looking at 244 ->d_parent of ->lookup() argument). 245 * we are called from ->rename(). 246 * the child's ->d_lock is held 247 248Audit your code and add locking if needed. Notice that any place that is 249not protected by the conditions above is risky even in the old tree - you 250had been relying on BKL and that's prone to screwups. Old tree had quite 251a few holes of that kind - unprotected access to ->d_parent leading to 252anything from oops to silent memory corruption. 253 254--- 255 256**mandatory** 257 258FS_NOMOUNT is gone. If you use it - just set SB_NOUSER in flags 259(see rootfs for one kind of solution and bdev/socket/pipe for another). 260 261--- 262 263**recommended** 264 265Use bdev_read_only(bdev) instead of is_read_only(kdev). The latter 266is still alive, but only because of the mess in drivers/s390/block/dasd.c. 267As soon as it gets fixed is_read_only() will die. 268 269--- 270 271**mandatory** 272 273->permission() is called without BKL now. Grab it on entry, drop upon 274return - that will guarantee the same locking you used to have. If 275your method or its parts do not need BKL - better yet, now you can 276shift lock_kernel() and unlock_kernel() so that they would protect 277exactly what needs to be protected. 278 279--- 280 281**mandatory** 282 283->statfs() is now called without BKL held. BKL should have been 284shifted into individual fs sb_op functions where it's not clear that 285it's safe to remove it. If you don't need it, remove it. 286 287--- 288 289**mandatory** 290 291is_read_only() is gone; use bdev_read_only() instead. 292 293--- 294 295**mandatory** 296 297destroy_buffers() is gone; use invalidate_bdev(). 298 299--- 300 301**mandatory** 302 303fsync_dev() is gone; use fsync_bdev(). NOTE: lvm breakage is 304deliberate; as soon as struct block_device * is propagated in a reasonable 305way by that code fixing will become trivial; until then nothing can be 306done. 307 308**mandatory** 309 310block truncatation on error exit from ->write_begin, and ->direct_IO 311moved from generic methods (block_write_begin, cont_write_begin, 312nobh_write_begin, blockdev_direct_IO*) to callers. Take a look at 313ext2_write_failed and callers for an example. 314 315**mandatory** 316 317->truncate is gone. The whole truncate sequence needs to be 318implemented in ->setattr, which is now mandatory for filesystems 319implementing on-disk size changes. Start with a copy of the old inode_setattr 320and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to 321be in order of zeroing blocks using block_truncate_page or similar helpers, 322size update and on finally on-disk truncation which should not fail. 323setattr_prepare (which used to be inode_change_ok) now includes the size checks 324for ATTR_SIZE and must be called in the beginning of ->setattr unconditionally. 325 326**mandatory** 327 328->clear_inode() and ->delete_inode() are gone; ->evict_inode() should 329be used instead. It gets called whenever the inode is evicted, whether it has 330remaining links or not. Caller does *not* evict the pagecache or inode-associated 331metadata buffers; the method has to use truncate_inode_pages_final() to get rid 332of those. Caller makes sure async writeback cannot be running for the inode while 333(or after) ->evict_inode() is called. 334 335->drop_inode() returns int now; it's called on final iput() with 336inode->i_lock held and it returns true if filesystems wants the inode to be 337dropped. As before, generic_drop_inode() is still the default and it's been 338updated appropriately. generic_delete_inode() is also alive and it consists 339simply of return 1. Note that all actual eviction work is done by caller after 340->drop_inode() returns. 341 342As before, clear_inode() must be called exactly once on each call of 343->evict_inode() (as it used to be for each call of ->delete_inode()). Unlike 344before, if you are using inode-associated metadata buffers (i.e. 345mark_buffer_dirty_inode()), it's your responsibility to call 346invalidate_inode_buffers() before clear_inode(). 347 348NOTE: checking i_nlink in the beginning of ->write_inode() and bailing out 349if it's zero is not *and* *never* *had* *been* enough. Final unlink() and iput() 350may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly 351free the on-disk inode, you may end up doing that while ->write_inode() is writing 352to it. 353 354--- 355 356**mandatory** 357 358.d_delete() now only advises the dcache as to whether or not to cache 359unreferenced dentries, and is now only called when the dentry refcount goes to 3600. Even on 0 refcount transition, it must be able to tolerate being called 0, 3611, or more times (eg. constant, idempotent). 362 363--- 364 365**mandatory** 366 367.d_compare() calling convention and locking rules are significantly 368changed. Read updated documentation in Documentation/filesystems/vfs.rst (and 369look at examples of other filesystems) for guidance. 370 371--- 372 373**mandatory** 374 375.d_hash() calling convention and locking rules are significantly 376changed. Read updated documentation in Documentation/filesystems/vfs.rst (and 377look at examples of other filesystems) for guidance. 378 379--- 380 381**mandatory** 382 383dcache_lock is gone, replaced by fine grained locks. See fs/dcache.c 384for details of what locks to replace dcache_lock with in order to protect 385particular things. Most of the time, a filesystem only needs ->d_lock, which 386protects *all* the dcache state of a given dentry. 387 388--- 389 390**mandatory** 391 392Filesystems must RCU-free their inodes, if they can have been accessed 393via rcu-walk path walk (basically, if the file can have had a path name in the 394vfs namespace). 395 396Even though i_dentry and i_rcu share storage in a union, we will 397initialize the former in inode_init_always(), so just leave it alone in 398the callback. It used to be necessary to clean it there, but not anymore 399(starting at 3.2). 400 401--- 402 403**recommended** 404 405vfs now tries to do path walking in "rcu-walk mode", which avoids 406atomic operations and scalability hazards on dentries and inodes (see 407Documentation/filesystems/path-lookup.txt). d_hash and d_compare changes 408(above) are examples of the changes required to support this. For more complex 409filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so 410no changes are required to the filesystem. However, this is costly and loses 411the benefits of rcu-walk mode. We will begin to add filesystem callbacks that 412are rcu-walk aware, shown below. Filesystems should take advantage of this 413where possible. 414 415--- 416 417**mandatory** 418 419d_revalidate is a callback that is made on every path element (if 420the filesystem provides it), which requires dropping out of rcu-walk mode. This 421may now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should be 422returned if the filesystem cannot handle rcu-walk. See 423Documentation/filesystems/vfs.rst for more details. 424 425permission is an inode permission check that is called on many or all 426directory inodes on the way down a path walk (to check for exec permission). It 427must now be rcu-walk aware (mask & MAY_NOT_BLOCK). See 428Documentation/filesystems/vfs.rst for more details. 429 430--- 431 432**mandatory** 433 434In ->fallocate() you must check the mode option passed in. If your 435filesystem does not support hole punching (deallocating space in the middle of a 436file) you must return -EOPNOTSUPP if FALLOC_FL_PUNCH_HOLE is set in mode. 437Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set, 438so the i_size should not change when hole punching, even when puching the end of 439a file off. 440 441--- 442 443**mandatory** 444 445->get_sb() is gone. Switch to use of ->mount(). Typically it's just 446a matter of switching from calling ``get_sb_``... to ``mount_``... and changing 447the function type. If you were doing it manually, just switch from setting 448->mnt_root to some pointer to returning that pointer. On errors return 449ERR_PTR(...). 450 451--- 452 453**mandatory** 454 455->permission() and generic_permission()have lost flags 456argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask. 457 458generic_permission() has also lost the check_acl argument; ACL checking 459has been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_acl 460to read an ACL from disk. 461 462--- 463 464**mandatory** 465 466If you implement your own ->llseek() you must handle SEEK_HOLE and 467SEEK_DATA. You can hanle this by returning -EINVAL, but it would be nicer to 468support it in some way. The generic handler assumes that the entire file is 469data and there is a virtual hole at the end of the file. So if the provided 470offset is less than i_size and SEEK_DATA is specified, return the same offset. 471If the above is true for the offset and you are given SEEK_HOLE, return the end 472of the file. If the offset is i_size or greater return -ENXIO in either case. 473 474**mandatory** 475 476If you have your own ->fsync() you must make sure to call 477filemap_write_and_wait_range() so that all dirty pages are synced out properly. 478You must also keep in mind that ->fsync() is not called with i_mutex held 479anymore, so if you require i_mutex locking you must make sure to take it and 480release it yourself. 481 482--- 483 484**mandatory** 485 486d_alloc_root() is gone, along with a lot of bugs caused by code 487misusing it. Replacement: d_make_root(inode). On success d_make_root(inode) 488allocates and returns a new dentry instantiated with the passed in inode. 489On failure NULL is returned and the passed in inode is dropped so the reference 490to inode is consumed in all cases and failure handling need not do any cleanup 491for the inode. If d_make_root(inode) is passed a NULL inode it returns NULL 492and also requires no further error handling. Typical usage is:: 493 494 inode = foofs_new_inode(....); 495 s->s_root = d_make_root(inode); 496 if (!s->s_root) 497 /* Nothing needed for the inode cleanup */ 498 return -ENOMEM; 499 ... 500 501--- 502 503**mandatory** 504 505The witch is dead! Well, 2/3 of it, anyway. ->d_revalidate() and 506->lookup() do *not* take struct nameidata anymore; just the flags. 507 508--- 509 510**mandatory** 511 512->create() doesn't take ``struct nameidata *``; unlike the previous 513two, it gets "is it an O_EXCL or equivalent?" boolean argument. Note that 514local filesystems can ignore tha argument - they are guaranteed that the 515object doesn't exist. It's remote/distributed ones that might care... 516 517--- 518 519**mandatory** 520 521FS_REVAL_DOT is gone; if you used to have it, add ->d_weak_revalidate() 522in your dentry operations instead. 523 524--- 525 526**mandatory** 527 528vfs_readdir() is gone; switch to iterate_dir() instead 529 530--- 531 532**mandatory** 533 534->readdir() is gone now; switch to ->iterate() 535 536**mandatory** 537 538vfs_follow_link has been removed. Filesystems must use nd_set_link 539from ->follow_link for normal symlinks, or nd_jump_link for magic 540/proc/<pid> style links. 541 542--- 543 544**mandatory** 545 546iget5_locked()/ilookup5()/ilookup5_nowait() test() callback used to be 547called with both ->i_lock and inode_hash_lock held; the former is *not* 548taken anymore, so verify that your callbacks do not rely on it (none 549of the in-tree instances did). inode_hash_lock is still held, 550of course, so they are still serialized wrt removal from inode hash, 551as well as wrt set() callback of iget5_locked(). 552 553--- 554 555**mandatory** 556 557d_materialise_unique() is gone; d_splice_alias() does everything you 558need now. Remember that they have opposite orders of arguments ;-/ 559 560--- 561 562**mandatory** 563 564f_dentry is gone; use f_path.dentry, or, better yet, see if you can avoid 565it entirely. 566 567--- 568 569**mandatory** 570 571never call ->read() and ->write() directly; use __vfs_{read,write} or 572wrappers; instead of checking for ->write or ->read being NULL, look for 573FMODE_CAN_{WRITE,READ} in file->f_mode. 574 575--- 576 577**mandatory** 578 579do _not_ use new_sync_{read,write} for ->read/->write; leave it NULL 580instead. 581 582--- 583 584**mandatory** 585 ->aio_read/->aio_write are gone. Use ->read_iter/->write_iter. 586 587--- 588 589**recommended** 590 591for embedded ("fast") symlinks just set inode->i_link to wherever the 592symlink body is and use simple_follow_link() as ->follow_link(). 593 594--- 595 596**mandatory** 597 598calling conventions for ->follow_link() have changed. Instead of returning 599cookie and using nd_set_link() to store the body to traverse, we return 600the body to traverse and store the cookie using explicit void ** argument. 601nameidata isn't passed at all - nd_jump_link() doesn't need it and 602nd_[gs]et_link() is gone. 603 604--- 605 606**mandatory** 607 608calling conventions for ->put_link() have changed. It gets inode instead of 609dentry, it does not get nameidata at all and it gets called only when cookie 610is non-NULL. Note that link body isn't available anymore, so if you need it, 611store it as cookie. 612 613--- 614 615**mandatory** 616 617any symlink that might use page_follow_link_light/page_put_link() must 618have inode_nohighmem(inode) called before anything might start playing with 619its pagecache. No highmem pages should end up in the pagecache of such 620symlinks. That includes any preseeding that might be done during symlink 621creation. __page_symlink() will honour the mapping gfp flags, so once 622you've done inode_nohighmem() it's safe to use, but if you allocate and 623insert the page manually, make sure to use the right gfp flags. 624 625--- 626 627**mandatory** 628 629->follow_link() is replaced with ->get_link(); same API, except that 630 631 * ->get_link() gets inode as a separate argument 632 * ->get_link() may be called in RCU mode - in that case NULL 633 dentry is passed 634 635--- 636 637**mandatory** 638 639->get_link() gets struct delayed_call ``*done`` now, and should do 640set_delayed_call() where it used to set ``*cookie``. 641 642->put_link() is gone - just give the destructor to set_delayed_call() 643in ->get_link(). 644 645--- 646 647**mandatory** 648 649->getxattr() and xattr_handler.get() get dentry and inode passed separately. 650dentry might be yet to be attached to inode, so do _not_ use its ->d_inode 651in the instances. Rationale: !@#!@# security_d_instantiate() needs to be 652called before we attach dentry to inode. 653 654--- 655 656**mandatory** 657 658symlinks are no longer the only inodes that do *not* have i_bdev/i_cdev/ 659i_pipe/i_link union zeroed out at inode eviction. As the result, you can't 660assume that non-NULL value in ->i_nlink at ->destroy_inode() implies that 661it's a symlink. Checking ->i_mode is really needed now. In-tree we had 662to fix shmem_destroy_callback() that used to take that kind of shortcut; 663watch out, since that shortcut is no longer valid. 664 665--- 666 667**mandatory** 668 669->i_mutex is replaced with ->i_rwsem now. inode_lock() et.al. work as 670they used to - they just take it exclusive. However, ->lookup() may be 671called with parent locked shared. Its instances must not 672 673 * use d_instantiate) and d_rehash() separately - use d_add() or 674 d_splice_alias() instead. 675 * use d_rehash() alone - call d_add(new_dentry, NULL) instead. 676 * in the unlikely case when (read-only) access to filesystem 677 data structures needs exclusion for some reason, arrange it 678 yourself. None of the in-tree filesystems needed that. 679 * rely on ->d_parent and ->d_name not changing after dentry has 680 been fed to d_add() or d_splice_alias(). Again, none of the 681 in-tree instances relied upon that. 682 683We are guaranteed that lookups of the same name in the same directory 684will not happen in parallel ("same" in the sense of your ->d_compare()). 685Lookups on different names in the same directory can and do happen in 686parallel now. 687 688--- 689 690**recommended** 691 692->iterate_shared() is added; it's a parallel variant of ->iterate(). 693Exclusion on struct file level is still provided (as well as that 694between it and lseek on the same struct file), but if your directory 695has been opened several times, you can get these called in parallel. 696Exclusion between that method and all directory-modifying ones is 697still provided, of course. 698 699Often enough ->iterate() can serve as ->iterate_shared() without any 700changes - it is a read-only operation, after all. If you have any 701per-inode or per-dentry in-core data structures modified by ->iterate(), 702you might need something to serialize the access to them. If you 703do dcache pre-seeding, you'll need to switch to d_alloc_parallel() for 704that; look for in-tree examples. 705 706Old method is only used if the new one is absent; eventually it will 707be removed. Switch while you still can; the old one won't stay. 708 709--- 710 711**mandatory** 712 713->atomic_open() calls without O_CREAT may happen in parallel. 714 715--- 716 717**mandatory** 718 719->setxattr() and xattr_handler.set() get dentry and inode passed separately. 720dentry might be yet to be attached to inode, so do _not_ use its ->d_inode 721in the instances. Rationale: !@#!@# security_d_instantiate() needs to be 722called before we attach dentry to inode and !@#!@##!@$!$#!@#$!@$!@$ smack 723->d_instantiate() uses not just ->getxattr() but ->setxattr() as well. 724 725--- 726 727**mandatory** 728 729->d_compare() doesn't get parent as a separate argument anymore. If you 730used it for finding the struct super_block involved, dentry->d_sb will 731work just as well; if it's something more complicated, use dentry->d_parent. 732Just be careful not to assume that fetching it more than once will yield 733the same value - in RCU mode it could change under you. 734 735--- 736 737**mandatory** 738 739->rename() has an added flags argument. Any flags not handled by the 740filesystem should result in EINVAL being returned. 741 742--- 743 744 745**recommended** 746 747->readlink is optional for symlinks. Don't set, unless filesystem needs 748to fake something for readlink(2). 749 750--- 751 752**mandatory** 753 754->getattr() is now passed a struct path rather than a vfsmount and 755dentry separately, and it now has request_mask and query_flags arguments 756to specify the fields and sync type requested by statx. Filesystems not 757supporting any statx-specific features may ignore the new arguments. 758 759--- 760 761**mandatory** 762 763->atomic_open() calling conventions have changed. Gone is ``int *opened``, 764along with FILE_OPENED/FILE_CREATED. In place of those we have 765FMODE_OPENED/FMODE_CREATED, set in file->f_mode. Additionally, return 766value for 'called finish_no_open(), open it yourself' case has become 7670, not 1. Since finish_no_open() itself is returning 0 now, that part 768does not need any changes in ->atomic_open() instances. 769 770--- 771 772**mandatory** 773 774alloc_file() has become static now; two wrappers are to be used instead. 775alloc_file_pseudo(inode, vfsmount, name, flags, ops) is for the cases 776when dentry needs to be created; that's the majority of old alloc_file() 777users. Calling conventions: on success a reference to new struct file 778is returned and callers reference to inode is subsumed by that. On 779failure, ERR_PTR() is returned and no caller's references are affected, 780so the caller needs to drop the inode reference it held. 781alloc_file_clone(file, flags, ops) does not affect any caller's references. 782On success you get a new struct file sharing the mount/dentry with the 783original, on failure - ERR_PTR(). 784 785--- 786 787**mandatory** 788 789->clone_file_range() and ->dedupe_file_range have been replaced with 790->remap_file_range(). See Documentation/filesystems/vfs.rst for more 791information. 792 793--- 794 795**recommended** 796 797->lookup() instances doing an equivalent of:: 798 799 if (IS_ERR(inode)) 800 return ERR_CAST(inode); 801 return d_splice_alias(inode, dentry); 802 803don't need to bother with the check - d_splice_alias() will do the 804right thing when given ERR_PTR(...) as inode. Moreover, passing NULL 805inode to d_splice_alias() will also do the right thing (equivalent of 806d_add(dentry, NULL); return NULL;), so that kind of special cases 807also doesn't need a separate treatment. 808 809--- 810 811**strongly recommended** 812 813take the RCU-delayed parts of ->destroy_inode() into a new method - 814->free_inode(). If ->destroy_inode() becomes empty - all the better, 815just get rid of it. Synchronous work (e.g. the stuff that can't 816be done from an RCU callback, or any WARN_ON() where we want the 817stack trace) *might* be movable to ->evict_inode(); however, 818that goes only for the things that are not needed to balance something 819done by ->alloc_inode(). IOW, if it's cleaning up the stuff that 820might have accumulated over the life of in-core inode, ->evict_inode() 821might be a fit. 822 823Rules for inode destruction: 824 825 * if ->destroy_inode() is non-NULL, it gets called 826 * if ->free_inode() is non-NULL, it gets scheduled by call_rcu() 827 * combination of NULL ->destroy_inode and NULL ->free_inode is 828 treated as NULL/free_inode_nonrcu, to preserve the compatibility. 829 830Note that the callback (be it via ->free_inode() or explicit call_rcu() 831in ->destroy_inode()) is *NOT* ordered wrt superblock destruction; 832as the matter of fact, the superblock and all associated structures 833might be already gone. The filesystem driver is guaranteed to be still 834there, but that's it. Freeing memory in the callback is fine; doing 835more than that is possible, but requires a lot of care and is best 836avoided. 837 838--- 839 840**mandatory** 841 842DCACHE_RCUACCESS is gone; having an RCU delay on dentry freeing is the 843default. DCACHE_NORCU opts out, and only d_alloc_pseudo() has any 844business doing so. 845 846--- 847 848**mandatory** 849 850d_alloc_pseudo() is internal-only; uses outside of alloc_file_pseudo() are 851very suspect (and won't work in modules). Such uses are very likely to 852be misspelled d_alloc_anon(). 853