xref: /freebsd/sys/ufs/ffs/softdep.h (revision 884a2a699669ec61e2366e3e358342dbc94be24a)
1 /*-
2  * Copyright 1998, 2000 Marshall Kirk McKusick. All Rights Reserved.
3  *
4  * The soft updates code is derived from the appendix of a University
5  * of Michigan technical report (Gregory R. Ganger and Yale N. Patt,
6  * "Soft Updates: A Solution to the Metadata Update Problem in File
7  * Systems", CSE-TR-254-95, August 1995).
8  *
9  * Further information about soft updates can be obtained from:
10  *
11  *	Marshall Kirk McKusick		http://www.mckusick.com/softdep/
12  *	1614 Oxford Street		mckusick@mckusick.com
13  *	Berkeley, CA 94709-1608		+1-510-843-9542
14  *	USA
15  *
16  * Redistribution and use in source and binary forms, with or without
17  * modification, are permitted provided that the following conditions
18  * are met:
19  *
20  * 1. Redistributions of source code must retain the above copyright
21  *    notice, this list of conditions and the following disclaimer.
22  * 2. Redistributions in binary form must reproduce the above copyright
23  *    notice, this list of conditions and the following disclaimer in the
24  *    documentation and/or other materials provided with the distribution.
25  *
26  * THIS SOFTWARE IS PROVIDED BY MARSHALL KIRK MCKUSICK ``AS IS'' AND ANY
27  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
28  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
29  * DISCLAIMED.  IN NO EVENT SHALL MARSHALL KIRK MCKUSICK BE LIABLE FOR
30  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36  * SUCH DAMAGE.
37  *
38  *	@(#)softdep.h	9.7 (McKusick) 6/21/00
39  * $FreeBSD$
40  */
41 
42 #include <sys/queue.h>
43 
44 /*
45  * Allocation dependencies are handled with undo/redo on the in-memory
46  * copy of the data. A particular data dependency is eliminated when
47  * it is ALLCOMPLETE: that is ATTACHED, DEPCOMPLETE, and COMPLETE.
48  *
49  * The ATTACHED flag means that the data is not currently being written
50  * to disk.
51  *
52  * The UNDONE flag means that the data has been rolled back to a safe
53  * state for writing to the disk. When the I/O completes, the data is
54  * restored to its current form and the state reverts to ATTACHED.
55  * The data must be locked throughout the rollback, I/O, and roll
56  * forward so that the rolled back information is never visible to
57  * user processes.
58  *
59  * The COMPLETE flag indicates that the item has been written. For example,
60  * a dependency that requires that an inode be written will be marked
61  * COMPLETE after the inode has been written to disk.
62  *
63  * The DEPCOMPLETE flag indicates the completion of any other
64  * dependencies such as the writing of a cylinder group map has been
65  * completed. A dependency structure may be freed only when both it
66  * and its dependencies have completed and any rollbacks that are in
67  * progress have finished as indicated by the set of ALLCOMPLETE flags
68  * all being set.
69  *
70  * The two MKDIR flags indicate additional dependencies that must be done
71  * when creating a new directory. MKDIR_BODY is cleared when the directory
72  * data block containing the "." and ".." entries has been written.
73  * MKDIR_PARENT is cleared when the parent inode with the increased link
74  * count for ".." has been written. When both MKDIR flags have been
75  * cleared, the DEPCOMPLETE flag is set to indicate that the directory
76  * dependencies have been completed. The writing of the directory inode
77  * itself sets the COMPLETE flag which then allows the directory entry for
78  * the new directory to be written to disk. The RMDIR flag marks a dirrem
79  * structure as representing the removal of a directory rather than a
80  * file. When the removal dependencies are completed, additional work needs
81  * to be done* (an additional decrement of the associated inode, and a
82  * decrement of the parent inode).
83  *
84  * The DIRCHG flag marks a diradd structure as representing the changing
85  * of an existing entry rather than the addition of a new one. When
86  * the update is complete the dirrem associated with the inode for
87  * the old name must be added to the worklist to do the necessary
88  * reference count decrement.
89  *
90  * The GOINGAWAY flag indicates that the data structure is frozen from
91  * further change until its dependencies have been completed and its
92  * resources freed after which it will be discarded.
93  *
94  * The IOSTARTED flag prevents multiple calls to the I/O start routine from
95  * doing multiple rollbacks.
96  *
97  * The NEWBLOCK flag marks pagedep structures that have just been allocated,
98  * so must be claimed by the inode before all dependencies are complete.
99  *
100  * The INPROGRESS flag marks worklist structures that are still on the
101  * worklist, but are being considered for action by some process.
102  *
103  * The UFS1FMT flag indicates that the inode being processed is a ufs1 format.
104  *
105  * The EXTDATA flag indicates that the allocdirect describes an
106  * extended-attributes dependency.
107  *
108  * The ONWORKLIST flag shows whether the structure is currently linked
109  * onto a worklist.
110  *
111  * The UNLINK* flags track the progress of updating the on-disk linked
112  * list of active but unlinked inodes. When an inode is first unlinked
113  * it is marked as UNLINKED. When its on-disk di_freelink has been
114  * written its UNLINKNEXT flags is set. When its predecessor in the
115  * list has its di_freelink pointing at us its UNLINKPREV is set.
116  * When the on-disk list can reach it from the superblock, its
117  * UNLINKONLIST flag is set. Once all of these flags are set, it
118  * is safe to let its last name be removed.
119  */
120 #define	ATTACHED	0x000001
121 #define	UNDONE		0x000002
122 #define	COMPLETE	0x000004
123 #define	DEPCOMPLETE	0x000008
124 #define	MKDIR_PARENT	0x000010 /* diradd, mkdir, jaddref, jsegdep only */
125 #define	MKDIR_BODY	0x000020 /* diradd, mkdir, jaddref only */
126 #define	RMDIR		0x000040 /* dirrem only */
127 #define	DIRCHG		0x000080 /* diradd, dirrem only */
128 #define	GOINGAWAY	0x000100 /* indirdep, jremref only */
129 #define	IOSTARTED	0x000200 /* inodedep, pagedep, bmsafemap only */
130 #define	UNUSED400	0x000400 /* currently available. */
131 #define	NEWBLOCK	0x000800 /* pagedep, jaddref only */
132 #define	INPROGRESS	0x001000 /* dirrem, freeblks, freefrag, freefile only */
133 #define	UFS1FMT		0x002000 /* indirdep only */
134 #define	EXTDATA		0x004000 /* allocdirect only */
135 #define ONWORKLIST	0x008000
136 #define	IOWAITING	0x010000 /* Thread is waiting for IO to complete. */
137 #define	ONDEPLIST	0x020000 /* Structure is on a dependency list. */
138 #define	UNLINKED	0x040000 /* inodedep has been unlinked. */
139 #define	UNLINKNEXT	0x080000 /* inodedep has valid di_freelink */
140 #define	UNLINKPREV	0x100000 /* inodedep is pointed at in the unlink list */
141 #define	UNLINKONLIST	0x200000 /* inodedep is in the unlinked list on disk */
142 #define	UNLINKLINKS	(UNLINKNEXT | UNLINKPREV)
143 
144 #define	ALLCOMPLETE	(ATTACHED | COMPLETE | DEPCOMPLETE)
145 
146 /*
147  * The workitem queue.
148  *
149  * It is sometimes useful and/or necessary to clean up certain dependencies
150  * in the background rather than during execution of an application process
151  * or interrupt service routine. To realize this, we append dependency
152  * structures corresponding to such tasks to a "workitem" queue. In a soft
153  * updates implementation, most pending workitems should not wait for more
154  * than a couple of seconds, so the filesystem syncer process awakens once
155  * per second to process the items on the queue.
156  */
157 
158 /* LIST_HEAD(workhead, worklist);	-- declared in buf.h */
159 
160 /*
161  * Each request can be linked onto a work queue through its worklist structure.
162  * To avoid the need for a pointer to the structure itself, this structure
163  * MUST be declared FIRST in each type in which it appears! If more than one
164  * worklist is needed in the structure, then a wk_data field must be added
165  * and the macros below changed to use it.
166  */
167 struct worklist {
168 	LIST_ENTRY(worklist)	wk_list;	/* list of work requests */
169 	struct mount		*wk_mp;		/* Mount we live in */
170 	unsigned int		wk_type:8,	/* type of request */
171 				wk_state:24;	/* state flags */
172 };
173 #define WK_DATA(wk) ((void *)(wk))
174 #define WK_PAGEDEP(wk) ((struct pagedep *)(wk))
175 #define WK_INODEDEP(wk) ((struct inodedep *)(wk))
176 #define WK_BMSAFEMAP(wk) ((struct bmsafemap *)(wk))
177 #define	WK_NEWBLK(wk)  ((struct newblk *)(wk))
178 #define WK_ALLOCDIRECT(wk) ((struct allocdirect *)(wk))
179 #define WK_INDIRDEP(wk) ((struct indirdep *)(wk))
180 #define WK_ALLOCINDIR(wk) ((struct allocindir *)(wk))
181 #define WK_FREEFRAG(wk) ((struct freefrag *)(wk))
182 #define WK_FREEBLKS(wk) ((struct freeblks *)(wk))
183 #define WK_FREEWORK(wk) ((struct freework *)(wk))
184 #define WK_FREEFILE(wk) ((struct freefile *)(wk))
185 #define WK_DIRADD(wk) ((struct diradd *)(wk))
186 #define WK_MKDIR(wk) ((struct mkdir *)(wk))
187 #define WK_DIRREM(wk) ((struct dirrem *)(wk))
188 #define WK_NEWDIRBLK(wk) ((struct newdirblk *)(wk))
189 #define	WK_JADDREF(wk) ((struct jaddref *)(wk))
190 #define	WK_JREMREF(wk) ((struct jremref *)(wk))
191 #define	WK_JMVREF(wk) ((struct jmvref *)(wk))
192 #define	WK_JSEGDEP(wk) ((struct jsegdep *)(wk))
193 #define	WK_JSEG(wk) ((struct jseg *)(wk))
194 #define	WK_JNEWBLK(wk) ((struct jnewblk *)(wk))
195 #define	WK_JFREEBLK(wk) ((struct jfreeblk *)(wk))
196 #define	WK_FREEDEP(wk) ((struct freedep *)(wk))
197 #define	WK_JFREEFRAG(wk) ((struct jfreefrag *)(wk))
198 #define	WK_SBDEP(wk) ((struct sbdep *)wk)
199 #define	WK_JTRUNC(wk) ((struct jtrunc *)(wk))
200 
201 /*
202  * Various types of lists
203  */
204 LIST_HEAD(dirremhd, dirrem);
205 LIST_HEAD(diraddhd, diradd);
206 LIST_HEAD(newblkhd, newblk);
207 LIST_HEAD(inodedephd, inodedep);
208 LIST_HEAD(allocindirhd, allocindir);
209 LIST_HEAD(allocdirecthd, allocdirect);
210 TAILQ_HEAD(allocdirectlst, allocdirect);
211 LIST_HEAD(indirdephd, indirdep);
212 LIST_HEAD(jaddrefhd, jaddref);
213 LIST_HEAD(jremrefhd, jremref);
214 LIST_HEAD(jmvrefhd, jmvref);
215 LIST_HEAD(jnewblkhd, jnewblk);
216 LIST_HEAD(jfreeblkhd, jfreeblk);
217 LIST_HEAD(freeworkhd, freework);
218 TAILQ_HEAD(jseglst, jseg);
219 TAILQ_HEAD(inoreflst, inoref);
220 
221 /*
222  * The "pagedep" structure tracks the various dependencies related to
223  * a particular directory page. If a directory page has any dependencies,
224  * it will have a pagedep linked to its associated buffer. The
225  * pd_dirremhd list holds the list of dirrem requests which decrement
226  * inode reference counts. These requests are processed after the
227  * directory page with the corresponding zero'ed entries has been
228  * written. The pd_diraddhd list maintains the list of diradd requests
229  * which cannot be committed until their corresponding inode has been
230  * written to disk. Because a directory may have many new entries
231  * being created, several lists are maintained hashed on bits of the
232  * offset of the entry into the directory page to keep the lists from
233  * getting too long. Once a new directory entry has been cleared to
234  * be written, it is moved to the pd_pendinghd list. After the new
235  * entry has been written to disk it is removed from the pd_pendinghd
236  * list, any removed operations are done, and the dependency structure
237  * is freed.
238  */
239 #define DAHASHSZ 5
240 #define DIRADDHASH(offset) (((offset) >> 2) % DAHASHSZ)
241 struct pagedep {
242 	struct	worklist pd_list;	/* page buffer */
243 #	define	pd_state pd_list.wk_state /* check for multiple I/O starts */
244 	LIST_ENTRY(pagedep) pd_hash;	/* hashed lookup */
245 	ino_t	pd_ino;			/* associated file */
246 	ufs_lbn_t pd_lbn;		/* block within file */
247 	struct	newdirblk *pd_newdirblk; /* associated newdirblk if NEWBLOCK */
248 	struct	dirremhd pd_dirremhd;	/* dirrem's waiting for page */
249 	struct	diraddhd pd_diraddhd[DAHASHSZ]; /* diradd dir entry updates */
250 	struct	diraddhd pd_pendinghd;	/* directory entries awaiting write */
251 	struct	jmvrefhd pd_jmvrefhd;	/* Dependent journal writes. */
252 };
253 
254 /*
255  * The "inodedep" structure tracks the set of dependencies associated
256  * with an inode. One task that it must manage is delayed operations
257  * (i.e., work requests that must be held until the inodedep's associated
258  * inode has been written to disk). Getting an inode from its incore
259  * state to the disk requires two steps to be taken by the filesystem
260  * in this order: first the inode must be copied to its disk buffer by
261  * the VOP_UPDATE operation; second the inode's buffer must be written
262  * to disk. To ensure that both operations have happened in the required
263  * order, the inodedep maintains two lists. Delayed operations are
264  * placed on the id_inowait list. When the VOP_UPDATE is done, all
265  * operations on the id_inowait list are moved to the id_bufwait list.
266  * When the buffer is written, the items on the id_bufwait list can be
267  * safely moved to the work queue to be processed. A second task of the
268  * inodedep structure is to track the status of block allocation within
269  * the inode.  Each block that is allocated is represented by an
270  * "allocdirect" structure (see below). It is linked onto the id_newinoupdt
271  * list until both its contents and its allocation in the cylinder
272  * group map have been written to disk. Once these dependencies have been
273  * satisfied, it is removed from the id_newinoupdt list and any followup
274  * actions such as releasing the previous block or fragment are placed
275  * on the id_inowait list. When an inode is updated (a VOP_UPDATE is
276  * done), the "inodedep" structure is linked onto the buffer through
277  * its worklist. Thus, it will be notified when the buffer is about
278  * to be written and when it is done. At the update time, all the
279  * elements on the id_newinoupdt list are moved to the id_inoupdt list
280  * since those changes are now relevant to the copy of the inode in the
281  * buffer. Also at update time, the tasks on the id_inowait list are
282  * moved to the id_bufwait list so that they will be executed when
283  * the updated inode has been written to disk. When the buffer containing
284  * the inode is written to disk, any updates listed on the id_inoupdt
285  * list are rolled back as they are not yet safe. Following the write,
286  * the changes are once again rolled forward and any actions on the
287  * id_bufwait list are processed (since those actions are now safe).
288  * The entries on the id_inoupdt and id_newinoupdt lists must be kept
289  * sorted by logical block number to speed the calculation of the size
290  * of the rolled back inode (see explanation in initiate_write_inodeblock).
291  * When a directory entry is created, it is represented by a diradd.
292  * The diradd is added to the id_inowait list as it cannot be safely
293  * written to disk until the inode that it represents is on disk. After
294  * the inode is written, the id_bufwait list is processed and the diradd
295  * entries are moved to the id_pendinghd list where they remain until
296  * the directory block containing the name has been written to disk.
297  * The purpose of keeping the entries on the id_pendinghd list is so that
298  * the softdep_fsync function can find and push the inode's directory
299  * name(s) as part of the fsync operation for that file.
300  */
301 struct inodedep {
302 	struct	worklist id_list;	/* buffer holding inode block */
303 #	define	id_state id_list.wk_state /* inode dependency state */
304 	LIST_ENTRY(inodedep) id_hash;	/* hashed lookup */
305 	TAILQ_ENTRY(inodedep) id_unlinked;	/* Unlinked but ref'd inodes */
306 	struct	fs *id_fs;		/* associated filesystem */
307 	ino_t	id_ino;			/* dependent inode */
308 	nlink_t	id_nlinkdelta;		/* saved effective link count */
309 	nlink_t	id_savednlink;		/* Link saved during rollback */
310 	LIST_ENTRY(inodedep) id_deps;	/* bmsafemap's list of inodedep's */
311 	struct	bmsafemap *id_bmsafemap; /* related bmsafemap (if pending) */
312 	struct	diradd *id_mkdiradd;	/* diradd for a mkdir. */
313 	struct	inoreflst id_inoreflst;	/* Inode reference adjustments. */
314 	long	id_savedextsize;	/* ext size saved during rollback */
315 	off_t	id_savedsize;		/* file size saved during rollback */
316 	struct	dirremhd id_dirremhd;	/* Removals pending. */
317 	struct	workhead id_pendinghd;	/* entries awaiting directory write */
318 	struct	workhead id_bufwait;	/* operations after inode written */
319 	struct	workhead id_inowait;	/* operations waiting inode update */
320 	struct	allocdirectlst id_inoupdt; /* updates before inode written */
321 	struct	allocdirectlst id_newinoupdt; /* updates when inode written */
322 	struct	allocdirectlst id_extupdt; /* extdata updates pre-inode write */
323 	struct	allocdirectlst id_newextupdt; /* extdata updates at ino write */
324 	union {
325 	struct	ufs1_dinode *idu_savedino1; /* saved ufs1_dinode contents */
326 	struct	ufs2_dinode *idu_savedino2; /* saved ufs2_dinode contents */
327 	} id_un;
328 };
329 #define id_savedino1 id_un.idu_savedino1
330 #define id_savedino2 id_un.idu_savedino2
331 
332 /*
333  * A "bmsafemap" structure maintains a list of dependency structures
334  * that depend on the update of a particular cylinder group map.
335  * It has lists for newblks, allocdirects, allocindirs, and inodedeps.
336  * It is attached to the buffer of a cylinder group block when any of
337  * these things are allocated from the cylinder group. It is freed
338  * after the cylinder group map is written and the state of its
339  * dependencies are updated with DEPCOMPLETE to indicate that it has
340  * been processed.
341  */
342 struct bmsafemap {
343 	struct	worklist sm_list;	/* cylgrp buffer */
344 #	define	sm_state sm_list.wk_state
345 	int	sm_cg;
346 	LIST_ENTRY(bmsafemap) sm_hash;	/* Hash links. */
347 	struct	buf *sm_buf;		/* associated buffer */
348 	struct	allocdirecthd sm_allocdirecthd; /* allocdirect deps */
349 	struct	allocdirecthd sm_allocdirectwr; /* writing allocdirect deps */
350 	struct	allocindirhd sm_allocindirhd; /* allocindir deps */
351 	struct	allocindirhd sm_allocindirwr; /* writing allocindir deps */
352 	struct	inodedephd sm_inodedephd; /* inodedep deps */
353 	struct	inodedephd sm_inodedepwr; /* writing inodedep deps */
354 	struct	newblkhd sm_newblkhd;	/* newblk deps */
355 	struct	newblkhd sm_newblkwr;	/* writing newblk deps */
356 	struct	jaddrefhd sm_jaddrefhd;	/* Pending inode allocations. */
357 	struct	jnewblkhd sm_jnewblkhd;	/* Pending block allocations. */
358 };
359 
360 /*
361  * A "newblk" structure is attached to a bmsafemap structure when a block
362  * or fragment is allocated from a cylinder group. Its state is set to
363  * DEPCOMPLETE when its cylinder group map is written. It is converted to
364  * an allocdirect or allocindir allocation once the allocator calls the
365  * appropriate setup function. It will initially be linked onto a bmsafemap
366  * list. Once converted it can be linked onto the lists described for
367  * allocdirect or allocindir as described below.
368  */
369 struct newblk {
370 	struct	worklist nb_list;	/* See comment above. */
371 #	define	nb_state nb_list.wk_state
372 	LIST_ENTRY(newblk) nb_hash;	/* Hashed lookup. */
373 	LIST_ENTRY(newblk) nb_deps;	/* Bmsafemap's list of newblks. */
374 	struct	jnewblk *nb_jnewblk;	/* New block journal entry. */
375 	struct	bmsafemap *nb_bmsafemap;/* Cylgrp dep (if pending). */
376 	struct	freefrag *nb_freefrag;	/* Fragment to be freed (if any). */
377 	struct	indirdephd nb_indirdeps; /* Children indirect blocks. */
378 	struct	workhead nb_newdirblk;	/* Dir block to notify when written. */
379 	struct	workhead nb_jwork;	/* Journal work pending. */
380 	ufs2_daddr_t	nb_newblkno;	/* New value of block pointer. */
381 };
382 
383 /*
384  * An "allocdirect" structure is attached to an "inodedep" when a new block
385  * or fragment is allocated and pointed to by the inode described by
386  * "inodedep". The worklist is linked to the buffer that holds the block.
387  * When the block is first allocated, it is linked to the bmsafemap
388  * structure associated with the buffer holding the cylinder group map
389  * from which it was allocated. When the cylinder group map is written
390  * to disk, ad_state has the DEPCOMPLETE flag set. When the block itself
391  * is written, the COMPLETE flag is set. Once both the cylinder group map
392  * and the data itself have been written, it is safe to write the inode
393  * that claims the block. If there was a previous fragment that had been
394  * allocated before the file was increased in size, the old fragment may
395  * be freed once the inode claiming the new block is written to disk.
396  * This ad_fragfree request is attached to the id_inowait list of the
397  * associated inodedep (pointed to by ad_inodedep) for processing after
398  * the inode is written. When a block is allocated to a directory, an
399  * fsync of a file whose name is within that block must ensure not only
400  * that the block containing the file name has been written, but also
401  * that the on-disk inode references that block. When a new directory
402  * block is created, we allocate a newdirblk structure which is linked
403  * to the associated allocdirect (on its ad_newdirblk list). When the
404  * allocdirect has been satisfied, the newdirblk structure is moved to
405  * the inodedep id_bufwait list of its directory to await the inode
406  * being written. When the inode is written, the directory entries are
407  * fully committed and can be deleted from their pagedep->id_pendinghd
408  * and inodedep->id_pendinghd lists.
409  */
410 struct allocdirect {
411 	struct	newblk ad_block;	/* Common block logic */
412 #	define	ad_state ad_block.nb_list.wk_state /* block pointer state */
413 	TAILQ_ENTRY(allocdirect) ad_next; /* inodedep's list of allocdirect's */
414 	struct	inodedep *ad_inodedep;	/* associated inodedep */
415 	ufs2_daddr_t	ad_oldblkno;	/* old value of block pointer */
416 	int		ad_offset;	/* Pointer offset in parent. */
417 	long		ad_newsize;	/* size of new block */
418 	long		ad_oldsize;	/* size of old block */
419 };
420 #define	ad_newblkno	ad_block.nb_newblkno
421 #define	ad_freefrag	ad_block.nb_freefrag
422 #define	ad_newdirblk	ad_block.nb_newdirblk
423 
424 /*
425  * A single "indirdep" structure manages all allocation dependencies for
426  * pointers in an indirect block. The up-to-date state of the indirect
427  * block is stored in ir_savedata. The set of pointers that may be safely
428  * written to the disk is stored in ir_safecopy. The state field is used
429  * only to track whether the buffer is currently being written (in which
430  * case it is not safe to update ir_safecopy). Ir_deplisthd contains the
431  * list of allocindir structures, one for each block that needs to be
432  * written to disk. Once the block and its bitmap allocation have been
433  * written the safecopy can be updated to reflect the allocation and the
434  * allocindir structure freed. If ir_state indicates that an I/O on the
435  * indirect block is in progress when ir_safecopy is to be updated, the
436  * update is deferred by placing the allocindir on the ir_donehd list.
437  * When the I/O on the indirect block completes, the entries on the
438  * ir_donehd list are processed by updating their corresponding ir_safecopy
439  * pointers and then freeing the allocindir structure.
440  */
441 struct indirdep {
442 	struct	worklist ir_list;	/* buffer holding indirect block */
443 #	define	ir_state ir_list.wk_state /* indirect block pointer state */
444 	LIST_ENTRY(indirdep) ir_next;	/* alloc{direct,indir} list */
445 	caddr_t	ir_saveddata;		/* buffer cache contents */
446 	struct	buf *ir_savebp;		/* buffer holding safe copy */
447 	struct	allocindirhd ir_completehd; /* waiting for indirdep complete */
448 	struct	allocindirhd ir_writehd; /* Waiting for the pointer write. */
449 	struct	allocindirhd ir_donehd;	/* done waiting to update safecopy */
450 	struct	allocindirhd ir_deplisthd; /* allocindir deps for this block */
451 	struct	jnewblkhd ir_jnewblkhd;	/* Canceled block allocations. */
452 	struct	workhead ir_jwork;	/* Journal work pending. */
453 };
454 
455 /*
456  * An "allocindir" structure is attached to an "indirdep" when a new block
457  * is allocated and pointed to by the indirect block described by the
458  * "indirdep". The worklist is linked to the buffer that holds the new block.
459  * When the block is first allocated, it is linked to the bmsafemap
460  * structure associated with the buffer holding the cylinder group map
461  * from which it was allocated. When the cylinder group map is written
462  * to disk, ai_state has the DEPCOMPLETE flag set. When the block itself
463  * is written, the COMPLETE flag is set. Once both the cylinder group map
464  * and the data itself have been written, it is safe to write the entry in
465  * the indirect block that claims the block; the "allocindir" dependency
466  * can then be freed as it is no longer applicable.
467  */
468 struct allocindir {
469 	struct	newblk ai_block;	/* Common block area */
470 #	define	ai_state ai_block.nb_list.wk_state /* indirect pointer state */
471 	LIST_ENTRY(allocindir) ai_next;	/* indirdep's list of allocindir's */
472 	struct	indirdep *ai_indirdep;	/* address of associated indirdep */
473 	ufs2_daddr_t	ai_oldblkno;	/* old value of block pointer */
474 	int		ai_offset;	/* Pointer offset in parent. */
475 };
476 #define	ai_newblkno	ai_block.nb_newblkno
477 #define	ai_freefrag	ai_block.nb_freefrag
478 #define	ai_newdirblk	ai_block.nb_newdirblk
479 
480 /*
481  * The allblk union is used to size the newblk structure on allocation so
482  * that it may be any one of three types.
483  */
484 union allblk {
485 	struct	allocindir ab_allocindir;
486 	struct	allocdirect ab_allocdirect;
487 	struct	newblk	ab_newblk;
488 };
489 
490 /*
491  * A "freefrag" structure is attached to an "inodedep" when a previously
492  * allocated fragment is replaced with a larger fragment, rather than extended.
493  * The "freefrag" structure is constructed and attached when the replacement
494  * block is first allocated. It is processed after the inode claiming the
495  * bigger block that replaces it has been written to disk.
496  */
497 struct freefrag {
498 	struct	worklist ff_list;	/* id_inowait or delayed worklist */
499 #	define	ff_state ff_list.wk_state
500 	struct	worklist *ff_jdep;	/* Associated journal entry. */
501 	struct	workhead ff_jwork;	/* Journal work pending. */
502 	ufs2_daddr_t ff_blkno;		/* fragment physical block number */
503 	long	ff_fragsize;		/* size of fragment being deleted */
504 	ino_t	ff_inum;		/* owning inode number */
505 };
506 
507 /*
508  * A "freeblks" structure is attached to an "inodedep" when the
509  * corresponding file's length is reduced to zero. It records all
510  * the information needed to free the blocks of a file after its
511  * zero'ed inode has been written to disk.  The actual work is done
512  * by child freework structures which are responsible for individual
513  * inode pointers while freeblks is responsible for retiring the
514  * entire operation when it is complete and holding common members.
515  */
516 struct freeblks {
517 	struct	worklist fb_list;	/* id_inowait or delayed worklist */
518 #	define	fb_state fb_list.wk_state /* inode and dirty block state */
519 	struct	jfreeblkhd fb_jfreeblkhd; /* Journal entries pending */
520 	struct	workhead fb_freeworkhd;	/* Work items pending */
521 	struct	workhead fb_jwork;	/* Journal work pending */
522 	ino_t	fb_previousinum;	/* inode of previous owner of blocks */
523 	uid_t	fb_uid;			/* uid of previous owner of blocks */
524 	struct	vnode *fb_devvp;	/* filesystem device vnode */
525 	ufs2_daddr_t fb_chkcnt;		/* used to check cnt of blks released */
526 	int	fb_ref;			/* Children outstanding. */
527 };
528 
529 /*
530  * A "freework" structure handles the release of a tree of blocks or a single
531  * block.  Each indirect block in a tree is allocated its own freework
532  * structure so that the indirect block may be freed only when all of its
533  * children are freed.  In this way we enforce the rule that an allocated
534  * block must have a valid path to a root that is journaled.  Each child
535  * block acquires a reference and when the ref hits zero the parent ref
536  * is decremented.  If there is no parent the freeblks ref is decremented.
537  */
538 struct freework {
539 	struct	worklist fw_list;		/* Delayed worklist. */
540 #	define	fw_state fw_list.wk_state
541 	LIST_ENTRY(freework) fw_next;		/* For seg journal list. */
542 	struct	jnewblk  *fw_jnewblk;		/* Journal entry to cancel. */
543 	struct	freeblks *fw_freeblks;		/* Root of operation. */
544 	struct	freework *fw_parent;		/* Parent indirect. */
545 	ufs2_daddr_t	 fw_blkno;		/* Our block #. */
546 	ufs_lbn_t	 fw_lbn;		/* Original lbn before free. */
547 	int		 fw_frags;		/* Number of frags. */
548 	int		 fw_ref;		/* Number of children out. */
549 	int		 fw_off;		/* Current working position. */
550 	struct	workhead fw_jwork;		/* Journal work pending. */
551 };
552 
553 /*
554  * A "freedep" structure is allocated to track the completion of a bitmap
555  * write for a freework.  One freedep may cover many freed blocks so long
556  * as they reside in the same cylinder group.  When the cg is written
557  * the freedep decrements the ref on the freework which may permit it
558  * to be freed as well.
559  */
560 struct freedep {
561 	struct	worklist fd_list;	/* Delayed worklist. */
562 	struct	freework *fd_freework;	/* Parent freework. */
563 };
564 
565 /*
566  * A "freefile" structure is attached to an inode when its
567  * link count is reduced to zero. It marks the inode as free in
568  * the cylinder group map after the zero'ed inode has been written
569  * to disk and any associated blocks and fragments have been freed.
570  */
571 struct freefile {
572 	struct	worklist fx_list;	/* id_inowait or delayed worklist */
573 	mode_t	fx_mode;		/* mode of inode */
574 	ino_t	fx_oldinum;		/* inum of the unlinked file */
575 	struct	vnode *fx_devvp;	/* filesystem device vnode */
576 	struct	workhead fx_jwork;	/* journal work pending. */
577 };
578 
579 /*
580  * A "diradd" structure is linked to an "inodedep" id_inowait list when a
581  * new directory entry is allocated that references the inode described
582  * by "inodedep". When the inode itself is written (either the initial
583  * allocation for new inodes or with the increased link count for
584  * existing inodes), the COMPLETE flag is set in da_state. If the entry
585  * is for a newly allocated inode, the "inodedep" structure is associated
586  * with a bmsafemap which prevents the inode from being written to disk
587  * until the cylinder group has been updated. Thus the da_state COMPLETE
588  * flag cannot be set until the inode bitmap dependency has been removed.
589  * When creating a new file, it is safe to write the directory entry that
590  * claims the inode once the referenced inode has been written. Since
591  * writing the inode clears the bitmap dependencies, the DEPCOMPLETE flag
592  * in the diradd can be set unconditionally when creating a file. When
593  * creating a directory, there are two additional dependencies described by
594  * mkdir structures (see their description below). When these dependencies
595  * are resolved the DEPCOMPLETE flag is set in the diradd structure.
596  * If there are multiple links created to the same inode, there will be
597  * a separate diradd structure created for each link. The diradd is
598  * linked onto the pg_diraddhd list of the pagedep for the directory
599  * page that contains the entry. When a directory page is written,
600  * the pg_diraddhd list is traversed to rollback any entries that are
601  * not yet ready to be written to disk. If a directory entry is being
602  * changed (by rename) rather than added, the DIRCHG flag is set and
603  * the da_previous entry points to the entry that will be "removed"
604  * once the new entry has been committed. During rollback, entries
605  * with da_previous are replaced with the previous inode number rather
606  * than zero.
607  *
608  * The overlaying of da_pagedep and da_previous is done to keep the
609  * structure down. If a da_previous entry is present, the pointer to its
610  * pagedep is available in the associated dirrem entry. If the DIRCHG flag
611  * is set, the da_previous entry is valid; if not set the da_pagedep entry
612  * is valid. The DIRCHG flag never changes; it is set when the structure
613  * is created if appropriate and is never cleared.
614  */
615 struct diradd {
616 	struct	worklist da_list;	/* id_inowait or id_pendinghd list */
617 #	define	da_state da_list.wk_state /* state of the new directory entry */
618 	LIST_ENTRY(diradd) da_pdlist;	/* pagedep holding directory block */
619 	doff_t	da_offset;		/* offset of new dir entry in dir blk */
620 	ino_t	da_newinum;		/* inode number for the new dir entry */
621 	union {
622 	struct	dirrem *dau_previous;	/* entry being replaced in dir change */
623 	struct	pagedep *dau_pagedep;	/* pagedep dependency for addition */
624 	} da_un;
625 	struct workhead da_jwork;	/* Journal work awaiting completion. */
626 };
627 #define da_previous da_un.dau_previous
628 #define da_pagedep da_un.dau_pagedep
629 
630 /*
631  * Two "mkdir" structures are needed to track the additional dependencies
632  * associated with creating a new directory entry. Normally a directory
633  * addition can be committed as soon as the newly referenced inode has been
634  * written to disk with its increased link count. When a directory is
635  * created there are two additional dependencies: writing the directory
636  * data block containing the "." and ".." entries (MKDIR_BODY) and writing
637  * the parent inode with the increased link count for ".." (MKDIR_PARENT).
638  * These additional dependencies are tracked by two mkdir structures that
639  * reference the associated "diradd" structure. When they have completed,
640  * they set the DEPCOMPLETE flag on the diradd so that it knows that its
641  * extra dependencies have been completed. The md_state field is used only
642  * to identify which type of dependency the mkdir structure is tracking.
643  * It is not used in the mainline code for any purpose other than consistency
644  * checking. All the mkdir structures in the system are linked together on
645  * a list. This list is needed so that a diradd can find its associated
646  * mkdir structures and deallocate them if it is prematurely freed (as for
647  * example if a mkdir is immediately followed by a rmdir of the same directory).
648  * Here, the free of the diradd must traverse the list to find the associated
649  * mkdir structures that reference it. The deletion would be faster if the
650  * diradd structure were simply augmented to have two pointers that referenced
651  * the associated mkdir's. However, this would increase the size of the diradd
652  * structure to speed a very infrequent operation.
653  */
654 struct mkdir {
655 	struct	worklist md_list;	/* id_inowait or buffer holding dir */
656 #	define	md_state md_list.wk_state /* type: MKDIR_PARENT or MKDIR_BODY */
657 	struct	diradd *md_diradd;	/* associated diradd */
658 	struct	jaddref *md_jaddref;	/* dependent jaddref. */
659 	struct	buf *md_buf;		/* MKDIR_BODY: buffer holding dir */
660 	LIST_ENTRY(mkdir) md_mkdirs;	/* list of all mkdirs */
661 };
662 
663 /*
664  * A "dirrem" structure describes an operation to decrement the link
665  * count on an inode. The dirrem structure is attached to the pg_dirremhd
666  * list of the pagedep for the directory page that contains the entry.
667  * It is processed after the directory page with the deleted entry has
668  * been written to disk.
669  */
670 struct dirrem {
671 	struct	worklist dm_list;	/* delayed worklist */
672 #	define	dm_state dm_list.wk_state /* state of the old directory entry */
673 	LIST_ENTRY(dirrem) dm_next;	/* pagedep's list of dirrem's */
674 	LIST_ENTRY(dirrem) dm_inonext;	/* inodedep's list of dirrem's */
675 	struct	jremrefhd dm_jremrefhd;	/* Pending remove reference deps. */
676 	ino_t	dm_oldinum;		/* inum of the removed dir entry */
677 	union {
678 	struct	pagedep *dmu_pagedep;	/* pagedep dependency for remove */
679 	ino_t	dmu_dirinum;		/* parent inode number (for rmdir) */
680 	} dm_un;
681 	struct workhead dm_jwork;	/* Journal work awaiting completion. */
682 };
683 #define dm_pagedep dm_un.dmu_pagedep
684 #define dm_dirinum dm_un.dmu_dirinum
685 
686 /*
687  * A "newdirblk" structure tracks the progress of a newly allocated
688  * directory block from its creation until it is claimed by its on-disk
689  * inode. When a block is allocated to a directory, an fsync of a file
690  * whose name is within that block must ensure not only that the block
691  * containing the file name has been written, but also that the on-disk
692  * inode references that block. When a new directory block is created,
693  * we allocate a newdirblk structure which is linked to the associated
694  * allocdirect (on its ad_newdirblk list). When the allocdirect has been
695  * satisfied, the newdirblk structure is moved to the inodedep id_bufwait
696  * list of its directory to await the inode being written. When the inode
697  * is written, the directory entries are fully committed and can be
698  * deleted from their pagedep->id_pendinghd and inodedep->id_pendinghd
699  * lists. Note that we could track directory blocks allocated to indirect
700  * blocks using a similar scheme with the allocindir structures. Rather
701  * than adding this level of complexity, we simply write those newly
702  * allocated indirect blocks synchronously as such allocations are rare.
703  * In the case of a new directory the . and .. links are tracked with
704  * a mkdir rather than a pagedep.  In this case we track the mkdir
705  * so it can be released when it is written.  A workhead is used
706  * to simplify canceling a mkdir that is removed by a subsequent dirrem.
707  */
708 struct newdirblk {
709 	struct	worklist db_list;	/* id_inowait or pg_newdirblk */
710 #	define	db_state db_list.wk_state /* unused */
711 	struct	pagedep *db_pagedep;	/* associated pagedep */
712 	struct	workhead db_mkdir;
713 };
714 
715 /*
716  * The inoref structure holds the elements common to jaddref and jremref
717  * so they may easily be queued in-order on the inodedep.
718  */
719 struct inoref {
720 	struct	worklist if_list;	/* Journal pending or jseg entries. */
721 #	define	if_state if_list.wk_state
722 	TAILQ_ENTRY(inoref) if_deps;	/* Links for inodedep. */
723 	struct	jsegdep	*if_jsegdep;	/* Will track our journal record. */
724 	off_t		if_diroff;	/* Directory offset. */
725 	ino_t		if_ino;		/* Inode number. */
726 	ino_t		if_parent;	/* Parent inode number. */
727 	nlink_t		if_nlink;	/* nlink before addition. */
728 	uint16_t	if_mode;	/* File mode, needed for IFMT. */
729 };
730 
731 /*
732  * A "jaddref" structure tracks a new reference (link count) on an inode
733  * and prevents the link count increase and bitmap allocation until a
734  * journal entry can be written.  Once the journal entry is written,
735  * the inode is put on the pendinghd of the bmsafemap and a diradd or
736  * mkdir entry is placed on the bufwait list of the inode.  The DEPCOMPLETE
737  * flag is used to indicate that all of the required information for writing
738  * the journal entry is present.  MKDIR_BODY and MKDIR_PARENT are used to
739  * differentiate . and .. links from regular file names.  NEWBLOCK indicates
740  * a bitmap is still pending.  If a new reference is canceled by a delete
741  * prior to writing the journal the jaddref write is canceled and the
742  * structure persists to prevent any disk-visible changes until it is
743  * ultimately released when the file is freed or the link is dropped again.
744  */
745 struct jaddref {
746 	struct	inoref	ja_ref;		/* see inoref above. */
747 #	define	ja_list	ja_ref.if_list	/* Jrnl pending, id_inowait, dm_jwork.*/
748 #	define	ja_state ja_ref.if_list.wk_state
749 	LIST_ENTRY(jaddref) ja_bmdeps;	/* Links for bmsafemap. */
750 	union {
751 		struct	diradd	*jau_diradd;	/* Pending diradd. */
752 		struct	mkdir	*jau_mkdir;	/* MKDIR_{PARENT,BODY} */
753 	} ja_un;
754 };
755 #define	ja_diradd	ja_un.jau_diradd
756 #define	ja_mkdir	ja_un.jau_mkdir
757 #define	ja_diroff	ja_ref.if_diroff
758 #define	ja_ino		ja_ref.if_ino
759 #define	ja_parent	ja_ref.if_parent
760 #define	ja_mode		ja_ref.if_mode
761 
762 /*
763  * A "jremref" structure tracks a removed reference (unlink) on an
764  * inode and prevents the directory remove from proceeding until the
765  * journal entry is written.  Once the journal has been written the remove
766  * may proceed as normal.
767  */
768 struct jremref {
769 	struct	inoref	jr_ref;		/* see inoref above. */
770 #	define	jr_list	jr_ref.if_list	/* Linked to softdep_journal_pending. */
771 #	define	jr_state jr_ref.if_list.wk_state
772 	LIST_ENTRY(jremref) jr_deps;	/* Links for dirrem. */
773 	struct	dirrem	*jr_dirrem;	/* Back pointer to dirrem. */
774 };
775 
776 /*
777  * A "jmvref" structure tracks a name relocations within the same
778  * directory block that occur as a result of directory compaction.
779  * It prevents the updated directory entry from being written to disk
780  * until the journal entry is written. Once the journal has been
781  * written the compacted directory may be written to disk.
782  */
783 struct jmvref {
784 	struct	worklist jm_list;	/* Linked to softdep_journal_pending. */
785 	LIST_ENTRY(jmvref) jm_deps;	/* Jmvref on pagedep. */
786 	struct pagedep	*jm_pagedep;	/* Back pointer to pagedep. */
787 	ino_t		jm_parent;	/* Containing directory inode number. */
788 	ino_t		jm_ino;		/* Inode number of our entry. */
789 	off_t		jm_oldoff;	/* Our old offset in directory. */
790 	off_t		jm_newoff;	/* Our new offset in directory. */
791 };
792 
793 /*
794  * A "jnewblk" structure tracks a newly allocated block or fragment and
795  * prevents the direct or indirect block pointer as well as the cg bitmap
796  * from being written until it is logged.  After it is logged the jsegdep
797  * is attached to the allocdirect or allocindir until the operation is
798  * completed or reverted.  If the operation is reverted prior to the journal
799  * write the jnewblk structure is maintained to prevent the bitmaps from
800  * reaching the disk.  Ultimately the jnewblk structure will be passed
801  * to the free routine as the in memory cg is modified back to the free
802  * state at which time it can be released. It may be held on any of the
803  * fx_jwork, fw_jwork, fb_jwork, ff_jwork, nb_jwork, or ir_jwork lists.
804  */
805 struct jnewblk {
806 	struct	worklist jn_list;	/* See lists above. */
807 #	define	jn_state jn_list.wk_state
808 	struct	jsegdep	*jn_jsegdep;	/* Will track our journal record. */
809 	LIST_ENTRY(jnewblk) jn_deps;	/* Jnewblks on sm_jnewblkhd. */
810 	LIST_ENTRY(jnewblk) jn_indirdeps; /* Jnewblks on ir_jnewblkhd. */
811 	struct	worklist *jn_dep;	/* Dependency to ref completed seg. */
812 	ino_t		jn_ino;		/* Ino to which allocated. */
813 	ufs_lbn_t	jn_lbn;		/* Lbn to which allocated. */
814 	ufs2_daddr_t	jn_blkno;	/* Blkno allocated */
815 	int		jn_oldfrags;	/* Previous fragments when extended. */
816 	int		jn_frags;	/* Number of fragments. */
817 };
818 
819 /*
820  * A "jfreeblk" structure tracks the journal write for freeing a block
821  * or tree of blocks.  The block pointer must not be cleared in the inode
822  * or indirect prior to the jfreeblk being written to the journal.
823  */
824 struct jfreeblk {
825 	struct	worklist jf_list;	/* Linked to softdep_journal_pending. */
826 #	define	jf_state jf_list.wk_state
827 	struct	jsegdep	*jf_jsegdep;	/* Will track our journal record. */
828 	struct freeblks	*jf_freeblks;	/* Back pointer to freeblks. */
829 	LIST_ENTRY(jfreeblk) jf_deps;	/* Jfreeblk on fb_jfreeblkhd. */
830 	ino_t		jf_ino;		/* Ino from which blocks freed. */
831 	ufs_lbn_t	jf_lbn;		/* Lbn from which blocks freed. */
832 	ufs2_daddr_t	jf_blkno;	/* Blkno being freed. */
833 	int		jf_frags;	/* Number of frags being freed. */
834 };
835 
836 /*
837  * A "jfreefrag" tracks the freeing of a single block when a fragment is
838  * extended or an indirect page is replaced.  It is not part of a larger
839  * freeblks operation.
840  */
841 struct jfreefrag {
842 	struct	worklist fr_list;	/* Linked to softdep_journal_pending. */
843 #	define	fr_state fr_list.wk_state
844 	struct	jsegdep	*fr_jsegdep;	/* Will track our journal record. */
845 	struct freefrag	*fr_freefrag;	/* Back pointer to freefrag. */
846 	ino_t		fr_ino;		/* Ino from which frag freed. */
847 	ufs_lbn_t	fr_lbn;		/* Lbn from which frag freed. */
848 	ufs2_daddr_t	fr_blkno;	/* Blkno being freed. */
849 	int		fr_frags;	/* Size of frag being freed. */
850 };
851 
852 /*
853  * A "jtrunc" journals the intent to truncate an inode to a non-zero
854  * value.  This is done synchronously prior to the synchronous partial
855  * truncation process.  The jsegdep is not released until the truncation
856  * is complete and the truncated inode is fsync'd.
857  */
858 struct jtrunc {
859 	struct	worklist jt_list;	/* Linked to softdep_journal_pending. */
860 	struct	jsegdep	*jt_jsegdep;	/* Will track our journal record. */
861 	ino_t		 jt_ino;	/* Ino being truncated. */
862 	off_t		 jt_size;	/* Final file size. */
863 	int		 jt_extsize;	/* Final extent size. */
864 };
865 
866 /*
867  * A "jsegdep" structure tracks a single reference to a written journal
868  * segment so the journal space can be reclaimed when all dependencies
869  * have been written. It can hang off of id_inowait, dm_jwork, da_jwork,
870  * nb_jwork, ff_jwork, or fb_jwork lists.
871  */
872 struct jsegdep {
873 	struct	worklist jd_list;	/* See above for lists. */
874 #	define	jd_state jd_list.wk_state
875 	struct	jseg	*jd_seg;	/* Our journal record. */
876 };
877 
878 /*
879  * A "jseg" structure contains all of the journal records written in a
880  * single disk write.  The jaddref and jremref structures are linked into
881  * js_entries so thay may be completed when the write completes.  The
882  * js_entries also include the write dependency structures: jmvref,
883  * jnewblk, jfreeblk, jfreefrag, and jtrunc.  The js_refs field counts
884  * the number of entries on the js_entries list. Thus there is a single
885  * jseg entry to describe each journal write.
886  */
887 struct jseg {
888 	struct	worklist js_list;	/* b_deps link for journal */
889 #	define	js_state js_list.wk_state
890 	struct	workhead js_entries;	/* Entries awaiting write */
891 	LIST_HEAD(, freework) js_indirs;/* List of indirects in this seg. */
892 	TAILQ_ENTRY(jseg) js_next;	/* List of all unfinished segments. */
893 	struct	jblocks *js_jblocks;	/* Back pointer to block/seg list */
894 	struct	buf *js_buf;		/* Buffer while unwritten */
895 	uint64_t js_seq;		/* Journal record sequence number. */
896 	uint64_t js_oldseq;		/* Oldest valid sequence number. */
897 	int	js_size;		/* Size of journal record in bytes. */
898 	int	js_cnt;			/* Total items allocated. */
899 	int	js_refs;		/* Count of js_entries items. */
900 };
901 
902 /*
903  * A 'sbdep' structure tracks the head of the free inode list and
904  * superblock writes.  This makes sure the superblock is always pointing at
905  * the first possible unlinked inode for the suj recovery process.  If a
906  * block write completes and we discover a new head is available the buf
907  * is dirtied and the dep is kept. See the description of the UNLINK*
908  * flags above for more details.
909  */
910 struct sbdep {
911 	struct	worklist sb_list;	/* b_dep linkage */
912 	struct	fs	*sb_fs;		/* Filesystem pointer within buf. */
913 	struct	ufsmount *sb_ump;	/* Our mount structure */
914 };
915