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TOMOYO Linux Cross Reference
Linux/fs/ceph/snap.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 #include <linux/ceph/ceph_debug.h>
  3 
  4 #include <linux/sort.h>
  5 #include <linux/slab.h>
  6 
  7 #include "super.h"
  8 #include "mds_client.h"
  9 
 10 #include <linux/ceph/decode.h>
 11 
 12 /*
 13  * Snapshots in ceph are driven in large part by cooperation from the
 14  * client.  In contrast to local file systems or file servers that
 15  * implement snapshots at a single point in the system, ceph's
 16  * distributed access to storage requires clients to help decide
 17  * whether a write logically occurs before or after a recently created
 18  * snapshot.
 19  *
 20  * This provides a perfect instantanous client-wide snapshot.  Between
 21  * clients, however, snapshots may appear to be applied at slightly
 22  * different points in time, depending on delays in delivering the
 23  * snapshot notification.
 24  *
 25  * Snapshots are _not_ file system-wide.  Instead, each snapshot
 26  * applies to the subdirectory nested beneath some directory.  This
 27  * effectively divides the hierarchy into multiple "realms," where all
 28  * of the files contained by each realm share the same set of
 29  * snapshots.  An individual realm's snap set contains snapshots
 30  * explicitly created on that realm, as well as any snaps in its
 31  * parent's snap set _after_ the point at which the parent became it's
 32  * parent (due to, say, a rename).  Similarly, snaps from prior parents
 33  * during the time intervals during which they were the parent are included.
 34  *
 35  * The client is spared most of this detail, fortunately... it must only
 36  * maintains a hierarchy of realms reflecting the current parent/child
 37  * realm relationship, and for each realm has an explicit list of snaps
 38  * inherited from prior parents.
 39  *
 40  * A snap_realm struct is maintained for realms containing every inode
 41  * with an open cap in the system.  (The needed snap realm information is
 42  * provided by the MDS whenever a cap is issued, i.e., on open.)  A 'seq'
 43  * version number is used to ensure that as realm parameters change (new
 44  * snapshot, new parent, etc.) the client's realm hierarchy is updated.
 45  *
 46  * The realm hierarchy drives the generation of a 'snap context' for each
 47  * realm, which simply lists the resulting set of snaps for the realm.  This
 48  * is attached to any writes sent to OSDs.
 49  */
 50 /*
 51  * Unfortunately error handling is a bit mixed here.  If we get a snap
 52  * update, but don't have enough memory to update our realm hierarchy,
 53  * it's not clear what we can do about it (besides complaining to the
 54  * console).
 55  */
 56 
 57 
 58 /*
 59  * increase ref count for the realm
 60  *
 61  * caller must hold snap_rwsem for write.
 62  */
 63 void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
 64                          struct ceph_snap_realm *realm)
 65 {
 66         dout("get_realm %p %d -> %d\n", realm,
 67              atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
 68         /*
 69          * since we _only_ increment realm refs or empty the empty
 70          * list with snap_rwsem held, adjusting the empty list here is
 71          * safe.  we do need to protect against concurrent empty list
 72          * additions, however.
 73          */
 74         if (atomic_inc_return(&realm->nref) == 1) {
 75                 spin_lock(&mdsc->snap_empty_lock);
 76                 list_del_init(&realm->empty_item);
 77                 spin_unlock(&mdsc->snap_empty_lock);
 78         }
 79 }
 80 
 81 static void __insert_snap_realm(struct rb_root *root,
 82                                 struct ceph_snap_realm *new)
 83 {
 84         struct rb_node **p = &root->rb_node;
 85         struct rb_node *parent = NULL;
 86         struct ceph_snap_realm *r = NULL;
 87 
 88         while (*p) {
 89                 parent = *p;
 90                 r = rb_entry(parent, struct ceph_snap_realm, node);
 91                 if (new->ino < r->ino)
 92                         p = &(*p)->rb_left;
 93                 else if (new->ino > r->ino)
 94                         p = &(*p)->rb_right;
 95                 else
 96                         BUG();
 97         }
 98 
 99         rb_link_node(&new->node, parent, p);
100         rb_insert_color(&new->node, root);
101 }
102 
103 /*
104  * create and get the realm rooted at @ino and bump its ref count.
105  *
106  * caller must hold snap_rwsem for write.
107  */
108 static struct ceph_snap_realm *ceph_create_snap_realm(
109         struct ceph_mds_client *mdsc,
110         u64 ino)
111 {
112         struct ceph_snap_realm *realm;
113 
114         realm = kzalloc(sizeof(*realm), GFP_NOFS);
115         if (!realm)
116                 return ERR_PTR(-ENOMEM);
117 
118         atomic_set(&realm->nref, 1);    /* for caller */
119         realm->ino = ino;
120         INIT_LIST_HEAD(&realm->children);
121         INIT_LIST_HEAD(&realm->child_item);
122         INIT_LIST_HEAD(&realm->empty_item);
123         INIT_LIST_HEAD(&realm->dirty_item);
124         INIT_LIST_HEAD(&realm->inodes_with_caps);
125         spin_lock_init(&realm->inodes_with_caps_lock);
126         __insert_snap_realm(&mdsc->snap_realms, realm);
127         dout("create_snap_realm %llx %p\n", realm->ino, realm);
128         return realm;
129 }
130 
131 /*
132  * lookup the realm rooted at @ino.
133  *
134  * caller must hold snap_rwsem for write.
135  */
136 static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
137                                                    u64 ino)
138 {
139         struct rb_node *n = mdsc->snap_realms.rb_node;
140         struct ceph_snap_realm *r;
141 
142         while (n) {
143                 r = rb_entry(n, struct ceph_snap_realm, node);
144                 if (ino < r->ino)
145                         n = n->rb_left;
146                 else if (ino > r->ino)
147                         n = n->rb_right;
148                 else {
149                         dout("lookup_snap_realm %llx %p\n", r->ino, r);
150                         return r;
151                 }
152         }
153         return NULL;
154 }
155 
156 struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc,
157                                                u64 ino)
158 {
159         struct ceph_snap_realm *r;
160         r = __lookup_snap_realm(mdsc, ino);
161         if (r)
162                 ceph_get_snap_realm(mdsc, r);
163         return r;
164 }
165 
166 static void __put_snap_realm(struct ceph_mds_client *mdsc,
167                              struct ceph_snap_realm *realm);
168 
169 /*
170  * called with snap_rwsem (write)
171  */
172 static void __destroy_snap_realm(struct ceph_mds_client *mdsc,
173                                  struct ceph_snap_realm *realm)
174 {
175         dout("__destroy_snap_realm %p %llx\n", realm, realm->ino);
176 
177         rb_erase(&realm->node, &mdsc->snap_realms);
178 
179         if (realm->parent) {
180                 list_del_init(&realm->child_item);
181                 __put_snap_realm(mdsc, realm->parent);
182         }
183 
184         kfree(realm->prior_parent_snaps);
185         kfree(realm->snaps);
186         ceph_put_snap_context(realm->cached_context);
187         kfree(realm);
188 }
189 
190 /*
191  * caller holds snap_rwsem (write)
192  */
193 static void __put_snap_realm(struct ceph_mds_client *mdsc,
194                              struct ceph_snap_realm *realm)
195 {
196         dout("__put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
197              atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
198         if (atomic_dec_and_test(&realm->nref))
199                 __destroy_snap_realm(mdsc, realm);
200 }
201 
202 /*
203  * caller needn't hold any locks
204  */
205 void ceph_put_snap_realm(struct ceph_mds_client *mdsc,
206                          struct ceph_snap_realm *realm)
207 {
208         dout("put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
209              atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
210         if (!atomic_dec_and_test(&realm->nref))
211                 return;
212 
213         if (down_write_trylock(&mdsc->snap_rwsem)) {
214                 __destroy_snap_realm(mdsc, realm);
215                 up_write(&mdsc->snap_rwsem);
216         } else {
217                 spin_lock(&mdsc->snap_empty_lock);
218                 list_add(&realm->empty_item, &mdsc->snap_empty);
219                 spin_unlock(&mdsc->snap_empty_lock);
220         }
221 }
222 
223 /*
224  * Clean up any realms whose ref counts have dropped to zero.  Note
225  * that this does not include realms who were created but not yet
226  * used.
227  *
228  * Called under snap_rwsem (write)
229  */
230 static void __cleanup_empty_realms(struct ceph_mds_client *mdsc)
231 {
232         struct ceph_snap_realm *realm;
233 
234         spin_lock(&mdsc->snap_empty_lock);
235         while (!list_empty(&mdsc->snap_empty)) {
236                 realm = list_first_entry(&mdsc->snap_empty,
237                                    struct ceph_snap_realm, empty_item);
238                 list_del(&realm->empty_item);
239                 spin_unlock(&mdsc->snap_empty_lock);
240                 __destroy_snap_realm(mdsc, realm);
241                 spin_lock(&mdsc->snap_empty_lock);
242         }
243         spin_unlock(&mdsc->snap_empty_lock);
244 }
245 
246 void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc)
247 {
248         down_write(&mdsc->snap_rwsem);
249         __cleanup_empty_realms(mdsc);
250         up_write(&mdsc->snap_rwsem);
251 }
252 
253 /*
254  * adjust the parent realm of a given @realm.  adjust child list, and parent
255  * pointers, and ref counts appropriately.
256  *
257  * return true if parent was changed, 0 if unchanged, <0 on error.
258  *
259  * caller must hold snap_rwsem for write.
260  */
261 static int adjust_snap_realm_parent(struct ceph_mds_client *mdsc,
262                                     struct ceph_snap_realm *realm,
263                                     u64 parentino)
264 {
265         struct ceph_snap_realm *parent;
266 
267         if (realm->parent_ino == parentino)
268                 return 0;
269 
270         parent = ceph_lookup_snap_realm(mdsc, parentino);
271         if (!parent) {
272                 parent = ceph_create_snap_realm(mdsc, parentino);
273                 if (IS_ERR(parent))
274                         return PTR_ERR(parent);
275         }
276         dout("adjust_snap_realm_parent %llx %p: %llx %p -> %llx %p\n",
277              realm->ino, realm, realm->parent_ino, realm->parent,
278              parentino, parent);
279         if (realm->parent) {
280                 list_del_init(&realm->child_item);
281                 ceph_put_snap_realm(mdsc, realm->parent);
282         }
283         realm->parent_ino = parentino;
284         realm->parent = parent;
285         list_add(&realm->child_item, &parent->children);
286         return 1;
287 }
288 
289 
290 static int cmpu64_rev(const void *a, const void *b)
291 {
292         if (*(u64 *)a < *(u64 *)b)
293                 return 1;
294         if (*(u64 *)a > *(u64 *)b)
295                 return -1;
296         return 0;
297 }
298 
299 
300 /*
301  * build the snap context for a given realm.
302  */
303 static int build_snap_context(struct ceph_snap_realm *realm,
304                               struct list_head* dirty_realms)
305 {
306         struct ceph_snap_realm *parent = realm->parent;
307         struct ceph_snap_context *snapc;
308         int err = 0;
309         u32 num = realm->num_prior_parent_snaps + realm->num_snaps;
310 
311         /*
312          * build parent context, if it hasn't been built.
313          * conservatively estimate that all parent snaps might be
314          * included by us.
315          */
316         if (parent) {
317                 if (!parent->cached_context) {
318                         err = build_snap_context(parent, dirty_realms);
319                         if (err)
320                                 goto fail;
321                 }
322                 num += parent->cached_context->num_snaps;
323         }
324 
325         /* do i actually need to update?  not if my context seq
326            matches realm seq, and my parents' does to.  (this works
327            because we rebuild_snap_realms() works _downward_ in
328            hierarchy after each update.) */
329         if (realm->cached_context &&
330             realm->cached_context->seq == realm->seq &&
331             (!parent ||
332              realm->cached_context->seq >= parent->cached_context->seq)) {
333                 dout("build_snap_context %llx %p: %p seq %lld (%u snaps)"
334                      " (unchanged)\n",
335                      realm->ino, realm, realm->cached_context,
336                      realm->cached_context->seq,
337                      (unsigned int)realm->cached_context->num_snaps);
338                 return 0;
339         }
340 
341         /* alloc new snap context */
342         err = -ENOMEM;
343         if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
344                 goto fail;
345         snapc = ceph_create_snap_context(num, GFP_NOFS);
346         if (!snapc)
347                 goto fail;
348 
349         /* build (reverse sorted) snap vector */
350         num = 0;
351         snapc->seq = realm->seq;
352         if (parent) {
353                 u32 i;
354 
355                 /* include any of parent's snaps occurring _after_ my
356                    parent became my parent */
357                 for (i = 0; i < parent->cached_context->num_snaps; i++)
358                         if (parent->cached_context->snaps[i] >=
359                             realm->parent_since)
360                                 snapc->snaps[num++] =
361                                         parent->cached_context->snaps[i];
362                 if (parent->cached_context->seq > snapc->seq)
363                         snapc->seq = parent->cached_context->seq;
364         }
365         memcpy(snapc->snaps + num, realm->snaps,
366                sizeof(u64)*realm->num_snaps);
367         num += realm->num_snaps;
368         memcpy(snapc->snaps + num, realm->prior_parent_snaps,
369                sizeof(u64)*realm->num_prior_parent_snaps);
370         num += realm->num_prior_parent_snaps;
371 
372         sort(snapc->snaps, num, sizeof(u64), cmpu64_rev, NULL);
373         snapc->num_snaps = num;
374         dout("build_snap_context %llx %p: %p seq %lld (%u snaps)\n",
375              realm->ino, realm, snapc, snapc->seq,
376              (unsigned int) snapc->num_snaps);
377 
378         ceph_put_snap_context(realm->cached_context);
379         realm->cached_context = snapc;
380         /* queue realm for cap_snap creation */
381         list_add_tail(&realm->dirty_item, dirty_realms);
382         return 0;
383 
384 fail:
385         /*
386          * if we fail, clear old (incorrect) cached_context... hopefully
387          * we'll have better luck building it later
388          */
389         if (realm->cached_context) {
390                 ceph_put_snap_context(realm->cached_context);
391                 realm->cached_context = NULL;
392         }
393         pr_err("build_snap_context %llx %p fail %d\n", realm->ino,
394                realm, err);
395         return err;
396 }
397 
398 /*
399  * rebuild snap context for the given realm and all of its children.
400  */
401 static void rebuild_snap_realms(struct ceph_snap_realm *realm,
402                                 struct list_head *dirty_realms)
403 {
404         struct ceph_snap_realm *child;
405 
406         dout("rebuild_snap_realms %llx %p\n", realm->ino, realm);
407         build_snap_context(realm, dirty_realms);
408 
409         list_for_each_entry(child, &realm->children, child_item)
410                 rebuild_snap_realms(child, dirty_realms);
411 }
412 
413 
414 /*
415  * helper to allocate and decode an array of snapids.  free prior
416  * instance, if any.
417  */
418 static int dup_array(u64 **dst, __le64 *src, u32 num)
419 {
420         u32 i;
421 
422         kfree(*dst);
423         if (num) {
424                 *dst = kcalloc(num, sizeof(u64), GFP_NOFS);
425                 if (!*dst)
426                         return -ENOMEM;
427                 for (i = 0; i < num; i++)
428                         (*dst)[i] = get_unaligned_le64(src + i);
429         } else {
430                 *dst = NULL;
431         }
432         return 0;
433 }
434 
435 static bool has_new_snaps(struct ceph_snap_context *o,
436                           struct ceph_snap_context *n)
437 {
438         if (n->num_snaps == 0)
439                 return false;
440         /* snaps are in descending order */
441         return n->snaps[0] > o->seq;
442 }
443 
444 /*
445  * When a snapshot is applied, the size/mtime inode metadata is queued
446  * in a ceph_cap_snap (one for each snapshot) until writeback
447  * completes and the metadata can be flushed back to the MDS.
448  *
449  * However, if a (sync) write is currently in-progress when we apply
450  * the snapshot, we have to wait until the write succeeds or fails
451  * (and a final size/mtime is known).  In this case the
452  * cap_snap->writing = 1, and is said to be "pending."  When the write
453  * finishes, we __ceph_finish_cap_snap().
454  *
455  * Caller must hold snap_rwsem for read (i.e., the realm topology won't
456  * change).
457  */
458 void ceph_queue_cap_snap(struct ceph_inode_info *ci)
459 {
460         struct inode *inode = &ci->vfs_inode;
461         struct ceph_cap_snap *capsnap;
462         struct ceph_snap_context *old_snapc, *new_snapc;
463         int used, dirty;
464 
465         capsnap = kzalloc(sizeof(*capsnap), GFP_NOFS);
466         if (!capsnap) {
467                 pr_err("ENOMEM allocating ceph_cap_snap on %p\n", inode);
468                 return;
469         }
470 
471         spin_lock(&ci->i_ceph_lock);
472         used = __ceph_caps_used(ci);
473         dirty = __ceph_caps_dirty(ci);
474 
475         old_snapc = ci->i_head_snapc;
476         new_snapc = ci->i_snap_realm->cached_context;
477 
478         /*
479          * If there is a write in progress, treat that as a dirty Fw,
480          * even though it hasn't completed yet; by the time we finish
481          * up this capsnap it will be.
482          */
483         if (used & CEPH_CAP_FILE_WR)
484                 dirty |= CEPH_CAP_FILE_WR;
485 
486         if (__ceph_have_pending_cap_snap(ci)) {
487                 /* there is no point in queuing multiple "pending" cap_snaps,
488                    as no new writes are allowed to start when pending, so any
489                    writes in progress now were started before the previous
490                    cap_snap.  lucky us. */
491                 dout("queue_cap_snap %p already pending\n", inode);
492                 goto update_snapc;
493         }
494         if (ci->i_wrbuffer_ref_head == 0 &&
495             !(dirty & (CEPH_CAP_ANY_EXCL|CEPH_CAP_FILE_WR))) {
496                 dout("queue_cap_snap %p nothing dirty|writing\n", inode);
497                 goto update_snapc;
498         }
499 
500         BUG_ON(!old_snapc);
501 
502         /*
503          * There is no need to send FLUSHSNAP message to MDS if there is
504          * no new snapshot. But when there is dirty pages or on-going
505          * writes, we still need to create cap_snap. cap_snap is needed
506          * by the write path and page writeback path.
507          *
508          * also see ceph_try_drop_cap_snap()
509          */
510         if (has_new_snaps(old_snapc, new_snapc)) {
511                 if (dirty & (CEPH_CAP_ANY_EXCL|CEPH_CAP_FILE_WR))
512                         capsnap->need_flush = true;
513         } else {
514                 if (!(used & CEPH_CAP_FILE_WR) &&
515                     ci->i_wrbuffer_ref_head == 0) {
516                         dout("queue_cap_snap %p "
517                              "no new_snap|dirty_page|writing\n", inode);
518                         goto update_snapc;
519                 }
520         }
521 
522         dout("queue_cap_snap %p cap_snap %p queuing under %p %s %s\n",
523              inode, capsnap, old_snapc, ceph_cap_string(dirty),
524              capsnap->need_flush ? "" : "no_flush");
525         ihold(inode);
526 
527         refcount_set(&capsnap->nref, 1);
528         INIT_LIST_HEAD(&capsnap->ci_item);
529 
530         capsnap->follows = old_snapc->seq;
531         capsnap->issued = __ceph_caps_issued(ci, NULL);
532         capsnap->dirty = dirty;
533 
534         capsnap->mode = inode->i_mode;
535         capsnap->uid = inode->i_uid;
536         capsnap->gid = inode->i_gid;
537 
538         if (dirty & CEPH_CAP_XATTR_EXCL) {
539                 __ceph_build_xattrs_blob(ci);
540                 capsnap->xattr_blob =
541                         ceph_buffer_get(ci->i_xattrs.blob);
542                 capsnap->xattr_version = ci->i_xattrs.version;
543         } else {
544                 capsnap->xattr_blob = NULL;
545                 capsnap->xattr_version = 0;
546         }
547 
548         capsnap->inline_data = ci->i_inline_version != CEPH_INLINE_NONE;
549 
550         /* dirty page count moved from _head to this cap_snap;
551            all subsequent writes page dirties occur _after_ this
552            snapshot. */
553         capsnap->dirty_pages = ci->i_wrbuffer_ref_head;
554         ci->i_wrbuffer_ref_head = 0;
555         capsnap->context = old_snapc;
556         list_add_tail(&capsnap->ci_item, &ci->i_cap_snaps);
557 
558         if (used & CEPH_CAP_FILE_WR) {
559                 dout("queue_cap_snap %p cap_snap %p snapc %p"
560                      " seq %llu used WR, now pending\n", inode,
561                      capsnap, old_snapc, old_snapc->seq);
562                 capsnap->writing = 1;
563         } else {
564                 /* note mtime, size NOW. */
565                 __ceph_finish_cap_snap(ci, capsnap);
566         }
567         capsnap = NULL;
568         old_snapc = NULL;
569 
570 update_snapc:
571        if (ci->i_wrbuffer_ref_head == 0 &&
572            ci->i_wr_ref == 0 &&
573            ci->i_dirty_caps == 0 &&
574            ci->i_flushing_caps == 0) {
575                ci->i_head_snapc = NULL;
576        } else {
577                 ci->i_head_snapc = ceph_get_snap_context(new_snapc);
578                 dout(" new snapc is %p\n", new_snapc);
579         }
580         spin_unlock(&ci->i_ceph_lock);
581 
582         kfree(capsnap);
583         ceph_put_snap_context(old_snapc);
584 }
585 
586 /*
587  * Finalize the size, mtime for a cap_snap.. that is, settle on final values
588  * to be used for the snapshot, to be flushed back to the mds.
589  *
590  * If capsnap can now be flushed, add to snap_flush list, and return 1.
591  *
592  * Caller must hold i_ceph_lock.
593  */
594 int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
595                             struct ceph_cap_snap *capsnap)
596 {
597         struct inode *inode = &ci->vfs_inode;
598         struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
599 
600         BUG_ON(capsnap->writing);
601         capsnap->size = inode->i_size;
602         capsnap->mtime = inode->i_mtime;
603         capsnap->atime = inode->i_atime;
604         capsnap->ctime = inode->i_ctime;
605         capsnap->time_warp_seq = ci->i_time_warp_seq;
606         capsnap->truncate_size = ci->i_truncate_size;
607         capsnap->truncate_seq = ci->i_truncate_seq;
608         if (capsnap->dirty_pages) {
609                 dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu "
610                      "still has %d dirty pages\n", inode, capsnap,
611                      capsnap->context, capsnap->context->seq,
612                      ceph_cap_string(capsnap->dirty), capsnap->size,
613                      capsnap->dirty_pages);
614                 return 0;
615         }
616 
617         ci->i_ceph_flags |= CEPH_I_FLUSH_SNAPS;
618         dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu\n",
619              inode, capsnap, capsnap->context,
620              capsnap->context->seq, ceph_cap_string(capsnap->dirty),
621              capsnap->size);
622 
623         spin_lock(&mdsc->snap_flush_lock);
624         if (list_empty(&ci->i_snap_flush_item))
625                 list_add_tail(&ci->i_snap_flush_item, &mdsc->snap_flush_list);
626         spin_unlock(&mdsc->snap_flush_lock);
627         return 1;  /* caller may want to ceph_flush_snaps */
628 }
629 
630 /*
631  * Queue cap_snaps for snap writeback for this realm and its children.
632  * Called under snap_rwsem, so realm topology won't change.
633  */
634 static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
635 {
636         struct ceph_inode_info *ci;
637         struct inode *lastinode = NULL;
638 
639         dout("queue_realm_cap_snaps %p %llx inodes\n", realm, realm->ino);
640 
641         spin_lock(&realm->inodes_with_caps_lock);
642         list_for_each_entry(ci, &realm->inodes_with_caps, i_snap_realm_item) {
643                 struct inode *inode = igrab(&ci->vfs_inode);
644                 if (!inode)
645                         continue;
646                 spin_unlock(&realm->inodes_with_caps_lock);
647                 iput(lastinode);
648                 lastinode = inode;
649                 ceph_queue_cap_snap(ci);
650                 spin_lock(&realm->inodes_with_caps_lock);
651         }
652         spin_unlock(&realm->inodes_with_caps_lock);
653         iput(lastinode);
654 
655         dout("queue_realm_cap_snaps %p %llx done\n", realm, realm->ino);
656 }
657 
658 /*
659  * Parse and apply a snapblob "snap trace" from the MDS.  This specifies
660  * the snap realm parameters from a given realm and all of its ancestors,
661  * up to the root.
662  *
663  * Caller must hold snap_rwsem for write.
664  */
665 int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
666                            void *p, void *e, bool deletion,
667                            struct ceph_snap_realm **realm_ret)
668 {
669         struct ceph_mds_snap_realm *ri;    /* encoded */
670         __le64 *snaps;                     /* encoded */
671         __le64 *prior_parent_snaps;        /* encoded */
672         struct ceph_snap_realm *realm = NULL;
673         struct ceph_snap_realm *first_realm = NULL;
674         int invalidate = 0;
675         int err = -ENOMEM;
676         LIST_HEAD(dirty_realms);
677 
678         dout("update_snap_trace deletion=%d\n", deletion);
679 more:
680         ceph_decode_need(&p, e, sizeof(*ri), bad);
681         ri = p;
682         p += sizeof(*ri);
683         ceph_decode_need(&p, e, sizeof(u64)*(le32_to_cpu(ri->num_snaps) +
684                             le32_to_cpu(ri->num_prior_parent_snaps)), bad);
685         snaps = p;
686         p += sizeof(u64) * le32_to_cpu(ri->num_snaps);
687         prior_parent_snaps = p;
688         p += sizeof(u64) * le32_to_cpu(ri->num_prior_parent_snaps);
689 
690         realm = ceph_lookup_snap_realm(mdsc, le64_to_cpu(ri->ino));
691         if (!realm) {
692                 realm = ceph_create_snap_realm(mdsc, le64_to_cpu(ri->ino));
693                 if (IS_ERR(realm)) {
694                         err = PTR_ERR(realm);
695                         goto fail;
696                 }
697         }
698 
699         /* ensure the parent is correct */
700         err = adjust_snap_realm_parent(mdsc, realm, le64_to_cpu(ri->parent));
701         if (err < 0)
702                 goto fail;
703         invalidate += err;
704 
705         if (le64_to_cpu(ri->seq) > realm->seq) {
706                 dout("update_snap_trace updating %llx %p %lld -> %lld\n",
707                      realm->ino, realm, realm->seq, le64_to_cpu(ri->seq));
708                 /* update realm parameters, snap lists */
709                 realm->seq = le64_to_cpu(ri->seq);
710                 realm->created = le64_to_cpu(ri->created);
711                 realm->parent_since = le64_to_cpu(ri->parent_since);
712 
713                 realm->num_snaps = le32_to_cpu(ri->num_snaps);
714                 err = dup_array(&realm->snaps, snaps, realm->num_snaps);
715                 if (err < 0)
716                         goto fail;
717 
718                 realm->num_prior_parent_snaps =
719                         le32_to_cpu(ri->num_prior_parent_snaps);
720                 err = dup_array(&realm->prior_parent_snaps, prior_parent_snaps,
721                                 realm->num_prior_parent_snaps);
722                 if (err < 0)
723                         goto fail;
724 
725                 if (realm->seq > mdsc->last_snap_seq)
726                         mdsc->last_snap_seq = realm->seq;
727 
728                 invalidate = 1;
729         } else if (!realm->cached_context) {
730                 dout("update_snap_trace %llx %p seq %lld new\n",
731                      realm->ino, realm, realm->seq);
732                 invalidate = 1;
733         } else {
734                 dout("update_snap_trace %llx %p seq %lld unchanged\n",
735                      realm->ino, realm, realm->seq);
736         }
737 
738         dout("done with %llx %p, invalidated=%d, %p %p\n", realm->ino,
739              realm, invalidate, p, e);
740 
741         /* invalidate when we reach the _end_ (root) of the trace */
742         if (invalidate && p >= e)
743                 rebuild_snap_realms(realm, &dirty_realms);
744 
745         if (!first_realm)
746                 first_realm = realm;
747         else
748                 ceph_put_snap_realm(mdsc, realm);
749 
750         if (p < e)
751                 goto more;
752 
753         /*
754          * queue cap snaps _after_ we've built the new snap contexts,
755          * so that i_head_snapc can be set appropriately.
756          */
757         while (!list_empty(&dirty_realms)) {
758                 realm = list_first_entry(&dirty_realms, struct ceph_snap_realm,
759                                          dirty_item);
760                 list_del_init(&realm->dirty_item);
761                 queue_realm_cap_snaps(realm);
762         }
763 
764         if (realm_ret)
765                 *realm_ret = first_realm;
766         else
767                 ceph_put_snap_realm(mdsc, first_realm);
768 
769         __cleanup_empty_realms(mdsc);
770         return 0;
771 
772 bad:
773         err = -EINVAL;
774 fail:
775         if (realm && !IS_ERR(realm))
776                 ceph_put_snap_realm(mdsc, realm);
777         if (first_realm)
778                 ceph_put_snap_realm(mdsc, first_realm);
779         pr_err("update_snap_trace error %d\n", err);
780         return err;
781 }
782 
783 
784 /*
785  * Send any cap_snaps that are queued for flush.  Try to carry
786  * s_mutex across multiple snap flushes to avoid locking overhead.
787  *
788  * Caller holds no locks.
789  */
790 static void flush_snaps(struct ceph_mds_client *mdsc)
791 {
792         struct ceph_inode_info *ci;
793         struct inode *inode;
794         struct ceph_mds_session *session = NULL;
795 
796         dout("flush_snaps\n");
797         spin_lock(&mdsc->snap_flush_lock);
798         while (!list_empty(&mdsc->snap_flush_list)) {
799                 ci = list_first_entry(&mdsc->snap_flush_list,
800                                 struct ceph_inode_info, i_snap_flush_item);
801                 inode = &ci->vfs_inode;
802                 ihold(inode);
803                 spin_unlock(&mdsc->snap_flush_lock);
804                 ceph_flush_snaps(ci, &session);
805                 iput(inode);
806                 spin_lock(&mdsc->snap_flush_lock);
807         }
808         spin_unlock(&mdsc->snap_flush_lock);
809 
810         if (session) {
811                 mutex_unlock(&session->s_mutex);
812                 ceph_put_mds_session(session);
813         }
814         dout("flush_snaps done\n");
815 }
816 
817 
818 /*
819  * Handle a snap notification from the MDS.
820  *
821  * This can take two basic forms: the simplest is just a snap creation
822  * or deletion notification on an existing realm.  This should update the
823  * realm and its children.
824  *
825  * The more difficult case is realm creation, due to snap creation at a
826  * new point in the file hierarchy, or due to a rename that moves a file or
827  * directory into another realm.
828  */
829 void ceph_handle_snap(struct ceph_mds_client *mdsc,
830                       struct ceph_mds_session *session,
831                       struct ceph_msg *msg)
832 {
833         struct super_block *sb = mdsc->fsc->sb;
834         int mds = session->s_mds;
835         u64 split;
836         int op;
837         int trace_len;
838         struct ceph_snap_realm *realm = NULL;
839         void *p = msg->front.iov_base;
840         void *e = p + msg->front.iov_len;
841         struct ceph_mds_snap_head *h;
842         int num_split_inos, num_split_realms;
843         __le64 *split_inos = NULL, *split_realms = NULL;
844         int i;
845         int locked_rwsem = 0;
846 
847         /* decode */
848         if (msg->front.iov_len < sizeof(*h))
849                 goto bad;
850         h = p;
851         op = le32_to_cpu(h->op);
852         split = le64_to_cpu(h->split);   /* non-zero if we are splitting an
853                                           * existing realm */
854         num_split_inos = le32_to_cpu(h->num_split_inos);
855         num_split_realms = le32_to_cpu(h->num_split_realms);
856         trace_len = le32_to_cpu(h->trace_len);
857         p += sizeof(*h);
858 
859         dout("handle_snap from mds%d op %s split %llx tracelen %d\n", mds,
860              ceph_snap_op_name(op), split, trace_len);
861 
862         mutex_lock(&session->s_mutex);
863         session->s_seq++;
864         mutex_unlock(&session->s_mutex);
865 
866         down_write(&mdsc->snap_rwsem);
867         locked_rwsem = 1;
868 
869         if (op == CEPH_SNAP_OP_SPLIT) {
870                 struct ceph_mds_snap_realm *ri;
871 
872                 /*
873                  * A "split" breaks part of an existing realm off into
874                  * a new realm.  The MDS provides a list of inodes
875                  * (with caps) and child realms that belong to the new
876                  * child.
877                  */
878                 split_inos = p;
879                 p += sizeof(u64) * num_split_inos;
880                 split_realms = p;
881                 p += sizeof(u64) * num_split_realms;
882                 ceph_decode_need(&p, e, sizeof(*ri), bad);
883                 /* we will peek at realm info here, but will _not_
884                  * advance p, as the realm update will occur below in
885                  * ceph_update_snap_trace. */
886                 ri = p;
887 
888                 realm = ceph_lookup_snap_realm(mdsc, split);
889                 if (!realm) {
890                         realm = ceph_create_snap_realm(mdsc, split);
891                         if (IS_ERR(realm))
892                                 goto out;
893                 }
894 
895                 dout("splitting snap_realm %llx %p\n", realm->ino, realm);
896                 for (i = 0; i < num_split_inos; i++) {
897                         struct ceph_vino vino = {
898                                 .ino = le64_to_cpu(split_inos[i]),
899                                 .snap = CEPH_NOSNAP,
900                         };
901                         struct inode *inode = ceph_find_inode(sb, vino);
902                         struct ceph_inode_info *ci;
903                         struct ceph_snap_realm *oldrealm;
904 
905                         if (!inode)
906                                 continue;
907                         ci = ceph_inode(inode);
908 
909                         spin_lock(&ci->i_ceph_lock);
910                         if (!ci->i_snap_realm)
911                                 goto skip_inode;
912                         /*
913                          * If this inode belongs to a realm that was
914                          * created after our new realm, we experienced
915                          * a race (due to another split notifications
916                          * arriving from a different MDS).  So skip
917                          * this inode.
918                          */
919                         if (ci->i_snap_realm->created >
920                             le64_to_cpu(ri->created)) {
921                                 dout(" leaving %p in newer realm %llx %p\n",
922                                      inode, ci->i_snap_realm->ino,
923                                      ci->i_snap_realm);
924                                 goto skip_inode;
925                         }
926                         dout(" will move %p to split realm %llx %p\n",
927                              inode, realm->ino, realm);
928                         /*
929                          * Move the inode to the new realm
930                          */
931                         oldrealm = ci->i_snap_realm;
932                         spin_lock(&oldrealm->inodes_with_caps_lock);
933                         list_del_init(&ci->i_snap_realm_item);
934                         spin_unlock(&oldrealm->inodes_with_caps_lock);
935 
936                         spin_lock(&realm->inodes_with_caps_lock);
937                         list_add(&ci->i_snap_realm_item,
938                                  &realm->inodes_with_caps);
939                         ci->i_snap_realm = realm;
940                         if (realm->ino == ci->i_vino.ino)
941                                 realm->inode = inode;
942                         spin_unlock(&realm->inodes_with_caps_lock);
943 
944                         spin_unlock(&ci->i_ceph_lock);
945 
946                         ceph_get_snap_realm(mdsc, realm);
947                         ceph_put_snap_realm(mdsc, oldrealm);
948 
949                         iput(inode);
950                         continue;
951 
952 skip_inode:
953                         spin_unlock(&ci->i_ceph_lock);
954                         iput(inode);
955                 }
956 
957                 /* we may have taken some of the old realm's children. */
958                 for (i = 0; i < num_split_realms; i++) {
959                         struct ceph_snap_realm *child =
960                                 __lookup_snap_realm(mdsc,
961                                            le64_to_cpu(split_realms[i]));
962                         if (!child)
963                                 continue;
964                         adjust_snap_realm_parent(mdsc, child, realm->ino);
965                 }
966         }
967 
968         /*
969          * update using the provided snap trace. if we are deleting a
970          * snap, we can avoid queueing cap_snaps.
971          */
972         ceph_update_snap_trace(mdsc, p, e,
973                                op == CEPH_SNAP_OP_DESTROY, NULL);
974 
975         if (op == CEPH_SNAP_OP_SPLIT)
976                 /* we took a reference when we created the realm, above */
977                 ceph_put_snap_realm(mdsc, realm);
978 
979         __cleanup_empty_realms(mdsc);
980 
981         up_write(&mdsc->snap_rwsem);
982 
983         flush_snaps(mdsc);
984         return;
985 
986 bad:
987         pr_err("corrupt snap message from mds%d\n", mds);
988         ceph_msg_dump(msg);
989 out:
990         if (locked_rwsem)
991                 up_write(&mdsc->snap_rwsem);
992         return;
993 }
994 

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