xref: /linux/fs/afs/super.c (revision b7019ac550eb3916f34d79db583e9b7ea2524afa) 
1 /* AFS superblock handling
2  *
3  * Copyright (c) 2002, 2007, 2018 Red Hat, Inc. All rights reserved.
4  *
5  * This software may be freely redistributed under the terms of the
6  * GNU General Public License.
7  *
8  * You should have received a copy of the GNU General Public License
9  * along with this program; if not, write to the Free Software
10  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
11  *
12  * Authors: David Howells <dhowells@redhat.com>
13  *          David Woodhouse <dwmw2@infradead.org>
14  *
15  */
16 
17 #include <linux/kernel.h>
18 #include <linux/module.h>
19 #include <linux/mount.h>
20 #include <linux/init.h>
21 #include <linux/slab.h>
22 #include <linux/fs.h>
23 #include <linux/pagemap.h>
24 #include <linux/fs_parser.h>
25 #include <linux/statfs.h>
26 #include <linux/sched.h>
27 #include <linux/nsproxy.h>
28 #include <linux/magic.h>
29 #include <net/net_namespace.h>
30 #include "internal.h"
31 
32 static void afs_i_init_once(void *foo);
33 static void afs_kill_super(struct super_block *sb);
34 static struct inode *afs_alloc_inode(struct super_block *sb);
35 static void afs_destroy_inode(struct inode *inode);
36 static void afs_free_inode(struct inode *inode);
37 static int afs_statfs(struct dentry *dentry, struct kstatfs *buf);
38 static int afs_show_devname(struct seq_file *m, struct dentry *root);
39 static int afs_show_options(struct seq_file *m, struct dentry *root);
40 static int afs_init_fs_context(struct fs_context *fc);
41 static const struct fs_parameter_description afs_fs_parameters;
42 
43 struct file_system_type afs_fs_type = {
44 	.owner			= THIS_MODULE,
45 	.name			= "afs",
46 	.init_fs_context	= afs_init_fs_context,
47 	.parameters		= &afs_fs_parameters,
48 	.kill_sb		= afs_kill_super,
49 	.fs_flags		= FS_RENAME_DOES_D_MOVE,
50 };
51 MODULE_ALIAS_FS("afs");
52 
53 int afs_net_id;
54 
55 static const struct super_operations afs_super_ops = {
56 	.statfs		= afs_statfs,
57 	.alloc_inode	= afs_alloc_inode,
58 	.drop_inode	= afs_drop_inode,
59 	.destroy_inode	= afs_destroy_inode,
60 	.free_inode	= afs_free_inode,
61 	.evict_inode	= afs_evict_inode,
62 	.show_devname	= afs_show_devname,
63 	.show_options	= afs_show_options,
64 };
65 
66 static struct kmem_cache *afs_inode_cachep;
67 static atomic_t afs_count_active_inodes;
68 
69 enum afs_param {
70 	Opt_autocell,
71 	Opt_dyn,
72 	Opt_flock,
73 	Opt_source,
74 };
75 
76 static const struct fs_parameter_spec afs_param_specs[] = {
77 	fsparam_flag  ("autocell",	Opt_autocell),
78 	fsparam_flag  ("dyn",		Opt_dyn),
79 	fsparam_enum  ("flock",		Opt_flock),
80 	fsparam_string("source",	Opt_source),
81 	{}
82 };
83 
84 static const struct fs_parameter_enum afs_param_enums[] = {
85 	{ Opt_flock,	"local",	afs_flock_mode_local },
86 	{ Opt_flock,	"openafs",	afs_flock_mode_openafs },
87 	{ Opt_flock,	"strict",	afs_flock_mode_strict },
88 	{ Opt_flock,	"write",	afs_flock_mode_write },
89 	{}
90 };
91 
92 static const struct fs_parameter_description afs_fs_parameters = {
93 	.name		= "kAFS",
94 	.specs		= afs_param_specs,
95 	.enums		= afs_param_enums,
96 };
97 
98 /*
99  * initialise the filesystem
100  */
101 int __init afs_fs_init(void)
102 {
103 	int ret;
104 
105 	_enter("");
106 
107 	/* create ourselves an inode cache */
108 	atomic_set(&afs_count_active_inodes, 0);
109 
110 	ret = -ENOMEM;
111 	afs_inode_cachep = kmem_cache_create("afs_inode_cache",
112 					     sizeof(struct afs_vnode),
113 					     0,
114 					     SLAB_HWCACHE_ALIGN|SLAB_ACCOUNT,
115 					     afs_i_init_once);
116 	if (!afs_inode_cachep) {
117 		printk(KERN_NOTICE "kAFS: Failed to allocate inode cache\n");
118 		return ret;
119 	}
120 
121 	/* now export our filesystem to lesser mortals */
122 	ret = register_filesystem(&afs_fs_type);
123 	if (ret < 0) {
124 		kmem_cache_destroy(afs_inode_cachep);
125 		_leave(" = %d", ret);
126 		return ret;
127 	}
128 
129 	_leave(" = 0");
130 	return 0;
131 }
132 
133 /*
134  * clean up the filesystem
135  */
136 void afs_fs_exit(void)
137 {
138 	_enter("");
139 
140 	afs_mntpt_kill_timer();
141 	unregister_filesystem(&afs_fs_type);
142 
143 	if (atomic_read(&afs_count_active_inodes) != 0) {
144 		printk("kAFS: %d active inode objects still present\n",
145 		       atomic_read(&afs_count_active_inodes));
146 		BUG();
147 	}
148 
149 	/*
150 	 * Make sure all delayed rcu free inodes are flushed before we
151 	 * destroy cache.
152 	 */
153 	rcu_barrier();
154 	kmem_cache_destroy(afs_inode_cachep);
155 	_leave("");
156 }
157 
158 /*
159  * Display the mount device name in /proc/mounts.
160  */
161 static int afs_show_devname(struct seq_file *m, struct dentry *root)
162 {
163 	struct afs_super_info *as = AFS_FS_S(root->d_sb);
164 	struct afs_volume *volume = as->volume;
165 	struct afs_cell *cell = as->cell;
166 	const char *suf = "";
167 	char pref = '%';
168 
169 	if (as->dyn_root) {
170 		seq_puts(m, "none");
171 		return 0;
172 	}
173 
174 	switch (volume->type) {
175 	case AFSVL_RWVOL:
176 		break;
177 	case AFSVL_ROVOL:
178 		pref = '#';
179 		if (volume->type_force)
180 			suf = ".readonly";
181 		break;
182 	case AFSVL_BACKVOL:
183 		pref = '#';
184 		suf = ".backup";
185 		break;
186 	}
187 
188 	seq_printf(m, "%c%s:%s%s", pref, cell->name, volume->name, suf);
189 	return 0;
190 }
191 
192 /*
193  * Display the mount options in /proc/mounts.
194  */
195 static int afs_show_options(struct seq_file *m, struct dentry *root)
196 {
197 	struct afs_super_info *as = AFS_FS_S(root->d_sb);
198 	const char *p = NULL;
199 
200 	if (as->dyn_root)
201 		seq_puts(m, ",dyn");
202 	if (test_bit(AFS_VNODE_AUTOCELL, &AFS_FS_I(d_inode(root))->flags))
203 		seq_puts(m, ",autocell");
204 	switch (as->flock_mode) {
205 	case afs_flock_mode_unset:	break;
206 	case afs_flock_mode_local:	p = "local";	break;
207 	case afs_flock_mode_openafs:	p = "openafs";	break;
208 	case afs_flock_mode_strict:	p = "strict";	break;
209 	case afs_flock_mode_write:	p = "write";	break;
210 	}
211 	if (p)
212 		seq_printf(m, ",flock=%s", p);
213 
214 	return 0;
215 }
216 
217 /*
218  * Parse the source name to get cell name, volume name, volume type and R/W
219  * selector.
220  *
221  * This can be one of the following:
222  *	"%[cell:]volume[.]"		R/W volume
223  *	"#[cell:]volume[.]"		R/O or R/W volume (R/O parent),
224  *					 or R/W (R/W parent) volume
225  *	"%[cell:]volume.readonly"	R/O volume
226  *	"#[cell:]volume.readonly"	R/O volume
227  *	"%[cell:]volume.backup"		Backup volume
228  *	"#[cell:]volume.backup"		Backup volume
229  */
230 static int afs_parse_source(struct fs_context *fc, struct fs_parameter *param)
231 {
232 	struct afs_fs_context *ctx = fc->fs_private;
233 	struct afs_cell *cell;
234 	const char *cellname, *suffix, *name = param->string;
235 	int cellnamesz;
236 
237 	_enter(",%s", name);
238 
239 	if (!name) {
240 		printk(KERN_ERR "kAFS: no volume name specified\n");
241 		return -EINVAL;
242 	}
243 
244 	if ((name[0] != '%' && name[0] != '#') || !name[1]) {
245 		/* To use dynroot, we don't want to have to provide a source */
246 		if (strcmp(name, "none") == 0) {
247 			ctx->no_cell = true;
248 			return 0;
249 		}
250 		printk(KERN_ERR "kAFS: unparsable volume name\n");
251 		return -EINVAL;
252 	}
253 
254 	/* determine the type of volume we're looking for */
255 	if (name[0] == '%') {
256 		ctx->type = AFSVL_RWVOL;
257 		ctx->force = true;
258 	}
259 	name++;
260 
261 	/* split the cell name out if there is one */
262 	ctx->volname = strchr(name, ':');
263 	if (ctx->volname) {
264 		cellname = name;
265 		cellnamesz = ctx->volname - name;
266 		ctx->volname++;
267 	} else {
268 		ctx->volname = name;
269 		cellname = NULL;
270 		cellnamesz = 0;
271 	}
272 
273 	/* the volume type is further affected by a possible suffix */
274 	suffix = strrchr(ctx->volname, '.');
275 	if (suffix) {
276 		if (strcmp(suffix, ".readonly") == 0) {
277 			ctx->type = AFSVL_ROVOL;
278 			ctx->force = true;
279 		} else if (strcmp(suffix, ".backup") == 0) {
280 			ctx->type = AFSVL_BACKVOL;
281 			ctx->force = true;
282 		} else if (suffix[1] == 0) {
283 		} else {
284 			suffix = NULL;
285 		}
286 	}
287 
288 	ctx->volnamesz = suffix ?
289 		suffix - ctx->volname : strlen(ctx->volname);
290 
291 	_debug("cell %*.*s [%p]",
292 	       cellnamesz, cellnamesz, cellname ?: "", ctx->cell);
293 
294 	/* lookup the cell record */
295 	if (cellname) {
296 		cell = afs_lookup_cell(ctx->net, cellname, cellnamesz,
297 				       NULL, false);
298 		if (IS_ERR(cell)) {
299 			pr_err("kAFS: unable to lookup cell '%*.*s'\n",
300 			       cellnamesz, cellnamesz, cellname ?: "");
301 			return PTR_ERR(cell);
302 		}
303 		afs_put_cell(ctx->net, ctx->cell);
304 		ctx->cell = cell;
305 	}
306 
307 	_debug("CELL:%s [%p] VOLUME:%*.*s SUFFIX:%s TYPE:%d%s",
308 	       ctx->cell->name, ctx->cell,
309 	       ctx->volnamesz, ctx->volnamesz, ctx->volname,
310 	       suffix ?: "-", ctx->type, ctx->force ? " FORCE" : "");
311 
312 	fc->source = param->string;
313 	param->string = NULL;
314 	return 0;
315 }
316 
317 /*
318  * Parse a single mount parameter.
319  */
320 static int afs_parse_param(struct fs_context *fc, struct fs_parameter *param)
321 {
322 	struct fs_parse_result result;
323 	struct afs_fs_context *ctx = fc->fs_private;
324 	int opt;
325 
326 	opt = fs_parse(fc, &afs_fs_parameters, param, &result);
327 	if (opt < 0)
328 		return opt;
329 
330 	switch (opt) {
331 	case Opt_source:
332 		return afs_parse_source(fc, param);
333 
334 	case Opt_autocell:
335 		ctx->autocell = true;
336 		break;
337 
338 	case Opt_dyn:
339 		ctx->dyn_root = true;
340 		break;
341 
342 	case Opt_flock:
343 		ctx->flock_mode = result.uint_32;
344 		break;
345 
346 	default:
347 		return -EINVAL;
348 	}
349 
350 	_leave(" = 0");
351 	return 0;
352 }
353 
354 /*
355  * Validate the options, get the cell key and look up the volume.
356  */
357 static int afs_validate_fc(struct fs_context *fc)
358 {
359 	struct afs_fs_context *ctx = fc->fs_private;
360 	struct afs_volume *volume;
361 	struct key *key;
362 
363 	if (!ctx->dyn_root) {
364 		if (ctx->no_cell) {
365 			pr_warn("kAFS: Can only specify source 'none' with -o dyn\n");
366 			return -EINVAL;
367 		}
368 
369 		if (!ctx->cell) {
370 			pr_warn("kAFS: No cell specified\n");
371 			return -EDESTADDRREQ;
372 		}
373 
374 		/* We try to do the mount securely. */
375 		key = afs_request_key(ctx->cell);
376 		if (IS_ERR(key))
377 			return PTR_ERR(key);
378 
379 		ctx->key = key;
380 
381 		if (ctx->volume) {
382 			afs_put_volume(ctx->cell, ctx->volume);
383 			ctx->volume = NULL;
384 		}
385 
386 		volume = afs_create_volume(ctx);
387 		if (IS_ERR(volume))
388 			return PTR_ERR(volume);
389 
390 		ctx->volume = volume;
391 	}
392 
393 	return 0;
394 }
395 
396 /*
397  * check a superblock to see if it's the one we're looking for
398  */
399 static int afs_test_super(struct super_block *sb, struct fs_context *fc)
400 {
401 	struct afs_fs_context *ctx = fc->fs_private;
402 	struct afs_super_info *as = AFS_FS_S(sb);
403 
404 	return (as->net_ns == fc->net_ns &&
405 		as->volume &&
406 		as->volume->vid == ctx->volume->vid &&
407 		!as->dyn_root);
408 }
409 
410 static int afs_dynroot_test_super(struct super_block *sb, struct fs_context *fc)
411 {
412 	struct afs_super_info *as = AFS_FS_S(sb);
413 
414 	return (as->net_ns == fc->net_ns &&
415 		as->dyn_root);
416 }
417 
418 static int afs_set_super(struct super_block *sb, struct fs_context *fc)
419 {
420 	return set_anon_super(sb, NULL);
421 }
422 
423 /*
424  * fill in the superblock
425  */
426 static int afs_fill_super(struct super_block *sb, struct afs_fs_context *ctx)
427 {
428 	struct afs_super_info *as = AFS_FS_S(sb);
429 	struct afs_iget_data iget_data;
430 	struct inode *inode = NULL;
431 	int ret;
432 
433 	_enter("");
434 
435 	/* fill in the superblock */
436 	sb->s_blocksize		= PAGE_SIZE;
437 	sb->s_blocksize_bits	= PAGE_SHIFT;
438 	sb->s_magic		= AFS_FS_MAGIC;
439 	sb->s_op		= &afs_super_ops;
440 	if (!as->dyn_root)
441 		sb->s_xattr	= afs_xattr_handlers;
442 	ret = super_setup_bdi(sb);
443 	if (ret)
444 		return ret;
445 	sb->s_bdi->ra_pages	= VM_READAHEAD_PAGES;
446 
447 	/* allocate the root inode and dentry */
448 	if (as->dyn_root) {
449 		inode = afs_iget_pseudo_dir(sb, true);
450 		sb->s_flags	|= SB_RDONLY;
451 	} else {
452 		sprintf(sb->s_id, "%llu", as->volume->vid);
453 		afs_activate_volume(as->volume);
454 		iget_data.fid.vid	= as->volume->vid;
455 		iget_data.fid.vnode	= 1;
456 		iget_data.fid.vnode_hi	= 0;
457 		iget_data.fid.unique	= 1;
458 		iget_data.cb_v_break	= as->volume->cb_v_break;
459 		iget_data.cb_s_break	= 0;
460 		inode = afs_iget(sb, ctx->key, &iget_data, NULL, NULL, NULL);
461 	}
462 
463 	if (IS_ERR(inode))
464 		return PTR_ERR(inode);
465 
466 	if (ctx->autocell || as->dyn_root)
467 		set_bit(AFS_VNODE_AUTOCELL, &AFS_FS_I(inode)->flags);
468 
469 	ret = -ENOMEM;
470 	sb->s_root = d_make_root(inode);
471 	if (!sb->s_root)
472 		goto error;
473 
474 	if (as->dyn_root) {
475 		sb->s_d_op = &afs_dynroot_dentry_operations;
476 		ret = afs_dynroot_populate(sb);
477 		if (ret < 0)
478 			goto error;
479 	} else {
480 		sb->s_d_op = &afs_fs_dentry_operations;
481 	}
482 
483 	_leave(" = 0");
484 	return 0;
485 
486 error:
487 	_leave(" = %d", ret);
488 	return ret;
489 }
490 
491 static struct afs_super_info *afs_alloc_sbi(struct fs_context *fc)
492 {
493 	struct afs_fs_context *ctx = fc->fs_private;
494 	struct afs_super_info *as;
495 
496 	as = kzalloc(sizeof(struct afs_super_info), GFP_KERNEL);
497 	if (as) {
498 		as->net_ns = get_net(fc->net_ns);
499 		as->flock_mode = ctx->flock_mode;
500 		if (ctx->dyn_root) {
501 			as->dyn_root = true;
502 		} else {
503 			as->cell = afs_get_cell(ctx->cell);
504 			as->volume = __afs_get_volume(ctx->volume);
505 		}
506 	}
507 	return as;
508 }
509 
510 static void afs_destroy_sbi(struct afs_super_info *as)
511 {
512 	if (as) {
513 		afs_put_volume(as->cell, as->volume);
514 		afs_put_cell(afs_net(as->net_ns), as->cell);
515 		put_net(as->net_ns);
516 		kfree(as);
517 	}
518 }
519 
520 static void afs_kill_super(struct super_block *sb)
521 {
522 	struct afs_super_info *as = AFS_FS_S(sb);
523 	struct afs_net *net = afs_net(as->net_ns);
524 
525 	if (as->dyn_root)
526 		afs_dynroot_depopulate(sb);
527 
528 	/* Clear the callback interests (which will do ilookup5) before
529 	 * deactivating the superblock.
530 	 */
531 	if (as->volume)
532 		afs_clear_callback_interests(net, as->volume->servers);
533 	kill_anon_super(sb);
534 	if (as->volume)
535 		afs_deactivate_volume(as->volume);
536 	afs_destroy_sbi(as);
537 }
538 
539 /*
540  * Get an AFS superblock and root directory.
541  */
542 static int afs_get_tree(struct fs_context *fc)
543 {
544 	struct afs_fs_context *ctx = fc->fs_private;
545 	struct super_block *sb;
546 	struct afs_super_info *as;
547 	int ret;
548 
549 	ret = afs_validate_fc(fc);
550 	if (ret)
551 		goto error;
552 
553 	_enter("");
554 
555 	/* allocate a superblock info record */
556 	ret = -ENOMEM;
557 	as = afs_alloc_sbi(fc);
558 	if (!as)
559 		goto error;
560 	fc->s_fs_info = as;
561 
562 	/* allocate a deviceless superblock */
563 	sb = sget_fc(fc,
564 		     as->dyn_root ? afs_dynroot_test_super : afs_test_super,
565 		     afs_set_super);
566 	if (IS_ERR(sb)) {
567 		ret = PTR_ERR(sb);
568 		goto error;
569 	}
570 
571 	if (!sb->s_root) {
572 		/* initial superblock/root creation */
573 		_debug("create");
574 		ret = afs_fill_super(sb, ctx);
575 		if (ret < 0)
576 			goto error_sb;
577 		sb->s_flags |= SB_ACTIVE;
578 	} else {
579 		_debug("reuse");
580 		ASSERTCMP(sb->s_flags, &, SB_ACTIVE);
581 	}
582 
583 	fc->root = dget(sb->s_root);
584 	trace_afs_get_tree(as->cell, as->volume);
585 	_leave(" = 0 [%p]", sb);
586 	return 0;
587 
588 error_sb:
589 	deactivate_locked_super(sb);
590 error:
591 	_leave(" = %d", ret);
592 	return ret;
593 }
594 
595 static void afs_free_fc(struct fs_context *fc)
596 {
597 	struct afs_fs_context *ctx = fc->fs_private;
598 
599 	afs_destroy_sbi(fc->s_fs_info);
600 	afs_put_volume(ctx->cell, ctx->volume);
601 	afs_put_cell(ctx->net, ctx->cell);
602 	key_put(ctx->key);
603 	kfree(ctx);
604 }
605 
606 static const struct fs_context_operations afs_context_ops = {
607 	.free		= afs_free_fc,
608 	.parse_param	= afs_parse_param,
609 	.get_tree	= afs_get_tree,
610 };
611 
612 /*
613  * Set up the filesystem mount context.
614  */
615 static int afs_init_fs_context(struct fs_context *fc)
616 {
617 	struct afs_fs_context *ctx;
618 	struct afs_cell *cell;
619 
620 	ctx = kzalloc(sizeof(struct afs_fs_context), GFP_KERNEL);
621 	if (!ctx)
622 		return -ENOMEM;
623 
624 	ctx->type = AFSVL_ROVOL;
625 	ctx->net = afs_net(fc->net_ns);
626 
627 	/* Default to the workstation cell. */
628 	rcu_read_lock();
629 	cell = afs_lookup_cell_rcu(ctx->net, NULL, 0);
630 	rcu_read_unlock();
631 	if (IS_ERR(cell))
632 		cell = NULL;
633 	ctx->cell = cell;
634 
635 	fc->fs_private = ctx;
636 	fc->ops = &afs_context_ops;
637 	return 0;
638 }
639 
640 /*
641  * Initialise an inode cache slab element prior to any use.  Note that
642  * afs_alloc_inode() *must* reset anything that could incorrectly leak from one
643  * inode to another.
644  */
645 static void afs_i_init_once(void *_vnode)
646 {
647 	struct afs_vnode *vnode = _vnode;
648 
649 	memset(vnode, 0, sizeof(*vnode));
650 	inode_init_once(&vnode->vfs_inode);
651 	mutex_init(&vnode->io_lock);
652 	init_rwsem(&vnode->validate_lock);
653 	spin_lock_init(&vnode->wb_lock);
654 	spin_lock_init(&vnode->lock);
655 	INIT_LIST_HEAD(&vnode->wb_keys);
656 	INIT_LIST_HEAD(&vnode->pending_locks);
657 	INIT_LIST_HEAD(&vnode->granted_locks);
658 	INIT_DELAYED_WORK(&vnode->lock_work, afs_lock_work);
659 	seqlock_init(&vnode->cb_lock);
660 }
661 
662 /*
663  * allocate an AFS inode struct from our slab cache
664  */
665 static struct inode *afs_alloc_inode(struct super_block *sb)
666 {
667 	struct afs_vnode *vnode;
668 
669 	vnode = kmem_cache_alloc(afs_inode_cachep, GFP_KERNEL);
670 	if (!vnode)
671 		return NULL;
672 
673 	atomic_inc(&afs_count_active_inodes);
674 
675 	/* Reset anything that shouldn't leak from one inode to the next. */
676 	memset(&vnode->fid, 0, sizeof(vnode->fid));
677 	memset(&vnode->status, 0, sizeof(vnode->status));
678 
679 	vnode->volume		= NULL;
680 	vnode->lock_key		= NULL;
681 	vnode->permit_cache	= NULL;
682 	RCU_INIT_POINTER(vnode->cb_interest, NULL);
683 #ifdef CONFIG_AFS_FSCACHE
684 	vnode->cache		= NULL;
685 #endif
686 
687 	vnode->flags		= 1 << AFS_VNODE_UNSET;
688 	vnode->lock_state	= AFS_VNODE_LOCK_NONE;
689 
690 	init_rwsem(&vnode->rmdir_lock);
691 
692 	_leave(" = %p", &vnode->vfs_inode);
693 	return &vnode->vfs_inode;
694 }
695 
696 static void afs_free_inode(struct inode *inode)
697 {
698 	kmem_cache_free(afs_inode_cachep, AFS_FS_I(inode));
699 }
700 
701 /*
702  * destroy an AFS inode struct
703  */
704 static void afs_destroy_inode(struct inode *inode)
705 {
706 	struct afs_vnode *vnode = AFS_FS_I(inode);
707 
708 	_enter("%p{%llx:%llu}", inode, vnode->fid.vid, vnode->fid.vnode);
709 
710 	_debug("DESTROY INODE %p", inode);
711 
712 	ASSERTCMP(rcu_access_pointer(vnode->cb_interest), ==, NULL);
713 
714 	atomic_dec(&afs_count_active_inodes);
715 }
716 
717 /*
718  * return information about an AFS volume
719  */
720 static int afs_statfs(struct dentry *dentry, struct kstatfs *buf)
721 {
722 	struct afs_super_info *as = AFS_FS_S(dentry->d_sb);
723 	struct afs_fs_cursor fc;
724 	struct afs_volume_status vs;
725 	struct afs_vnode *vnode = AFS_FS_I(d_inode(dentry));
726 	struct key *key;
727 	int ret;
728 
729 	buf->f_type	= dentry->d_sb->s_magic;
730 	buf->f_bsize	= AFS_BLOCK_SIZE;
731 	buf->f_namelen	= AFSNAMEMAX - 1;
732 
733 	if (as->dyn_root) {
734 		buf->f_blocks	= 1;
735 		buf->f_bavail	= 0;
736 		buf->f_bfree	= 0;
737 		return 0;
738 	}
739 
740 	key = afs_request_key(vnode->volume->cell);
741 	if (IS_ERR(key))
742 		return PTR_ERR(key);
743 
744 	ret = -ERESTARTSYS;
745 	if (afs_begin_vnode_operation(&fc, vnode, key, true)) {
746 		fc.flags |= AFS_FS_CURSOR_NO_VSLEEP;
747 		while (afs_select_fileserver(&fc)) {
748 			fc.cb_break = afs_calc_vnode_cb_break(vnode);
749 			afs_fs_get_volume_status(&fc, &vs);
750 		}
751 
752 		afs_check_for_remote_deletion(&fc, fc.vnode);
753 		ret = afs_end_vnode_operation(&fc);
754 	}
755 
756 	key_put(key);
757 
758 	if (ret == 0) {
759 		if (vs.max_quota == 0)
760 			buf->f_blocks = vs.part_max_blocks;
761 		else
762 			buf->f_blocks = vs.max_quota;
763 		buf->f_bavail = buf->f_bfree = buf->f_blocks - vs.blocks_in_use;
764 	}
765 
766 	return ret;
767 }
768