Root/fs/super.c

1/*
2 * linux/fs/super.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 *
6 * super.c contains code to handle: - mount structures
7 * - super-block tables
8 * - filesystem drivers list
9 * - mount system call
10 * - umount system call
11 * - ustat system call
12 *
13 * GK 2/5/95 - Changed to support mounting the root fs via NFS
14 *
15 * Added kerneld support: Jacques Gelinas and Bjorn Ekwall
16 * Added change_root: Werner Almesberger & Hans Lermen, Feb '96
17 * Added options to /proc/mounts:
18 * Torbj√∂rn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
19 * Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
20 * Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
21 */
22
23#include <linux/module.h>
24#include <linux/slab.h>
25#include <linux/acct.h>
26#include <linux/blkdev.h>
27#include <linux/mount.h>
28#include <linux/security.h>
29#include <linux/writeback.h> /* for the emergency remount stuff */
30#include <linux/idr.h>
31#include <linux/mutex.h>
32#include <linux/backing-dev.h>
33#include <linux/rculist_bl.h>
34#include <linux/cleancache.h>
35#include "internal.h"
36
37
38LIST_HEAD(super_blocks);
39DEFINE_SPINLOCK(sb_lock);
40
41/**
42 * alloc_super - create new superblock
43 * @type: filesystem type superblock should belong to
44 *
45 * Allocates and initializes a new &struct super_block. alloc_super()
46 * returns a pointer new superblock or %NULL if allocation had failed.
47 */
48static struct super_block *alloc_super(struct file_system_type *type)
49{
50    struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
51    static const struct super_operations default_op;
52
53    if (s) {
54        if (security_sb_alloc(s)) {
55            kfree(s);
56            s = NULL;
57            goto out;
58        }
59#ifdef CONFIG_SMP
60        s->s_files = alloc_percpu(struct list_head);
61        if (!s->s_files) {
62            security_sb_free(s);
63            kfree(s);
64            s = NULL;
65            goto out;
66        } else {
67            int i;
68
69            for_each_possible_cpu(i)
70                INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
71        }
72#else
73        INIT_LIST_HEAD(&s->s_files);
74#endif
75        s->s_bdi = &default_backing_dev_info;
76        INIT_LIST_HEAD(&s->s_instances);
77        INIT_HLIST_BL_HEAD(&s->s_anon);
78        INIT_LIST_HEAD(&s->s_inodes);
79        INIT_LIST_HEAD(&s->s_dentry_lru);
80        init_rwsem(&s->s_umount);
81        mutex_init(&s->s_lock);
82        lockdep_set_class(&s->s_umount, &type->s_umount_key);
83        /*
84         * The locking rules for s_lock are up to the
85         * filesystem. For example ext3fs has different
86         * lock ordering than usbfs:
87         */
88        lockdep_set_class(&s->s_lock, &type->s_lock_key);
89        /*
90         * sget() can have s_umount recursion.
91         *
92         * When it cannot find a suitable sb, it allocates a new
93         * one (this one), and tries again to find a suitable old
94         * one.
95         *
96         * In case that succeeds, it will acquire the s_umount
97         * lock of the old one. Since these are clearly distrinct
98         * locks, and this object isn't exposed yet, there's no
99         * risk of deadlocks.
100         *
101         * Annotate this by putting this lock in a different
102         * subclass.
103         */
104        down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
105        s->s_count = 1;
106        atomic_set(&s->s_active, 1);
107        mutex_init(&s->s_vfs_rename_mutex);
108        lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
109        mutex_init(&s->s_dquot.dqio_mutex);
110        mutex_init(&s->s_dquot.dqonoff_mutex);
111        init_rwsem(&s->s_dquot.dqptr_sem);
112        init_waitqueue_head(&s->s_wait_unfrozen);
113        s->s_maxbytes = MAX_NON_LFS;
114        s->s_op = &default_op;
115        s->s_time_gran = 1000000000;
116        s->cleancache_poolid = -1;
117    }
118out:
119    return s;
120}
121
122/**
123 * destroy_super - frees a superblock
124 * @s: superblock to free
125 *
126 * Frees a superblock.
127 */
128static inline void destroy_super(struct super_block *s)
129{
130#ifdef CONFIG_SMP
131    free_percpu(s->s_files);
132#endif
133    security_sb_free(s);
134    kfree(s->s_subtype);
135    kfree(s->s_options);
136    kfree(s);
137}
138
139/* Superblock refcounting */
140
141/*
142 * Drop a superblock's refcount. The caller must hold sb_lock.
143 */
144void __put_super(struct super_block *sb)
145{
146    if (!--sb->s_count) {
147        list_del_init(&sb->s_list);
148        destroy_super(sb);
149    }
150}
151
152/**
153 * put_super - drop a temporary reference to superblock
154 * @sb: superblock in question
155 *
156 * Drops a temporary reference, frees superblock if there's no
157 * references left.
158 */
159void put_super(struct super_block *sb)
160{
161    spin_lock(&sb_lock);
162    __put_super(sb);
163    spin_unlock(&sb_lock);
164}
165
166
167/**
168 * deactivate_locked_super - drop an active reference to superblock
169 * @s: superblock to deactivate
170 *
171 * Drops an active reference to superblock, converting it into a temprory
172 * one if there is no other active references left. In that case we
173 * tell fs driver to shut it down and drop the temporary reference we
174 * had just acquired.
175 *
176 * Caller holds exclusive lock on superblock; that lock is released.
177 */
178void deactivate_locked_super(struct super_block *s)
179{
180    struct file_system_type *fs = s->s_type;
181    if (atomic_dec_and_test(&s->s_active)) {
182        cleancache_flush_fs(s);
183        fs->kill_sb(s);
184        /*
185         * We need to call rcu_barrier so all the delayed rcu free
186         * inodes are flushed before we release the fs module.
187         */
188        rcu_barrier();
189        put_filesystem(fs);
190        put_super(s);
191    } else {
192        up_write(&s->s_umount);
193    }
194}
195
196EXPORT_SYMBOL(deactivate_locked_super);
197
198/**
199 * deactivate_super - drop an active reference to superblock
200 * @s: superblock to deactivate
201 *
202 * Variant of deactivate_locked_super(), except that superblock is *not*
203 * locked by caller. If we are going to drop the final active reference,
204 * lock will be acquired prior to that.
205 */
206void deactivate_super(struct super_block *s)
207{
208        if (!atomic_add_unless(&s->s_active, -1, 1)) {
209        down_write(&s->s_umount);
210        deactivate_locked_super(s);
211    }
212}
213
214EXPORT_SYMBOL(deactivate_super);
215
216/**
217 * grab_super - acquire an active reference
218 * @s: reference we are trying to make active
219 *
220 * Tries to acquire an active reference. grab_super() is used when we
221 * had just found a superblock in super_blocks or fs_type->fs_supers
222 * and want to turn it into a full-blown active reference. grab_super()
223 * is called with sb_lock held and drops it. Returns 1 in case of
224 * success, 0 if we had failed (superblock contents was already dead or
225 * dying when grab_super() had been called).
226 */
227static int grab_super(struct super_block *s) __releases(sb_lock)
228{
229    if (atomic_inc_not_zero(&s->s_active)) {
230        spin_unlock(&sb_lock);
231        return 1;
232    }
233    /* it's going away */
234    s->s_count++;
235    spin_unlock(&sb_lock);
236    /* wait for it to die */
237    down_write(&s->s_umount);
238    up_write(&s->s_umount);
239    put_super(s);
240    return 0;
241}
242
243/*
244 * Superblock locking. We really ought to get rid of these two.
245 */
246void lock_super(struct super_block * sb)
247{
248    get_fs_excl();
249    mutex_lock(&sb->s_lock);
250}
251
252void unlock_super(struct super_block * sb)
253{
254    put_fs_excl();
255    mutex_unlock(&sb->s_lock);
256}
257
258EXPORT_SYMBOL(lock_super);
259EXPORT_SYMBOL(unlock_super);
260
261/**
262 * generic_shutdown_super - common helper for ->kill_sb()
263 * @sb: superblock to kill
264 *
265 * generic_shutdown_super() does all fs-independent work on superblock
266 * shutdown. Typical ->kill_sb() should pick all fs-specific objects
267 * that need destruction out of superblock, call generic_shutdown_super()
268 * and release aforementioned objects. Note: dentries and inodes _are_
269 * taken care of and do not need specific handling.
270 *
271 * Upon calling this function, the filesystem may no longer alter or
272 * rearrange the set of dentries belonging to this super_block, nor may it
273 * change the attachments of dentries to inodes.
274 */
275void generic_shutdown_super(struct super_block *sb)
276{
277    const struct super_operations *sop = sb->s_op;
278
279
280    if (sb->s_root) {
281        shrink_dcache_for_umount(sb);
282        sync_filesystem(sb);
283        get_fs_excl();
284        sb->s_flags &= ~MS_ACTIVE;
285
286        fsnotify_unmount_inodes(&sb->s_inodes);
287
288        evict_inodes(sb);
289
290        if (sop->put_super)
291            sop->put_super(sb);
292
293        if (!list_empty(&sb->s_inodes)) {
294            printk("VFS: Busy inodes after unmount of %s. "
295               "Self-destruct in 5 seconds. Have a nice day...\n",
296               sb->s_id);
297        }
298        put_fs_excl();
299    }
300    spin_lock(&sb_lock);
301    /* should be initialized for __put_super_and_need_restart() */
302    list_del_init(&sb->s_instances);
303    spin_unlock(&sb_lock);
304    up_write(&sb->s_umount);
305}
306
307EXPORT_SYMBOL(generic_shutdown_super);
308
309/**
310 * sget - find or create a superblock
311 * @type: filesystem type superblock should belong to
312 * @test: comparison callback
313 * @set: setup callback
314 * @data: argument to each of them
315 */
316struct super_block *sget(struct file_system_type *type,
317            int (*test)(struct super_block *,void *),
318            int (*set)(struct super_block *,void *),
319            void *data)
320{
321    struct super_block *s = NULL;
322    struct super_block *old;
323    int err;
324
325retry:
326    spin_lock(&sb_lock);
327    if (test) {
328        list_for_each_entry(old, &type->fs_supers, s_instances) {
329            if (!test(old, data))
330                continue;
331            if (!grab_super(old))
332                goto retry;
333            if (s) {
334                up_write(&s->s_umount);
335                destroy_super(s);
336                s = NULL;
337            }
338            down_write(&old->s_umount);
339            if (unlikely(!(old->s_flags & MS_BORN))) {
340                deactivate_locked_super(old);
341                goto retry;
342            }
343            return old;
344        }
345    }
346    if (!s) {
347        spin_unlock(&sb_lock);
348        s = alloc_super(type);
349        if (!s)
350            return ERR_PTR(-ENOMEM);
351        goto retry;
352    }
353        
354    err = set(s, data);
355    if (err) {
356        spin_unlock(&sb_lock);
357        up_write(&s->s_umount);
358        destroy_super(s);
359        return ERR_PTR(err);
360    }
361    s->s_type = type;
362    strlcpy(s->s_id, type->name, sizeof(s->s_id));
363    list_add_tail(&s->s_list, &super_blocks);
364    list_add(&s->s_instances, &type->fs_supers);
365    spin_unlock(&sb_lock);
366    get_filesystem(type);
367    return s;
368}
369
370EXPORT_SYMBOL(sget);
371
372void drop_super(struct super_block *sb)
373{
374    up_read(&sb->s_umount);
375    put_super(sb);
376}
377
378EXPORT_SYMBOL(drop_super);
379
380/**
381 * sync_supers - helper for periodic superblock writeback
382 *
383 * Call the write_super method if present on all dirty superblocks in
384 * the system. This is for the periodic writeback used by most older
385 * filesystems. For data integrity superblock writeback use
386 * sync_filesystems() instead.
387 *
388 * Note: check the dirty flag before waiting, so we don't
389 * hold up the sync while mounting a device. (The newly
390 * mounted device won't need syncing.)
391 */
392void sync_supers(void)
393{
394    struct super_block *sb, *p = NULL;
395
396    spin_lock(&sb_lock);
397    list_for_each_entry(sb, &super_blocks, s_list) {
398        if (list_empty(&sb->s_instances))
399            continue;
400        if (sb->s_op->write_super && sb->s_dirt) {
401            sb->s_count++;
402            spin_unlock(&sb_lock);
403
404            down_read(&sb->s_umount);
405            if (sb->s_root && sb->s_dirt)
406                sb->s_op->write_super(sb);
407            up_read(&sb->s_umount);
408
409            spin_lock(&sb_lock);
410            if (p)
411                __put_super(p);
412            p = sb;
413        }
414    }
415    if (p)
416        __put_super(p);
417    spin_unlock(&sb_lock);
418}
419
420/**
421 * iterate_supers - call function for all active superblocks
422 * @f: function to call
423 * @arg: argument to pass to it
424 *
425 * Scans the superblock list and calls given function, passing it
426 * locked superblock and given argument.
427 */
428void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
429{
430    struct super_block *sb, *p = NULL;
431
432    spin_lock(&sb_lock);
433    list_for_each_entry(sb, &super_blocks, s_list) {
434        if (list_empty(&sb->s_instances))
435            continue;
436        sb->s_count++;
437        spin_unlock(&sb_lock);
438
439        down_read(&sb->s_umount);
440        if (sb->s_root)
441            f(sb, arg);
442        up_read(&sb->s_umount);
443
444        spin_lock(&sb_lock);
445        if (p)
446            __put_super(p);
447        p = sb;
448    }
449    if (p)
450        __put_super(p);
451    spin_unlock(&sb_lock);
452}
453
454/**
455 * get_super - get the superblock of a device
456 * @bdev: device to get the superblock for
457 *
458 * Scans the superblock list and finds the superblock of the file system
459 * mounted on the device given. %NULL is returned if no match is found.
460 */
461
462struct super_block *get_super(struct block_device *bdev)
463{
464    struct super_block *sb;
465
466    if (!bdev)
467        return NULL;
468
469    spin_lock(&sb_lock);
470rescan:
471    list_for_each_entry(sb, &super_blocks, s_list) {
472        if (list_empty(&sb->s_instances))
473            continue;
474        if (sb->s_bdev == bdev) {
475            sb->s_count++;
476            spin_unlock(&sb_lock);
477            down_read(&sb->s_umount);
478            /* still alive? */
479            if (sb->s_root)
480                return sb;
481            up_read(&sb->s_umount);
482            /* nope, got unmounted */
483            spin_lock(&sb_lock);
484            __put_super(sb);
485            goto rescan;
486        }
487    }
488    spin_unlock(&sb_lock);
489    return NULL;
490}
491
492EXPORT_SYMBOL(get_super);
493
494/**
495 * get_active_super - get an active reference to the superblock of a device
496 * @bdev: device to get the superblock for
497 *
498 * Scans the superblock list and finds the superblock of the file system
499 * mounted on the device given. Returns the superblock with an active
500 * reference or %NULL if none was found.
501 */
502struct super_block *get_active_super(struct block_device *bdev)
503{
504    struct super_block *sb;
505
506    if (!bdev)
507        return NULL;
508
509restart:
510    spin_lock(&sb_lock);
511    list_for_each_entry(sb, &super_blocks, s_list) {
512        if (list_empty(&sb->s_instances))
513            continue;
514        if (sb->s_bdev == bdev) {
515            if (grab_super(sb)) /* drops sb_lock */
516                return sb;
517            else
518                goto restart;
519        }
520    }
521    spin_unlock(&sb_lock);
522    return NULL;
523}
524 
525struct super_block *user_get_super(dev_t dev)
526{
527    struct super_block *sb;
528
529    spin_lock(&sb_lock);
530rescan:
531    list_for_each_entry(sb, &super_blocks, s_list) {
532        if (list_empty(&sb->s_instances))
533            continue;
534        if (sb->s_dev == dev) {
535            sb->s_count++;
536            spin_unlock(&sb_lock);
537            down_read(&sb->s_umount);
538            /* still alive? */
539            if (sb->s_root)
540                return sb;
541            up_read(&sb->s_umount);
542            /* nope, got unmounted */
543            spin_lock(&sb_lock);
544            __put_super(sb);
545            goto rescan;
546        }
547    }
548    spin_unlock(&sb_lock);
549    return NULL;
550}
551
552/**
553 * do_remount_sb - asks filesystem to change mount options.
554 * @sb: superblock in question
555 * @flags: numeric part of options
556 * @data: the rest of options
557 * @force: whether or not to force the change
558 *
559 * Alters the mount options of a mounted file system.
560 */
561int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
562{
563    int retval;
564    int remount_ro;
565
566    if (sb->s_frozen != SB_UNFROZEN)
567        return -EBUSY;
568
569#ifdef CONFIG_BLOCK
570    if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
571        return -EACCES;
572#endif
573
574    if (flags & MS_RDONLY)
575        acct_auto_close(sb);
576    shrink_dcache_sb(sb);
577    sync_filesystem(sb);
578
579    remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
580
581    /* If we are remounting RDONLY and current sb is read/write,
582       make sure there are no rw files opened */
583    if (remount_ro) {
584        if (force)
585            mark_files_ro(sb);
586        else if (!fs_may_remount_ro(sb))
587            return -EBUSY;
588    }
589
590    if (sb->s_op->remount_fs) {
591        retval = sb->s_op->remount_fs(sb, &flags, data);
592        if (retval)
593            return retval;
594    }
595    sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
596
597    /*
598     * Some filesystems modify their metadata via some other path than the
599     * bdev buffer cache (eg. use a private mapping, or directories in
600     * pagecache, etc). Also file data modifications go via their own
601     * mappings. So If we try to mount readonly then copy the filesystem
602     * from bdev, we could get stale data, so invalidate it to give a best
603     * effort at coherency.
604     */
605    if (remount_ro && sb->s_bdev)
606        invalidate_bdev(sb->s_bdev);
607    return 0;
608}
609
610static void do_emergency_remount(struct work_struct *work)
611{
612    struct super_block *sb, *p = NULL;
613
614    spin_lock(&sb_lock);
615    list_for_each_entry(sb, &super_blocks, s_list) {
616        if (list_empty(&sb->s_instances))
617            continue;
618        sb->s_count++;
619        spin_unlock(&sb_lock);
620        down_write(&sb->s_umount);
621        if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
622            /*
623             * What lock protects sb->s_flags??
624             */
625            do_remount_sb(sb, MS_RDONLY, NULL, 1);
626        }
627        up_write(&sb->s_umount);
628        spin_lock(&sb_lock);
629        if (p)
630            __put_super(p);
631        p = sb;
632    }
633    if (p)
634        __put_super(p);
635    spin_unlock(&sb_lock);
636    kfree(work);
637    printk("Emergency Remount complete\n");
638}
639
640void emergency_remount(void)
641{
642    struct work_struct *work;
643
644    work = kmalloc(sizeof(*work), GFP_ATOMIC);
645    if (work) {
646        INIT_WORK(work, do_emergency_remount);
647        schedule_work(work);
648    }
649}
650
651/*
652 * Unnamed block devices are dummy devices used by virtual
653 * filesystems which don't use real block-devices. -- jrs
654 */
655
656static DEFINE_IDA(unnamed_dev_ida);
657static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
658static int unnamed_dev_start = 0; /* don't bother trying below it */
659
660int set_anon_super(struct super_block *s, void *data)
661{
662    int dev;
663    int error;
664
665 retry:
666    if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
667        return -ENOMEM;
668    spin_lock(&unnamed_dev_lock);
669    error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
670    if (!error)
671        unnamed_dev_start = dev + 1;
672    spin_unlock(&unnamed_dev_lock);
673    if (error == -EAGAIN)
674        /* We raced and lost with another CPU. */
675        goto retry;
676    else if (error)
677        return -EAGAIN;
678
679    if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
680        spin_lock(&unnamed_dev_lock);
681        ida_remove(&unnamed_dev_ida, dev);
682        if (unnamed_dev_start > dev)
683            unnamed_dev_start = dev;
684        spin_unlock(&unnamed_dev_lock);
685        return -EMFILE;
686    }
687    s->s_dev = MKDEV(0, dev & MINORMASK);
688    s->s_bdi = &noop_backing_dev_info;
689    return 0;
690}
691
692EXPORT_SYMBOL(set_anon_super);
693
694void kill_anon_super(struct super_block *sb)
695{
696    int slot = MINOR(sb->s_dev);
697
698    generic_shutdown_super(sb);
699    spin_lock(&unnamed_dev_lock);
700    ida_remove(&unnamed_dev_ida, slot);
701    if (slot < unnamed_dev_start)
702        unnamed_dev_start = slot;
703    spin_unlock(&unnamed_dev_lock);
704}
705
706EXPORT_SYMBOL(kill_anon_super);
707
708void kill_litter_super(struct super_block *sb)
709{
710    if (sb->s_root)
711        d_genocide(sb->s_root);
712    kill_anon_super(sb);
713}
714
715EXPORT_SYMBOL(kill_litter_super);
716
717static int ns_test_super(struct super_block *sb, void *data)
718{
719    return sb->s_fs_info == data;
720}
721
722static int ns_set_super(struct super_block *sb, void *data)
723{
724    sb->s_fs_info = data;
725    return set_anon_super(sb, NULL);
726}
727
728struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
729    void *data, int (*fill_super)(struct super_block *, void *, int))
730{
731    struct super_block *sb;
732
733    sb = sget(fs_type, ns_test_super, ns_set_super, data);
734    if (IS_ERR(sb))
735        return ERR_CAST(sb);
736
737    if (!sb->s_root) {
738        int err;
739        sb->s_flags = flags;
740        err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
741        if (err) {
742            deactivate_locked_super(sb);
743            return ERR_PTR(err);
744        }
745
746        sb->s_flags |= MS_ACTIVE;
747    }
748
749    return dget(sb->s_root);
750}
751
752EXPORT_SYMBOL(mount_ns);
753
754#ifdef CONFIG_BLOCK
755static int set_bdev_super(struct super_block *s, void *data)
756{
757    s->s_bdev = data;
758    s->s_dev = s->s_bdev->bd_dev;
759
760    /*
761     * We set the bdi here to the queue backing, file systems can
762     * overwrite this in ->fill_super()
763     */
764    s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
765    return 0;
766}
767
768static int test_bdev_super(struct super_block *s, void *data)
769{
770    return (void *)s->s_bdev == data;
771}
772
773struct dentry *mount_bdev(struct file_system_type *fs_type,
774    int flags, const char *dev_name, void *data,
775    int (*fill_super)(struct super_block *, void *, int))
776{
777    struct block_device *bdev;
778    struct super_block *s;
779    fmode_t mode = FMODE_READ | FMODE_EXCL;
780    int error = 0;
781
782    if (!(flags & MS_RDONLY))
783        mode |= FMODE_WRITE;
784
785    bdev = blkdev_get_by_path(dev_name, mode, fs_type);
786    if (IS_ERR(bdev))
787        return ERR_CAST(bdev);
788
789    /*
790     * once the super is inserted into the list by sget, s_umount
791     * will protect the lockfs code from trying to start a snapshot
792     * while we are mounting
793     */
794    mutex_lock(&bdev->bd_fsfreeze_mutex);
795    if (bdev->bd_fsfreeze_count > 0) {
796        mutex_unlock(&bdev->bd_fsfreeze_mutex);
797        error = -EBUSY;
798        goto error_bdev;
799    }
800    s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
801    mutex_unlock(&bdev->bd_fsfreeze_mutex);
802    if (IS_ERR(s))
803        goto error_s;
804
805    if (s->s_root) {
806        if ((flags ^ s->s_flags) & MS_RDONLY) {
807            deactivate_locked_super(s);
808            error = -EBUSY;
809            goto error_bdev;
810        }
811
812        /*
813         * s_umount nests inside bd_mutex during
814         * __invalidate_device(). blkdev_put() acquires
815         * bd_mutex and can't be called under s_umount. Drop
816         * s_umount temporarily. This is safe as we're
817         * holding an active reference.
818         */
819        up_write(&s->s_umount);
820        blkdev_put(bdev, mode);
821        down_write(&s->s_umount);
822    } else {
823        char b[BDEVNAME_SIZE];
824
825        s->s_flags = flags | MS_NOSEC;
826        s->s_mode = mode;
827        strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
828        sb_set_blocksize(s, block_size(bdev));
829        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
830        if (error) {
831            deactivate_locked_super(s);
832            goto error;
833        }
834
835        s->s_flags |= MS_ACTIVE;
836        bdev->bd_super = s;
837    }
838
839    return dget(s->s_root);
840
841error_s:
842    error = PTR_ERR(s);
843error_bdev:
844    blkdev_put(bdev, mode);
845error:
846    return ERR_PTR(error);
847}
848EXPORT_SYMBOL(mount_bdev);
849
850void kill_block_super(struct super_block *sb)
851{
852    struct block_device *bdev = sb->s_bdev;
853    fmode_t mode = sb->s_mode;
854
855    bdev->bd_super = NULL;
856    generic_shutdown_super(sb);
857    sync_blockdev(bdev);
858    WARN_ON_ONCE(!(mode & FMODE_EXCL));
859    blkdev_put(bdev, mode | FMODE_EXCL);
860}
861
862EXPORT_SYMBOL(kill_block_super);
863#endif
864
865struct dentry *mount_nodev(struct file_system_type *fs_type,
866    int flags, void *data,
867    int (*fill_super)(struct super_block *, void *, int))
868{
869    int error;
870    struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
871
872    if (IS_ERR(s))
873        return ERR_CAST(s);
874
875    s->s_flags = flags;
876
877    error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
878    if (error) {
879        deactivate_locked_super(s);
880        return ERR_PTR(error);
881    }
882    s->s_flags |= MS_ACTIVE;
883    return dget(s->s_root);
884}
885EXPORT_SYMBOL(mount_nodev);
886
887static int compare_single(struct super_block *s, void *p)
888{
889    return 1;
890}
891
892struct dentry *mount_single(struct file_system_type *fs_type,
893    int flags, void *data,
894    int (*fill_super)(struct super_block *, void *, int))
895{
896    struct super_block *s;
897    int error;
898
899    s = sget(fs_type, compare_single, set_anon_super, NULL);
900    if (IS_ERR(s))
901        return ERR_CAST(s);
902    if (!s->s_root) {
903        s->s_flags = flags;
904        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
905        if (error) {
906            deactivate_locked_super(s);
907            return ERR_PTR(error);
908        }
909        s->s_flags |= MS_ACTIVE;
910    } else {
911        do_remount_sb(s, flags, data, 0);
912    }
913    return dget(s->s_root);
914}
915EXPORT_SYMBOL(mount_single);
916
917struct dentry *
918mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
919{
920    struct dentry *root;
921    struct super_block *sb;
922    char *secdata = NULL;
923    int error = -ENOMEM;
924
925    if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
926        secdata = alloc_secdata();
927        if (!secdata)
928            goto out;
929
930        error = security_sb_copy_data(data, secdata);
931        if (error)
932            goto out_free_secdata;
933    }
934
935    root = type->mount(type, flags, name, data);
936    if (IS_ERR(root)) {
937        error = PTR_ERR(root);
938        goto out_free_secdata;
939    }
940    sb = root->d_sb;
941    BUG_ON(!sb);
942    WARN_ON(!sb->s_bdi);
943    WARN_ON(sb->s_bdi == &default_backing_dev_info);
944    sb->s_flags |= MS_BORN;
945
946    error = security_sb_kern_mount(sb, flags, secdata);
947    if (error)
948        goto out_sb;
949
950    /*
951     * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
952     * but s_maxbytes was an unsigned long long for many releases. Throw
953     * this warning for a little while to try and catch filesystems that
954     * violate this rule.
955     */
956    WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
957        "negative value (%lld)\n", type->name, sb->s_maxbytes);
958
959    up_write(&sb->s_umount);
960    free_secdata(secdata);
961    return root;
962out_sb:
963    dput(root);
964    deactivate_locked_super(sb);
965out_free_secdata:
966    free_secdata(secdata);
967out:
968    return ERR_PTR(error);
969}
970
971/**
972 * freeze_super - lock the filesystem and force it into a consistent state
973 * @sb: the super to lock
974 *
975 * Syncs the super to make sure the filesystem is consistent and calls the fs's
976 * freeze_fs. Subsequent calls to this without first thawing the fs will return
977 * -EBUSY.
978 */
979int freeze_super(struct super_block *sb)
980{
981    int ret;
982
983    atomic_inc(&sb->s_active);
984    down_write(&sb->s_umount);
985    if (sb->s_frozen) {
986        deactivate_locked_super(sb);
987        return -EBUSY;
988    }
989
990    if (sb->s_flags & MS_RDONLY) {
991        sb->s_frozen = SB_FREEZE_TRANS;
992        smp_wmb();
993        up_write(&sb->s_umount);
994        return 0;
995    }
996
997    sb->s_frozen = SB_FREEZE_WRITE;
998    smp_wmb();
999
1000    sync_filesystem(sb);
1001
1002    sb->s_frozen = SB_FREEZE_TRANS;
1003    smp_wmb();
1004
1005    sync_blockdev(sb->s_bdev);
1006    if (sb->s_op->freeze_fs) {
1007        ret = sb->s_op->freeze_fs(sb);
1008        if (ret) {
1009            printk(KERN_ERR
1010                "VFS:Filesystem freeze failed\n");
1011            sb->s_frozen = SB_UNFROZEN;
1012            deactivate_locked_super(sb);
1013            return ret;
1014        }
1015    }
1016    up_write(&sb->s_umount);
1017    return 0;
1018}
1019EXPORT_SYMBOL(freeze_super);
1020
1021/**
1022 * thaw_super -- unlock filesystem
1023 * @sb: the super to thaw
1024 *
1025 * Unlocks the filesystem and marks it writeable again after freeze_super().
1026 */
1027int thaw_super(struct super_block *sb)
1028{
1029    int error;
1030
1031    down_write(&sb->s_umount);
1032    if (sb->s_frozen == SB_UNFROZEN) {
1033        up_write(&sb->s_umount);
1034        return -EINVAL;
1035    }
1036
1037    if (sb->s_flags & MS_RDONLY)
1038        goto out;
1039
1040    if (sb->s_op->unfreeze_fs) {
1041        error = sb->s_op->unfreeze_fs(sb);
1042        if (error) {
1043            printk(KERN_ERR
1044                "VFS:Filesystem thaw failed\n");
1045            sb->s_frozen = SB_FREEZE_TRANS;
1046            up_write(&sb->s_umount);
1047            return error;
1048        }
1049    }
1050
1051out:
1052    sb->s_frozen = SB_UNFROZEN;
1053    smp_wmb();
1054    wake_up(&sb->s_wait_unfrozen);
1055    deactivate_locked_super(sb);
1056
1057    return 0;
1058}
1059EXPORT_SYMBOL(thaw_super);
1060

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