root/fs/super.c

/*
 *  linux/fs/super.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  super.c contains code to handle: - mount structures
 *                                   - super-block tables
 *                                   - filesystem drivers list
 *                                   - mount system call
 *                                   - umount system call
 *                                   - ustat system call
 *
 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
 *
 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
 *  Added options to /proc/mounts:
 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/smp_lock.h>
#include <linux/acct.h>
#include <linux/blkdev.h>
#include <linux/quotaops.h>
#include <linux/namei.h>
#include <linux/buffer_head.h>          /* for fsync_super() */
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/vfs.h>
#include <linux/writeback.h>            /* for the emergency remount stuff */
#include <linux/idr.h>
#include <asm/uaccess.h>


void get_filesystem(struct file_system_type *fs);
void put_filesystem(struct file_system_type *fs);
struct file_system_type *get_fs_type(const char *name);

LIST_HEAD(super_blocks);
spinlock_t sb_lock = SPIN_LOCK_UNLOCKED;

/**
 *      alloc_super     -       create new superblock
 *
 *      Allocates and initializes a new &struct super_block.  alloc_super()
 *      returns a pointer new superblock or %NULL if allocation had failed.
 */
static struct super_block *alloc_super(void)
{
        struct super_block *s = kmalloc(sizeof(struct super_block),  GFP_USER);
        static struct super_operations default_op;

        if (s) {
                memset(s, 0, sizeof(struct super_block));
                if (security_sb_alloc(s)) {
                        kfree(s);
                        s = NULL;
                        goto out;
                }
                INIT_LIST_HEAD(&s->s_dirty);
                INIT_LIST_HEAD(&s->s_io);
                INIT_LIST_HEAD(&s->s_files);
                INIT_LIST_HEAD(&s->s_instances);
                INIT_HLIST_HEAD(&s->s_anon);
                init_rwsem(&s->s_umount);
                sema_init(&s->s_lock, 1);
                down_write(&s->s_umount);
                s->s_count = S_BIAS;
                atomic_set(&s->s_active, 1);
                sema_init(&s->s_vfs_rename_sem,1);
                sema_init(&s->s_dquot.dqio_sem, 1);
                sema_init(&s->s_dquot.dqonoff_sem, 1);
                init_rwsem(&s->s_dquot.dqptr_sem);
                init_waitqueue_head(&s->s_wait_unfrozen);
                s->s_maxbytes = MAX_NON_LFS;
                s->dq_op = sb_dquot_ops;
                s->s_qcop = sb_quotactl_ops;
                s->s_op = &default_op;
        }
out:
        return s;
}

/**
 *      destroy_super   -       frees a superblock
 *      @s: superblock to free
 *
 *      Frees a superblock.
 */
static inline void destroy_super(struct super_block *s)
{
        security_sb_free(s);
        kfree(s);
}

/* Superblock refcounting  */

/*
 * Drop a superblock's refcount.  Returns non-zero if the superblock was
 * destroyed.  The caller must hold sb_lock.
 */
int __put_super(struct super_block *sb)
{
        int ret = 0;

        if (!--sb->s_count) {
                destroy_super(sb);
                ret = 1;
        }
        return ret;
}

/**
 *      put_super       -       drop a temporary reference to superblock
 *      @s: superblock in question
 *
 *      Drops a temporary reference, frees superblock if there's no
 *      references left.
 */
static void put_super(struct super_block *sb)
{
        spin_lock(&sb_lock);
        __put_super(sb);
        spin_unlock(&sb_lock);
}


/**
 *      deactivate_super        -       drop an active reference to superblock
 *      @s: superblock to deactivate
 *
 *      Drops an active reference to superblock, acquiring a temprory one if
 *      there is no active references left.  In that case we lock superblock,
 *      tell fs driver to shut it down and drop the temporary reference we
 *      had just acquired.
 */
void deactivate_super(struct super_block *s)
{
        struct file_system_type *fs = s->s_type;
        if (atomic_dec_and_lock(&s->s_active, &sb_lock)) {
                s->s_count -= S_BIAS-1;
                spin_unlock(&sb_lock);
                down_write(&s->s_umount);
                fs->kill_sb(s);
                put_filesystem(fs);
                put_super(s);
        }
}

EXPORT_SYMBOL(deactivate_super);

/**
 *      grab_super - acquire an active reference
 *      @s: reference we are trying to make active
 *
 *      Tries to acquire an active reference.  grab_super() is used when we
 *      had just found a superblock in super_blocks or fs_type->fs_supers
 *      and want to turn it into a full-blown active reference.  grab_super()
 *      is called with sb_lock held and drops it.  Returns 1 in case of
 *      success, 0 if we had failed (superblock contents was already dead or
 *      dying when grab_super() had been called).
 */
static int grab_super(struct super_block *s)
{
        s->s_count++;
        spin_unlock(&sb_lock);
        down_write(&s->s_umount);
        if (s->s_root) {
                spin_lock(&sb_lock);
                if (s->s_count > S_BIAS) {
                        atomic_inc(&s->s_active);
                        s->s_count--;
                        spin_unlock(&sb_lock);
                        return 1;
                }
                spin_unlock(&sb_lock);
        }
        up_write(&s->s_umount);
        put_super(s);
        yield();
        return 0;
}

/**
 *      generic_shutdown_super  -       common helper for ->kill_sb()
 *      @sb: superblock to kill
 *
 *      generic_shutdown_super() does all fs-independent work on superblock
 *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 *      that need destruction out of superblock, call generic_shutdown_super()
 *      and release aforementioned objects.  Note: dentries and inodes _are_
 *      taken care of and do not need specific handling.
 */
void generic_shutdown_super(struct super_block *sb)
{
        struct dentry *root = sb->s_root;
        struct super_operations *sop = sb->s_op;

        if (root) {
                sb->s_root = NULL;
                shrink_dcache_parent(root);
                shrink_dcache_anon(&sb->s_anon);
                dput(root);
                fsync_super(sb);
                lock_super(sb);
                lock_kernel();
                sb->s_flags &= ~MS_ACTIVE;
                /* bad name - it should be evict_inodes() */
                invalidate_inodes(sb);

                if (sop->write_super && sb->s_dirt)
                        sop->write_super(sb);
                if (sop->put_super)
                        sop->put_super(sb);

                /* Forget any remaining inodes */
                if (invalidate_inodes(sb)) {
                        printk("VFS: Busy inodes after unmount. "
                           "Self-destruct in 5 seconds.  Have a nice day...\n");
                }

                unlock_kernel();
                unlock_super(sb);
        }
        spin_lock(&sb_lock);
        list_del(&sb->s_list);
        list_del(&sb->s_instances);
        spin_unlock(&sb_lock);
        up_write(&sb->s_umount);
}

EXPORT_SYMBOL(generic_shutdown_super);

/**
 *      sget    -       find or create a superblock
 *      @type:  filesystem type superblock should belong to
 *      @test:  comparison callback
 *      @set:   setup callback
 *      @data:  argument to each of them
 */
struct super_block *sget(struct file_system_type *type,
                        int (*test)(struct super_block *,void *),
                        int (*set)(struct super_block *,void *),
                        void *data)
{
        struct super_block *s = NULL;
        struct list_head *p;
        int err;

retry:
        spin_lock(&sb_lock);
        if (test) list_for_each(p, &type->fs_supers) {
                struct super_block *old;
                old = list_entry(p, struct super_block, s_instances);
                if (!test(old, data))
                        continue;
                if (!grab_super(old))
                        goto retry;
                if (s)
                        destroy_super(s);
                return old;
        }
        if (!s) {
                spin_unlock(&sb_lock);
                s = alloc_super();
                if (!s)
                        return ERR_PTR(-ENOMEM);
                goto retry;
        }
                
        err = set(s, data);
        if (err) {
                spin_unlock(&sb_lock);
                destroy_super(s);
                return ERR_PTR(err);
        }
        s->s_type = type;
        strlcpy(s->s_id, type->name, sizeof(s->s_id));
        list_add(&s->s_list, super_blocks.prev);
        list_add(&s->s_instances, &type->fs_supers);
        spin_unlock(&sb_lock);
        get_filesystem(type);
        return s;
}

EXPORT_SYMBOL(sget);

void drop_super(struct super_block *sb)
{
        up_read(&sb->s_umount);
        put_super(sb);
}

EXPORT_SYMBOL(drop_super);

static inline void write_super(struct super_block *sb)
{
        lock_super(sb);
        if (sb->s_root && sb->s_dirt)
                if (sb->s_op->write_super)
                        sb->s_op->write_super(sb);
        unlock_super(sb);
}

/*
 * Note: check the dirty flag before waiting, so we don't
 * hold up the sync while mounting a device. (The newly
 * mounted device won't need syncing.)
 */
void sync_supers(void)
{
        struct super_block * sb;
restart:
        spin_lock(&sb_lock);
        sb = sb_entry(super_blocks.next);
        while (sb != sb_entry(&super_blocks))
                if (sb->s_dirt) {
                        sb->s_count++;
                        spin_unlock(&sb_lock);
                        down_read(&sb->s_umount);
                        write_super(sb);
                        drop_super(sb);
                        goto restart;
                } else
                        sb = sb_entry(sb->s_list.next);
        spin_unlock(&sb_lock);
}

/*
 * Call the ->sync_fs super_op against all filesytems which are r/w and
 * which implement it.
 *
 * This operation is careful to avoid the livelock which could easily happen
 * if two or more filesystems are being continuously dirtied.  s_need_sync_fs
 * is used only here.  We set it against all filesystems and then clear it as
 * we sync them.  So redirtied filesystems are skipped.
 *
 * But if process A is currently running sync_filesytems and then process B
 * calls sync_filesystems as well, process B will set all the s_need_sync_fs
 * flags again, which will cause process A to resync everything.  Fix that with
 * a local mutex.
 *
 * (Fabian) Avoid sync_fs with clean fs & wait mode 0
 */
void sync_filesystems(int wait)
{
        struct super_block *sb;
        static DECLARE_MUTEX(mutex);

        down(&mutex);           /* Could be down_interruptible */
        spin_lock(&sb_lock);
        for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
                        sb = sb_entry(sb->s_list.next)) {
                if (!sb->s_op->sync_fs)
                        continue;
                if (sb->s_flags & MS_RDONLY)
                        continue;
                sb->s_need_sync_fs = 1;
        }
        spin_unlock(&sb_lock);

restart:
        spin_lock(&sb_lock);
        for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
                        sb = sb_entry(sb->s_list.next)) {
                if (!sb->s_need_sync_fs)
                        continue;
                sb->s_need_sync_fs = 0;
                if (sb->s_flags & MS_RDONLY)
                        continue;       /* hm.  Was remounted r/o meanwhile */
                sb->s_count++;
                spin_unlock(&sb_lock);
                down_read(&sb->s_umount);
                if (sb->s_root && (wait || sb->s_dirt))
                        sb->s_op->sync_fs(sb, wait);
                drop_super(sb);
                goto restart;
        }
        spin_unlock(&sb_lock);
        up(&mutex);
}

/**
 *      get_super - get the superblock of a device
 *      @bdev: device to get the superblock for
 *      
 *      Scans the superblock list and finds the superblock of the file system
 *      mounted on the device given. %NULL is returned if no match is found.
 */

struct super_block * get_super(struct block_device *bdev)
{
        struct list_head *p;
        if (!bdev)
                return NULL;
rescan:
        spin_lock(&sb_lock);
        list_for_each(p, &super_blocks) {
                struct super_block *s = sb_entry(p);
                if (s->s_bdev == bdev) {
                        s->s_count++;
                        spin_unlock(&sb_lock);
                        down_read(&s->s_umount);
                        if (s->s_root)
                                return s;
                        drop_super(s);
                        goto rescan;
                }
        }
        spin_unlock(&sb_lock);
        return NULL;
}

EXPORT_SYMBOL(get_super);
 
struct super_block * user_get_super(dev_t dev)
{
        struct list_head *p;

rescan:
        spin_lock(&sb_lock);
        list_for_each(p, &super_blocks) {
                struct super_block *s = sb_entry(p);
                if (s->s_dev ==  dev) {
                        s->s_count++;
                        spin_unlock(&sb_lock);
                        down_read(&s->s_umount);
                        if (s->s_root)
                                return s;
                        drop_super(s);
                        goto rescan;
                }
        }
        spin_unlock(&sb_lock);
        return NULL;
}

EXPORT_SYMBOL(user_get_super);

asmlinkage long sys_ustat(unsigned dev, struct ustat __user * ubuf)
{
        struct super_block *s;
        struct ustat tmp;
        struct kstatfs sbuf;
        int err = -EINVAL;

        s = user_get_super(new_decode_dev(dev));
        if (s == NULL)
                goto out;
        err = vfs_statfs(s, &sbuf);
        drop_super(s);
        if (err)
                goto out;

        memset(&tmp,0,sizeof(struct ustat));
        tmp.f_tfree = sbuf.f_bfree;
        tmp.f_tinode = sbuf.f_ffree;

        err = copy_to_user(ubuf,&tmp,sizeof(struct ustat)) ? -EFAULT : 0;
out:
        return err;
}

/**
 *      mark_files_ro
 *      @sb: superblock in question
 *
 *      All files are marked read/only.  We don't care about pending
 *      delete files so this should be used in 'force' mode only
 */

static void mark_files_ro(struct super_block *sb)
{
        struct file *f;

        file_list_lock();
        list_for_each_entry(f, &sb->s_files, f_list) {
                if (S_ISREG(f->f_dentry->d_inode->i_mode) && file_count(f))
                        f->f_mode &= ~FMODE_WRITE;
        }
        file_list_unlock();
}

/**
 *      do_remount_sb - asks filesystem to change mount options.
 *      @sb:    superblock in question
 *      @flags: numeric part of options
 *      @data:  the rest of options
 *      @force: whether or not to force the change
 *
 *      Alters the mount options of a mounted file system.
 */
int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
{
        int retval;
        
        if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
                return -EACCES;
        if (flags & MS_RDONLY)
                acct_auto_close(sb);
        shrink_dcache_sb(sb);
        fsync_super(sb);

        /* If we are remounting RDONLY and current sb is read/write,
           make sure there are no rw files opened */
        if ((flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY)) {
                if (force)
                        mark_files_ro(sb);
                else if (!fs_may_remount_ro(sb))
                        return -EBUSY;
        }

        if (sb->s_op->remount_fs) {
                lock_super(sb);
                retval = sb->s_op->remount_fs(sb, &flags, data);
                unlock_super(sb);
                if (retval)
                        return retval;
        }
        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
        return 0;
}

static void do_emergency_remount(unsigned long foo)
{
        struct super_block *sb;

        spin_lock(&sb_lock);
        list_for_each_entry(sb, &super_blocks, s_list) {
                sb->s_count++;
                spin_unlock(&sb_lock);
                down_read(&sb->s_umount);
                if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
                        /*
                         * ->remount_fs needs lock_kernel().
                         *
                         * What lock protects sb->s_flags??
                         */
                        lock_kernel();
                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
                        unlock_kernel();
                }
                drop_super(sb);
                spin_lock(&sb_lock);
        }
        spin_unlock(&sb_lock);
        printk("Emergency Remount complete\n");
}

void emergency_remount(void)
{
        pdflush_operation(do_emergency_remount, 0);
}

/*
 * Unnamed block devices are dummy devices used by virtual
 * filesystems which don't use real block-devices.  -- jrs
 */

static struct idr unnamed_dev_idr;
static spinlock_t unnamed_dev_lock = SPIN_LOCK_UNLOCKED;/* protects the above */

int set_anon_super(struct super_block *s, void *data)
{
        int dev;

        spin_lock(&unnamed_dev_lock);
        if (idr_pre_get(&unnamed_dev_idr, GFP_ATOMIC) == 0) {
                spin_unlock(&unnamed_dev_lock);
                return -ENOMEM;
        }
        dev = idr_get_new(&unnamed_dev_idr, NULL);
        spin_unlock(&unnamed_dev_lock);

        if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) {
                spin_lock(&unnamed_dev_lock);
                idr_remove(&unnamed_dev_idr, dev);
                spin_unlock(&unnamed_dev_lock);
                return -EMFILE;
        }
        s->s_dev = MKDEV(0, dev & MINORMASK);
        return 0;
}

EXPORT_SYMBOL(set_anon_super);

void kill_anon_super(struct super_block *sb)
{
        int slot = MINOR(sb->s_dev);

        generic_shutdown_super(sb);
        spin_lock(&unnamed_dev_lock);
        idr_remove(&unnamed_dev_idr, slot);
        spin_unlock(&unnamed_dev_lock);
}

EXPORT_SYMBOL(kill_anon_super);

void __init unnamed_dev_init(void)
{
        idr_init(&unnamed_dev_idr);
}

void kill_litter_super(struct super_block *sb)
{
        if (sb->s_root)
                d_genocide(sb->s_root);
        kill_anon_super(sb);
}

EXPORT_SYMBOL(kill_litter_super);

static int set_bdev_super(struct super_block *s, void *data)
{
        s->s_bdev = data;
        s->s_dev = s->s_bdev->bd_dev;
        return 0;
}

static int test_bdev_super(struct super_block *s, void *data)
{
        return (void *)s->s_bdev == data;
}

struct super_block *get_sb_bdev(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data,
        int (*fill_super)(struct super_block *, void *, int))
{
        struct block_device *bdev;
        struct super_block *s;
        int error = 0;

        bdev = open_bdev_excl(dev_name, flags, fs_type);
        if (IS_ERR(bdev))
                return (struct super_block *)bdev;

        /*
         * once the super is inserted into the list by sget, s_umount
         * will protect the lockfs code from trying to start a snapshot
         * while we are mounting
         */
        down(&bdev->bd_mount_sem);
        s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
        up(&bdev->bd_mount_sem);
        if (IS_ERR(s))
                goto out;

        if (s->s_root) {
                if ((flags ^ s->s_flags) & MS_RDONLY) {
                        up_write(&s->s_umount);
                        deactivate_super(s);
                        s = ERR_PTR(-EBUSY);
                }
                goto out;
        } else {
                char b[BDEVNAME_SIZE];

                s->s_flags = flags;
                strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
                s->s_old_blocksize = block_size(bdev);
                sb_set_blocksize(s, s->s_old_blocksize);
                error = fill_super(s, data, flags & MS_VERBOSE ? 1 : 0);
                if (error) {
                        up_write(&s->s_umount);
                        deactivate_super(s);
                        s = ERR_PTR(error);
                } else
                        s->s_flags |= MS_ACTIVE;
        }

        return s;

out:
        close_bdev_excl(bdev);
        return s;
}

EXPORT_SYMBOL(get_sb_bdev);

void kill_block_super(struct super_block *sb)
{
        struct block_device *bdev = sb->s_bdev;
        generic_shutdown_super(sb);
        set_blocksize(bdev, sb->s_old_blocksize);
        close_bdev_excl(bdev);
}

EXPORT_SYMBOL(kill_block_super);

struct super_block *get_sb_nodev(struct file_system_type *fs_type,
        int flags, void *data,
        int (*fill_super)(struct super_block *, void *, int))
{
        int error;
        struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);

        if (IS_ERR(s))
                return s;

        s->s_flags = flags;

        error = fill_super(s, data, flags & MS_VERBOSE ? 1 : 0);
        if (error) {
                up_write(&s->s_umount);
                deactivate_super(s);
                return ERR_PTR(error);
        }
        s->s_flags |= MS_ACTIVE;
        return s;
}

EXPORT_SYMBOL(get_sb_nodev);

static int compare_single(struct super_block *s, void *p)
{
        return 1;
}

struct super_block *get_sb_single(struct file_system_type *fs_type,
        int flags, void *data,
        int (*fill_super)(struct super_block *, void *, int))
{
        struct super_block *s;
        int error;

        s = sget(fs_type, compare_single, set_anon_super, NULL);
        if (IS_ERR(s))
                return s;
        if (!s->s_root) {
                s->s_flags = flags;
                error = fill_super(s, data, flags & MS_VERBOSE ? 1 : 0);
                if (error) {
                        up_write(&s->s_umount);
                        deactivate_super(s);
                        return ERR_PTR(error);
                }
                s->s_flags |= MS_ACTIVE;
        }
        do_remount_sb(s, flags, data, 0);
        return s;
}

EXPORT_SYMBOL(get_sb_single);

struct vfsmount *
do_kern_mount(const char *fstype, int flags, const char *name, void *data)
{
        struct file_system_type *type = get_fs_type(fstype);
        struct super_block *sb = ERR_PTR(-ENOMEM);
        struct vfsmount *mnt;
        int error;
        char *secdata = NULL;

        if (!type)
                return ERR_PTR(-ENODEV);

        mnt = alloc_vfsmnt(name);
        if (!mnt)
                goto out;

        if (data) {
                secdata = alloc_secdata();
                if (!secdata) {
                        sb = ERR_PTR(-ENOMEM);
                        goto out_mnt;
                }

                error = security_sb_copy_data(type, data, secdata);
                if (error) {
                        sb = ERR_PTR(error);
                        goto out_free_secdata;
                }
        }

        sb = type->get_sb(type, flags, name, data);
        if (IS_ERR(sb))
                goto out_free_secdata;
        error = security_sb_kern_mount(sb, secdata);
        if (error)
                goto out_sb;
        mnt->mnt_sb = sb;
        mnt->mnt_root = dget(sb->s_root);
        mnt->mnt_mountpoint = sb->s_root;
        mnt->mnt_parent = mnt;
        up_write(&sb->s_umount);
        put_filesystem(type);
        return mnt;
out_sb:
        up_write(&sb->s_umount);
        deactivate_super(sb);
        sb = ERR_PTR(error);
out_free_secdata:
        free_secdata(secdata);
out_mnt:
        free_vfsmnt(mnt);
out:
        put_filesystem(type);
        return (struct vfsmount *)sb;
}

struct vfsmount *kern_mount(struct file_system_type *type)
{
        return do_kern_mount(type->name, 0, type->name, NULL);
}

EXPORT_SYMBOL(kern_mount);