root/fs/libfs.c

/*
 *      fs/libfs.c
 *      Library for filesystems writers.
 */

#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/mount.h>
#include <linux/vfs.h>

int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
                   struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
        generic_fillattr(inode, stat);
        stat->blocks = inode->i_mapping->nrpages << (PAGE_CACHE_SHIFT - 9);
        return 0;
}

int simple_statfs(struct super_block *sb, struct kstatfs *buf)
{
        buf->f_type = sb->s_magic;
        buf->f_bsize = PAGE_CACHE_SIZE;
        buf->f_namelen = NAME_MAX;
        return 0;
}

/*
 * Lookup the data. This is trivial - if the dentry didn't already
 * exist, we know it is negative.
 */

struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);
        d_add(dentry, NULL);
        return NULL;
}

int simple_sync_file(struct file * file, struct dentry *dentry, int datasync)
{
        return 0;
}
 
int dcache_dir_open(struct inode *inode, struct file *file)
{
        static struct qstr cursor_name = {.len = 1, .name = "."};

        file->private_data = d_alloc(file->f_dentry, &cursor_name);

        return file->private_data ? 0 : -ENOMEM;
}

int dcache_dir_close(struct inode *inode, struct file *file)
{
        dput(file->private_data);
        return 0;
}

loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin)
{
        down(&file->f_dentry->d_inode->i_sem);
        switch (origin) {
                case 1:
                        offset += file->f_pos;
                case 0:
                        if (offset >= 0)
                                break;
                default:
                        up(&file->f_dentry->d_inode->i_sem);
                        return -EINVAL;
        }
        if (offset != file->f_pos) {
                file->f_pos = offset;
                if (file->f_pos >= 2) {
                        struct list_head *p;
                        struct dentry *cursor = file->private_data;
                        loff_t n = file->f_pos - 2;

                        spin_lock(&dcache_lock);
                        list_del(&cursor->d_child);
                        p = file->f_dentry->d_subdirs.next;
                        while (n && p != &file->f_dentry->d_subdirs) {
                                struct dentry *next;
                                next = list_entry(p, struct dentry, d_child);
                                if (!d_unhashed(next) && next->d_inode)
                                        n--;
                                p = p->next;
                        }
                        list_add_tail(&cursor->d_child, p);
                        spin_unlock(&dcache_lock);
                }
        }
        up(&file->f_dentry->d_inode->i_sem);
        return offset;
}

/* Relationship between i_mode and the DT_xxx types */
static inline unsigned char dt_type(struct inode *inode)
{
        return (inode->i_mode >> 12) & 15;
}

/*
 * Directory is locked and all positive dentries in it are safe, since
 * for ramfs-type trees they can't go away without unlink() or rmdir(),
 * both impossible due to the lock on directory.
 */

int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
        struct dentry *dentry = filp->f_dentry;
        struct dentry *cursor = filp->private_data;
        struct list_head *p, *q = &cursor->d_child;
        ino_t ino;
        int i = filp->f_pos;

        switch (i) {
                case 0:
                        ino = dentry->d_inode->i_ino;
                        if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                case 1:
                        ino = parent_ino(dentry);
                        if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
                                break;
                        filp->f_pos++;
                        i++;
                        /* fallthrough */
                default:
                        spin_lock(&dcache_lock);
                        if (filp->f_pos == 2) {
                                list_del(q);
                                list_add(q, &dentry->d_subdirs);
                        }
                        for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
                                struct dentry *next;
                                next = list_entry(p, struct dentry, d_child);
                                if (d_unhashed(next) || !next->d_inode)
                                        continue;

                                spin_unlock(&dcache_lock);
                                if (filldir(dirent, next->d_name.name, next->d_name.len, filp->f_pos, next->d_inode->i_ino, dt_type(next->d_inode)) < 0)
                                        return 0;
                                spin_lock(&dcache_lock);
                                /* next is still alive */
                                list_del(q);
                                list_add(q, p);
                                p = q;
                                filp->f_pos++;
                        }
                        spin_unlock(&dcache_lock);
        }
        return 0;
}

ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
{
        return -EISDIR;
}

struct file_operations simple_dir_operations = {
        .open           = dcache_dir_open,
        .release        = dcache_dir_close,
        .llseek         = dcache_dir_lseek,
        .read           = generic_read_dir,
        .readdir        = dcache_readdir,
};

struct inode_operations simple_dir_inode_operations = {
        .lookup         = simple_lookup,
};

/*
 * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
 * will never be mountable)
 */
struct super_block *
get_sb_pseudo(struct file_system_type *fs_type, char *name,
        struct super_operations *ops, unsigned long magic)
{
        struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
        static struct super_operations default_ops = {.statfs = simple_statfs};
        struct dentry *dentry;
        struct inode *root;
        struct qstr d_name = {.name = name, .len = strlen(name)};

        if (IS_ERR(s))
                return s;

        s->s_flags = MS_NOUSER;
        s->s_maxbytes = ~0ULL;
        s->s_blocksize = 1024;
        s->s_blocksize_bits = 10;
        s->s_magic = magic;
        s->s_op = ops ? ops : &default_ops;
        root = new_inode(s);
        if (!root)
                goto Enomem;
        root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
        root->i_uid = root->i_gid = 0;
        root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
        dentry = d_alloc(NULL, &d_name);
        if (!dentry) {
                iput(root);
                goto Enomem;
        }
        dentry->d_sb = s;
        dentry->d_parent = dentry;
        d_instantiate(dentry, root);
        s->s_root = dentry;
        s->s_flags |= MS_ACTIVE;
        return s;

Enomem:
        up_write(&s->s_umount);
        deactivate_super(s);
        return ERR_PTR(-ENOMEM);
}

int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = old_dentry->d_inode;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        inode->i_nlink++;
        atomic_inc(&inode->i_count);
        dget(dentry);
        d_instantiate(dentry, inode);
        return 0;
}

static inline int simple_positive(struct dentry *dentry)
{
        return dentry->d_inode && !d_unhashed(dentry);
}

int simple_empty(struct dentry *dentry)
{
        struct dentry *child;
        int ret = 0;

        spin_lock(&dcache_lock);
        list_for_each_entry(child, &dentry->d_subdirs, d_child)
                if (simple_positive(child))
                        goto out;
        ret = 1;
out:
        spin_unlock(&dcache_lock);
        return ret;
}

int simple_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = dentry->d_inode;

        inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
        inode->i_nlink--;
        dput(dentry);
        return 0;
}

int simple_rmdir(struct inode *dir, struct dentry *dentry)
{
        if (!simple_empty(dentry))
                return -ENOTEMPTY;

        dentry->d_inode->i_nlink--;
        simple_unlink(dir, dentry);
        dir->i_nlink--;
        return 0;
}

int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
                struct inode *new_dir, struct dentry *new_dentry)
{
        struct inode *inode = old_dentry->d_inode;
        int they_are_dirs = S_ISDIR(old_dentry->d_inode->i_mode);

        if (!simple_empty(new_dentry))
                return -ENOTEMPTY;

        if (new_dentry->d_inode) {
                simple_unlink(new_dir, new_dentry);
                if (they_are_dirs)
                        old_dir->i_nlink--;
        } else if (they_are_dirs) {
                old_dir->i_nlink--;
                new_dir->i_nlink++;
        }

        old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
                new_dir->i_mtime = inode->i_ctime = CURRENT_TIME;

        return 0;
}

int simple_readpage(struct file *file, struct page *page)
{
        void *kaddr;

        if (PageUptodate(page))
                goto out;

        kaddr = kmap_atomic(page, KM_USER0);
        memset(kaddr, 0, PAGE_CACHE_SIZE);
        kunmap_atomic(kaddr, KM_USER0);
        flush_dcache_page(page);
        SetPageUptodate(page);
out:
        unlock_page(page);
        return 0;
}

int simple_prepare_write(struct file *file, struct page *page,
                        unsigned from, unsigned to)
{
        if (!PageUptodate(page)) {
                if (to - from != PAGE_CACHE_SIZE) {
                        void *kaddr = kmap_atomic(page, KM_USER0);
                        memset(kaddr, 0, from);
                        memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
                        flush_dcache_page(page);
                        kunmap_atomic(kaddr, KM_USER0);
                }
                SetPageUptodate(page);
        }
        return 0;
}

int simple_commit_write(struct file *file, struct page *page,
                        unsigned offset, unsigned to)
{
        struct inode *inode = page->mapping->host;
        loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;

        /*
         * No need to use i_size_read() here, the i_size
         * cannot change under us because we hold the i_sem.
         */
        if (pos > inode->i_size)
                i_size_write(inode, pos);
        set_page_dirty(page);
        return 0;
}

int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
{
        static struct super_operations s_ops = {.statfs = simple_statfs};
        struct inode *inode;
        struct dentry *root;
        struct dentry *dentry;
        int i;

        s->s_blocksize = PAGE_CACHE_SIZE;
        s->s_blocksize_bits = PAGE_CACHE_SHIFT;
        s->s_magic = magic;
        s->s_op = &s_ops;

        inode = new_inode(s);
        if (!inode)
                return -ENOMEM;
        inode->i_mode = S_IFDIR | 0755;
        inode->i_uid = inode->i_gid = 0;
        inode->i_blksize = PAGE_CACHE_SIZE;
        inode->i_blocks = 0;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        inode->i_op = &simple_dir_inode_operations;
        inode->i_fop = &simple_dir_operations;
        root = d_alloc_root(inode);
        if (!root) {
                iput(inode);
                return -ENOMEM;
        }
        for (i = 0; !files->name || files->name[0]; i++, files++) {
                struct qstr name;
                if (!files->name)
                        continue;
                name.name = files->name;
                name.len = strlen(name.name);
                name.hash = full_name_hash(name.name, name.len);
                dentry = d_alloc(root, &name);
                if (!dentry)
                        goto out;
                inode = new_inode(s);
                if (!inode)
                        goto out;
                inode->i_mode = S_IFREG | files->mode;
                inode->i_uid = inode->i_gid = 0;
                inode->i_blksize = PAGE_CACHE_SIZE;
                inode->i_blocks = 0;
                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
                inode->i_fop = files->ops;
                inode->i_ino = i;
                d_add(dentry, inode);
        }
        s->s_root = root;
        return 0;
out:
        d_genocide(root);
        dput(root);
        return -ENOMEM;
}

static spinlock_t pin_fs_lock = SPIN_LOCK_UNLOCKED;

int simple_pin_fs(char *name, struct vfsmount **mount, int *count)
{
        struct vfsmount *mnt = NULL;
        spin_lock(&pin_fs_lock);
        if (unlikely(!*mount)) {
                spin_unlock(&pin_fs_lock);
                mnt = do_kern_mount(name, 0, name, NULL);
                if (IS_ERR(mnt))
                        return PTR_ERR(mnt);
                spin_lock(&pin_fs_lock);
                if (!*mount)
                        *mount = mnt;
        }
        mntget(*mount);
        ++*count;
        spin_unlock(&pin_fs_lock);
        mntput(mnt);
        return 0;
}

void simple_release_fs(struct vfsmount **mount, int *count)
{
        struct vfsmount *mnt;
        spin_lock(&pin_fs_lock);
        mnt = *mount;
        if (!--*count)
                *mount = NULL;
        spin_unlock(&pin_fs_lock);
        mntput(mnt);
}

EXPORT_SYMBOL(dcache_dir_close);
EXPORT_SYMBOL(dcache_dir_lseek);
EXPORT_SYMBOL(dcache_dir_open);
EXPORT_SYMBOL(dcache_readdir);
EXPORT_SYMBOL(generic_read_dir);
EXPORT_SYMBOL(simple_commit_write);
EXPORT_SYMBOL(simple_dir_inode_operations);
EXPORT_SYMBOL(simple_dir_operations);
EXPORT_SYMBOL(simple_empty);
EXPORT_SYMBOL(simple_fill_super);
EXPORT_SYMBOL(simple_getattr);
EXPORT_SYMBOL(simple_link);
EXPORT_SYMBOL(simple_lookup);
EXPORT_SYMBOL(simple_pin_fs);
EXPORT_SYMBOL(simple_prepare_write);
EXPORT_SYMBOL(simple_readpage);
EXPORT_SYMBOL(simple_release_fs);
EXPORT_SYMBOL(simple_rename);
EXPORT_SYMBOL(simple_rmdir);
EXPORT_SYMBOL(simple_statfs);
EXPORT_SYMBOL(simple_sync_file);
EXPORT_SYMBOL(simple_unlink);