fs/libfs.c



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

#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/quotaops.h>
#include <linux/mutex.h>
#include <linux/exportfs.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>

#include <asm/uaccess.h>

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

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 dentry *dentry, struct kstatfs *buf)
{
	buf->f_type = dentry->d_sb->s_magic;
	buf->f_bsize = PAGE_CACHE_SIZE;
	buf->f_namelen = NAME_MAX;
	return 0;
}

/*
 * Retaining negative dentries for an in-memory filesystem just wastes
 * memory and lookup time: arrange for them to be deleted immediately.
 */
static int simple_delete_dentry(const struct dentry *dentry)
{
	return 1;
}

/*
 * Lookup the data. This is trivial - if the dentry didn't already
 * exist, we know it is negative.  Set d_op to delete negative dentries.
 */
struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
	static const struct dentry_operations simple_dentry_operations = {
		.d_delete = simple_delete_dentry,
	};

	if (dentry->d_name.len > NAME_MAX)
		return ERR_PTR(-ENAMETOOLONG);
	d_set_d_op(dentry, &simple_dentry_operations);
	d_add(dentry, NULL);
	return NULL;
}

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_path.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)
{
	struct dentry *dentry = file->f_path.dentry;
	mutex_lock(&dentry->d_inode->i_mutex);
	switch (origin) {
		case 1:
			offset += file->f_pos;
		case 0:
			if (offset >= 0)
				break;
		default:
			mutex_unlock(&dentry->d_inode->i_mutex);
			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(&dentry->d_lock);
			/* d_lock not required for cursor */
			list_del(&cursor->d_u.d_child);
			p = dentry->d_subdirs.next;
			while (n && p != &dentry->d_subdirs) {
				struct dentry *next;
				next = list_entry(p, struct dentry, d_u.d_child);
				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
				if (simple_positive(next))
					n--;
				spin_unlock(&next->d_lock);
				p = p->next;
			}
			list_add_tail(&cursor->d_u.d_child, p);
			spin_unlock(&dentry->d_lock);
		}
	}
	mutex_unlock(&dentry->d_inode->i_mutex);
	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_path.dentry;
	struct dentry *cursor = filp->private_data;
	struct list_head *p, *q = &cursor->d_u.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(&dentry->d_lock);
			if (filp->f_pos == 2)
				list_move(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_u.d_child);
				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
				if (!simple_positive(next)) {
					spin_unlock(&next->d_lock);
					continue;
				}

				spin_unlock(&next->d_lock);
				spin_unlock(&dentry->d_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(&dentry->d_lock);
				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
				/* next is still alive */
				list_move(q, p);
				spin_unlock(&next->d_lock);
				p = q;
				filp->f_pos++;
			}