path: root/fs/libfs.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *	fs/libfs.c
 *	Library for filesystems writers.
 */

#include <linux/blkdev.h>
#include <linux/export.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/quotaops.h>
#include <linux/mutex.h>
#include <linux/namei.h>
#include <linux/exportfs.h>
#include <linux/iversion.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h> /* sync_mapping_buffers */
#include <linux/fs_context.h>
#include <linux/pseudo_fs.h>
#include <linux/fsnotify.h>
#include <linux/unicode.h>
#include <linux/fscrypt.h>

#include <linux/uaccess.h>

#include "internal.h"

int simple_getattr(struct user_namespace *mnt_userns, const struct path *path,
		   struct kstat *stat, u32 request_mask,
		   unsigned int query_flags)
{
	struct inode *inode = d_inode(path->dentry);
	generic_fillattr(&init_user_ns, inode, stat);
	stat->blocks = inode->i_mapping->nrpages << (PAGE_SHIFT - 9);
	return 0;
}
EXPORT_SYMBOL(simple_getattr);

int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
{
	buf->f_type = dentry->d_sb->s_magic;
	buf->f_bsize = PAGE_SIZE;
	buf->f_namelen = NAME_MAX;
	return 0;
}
EXPORT_SYMBOL(simple_statfs);

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

const struct dentry_operations simple_dentry_operations = {
	.d_delete = always_delete_dentry,
};
EXPORT_SYMBOL(simple_dentry_operations);

/*
 * 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, unsigned int flags)
{
	if (dentry->d_name.len > NAME_MAX)
		return ERR_PTR(-ENAMETOOLONG);
	if (!dentry->d_sb->s_d_op)
		d_set_d_op(dentry, &simple_dentry_operations);
	d_add(dentry, NULL);
	return NULL;
}
EXPORT_SYMBOL(simple_lookup);

int dcache_dir_open(struct inode *inode, struct file *file)
{
	file->private_data = d_alloc_cursor(file->f_path.dentry);

	return file->private_data ? 0 : -ENOMEM;
}
EXPORT_SYMBOL(dcache_dir_open);

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

/* parent is locked at least shared */
/*
 * Returns an element of siblings' list.
 * We are looking for <count>th positive after <p>; if
 * found, dentry is grabbed and returned to caller.
 * If no such element exists, NULL is returned.
 */
static struct dentry *scan_positives(struct dentry *cursor,
					struct list_head *p,
					loff_t count,
					struct dentry *last)
{
	struct dentry *dentry = cursor->d_parent, *found = NULL;

	spin_lock(&dentry->d_lock);
	while ((p = p->next) != &dentry->d_subdirs) {
		struct dentry *d = list_entry(p, struct dentry, d_child);
		// we must at least skip cursors, to avoid livelocks
		if (d->d_flags & DCACHE_DENTRY_CURSOR)
			continue;
		if (simple_positive(d) && !--count) {
			spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
			if (simple_positive(d))
				found = dget_dlock(d);
			spin_unlock(&d->d_lock);
			if (likely(found))
				break;
			count = 1;
		}
		if (need_resched()) {
			list_move(&cursor->d_child, p);
			p = &cursor->d_child;
			spin_unlock(&dentry->d_lock);
			cond_resched();
			spin_lock(&dentry->d_lock);
		}
	}
	spin_unlock(&dentry->d_lock);
	dput(last);
	return found;
}

loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
{
	struct dentry *dentry = file->f_path.dentry;
	switch (whence) {
		case 1:
			offset += file->f_pos;
			fallthrough;
		case 0:
			if (offset >= 0)
				break;
			fallthrough;
		default:
			return -EINVAL;
	}
	if (offset != file->f_pos) {
		struct dentry *cursor = file->private_data;
		struct dentry *to = NULL;

		inode_lock_shared(dentry->d_inode);

		if (offset > 2)
			to = scan_positives(cursor, &dentry->d_subdirs,
					    offset - 2, NULL);
		spin_lock(&dentry->d_lock);
		if (to)
			list_move(&cursor->d_child, &to->d_child);
		else
			list_del_init(&cursor->d_child);
		spin_unlock(&dentry->d_lock);
		dput(to);

		file->f_pos = offset;

		inode_unlock_shared(dentry->d_inode);
	}
	return offset;
}
EXPORT_SYMBOL(dcache_dir_lseek);

/* 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 *file, struct dir_context *ctx)
{
	struct dentry *dentry = file->f_path.dentry;
	struct dentry *cursor = file->private_data;
	struct list_head *anchor = &dentry->d_subdirs;
	struct dentry *next = NULL;
	struct list_head *p;

	if (!dir_emit_dots(file, ctx))
		return 0;

	if (ctx->pos == 2)
		p = anchor;
	else if (!list_empty(&cursor->d_child))
		p = &cursor->d_child;
	else
		return 0;

	while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
		if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
			      d_inode(next)->i_ino, dt_type(d_inode(next))))
			break;
		ctx->pos++;
		p = &next->d_child;
	}
	spin_lock(&dentry->d_lock);
	if (next)
		list_move_tail(&cursor->d_child, &next->d_child);
	else
		list_del_init(&cursor->d_child);
	spin_unlock(&dentry->d_lock);
	dput(next);

	return 0;
}
EXPORT_SYMBOL(dcache_readdir);

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

const struct file_operations simple_dir_operations = {
	.open		= dcache_dir_open,
	.release	= dcache_dir_c