dir.c

linux 内核源代码

/*
 *  linux/fs/ext2/dir.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card ([e-mail])
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/dir.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  ext2 directory handling functions
 *
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller ([e-mail]), 1995
 *
 * All code that works with directory layout had been switched to pagecache
 * and moved here. AV
 */

#include "ext2.h"
#include <linux/buffer_head.h>
#include <linux/pagemap.h>
#include <linux/swap.h>

typedef struct ext2_dir_entry_2 ext2_dirent;

static inline unsigned ext2_rec_len_from_disk(__le16 dlen)
{
	unsigned len = le16_to_cpu(dlen);

	if (len == EXT2_MAX_REC_LEN)
		return 1 << 16;
	return len;
}

static inline __le16 ext2_rec_len_to_disk(unsigned len)
{
	if (len == (1 << 16))
		return cpu_to_le16(EXT2_MAX_REC_LEN);
	else if (len > (1 << 16))
		BUG();
	return cpu_to_le16(len);
}

/*
 * ext2 uses block-sized chunks. Arguably, sector-sized ones would be
 * more robust, but we have what we have
 */
static inline unsigned ext2_chunk_size(struct inode *inode)
{
	return inode->i_sb->s_blocksize;
}

static inline void ext2_put_page(struct page *page)
{
	kunmap(page);
	page_cache_release(page);
}

static inline unsigned long dir_pages(struct inode *inode)
{
	return (inode->i_size+PAGE_CACHE_SIZE-1)>>PAGE_CACHE_SHIFT;
}

/*
 * Return the offset into page `page_nr' of the last valid
 * byte in that page, plus one.
 */
static unsigned
ext2_last_byte(struct inode *inode, unsigned long page_nr)
{
	unsigned last_byte = inode->i_size;

	last_byte -= page_nr << PAGE_CACHE_SHIFT;
	if (last_byte > PAGE_CACHE_SIZE)
		last_byte = PAGE_CACHE_SIZE;
	return last_byte;
}

static int ext2_commit_chunk(struct page *page, loff_t pos, unsigned len)
{
	struct address_space *mapping = page->mapping;
	struct inode *dir = mapping->host;
	int err = 0;

	dir->i_version++;
	block_write_end(NULL, mapping, pos, len, len, page, NULL);

	if (pos+len > dir->i_size) {
		i_size_write(dir, pos+len);
		mark_inode_dirty(dir);
	}

	if (IS_DIRSYNC(dir))
		err = write_one_page(page, 1);
	else
		unlock_page(page);

	return err;
}

static void ext2_check_page(struct page *page)
{
	struct inode *dir = page->mapping->host;
	struct super_block *sb = dir->i_sb;
	unsigned chunk_size = ext2_chunk_size(dir);
	char *kaddr = page_address(page);
	u32 max_inumber = le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count);
	unsigned offs, rec_len;
	unsigned limit = PAGE_CACHE_SIZE;
	ext2_dirent *p;
	char *error;

	if ((dir->i_size >> PAGE_CACHE_SHIFT) == page->index) {
		limit = dir->i_size & ~PAGE_CACHE_MASK;
		if (limit & (chunk_size - 1))
			goto Ebadsize;
		if (!limit)
			goto out;
	}
	for (offs = 0; offs <= limit - EXT2_DIR_REC_LEN(1); offs += rec_len) {
		p = (ext2_dirent *)(kaddr + offs);
		rec_len = ext2_rec_len_from_disk(p->rec_len);

		if (rec_len < EXT2_DIR_REC_LEN(1))
			goto Eshort;
		if (rec_len & 3)
			goto Ealign;
		if (rec_len < EXT2_DIR_REC_LEN(p->name_len))
			goto Enamelen;
		if (((offs + rec_len - 1) ^ offs) & ~(chunk_size-1))
			goto Espan;
		if (le32_to_cpu(p->inode) > max_inumber)
			goto Einumber;
	}
	if (offs != limit)
		goto Eend;
out:
	SetPageChecked(page);
	return;

	/* Too bad, we had an error */

Ebadsize:
	ext2_error(sb, "ext2_check_page",
		"size of directory #%lu is not a multiple of chunk size",
		dir->i_ino
	);
	goto fail;
Eshort:
	error = "rec_len is smaller than minimal";
	goto bad_entry;
Ealign:
	error = "unaligned directory entry";
	goto bad_entry;
Enamelen:
	error = "rec_len is too small for name_len";
	goto bad_entry;
Espan:
	error = "directory entry across blocks";
	goto bad_entry;
Einumber:
	error = "inode out of bounds";
bad_entry:
	ext2_error (sb, "ext2_check_page", "bad entry in directory #%lu: %s - "
		"offset=%lu, inode=%lu, rec_len=%d, name_len=%d",
		dir->i_ino, error, (page->index<<PAGE_CACHE_SHIFT)+offs,
		(unsigned long) le32_to_cpu(p->inode),
		rec_len, p->name_len);
	goto fail;
Eend:
	p = (ext2_dirent *)(kaddr + offs);
	ext2_error (sb, "ext2_check_page",
		"entry in directory #%lu spans the page boundary"
		"offset=%lu, inode=%lu",
		dir->i_ino, (page->index<<PAGE_CACHE_SHIFT)+offs,
		(unsigned long) le32_to_cpu(p->inode));
fail:
	SetPageChecked(page);
	SetPageError(page);
}

static struct page * ext2_get_page(struct inode *dir, unsigned long n)
{
	struct address_space *mapping = dir->i_mapping;
	struct page *page = read_mapping_page(mapping, n, NULL);
	if (!IS_ERR(page)) {
		kmap(page);
		if (!PageChecked(page))
			ext2_check_page(page);
		if (PageError(page))
			goto fail;
	}
	return page;

fail:
	ext2_put_page(page);
	return ERR_PTR(-EIO);
}

/*
 * NOTE! unlike strncmp, ext2_match returns 1 for success, 0 for failure.
 *
 * len <= EXT2_NAME_LEN and de != NULL are guaranteed by caller.
 */
static inline int ext2_match (int len, const char * const name,
					struct ext2_dir_entry_2 * de)
{
	if (len != de->name_len)
		return 0;
	if (!de->inode)
		return 0;
	return !memcmp(name, de->name, len);
}

/*
 * p is at least 6 bytes before the end of page
 */
static inline ext2_dirent *ext2_next_entry(ext2_dirent *p)
{
	return (ext2_dirent *)((char *)p +
			ext2_rec_len_from_disk(p->rec_len));
}

static inline unsigned 
ext2_validate_entry(char *base, unsigned offset, unsigned mask)
{
	ext2_dirent *de = (ext2_dirent*)(base + offset);
	ext2_dirent *p = (ext2_dirent*)(base + (offset&mask));
	while ((char*)p < (char*)de) {
		if (p->rec_len == 0)
			break;
		p = ext2_next_entry(p);
	}
	return (char *)p - base;
}

static unsigned char ext2_filetype_table[EXT2_FT_MAX] = {
	[EXT2_FT_UNKNOWN]	= DT_UNKNOWN,
	[EXT2_FT_REG_FILE]	= DT_REG,
	[EXT2_FT_DIR]		= DT_DIR,
	[EXT2_FT_CHRDEV]	= DT_CHR,
	[EXT2_FT_BLKDEV]	= DT_BLK,
	[EXT2_FT_FIFO]		= DT_FIFO,
	[EXT2_FT_SOCK]		= DT_SOCK,
	[EXT2_FT_SYMLINK]	= DT_LNK,
};

#define S_SHIFT 12
static unsigned char ext2_type_by_mode[S_IFMT >> S_SHIFT] = {
	[S_IFREG >> S_SHIFT]	= EXT2_FT_REG_FILE,
	[S_IFDIR >> S_SHIFT]	= EXT2_FT_DIR,
	[S_IFCHR >> S_SHIFT]	= EXT2_FT_CHRDEV,
	[S_IFBLK >> S_SHIFT]	= EXT2_FT_BLKDEV,
	[S_IFIFO >> S_SHIFT]	= EXT2_FT_FIFO,
	[S_IFSOCK >> S_SHIFT]	= EXT2_FT_SOCK,
	[S_IFLNK >> S_SHIFT]	= EXT2_FT_SYMLINK,
};

static inline void ext2_set_de_type(ext2_dirent *de, struct inode *inode)
{
	mode_t mode = inode->i_mode;
	if (EXT2_HAS_INCOMPAT_FEATURE(inode->i_sb, EXT2_FEATURE_INCOMPAT_FILETYPE))
		de->file_type = ext2_type_by_mode[(mode & S_IFMT)>>S_SHIFT];
	else
		de->file_type = 0;
}

static int
ext2_readdir (struct file * filp, void * dirent, filldir_t filldir)
{
	loff_t pos = filp->f_pos;
	struct inode *inode = filp->f_path.dentry->d_inode;
	struct super_block *sb = inode->i_sb;
	unsigned int offset = pos & ~PAGE_CACHE_MASK;
	unsigned long n = pos >> PAGE_CACHE_SHIFT;
	unsigned long npages = dir_pages(inode);
	unsigned chunk_mask = ~(ext2_chunk_size(inode)-1);
	unsigned char *types = NULL;
	int need_revalidate = filp->f_version != inode->i_version;

	if (pos > inode->i_size - EXT2_DIR_REC_LEN(1))
		return 0;

	if (EXT2_HAS_INCOMPAT_FEATURE(sb, EXT2_FEATURE_INCOMPAT_FILETYPE))
		types = ext2_filetype_table;

	for ( ; n < npages; n++, offset = 0) {
		char *kaddr, *limit;
		ext2_dirent *de;
		struct page *page = ext2_get_page(inode, n);

		if (IS_ERR(page)) {
			ext2_error(sb, __FUNCTION__,
				   "bad page in #%lu",
				   inode->i_ino);
			filp->f_pos += PAGE_CACHE_SIZE - offset;
			return -EIO;
		}
		kaddr = page_address(page);
		if (unlikely(need_revalidate)) {
			if (offset) {
				offset = ext2_validate_entry(kaddr, offset, chunk_mask);
				filp->f_pos = (n<<PAGE_CACHE_SHIFT) + offset;
			}
			filp->f_version = inode->i_version;
			need_revalidate = 0;
		}
		de = (ext2_dirent *)(kaddr+offset);
		limit = kaddr + ext2_last_byte(inode, n) - EXT2_DIR_REC_LEN(1);
		for ( ;(char*)de <= limit; de = ext2_next_entry(de)) {
			if (de->rec_len == 0) {
				ext2_error(sb, __FUNCTION__,
					"zero-length directory entry");
				ext2_put_page(page);
				return -EIO;
			}
			if (de->inode) {
				int over;
				unsigned char d_type = DT_UNKNOWN;

				if (types && de->file_type < EXT2_FT_MAX)
					d_type = types[de->file_type];

				offset = (char *)de - kaddr;
				over = filldir(dirent, de->name, de->name_len,
						(n<<PAGE_CACHE_SHIFT) | offset,
						le32_to_cpu(de->inode), d_type);
				if (over) {
					ext2_put_page(page);
					return 0;
				}
			}
			filp->f_pos += ext2_rec_len_from_disk(de->rec_len);
		}
		ext2_put_page(page);
	}
	return 0;
}

/*
 *	ext2_find_entry()
 *
 * finds an entry in the specified directory with the wanted name. It
 * returns the page in which the entry was found, and the entry itself
 * (as a parameter - res_dir). Page is returned mapped and unlocked.
 * Entry is guaranteed to be valid.
 */
struct ext2_dir_entry_2 * ext2_find_entry (struct inode * dir,
			struct dentry *dentry, struct page ** res_page)
{
	const char *name = dentry->d_name.name;