dir.c

linux环境下基于FAT的文件系统的通用代码

/*
 *  linux/fs/fat/dir.c
 *
 *  directory handling functions for fat-based filesystems
 *
 *  Written 1992,1993 by Werner Almesberger
 *
 *  Hidden files 1995 by Albert Cahalan <[e-mail]> <[e-mail]>
 *
 *  VFAT extensions by Gordon Chaffee <[e-mail]>
 *  Merged with msdos fs by Henrik Storner <[e-mail]>
 *  Rewritten for constant inumbers. Plugged buffer overrun in readdir(). AV
 *  Short name translation 1999, 2001 by Wolfram Pienkoss <[e-mail]>
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/smp_lock.h>
#include <linux/buffer_head.h>
#include <linux/compat.h>
#include <asm/uaccess.h>
#include "fat.h"

static inline loff_t fat_make_i_pos(struct super_block *sb,
				    struct buffer_head *bh,
				    struct msdos_dir_entry *de)
{
	return ((loff_t)bh->b_blocknr << MSDOS_SB(sb)->dir_per_block_bits)
		| (de - (struct msdos_dir_entry *)bh->b_data);
}

static inline void fat_dir_readahead(struct inode *dir, sector_t iblock,
				     sector_t phys)
{
	struct super_block *sb = dir->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct buffer_head *bh;
	int sec;

	/* This is not a first sector of cluster, or sec_per_clus == 1 */
	if ((iblock & (sbi->sec_per_clus - 1)) || sbi->sec_per_clus == 1)
		return;
	/* root dir of FAT12/FAT16 */
	if ((sbi->fat_bits != 32) && (dir->i_ino == MSDOS_ROOT_INO))
		return;

	bh = sb_find_get_block(sb, phys);
	if (bh == NULL || !buffer_uptodate(bh)) {
		for (sec = 0; sec < sbi->sec_per_clus; sec++)
			sb_breadahead(sb, phys + sec);
	}
	brelse(bh);
}

/* Returns the inode number of the directory entry at offset pos. If bh is
   non-NULL, it is brelse'd before. Pos is incremented. The buffer header is
   returned in bh.
   AV. Most often we do it item-by-item. Makes sense to optimize.
   AV. OK, there we go: if both bh and de are non-NULL we assume that we just
   AV. want the next entry (took one explicit de=NULL in vfat/namei.c).
   AV. It's done in fat_get_entry() (inlined), here the slow case lives.
   AV. Additionally, when we return -1 (i.e. reached the end of directory)
   AV. we make bh NULL.
 */
static int fat__get_entry(struct inode *dir, loff_t *pos,
			  struct buffer_head **bh, struct msdos_dir_entry **de)
{
	struct super_block *sb = dir->i_sb;
	sector_t phys, iblock;
	unsigned long mapped_blocks;
	int err, offset;

next:
	if (*bh)
		brelse(*bh);

	*bh = NULL;
	iblock = *pos >> sb->s_blocksize_bits;
	err = fat_bmap(dir, iblock, &phys, &mapped_blocks, 0);
	if (err || !phys)
		return -1;	/* beyond EOF or error */

	fat_dir_readahead(dir, iblock, phys);

	*bh = sb_bread(sb, phys);
	if (*bh == NULL) {
		printk(KERN_ERR "FAT: Directory bread(block %llu) failed\n",
		       (llu)phys);
		/* skip this block */
		*pos = (iblock + 1) << sb->s_blocksize_bits;
		goto next;
	}

	offset = *pos & (sb->s_blocksize - 1);
	*pos += sizeof(struct msdos_dir_entry);
	*de = (struct msdos_dir_entry *)((*bh)->b_data + offset);

	return 0;
}

static inline int fat_get_entry(struct inode *dir, loff_t *pos,
				struct buffer_head **bh,
				struct msdos_dir_entry **de)
{
	/* Fast stuff first */
	if (*bh && *de &&
	    (*de - (struct msdos_dir_entry *)(*bh)->b_data) < MSDOS_SB(dir->i_sb)->dir_per_block - 1) {
		*pos += sizeof(struct msdos_dir_entry);
		(*de)++;
		return 0;
	}
	return fat__get_entry(dir, pos, bh, de);
}

/*
 * Convert Unicode 16 to UTF-8, translated Unicode, or ASCII.
 * If uni_xlate is enabled and we can't get a 1:1 conversion, use a
 * colon as an escape character since it is normally invalid on the vfat
 * filesystem. The following four characters are the hexadecimal digits
 * of Unicode value. This lets us do a full dump and restore of Unicode
 * filenames. We could get into some trouble with long Unicode names,
 * but ignore that right now.
 * Ahem... Stack smashing in ring 0 isn't fun. Fixed.
 */
static int uni16_to_x8(unsigned char *ascii, const wchar_t *uni, int len,
		       int uni_xlate, struct nls_table *nls)
{
	const wchar_t *ip;
	wchar_t ec;
	unsigned char *op, nc;
	int charlen;
	int k;

	ip = uni;
	op = ascii;

	while (*ip && ((len - NLS_MAX_CHARSET_SIZE) > 0)) {
		ec = *ip++;
		if ( (charlen = nls->uni2char(ec, op, NLS_MAX_CHARSET_SIZE)) > 0) {
			op += charlen;
			len -= charlen;
		} else {
			if (uni_xlate == 1) {
				*op = ':';
				for (k = 4; k > 0; k--) {
					nc = ec & 0xF;
					op[k] = nc > 9	? nc + ('a' - 10)
							: nc + '0';
					ec >>= 4;
				}
				op += 5;
				len -= 5;
			} else {
				*op++ = '?';
				len--;
			}
		}
	}

	if (unlikely(*ip)) {
		printk(KERN_WARNING "FAT: filename was truncated while "
		       "converting.");
	}

	*op = 0;
	return (op - ascii);
}

static inline int fat_uni_to_x8(struct msdos_sb_info *sbi, const wchar_t *uni,
				unsigned char *buf, int size)
{
	if (sbi->options.utf8)
		return utf8_wcstombs(buf, uni, size);
	else
		return uni16_to_x8(buf, uni, size, sbi->options.unicode_xlate,
				   sbi->nls_io);
}

static inline int
fat_short2uni(struct nls_table *t, unsigned char *c, int clen, wchar_t *uni)
{
	int charlen;

	charlen = t->char2uni(c, clen, uni);
	if (charlen < 0) {
		*uni = 0x003f;	/* a question mark */
		charlen = 1;
	}
	return charlen;
}

static inline int
fat_short2lower_uni(struct nls_table *t, unsigned char *c, int clen, wchar_t *uni)
{
	int charlen;
	wchar_t wc;

	charlen = t->char2uni(c, clen, &wc);
	if (charlen < 0) {
		*uni = 0x003f;	/* a question mark */
		charlen = 1;
	} else if (charlen <= 1) {
		unsigned char nc = t->charset2lower[*c];

		if (!nc)
			nc = *c;

		if ( (charlen = t->char2uni(&nc, 1, uni)) < 0) {
			*uni = 0x003f;	/* a question mark */
			charlen = 1;
		}
	} else
		*uni = wc;

	return charlen;
}

static inline int
fat_shortname2uni(struct nls_table *nls, unsigned char *buf, int buf_size,
		  wchar_t *uni_buf, unsigned short opt, int lower)
{
	int len = 0;

	if (opt & VFAT_SFN_DISPLAY_LOWER)
		len =  fat_short2lower_uni(nls, buf, buf_size, uni_buf);
	else if (opt & VFAT_SFN_DISPLAY_WIN95)
		len = fat_short2uni(nls, buf, buf_size, uni_buf);
	else if (opt & VFAT_SFN_DISPLAY_WINNT) {
		if (lower)
			len = fat_short2lower_uni(nls, buf, buf_size, uni_buf);
		else
			len = fat_short2uni(nls, buf, buf_size, uni_buf);
	} else
		len = fat_short2uni(nls, buf, buf_size, uni_buf);

	return len;
}

static inline int fat_name_match(struct msdos_sb_info *sbi,
				 const unsigned char *a, int a_len,
				 const unsigned char *b, int b_len)
{
	if (a_len != b_len)
		return 0;

	if (sbi->options.name_check != 's')
		return !nls_strnicmp(sbi->nls_io, a, b, a_len);
	else
		return !memcmp(a, b, a_len);
}

enum { PARSE_INVALID = 1, PARSE_NOT_LONGNAME, PARSE_EOF, };

/**
 * fat_parse_long - Parse extended directory entry.
 *
 * This function returns zero on success, negative value on error, or one of
 * the following:
 *
 * %PARSE_INVALID - Directory entry is invalid.
 * %PARSE_NOT_LONGNAME - Directory entry does not contain longname.
 * %PARSE_EOF - Directory has no more entries.
 */
static int fat_parse_long(struct inode *dir, loff_t *pos,
			  struct buffer_head **bh, struct msdos_dir_entry **de,
			  wchar_t **unicode, unsigned char *nr_slots)
{
	struct msdos_dir_slot *ds;
	unsigned char id, slot, slots, alias_checksum;

	if (!*unicode) {
		*unicode = __getname();
		if (!*unicode) {
			brelse(*bh);
			return -ENOMEM;
		}
	}
parse_long:
	slots = 0;
	ds = (struct msdos_dir_slot *)*de;
	id = ds->id;
	if (!(id & 0x40))
		return PARSE_INVALID;
	slots = id & ~0x40;
	if (slots > 20 || !slots)	/* ceil(256 * 2 / 26) */
		return PARSE_INVALID;
	*nr_slots = slots;
	alias_checksum = ds->alias_checksum;

	slot = slots;
	while (1) {
		int offset;

		slot--;
		offset = slot * 13;
		fat16_towchar(*unicode + offset, ds->name0_4, 5);
		fat16_towchar(*unicode + offset + 5, ds->name5_10, 6);
		fat16_towchar(*unicode + offset + 11, ds->name11_12, 2);

		if (ds->id & 0x40)
			(*unicode)[offset + 13] = 0;
		if (fat_get_entry(dir, pos, bh, de) < 0)
			return PARSE_EOF;
		if (slot == 0)
			break;
		ds = (struct msdos_dir_slot *)*de;
		if (ds->attr != ATTR_EXT)
			return PARSE_NOT_LONGNAME;
		if ((ds->id & ~0x40) != slot)
			goto parse_long;
		if (ds->alias_checksum != alias_checksum)
			goto parse_long;
	}
	if ((*de)->name[0] == DELETED_FLAG)
		return PARSE_INVALID;
	if ((*de)->attr == ATTR_EXT)
		goto parse_long;
	if (IS_FREE((*de)->name) || ((*de)->attr & ATTR_VOLUME))
		return PARSE_INVALID;
	if (fat_checksum((*de)->name) != alias_checksum)
		*nr_slots = 0;

	return 0;
}

/*
 * Maximum buffer size of short name.
 * [(MSDOS_NAME + '.') * max one char + nul]
 * For msdos style, ['.' (hidden) + MSDOS_NAME + '.' + nul]
 */
#define FAT_MAX_SHORT_SIZE	((MSDOS_NAME + 1) * NLS_MAX_CHARSET_SIZE + 1)
/*
 * Maximum buffer size of unicode chars from slots.
 * [(max longname slots * 13 (size in a slot) + nul) * sizeof(wchar_t)]
 */
#define FAT_MAX_UNI_CHARS	((MSDOS_SLOTS - 1) * 13 + 1)
#define FAT_MAX_UNI_SIZE	(FAT_MAX_UNI_CHARS * sizeof(wchar_t))

/*
 * Return values: negative -> error, 0 -> not found, positive -> found,
 * value is the total amount of slots, including the shortname entry.
 */
int fat_search_long(struct inode *inode, const unsigned char *name,
		    int name_len, struct fat_slot_info *sinfo)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct buffer_head *bh = NULL;
	struct msdos_dir_entry *de;
	struct nls_table *nls_disk = sbi->nls_disk;
	unsigned char nr_slots;
	wchar_t bufuname[14];
	wchar_t *unicode = NULL;
	unsigned char work[MSDOS_NAME];
	unsigned char bufname[FAT_MAX_SHORT_SIZE];
	unsigned short opt_shortname = sbi->options.shortname;
	loff_t cpos = 0;
	int chl, i, j, last_u, err, len;

	err = -ENOENT;
	while (1) {
		if (fat_get_entry(inode, &cpos, &bh, &de) == -1)
			goto end_of_dir;
parse_record:
		nr_slots = 0;
		if (de->name[0] == DELETED_FLAG)
			continue;
		if (de->attr != ATTR_EXT && (de->attr & ATTR_VOLUME))
			continue;
		if (de->attr != ATTR_EXT && IS_FREE(de->name))
			continue;
		if (de->attr == ATTR_EXT) {
			int status = fat_parse_long(inode, &cpos, &bh, &de,
						    &unicode, &nr_slots);
			if (status < 0) {
				err = status;
				goto end_of_dir;
			} else if (status == PARSE_INVALID)
				continue;
			else if (status == PARSE_NOT_LONGNAME)
				goto parse_record;
			else if (status == PARSE_EOF)
				goto end_of_dir;
		}

		memcpy(work, de->name, sizeof(de->name));
		/* see namei.c, msdos_format_name */
		if (work[0] == 0x05)
			work[0] = 0xE5;
		for (i = 0, j = 0, last_u = 0; i < 8;) {
			if (!work[i])
				break;
			chl = fat_shortname2uni(nls_disk, &work[i], 8 - i,
						&bufuname[j++], opt_shortname,
						de->lcase & CASE_LOWER_BASE);
			if (chl <= 1) {
				if (work[i] != ' ')
					last_u = j;
			} else {
				last_u = j;
			}
			i += chl;
		}
		j = last_u;
		fat_short2uni(nls_disk, ".", 1, &bufuname[j++]);
		for (i = 8; i < MSDOS_NAME;) {
			if (!work[i])
				break;
			chl = fat_shortname2uni(nls_disk, &work[i],
						MSDOS_NAME - i,
						&bufuname[j++], opt_shortname,
						de->lcase & CASE_LOWER_EXT);
			if (chl <= 1) {
				if (work[i] != ' ')
					last_u = j;
			} else {
				last_u = j;
			}
			i += chl;
		}
		if (!last_u)
			continue;

		/* Compare shortname */
		bufuname[last_u] = 0x0000;
		len = fat_uni_to_x8(sbi, bufuname, bufname, sizeof(bufname));
		if (fat_name_match(sbi, name, name_len, bufname, len))
			goto found;

		if (nr_slots) {
			void *longname = unicode + FAT_MAX_UNI_CHARS;
			int size = PATH_MAX - FAT_MAX_UNI_SIZE;

			/* Compare longname */
			len = fat_uni_to_x8(sbi, unicode, longname, size);
			if (fat_name_match(sbi, name, name_len, longname, len))
				goto found;
		}
	}

found:
	nr_slots++;	/* include the de */
	sinfo->slot_off = cpos - nr_slots * sizeof(*de);
	sinfo->nr_slots = nr_slots;
	sinfo->de = de;
	sinfo->bh = bh;
	sinfo->i_pos = fat_make_i_pos(sb, sinfo->bh, sinfo->de);
	err = 0;
end_of_dir:
	if (unicode)
		__putname(unicode);

	return err;
}