namei_vfat.c

linux环境下基于FAT的文件系统的通用代码

/*
 *  linux/fs/vfat/namei.c
 *
 *  Written 1992,1993 by Werner Almesberger
 *
 *  Windows95/Windows NT compatible extended MSDOS filesystem
 *    by Gordon Chaffee Copyright (C) 1995.  Send bug reports for the
 *    VFAT filesystem to <[e-mail]>.  Specify
 *    what file operation caused you trouble and if you can duplicate
 *    the problem, send a script that demonstrates it.
 *
 *  Short name translation 1999, 2001 by Wolfram Pienkoss <[e-mail]>
 *
 *  Support Multibyte characters and cleanup by
 *				OGAWA Hirofumi <[e-mail]>
 */

#include <linux/module.h>
#include <linux/jiffies.h>
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/buffer_head.h>
#include <linux/namei.h>
#include "fat.h"

/*
 * If new entry was created in the parent, it could create the 8.3
 * alias (the shortname of logname).  So, the parent may have the
 * negative-dentry which matches the created 8.3 alias.
 *
 * If it happened, the negative dentry isn't actually negative
 * anymore.  So, drop it.
 */
static int vfat_revalidate_shortname(struct dentry *dentry)
{
	int ret = 1;
	spin_lock(&dentry->d_lock);
	if (dentry->d_time != dentry->d_parent->d_inode->i_version)
		ret = 0;
	spin_unlock(&dentry->d_lock);
	return ret;
}

static int vfat_revalidate(struct dentry *dentry, struct nameidata *nd)
{
	/* This is not negative dentry. Always valid. */
	if (dentry->d_inode)
		return 1;
	return vfat_revalidate_shortname(dentry);
}

static int vfat_revalidate_ci(struct dentry *dentry, struct nameidata *nd)
{
	/*
	 * This is not negative dentry. Always valid.
	 *
	 * Note, rename() to existing directory entry will have ->d_inode,
	 * and will use existing name which isn't specified name by user.
	 *
	 * We may be able to drop this positive dentry here. But dropping
	 * positive dentry isn't good idea. So it's unsupported like
	 * rename("filename", "FILENAME") for now.
	 */
	if (dentry->d_inode)
		return 1;

	/*
	 * This may be nfsd (or something), anyway, we can't see the
	 * intent of this. So, since this can be for creation, drop it.
	 */
	if (!nd)
		return 0;

	/*
	 * Drop the negative dentry, in order to make sure to use the
	 * case sensitive name which is specified by user if this is
	 * for creation.
	 */
	if (!(nd->flags & (LOOKUP_CONTINUE | LOOKUP_PARENT))) {
		if (nd->flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET))
			return 0;
	}

	return vfat_revalidate_shortname(dentry);
}

/* returns the length of a struct qstr, ignoring trailing dots */
static unsigned int vfat_striptail_len(struct qstr *qstr)
{
	unsigned int len = qstr->len;

	while (len && qstr->name[len - 1] == '.')
		len--;
	return len;
}

/*
 * Compute the hash for the vfat name corresponding to the dentry.
 * Note: if the name is invalid, we leave the hash code unchanged so
 * that the existing dentry can be used. The vfat fs routines will
 * return ENOENT or EINVAL as appropriate.
 */
static int vfat_hash(struct dentry *dentry, struct qstr *qstr)
{
	qstr->hash = full_name_hash(qstr->name, vfat_striptail_len(qstr));
	return 0;
}

/*
 * Compute the hash for the vfat name corresponding to the dentry.
 * Note: if the name is invalid, we leave the hash code unchanged so
 * that the existing dentry can be used. The vfat fs routines will
 * return ENOENT or EINVAL as appropriate.
 */
static int vfat_hashi(struct dentry *dentry, struct qstr *qstr)
{
	struct nls_table *t = MSDOS_SB(dentry->d_inode->i_sb)->nls_io;
	const unsigned char *name;
	unsigned int len;
	unsigned long hash;

	name = qstr->name;
	len = vfat_striptail_len(qstr);

	hash = init_name_hash();
	while (len--)
		hash = partial_name_hash(nls_tolower(t, *name++), hash);
	qstr->hash = end_name_hash(hash);

	return 0;
}

/*
 * Case insensitive compare of two vfat names.
 */
static int vfat_cmpi(struct dentry *dentry, struct qstr *a, struct qstr *b)
{
	struct nls_table *t = MSDOS_SB(dentry->d_inode->i_sb)->nls_io;
	unsigned int alen, blen;

	/* A filename cannot end in '.' or we treat it like it has none */
	alen = vfat_striptail_len(a);
	blen = vfat_striptail_len(b);
	if (alen == blen) {
		if (nls_strnicmp(t, a->name, b->name, alen) == 0)
			return 0;
	}
	return 1;
}

/*
 * Case sensitive compare of two vfat names.
 */
static int vfat_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
{
	unsigned int alen, blen;

	/* A filename cannot end in '.' or we treat it like it has none */
	alen = vfat_striptail_len(a);
	blen = vfat_striptail_len(b);
	if (alen == blen) {
		if (strncmp(a->name, b->name, alen) == 0)
			return 0;
	}
	return 1;
}

static struct dentry_operations vfat_ci_dentry_ops = {
	.d_revalidate	= vfat_revalidate_ci,
	.d_hash		= vfat_hashi,
	.d_compare	= vfat_cmpi,
};

static struct dentry_operations vfat_dentry_ops = {
	.d_revalidate	= vfat_revalidate,
	.d_hash		= vfat_hash,
	.d_compare	= vfat_cmp,
};

/* Characters that are undesirable in an MS-DOS file name */

static inline wchar_t vfat_bad_char(wchar_t w)
{
	return (w < 0x0020)
	    || (w == '*') || (w == '?') || (w == '<') || (w == '>')
	    || (w == '|') || (w == '"') || (w == ':') || (w == '/')
	    || (w == '\\');
}

static inline wchar_t vfat_replace_char(wchar_t w)
{
	return (w == '[') || (w == ']') || (w == ';') || (w == ',')
	    || (w == '+') || (w == '=');
}

static wchar_t vfat_skip_char(wchar_t w)
{
	return (w == '.') || (w == ' ');
}

static inline int vfat_is_used_badchars(const wchar_t *s, int len)
{
	int i;

	for (i = 0; i < len; i++)
		if (vfat_bad_char(s[i]))
			return -EINVAL;

	if (s[i - 1] == ' ') /* last character cannot be space */
		return -EINVAL;

	return 0;
}

static int vfat_find_form(struct inode *dir, unsigned char *name)
{
	struct fat_slot_info sinfo;
	int err = fat_scan(dir, name, &sinfo);
	if (err)
		return -ENOENT;
	brelse(sinfo.bh);
	return 0;
}

/*
 * 1) Valid characters for the 8.3 format alias are any combination of
 * letters, uppercase alphabets, digits, any of the
 * following special characters:
 *     $ % ' ` - @ { } ~ ! # ( ) & _ ^
 * In this case Longfilename is not stored in disk.
 *
 * WinNT's Extension:
 * File name and extension name is contain uppercase/lowercase
 * only. And it is expressed by CASE_LOWER_BASE and CASE_LOWER_EXT.
 *
 * 2) File name is 8.3 format, but it contain the uppercase and
 * lowercase char, muliti bytes char, etc. In this case numtail is not
 * added, but Longfilename is stored.
 *
 * 3) When the one except for the above, or the following special
 * character are contained:
 *        .   [ ] ; , + =
 * numtail is added, and Longfilename must be stored in disk .
 */
struct shortname_info {
	unsigned char lower:1,
		      upper:1,
		      valid:1;
};
#define INIT_SHORTNAME_INFO(x)	do {		\
	(x)->lower = 1;				\
	(x)->upper = 1;				\
	(x)->valid = 1;				\
} while (0)

static inline int to_shortname_char(struct nls_table *nls,
				    unsigned char *buf, int buf_size,
				    wchar_t *src, struct shortname_info *info)
{
	int len;

	if (vfat_skip_char(*src)) {
		info->valid = 0;
		return 0;
	}
	if (vfat_replace_char(*src)) {
		info->valid = 0;
		buf[0] = '_';
		return 1;
	}

	len = nls->uni2char(*src, buf, buf_size);
	if (len <= 0) {
		info->valid = 0;
		buf[0] = '_';
		len = 1;
	} else if (len == 1) {
		unsigned char prev = buf[0];

		if (buf[0] >= 0x7F) {
			info->lower = 0;
			info->upper = 0;
		}

		buf[0] = nls_toupper(nls, buf[0]);
		if (isalpha(buf[0])) {
			if (buf[0] == prev)
				info->lower = 0;
			else
				info->upper = 0;
		}
	} else {
		info->lower = 0;
		info->upper = 0;
	}

	return len;
}

/*
 * Given a valid longname, create a unique shortname.  Make sure the
 * shortname does not exist
 * Returns negative number on error, 0 for a normal
 * return, and 1 for valid shortname
 */
static int vfat_create_shortname(struct inode *dir, struct nls_table *nls,
				 wchar_t *uname, int ulen,
				 unsigned char *name_res, unsigned char *lcase)
{
	struct fat_mount_options *opts = &MSDOS_SB(dir->i_sb)->options;
	wchar_t *ip, *ext_start, *end, *name_start;
	unsigned char base[9], ext[4], buf[8], *p;
	unsigned char charbuf[NLS_MAX_CHARSET_SIZE];
	int chl, chi;
	int sz = 0, extlen, baselen, i, numtail_baselen, numtail2_baselen;
	int is_shortname;
	struct shortname_info base_info, ext_info;

	is_shortname = 1;
	INIT_SHORTNAME_INFO(&base_info);
	INIT_SHORTNAME_INFO(&ext_info);

	/* Now, we need to create a shortname from the long name */
	ext_start = end = &uname[ulen];
	while (--ext_start >= uname) {
		if (*ext_start == 0x002E) {	/* is `.' */
			if (ext_start == end - 1) {
				sz = ulen;
				ext_start = NULL;
			}
			break;
		}
	}

	if (ext_start == uname - 1) {
		sz = ulen;
		ext_start = NULL;
	} else if (ext_start) {
		/*
		 * Names which start with a dot could be just
		 * an extension eg. "...test".  In this case Win95
		 * uses the extension as the name and sets no extension.
		 */
		name_start = &uname[0];
		while (name_start < ext_start) {
			if (!vfat_skip_char(*name_start))
				break;
			name_start++;
		}
		if (name_start != ext_start) {
			sz = ext_start - uname;
			ext_start++;
		} else {
			sz = ulen;
			ext_start = NULL;
		}
	}

	numtail_baselen = 6;
	numtail2_baselen = 2;
	for (baselen = i = 0, p = base, ip = uname; i < sz; i++, ip++) {
		chl = to_shortname_char(nls, charbuf, sizeof(charbuf),
					ip, &base_info);
		if (chl == 0)
			continue;

		if (baselen < 2 && (baselen + chl) > 2)
			numtail2_baselen = baselen;
		if (baselen < 6 && (baselen + chl) > 6)
			numtail_baselen = baselen;
		for (chi = 0; chi < chl; chi++) {
			*p++ = charbuf[chi];
			baselen++;
			if (baselen >= 8)
				break;
		}
		if (baselen >= 8) {
			if ((chi < chl - 1) || (ip + 1) - uname < sz)
				is_shortname = 0;
			break;
		}
	}
	if (baselen == 0) {
		return -EINVAL;
	}

	extlen = 0;
	if (ext_start) {
		for (p = ext, ip = ext_start; extlen < 3 && ip < end; ip++) {
			chl = to_shortname_char(nls, charbuf, sizeof(charbuf),
						ip, &ext_info);
			if (chl == 0)
				continue;

			if ((extlen + chl) > 3) {
				is_shortname = 0;
				break;
			}
			for (chi = 0; chi < chl; chi++) {
				*p++ = charbuf[chi];
				extlen++;
			}
			if (extlen >= 3) {
				if (ip + 1 != end)
					is_shortname = 0;
				break;
			}
		}
	}
	ext[extlen] = '\0';
	base[baselen] = '\0';

	/* Yes, it can happen. ".\xe5" would do it. */
	if (base[0] == DELETED_FLAG)
		base[0] = 0x05;

	/* OK, at this point we know that base is not longer than 8 symbols,
	 * ext is not longer than 3, base is nonempty, both don't contain
	 * any bad symbols (lowercase transformed to uppercase).
	 */

	memset(name_res, ' ', MSDOS_NAME);
	memcpy(name_res, base, baselen);
	memcpy(name_res + 8, ext, extlen);
	*lcase = 0;
	if (is_shortname && base_info.valid && ext_info.valid) {
		if (vfat_find_form(dir, name_res) == 0)
			return -EEXIST;

		if (opts->shortname & VFAT_SFN_CREATE_WIN95) {
			return (base_info.upper && ext_info.upper);
		} else if (opts->shortname & VFAT_SFN_CREATE_WINNT) {
			if ((base_info.upper || base_info.lower) &&
			    (ext_info.upper || ext_info.lower)) {
				if (!base_info.upper && base_info.lower)
					*lcase |= CASE_LOWER_BASE;
				if (!ext_info.upper && ext_info.lower)
					*lcase |= CASE_LOWER_EXT;
				return 1;
			}
			return 0;
		} else {
			BUG();
		}
	}

	if (opts->numtail == 0)
		if (vfat_find_form(dir, name_res) < 0)
			return 0;

	/*
	 * Try to find a unique extension.  This used to
	 * iterate through all possibilities sequentially,
	 * but that gave extremely bad performance.  Windows
	 * only tries a few cases before using random
	 * values for part of the base.
	 */

	if (baselen > 6) {
		baselen = numtail_baselen;
		name_res[7] = ' ';
	}
	name_res[baselen] = '~';
	for (i = 1; i < 10; i++) {
		name_res[baselen + 1] = i + '0';
		if (vfat_find_form(dir, name_res) < 0)
			return 0;
	}

	i = jiffies & 0xffff;
	sz = (jiffies >> 16) & 0x7;
	if (baselen > 2) {
		baselen = numtail2_baselen;
		name_res[7] = ' ';
	}
	name_res[baselen + 4] = '~';
	name_res[baselen + 5] = '1' + sz;
	while (1) {
		sprintf(buf, "%04X", i);
		memcpy(&name_res[baselen], buf, 4);
		if (vfat_find_form(dir, name_res) < 0)
			break;
		i -= 11;
	}
	return 0;
}

/* Translate a string, including coded sequences into Unicode */
static int
xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,
	     int *longlen, int *outlen, int escape, int utf8,
	     struct nls_table *nls)
{
	const unsigned char *ip;
	unsigned char nc;
	unsigned char *op;
	unsigned int ec;
	int i, k, fill;
	int charlen;

	if (utf8) {
		int name_len = strlen(name);

		*outlen = utf8_mbstowcs((wchar_t *)outname, name, PATH_MAX);

		/*
		 * We stripped '.'s before and set len appropriately,
		 * but utf8_mbstowcs doesn't care about len
		 */
		*outlen -= (name_len - len);

		if (*outlen > 255)
			return -ENAMETOOLONG;

		op = &outname[*outlen * sizeof(wchar_t)];
	} else {
		if (nls) {
			for (i = 0, ip = name, op = outname, *outlen = 0;
			     i < len && *outlen <= 255;
			     *outlen += 1)
			{
				if (escape && (*ip == ':')) {
					if (i > len - 5)
						return -EINVAL;
					ec = 0;
					for (k = 1; k < 5; k++) {
						nc = ip[k];
						ec <<= 4;
						if (nc >= '0' && nc <= '9') {
							ec |= nc - '0';
							continue;
						}
						if (nc >= 'a' && nc <= 'f') {
							ec |= nc - ('a' - 10);
							continue;
						}
						if (nc >= 'A' && nc <= 'F') {
							ec |= nc - ('A' - 10);
							continue;
						}
						return -EINVAL;
					}
					*op++ = ec & 0xFF;
					*op++ = ec >> 8;
					ip += 5;
					i += 5;
				} else {
					if ((charlen = nls->char2uni(ip, len - i, (wchar_t *)op)) < 0)
						return -EINVAL;