mangle.c

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/*
 *  linux/fs/umsdos/mangle.c
 *
 *	Written 1993 by Jacques Gelinas 
 *
 * Control the mangling of file name to fit msdos name space.
 * Many optimisation by GLU == [e-mail] (GLAUDE DAVID)
 */

#include <linux/errno.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/umsdos_fs.h>

/*
	Complete the mangling of the MSDOS fake name
	based on the position of the entry in the EMD file.

	Simply complete the job of umsdos_parse; fill the extension.

	Beware that info->f_pos must be set.
*/
void umsdos_manglename (struct umsdos_info *info)
{
	if (info->msdos_reject){
		/* #Specification: file name / non MSDOS conforming / mangling
			Each non MSDOS conforming file has a special extension
			build from the entry position in the EMD file.

			This number is then transform in a base 32 number, where
			each digit is expressed like hexadecimal number, using
			digit and letter, except it uses 22 letters from 'a' to 'v'.
			The number 32 comes from 2**5. It is faster to split a binary
			number using a base which is a power of two. And I was 32
			when I started this project. Pick your answer :-) .

			If the result is '0', it is replace with '_', simply
			to make it odd.

			This is true for the first two character of the extension.
			The last one is taken from a list of odd character, which
			are:

				{ } ( ) ! ` ^ & @

			With this scheme, we can produce 9216 ( 9* 32 * 32)
			different extensions which should not clash with any useful
			extension already popular or meaningful. Since most directory
			have much less than 32 * 32 files in it, the first character
			of the extension of any mangle name will be {.

			Here are the reason to do this (this kind of mangling).

			-The mangling is deterministic. Just by the extension, we
			 are able to locate the entry in the EMD file.

			-By keeping to beginning of the file name almost unchanged,
			 we are helping the MSDOS user.

			-The mangling produces names not too ugly, so an msdos user
			 may live with it (remember it, type it, etc...).

			-The mangling produces names ugly enough so no one will
			 ever think of using such a name in real life. This is not
			 fool proof. I don't think there is a total solution to this.
		*/
		union {
			int entry_num;
			struct {
				unsigned num1:5,num2:5,num3:5;
			}num;
		} u;
		char *pt = info->fake.fname + info->fake.len;
		/* lookup for encoding the last character of the extension */
		/* It contain valid character after the ugly one to make sure */
		/* even if someone overflow the 32 * 32 * 9 limit, it still do */
		/* something */
		#define SPECIAL_MANGLING '{','}','(',')','!','`','^','&','@'
		static char lookup3[]={
			SPECIAL_MANGLING,
			/* This is the start of lookup12 */
			'_','1','2','3','4','5','6','7','8','9',
			'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o',
			'p','q','r','s','t','u','v' 
		};
		#define lookup12 (lookup3+9)
		u.entry_num = info->f_pos / UMSDOS_REC_SIZE;
		if (u.entry_num > (9* 32 * 32)){
			printk ("UMSDOS: More than 9216 file in a directory.\n"
				"This may break the mangling strategy.\n"
				"Not a killer problem. See doc.\n");
		}
		*pt++ = '.';
		*pt++ = lookup3 [u.num.num3];
		*pt++ = lookup12[u.num.num2];
		*pt++ = lookup12[u.num.num1];
		*pt = '\0';		/* help doing printk */	
		info->fake.len += 4;
		info->msdos_reject = 0;		/* Avoid mangling twice */
	}
}

/*
	Evaluate the record size needed to store of name of len character.
	The value returned is a multiple of UMSDOS_REC_SIZE.
*/
int umsdos_evalrecsize (int len)
{
	struct umsdos_dirent dirent;
	int nbrec = 1+((len-1+(dirent.name-(char*)&dirent))
                   / UMSDOS_REC_SIZE);
	return nbrec * UMSDOS_REC_SIZE;
	/*
	GLU	This should be inlined or something to speed it up to the max.
	GLU	nbrec is absolutely not needed to return the value.
	*/
}
#ifdef TEST
int umsdos_evalrecsize_old (int len)
{
	struct umsdos_dirent dirent;
	int size = len + (dirent.name-(char*)&dirent);
	int nbrec = size / UMSDOS_REC_SIZE;
	int extra = size % UMSDOS_REC_SIZE;
	if (extra > 0) nbrec++;
	return nbrec * UMSDOS_REC_SIZE;
}
#endif
/*
	Fill the struct info with the full and msdos name of a file
	Return 0 if all is ok, a negative error code otherwise.
*/
int umsdos_parse (
	const char *fname,
	int len,
	struct umsdos_info *info)
{
	int ret = -ENAMETOOLONG;
	/* #Specification: file name / too long
		If a file name exceed UMSDOS maxima, the file name is silently
		truncated. This makes it conformant with the other file system
		of Linux (minix and ext2 at least).
	*/
	if (len > UMSDOS_MAXNAME) len = UMSDOS_MAXNAME;
	{
		const char *firstpt=NULL;	/* First place we saw a . in fname */
		/* #Specification: file name / non MSDOS conforming / base length 0
			file name beginning with a period '.' are invalid for MsDOS.
			It needs absolutely a base name. So the file name is mangled
		*/
		int ivldchar = fname[0] == '.';/* At least one invalid character */
		int msdos_len = len;
		int base_len;
		/*
			cardinal_per_size tells if there exist at least one
			DOS pseudo devices on length n. See the test below.
		*/
		static const char cardinal_per_size[9]={
			0, 0, 0, 1, 1, 0, 1, 0, 1
		};
		/*
			lkp translate all character to acceptable character (for DOS).
			When lkp[n] == n, it means also it is an acceptable one.
			So it serve both as a flag and as a translator.
		*/
		static char lkp[256];
		static char is_init=0;
		if (!is_init){
			/*
				Initialisation of the array is easier and less error prone
				like this.
			*/
			int i;
			static const char *spc = "\"*+,/:;<=>?[\\]|~";
			is_init = 1;
			for (i=0; i<=32; i++) lkp[i] = '#';
			for (i=33; i<'A'; i++) lkp[i] = (char)i;
			for (i='A'; i<='Z'; i++) lkp[i] = (char)(i+('a'-'A'));
			for (i='Z'+1; i<127; i++) lkp[i] = (char)i;
			for (i=128; i<256; i++) lkp[i] = '#';

			lkp['.'] = '_';
			while (*spc != '\0') lkp[(unsigned char)(*spc++)] = '#';
		}
		/*	GLU
			file name which are longer than 8+'.'+3 are invalid for MsDOS.
			So the file name is to be mangled no more test needed.
			This Speed Up for long and very long name.
			The position of the last point is no more necessary anyway.
		*/
		if (len<=(8+1+3)){
			const char *pt = fname;
			const char *endpt = fname + len;
			while (pt < endpt){
				if (*pt == '.'){
					if (firstpt != NULL){
						/* 2 . in a file name. Reject */
						ivldchar = 1;
						break;
					}else{
						int extlen = (int)(endpt - pt);
						firstpt = pt;
						if (firstpt - fname > 8){
							/* base name longer than 8: reject */
							ivldchar = 1;
							break;
						}else if (extlen > 4){
							/* Extension longer than 4 (including .): reject */
							ivldchar = 1;
							break;
						}else if (extlen == 1){
							/* #Specification: file name / non MSDOS conforming / last char == .
								If the last character of a file name is
								a period, mangling is applied. MsDOS do
								not support those file name.
							*/
							ivldchar = 1;
							break;
						}else if (extlen == 4){
							/* #Specification: file name / non MSDOS conforming / mangling clash
								To avoid clash with	the umsdos mangling, any file
								with a special character as the first character
								of the extension will be mangled. This solve the
								following problem:

								#
								touch FILE
								# FILE is invalid for DOS, so mangling is applied
								# file.{_1 is created in the DOS directory
								touch file.{_1
								# To UMSDOS file point to a single DOS entry.
								# So file.{_1 has to be mangled.
								#
							*/	
							static char special[]={
								SPECIAL_MANGLING,'\0'
							};
							if (strchr(special,firstpt[1])!= NULL){
								ivldchar = 1;
								break;
							}
						}
					}
				}else if (lkp[(unsigned char)(*pt)] != *pt){
					ivldchar = 1;
					break;
				}
				pt++;
			}
		}else{
			ivldchar = 1;
		}
		if (ivldchar
			|| (firstpt == NULL && len > 8)
			|| (len == UMSDOS_EMD_NAMELEN
				&& memcmp(fname,UMSDOS_EMD_FILE,UMSDOS_EMD_NAMELEN)==0)){
			/* #Specification: file name / --linux-.---
				The name of the EMD file --linux-.--- is map to a mangled
				name. So UMSDOS does not restrict its use.
			*/
			/* #Specification: file name / non MSDOS conforming / mangling
				Non MSDOS conforming file name must use some alias to fit
				in the MSDOS name space.

				The strategy is simple. The name is simply truncated to
				8 char. points are replace with underscore and a
				number is given as an extension. This number correspond
				to the entry number in the EMD file. The EMD file
				only need to carry the real name.

				Upper case is also convert to lower case.
				Control character are converted to #.
				Space are converted to #.
				The following character are also converted to #.
				#
					" * + , / : ; < = > ? [ \ ] | ~
				#

				Sometime, the problem is not in MsDOS itself but in
				command.com.
			*/
			int i;
			char *pt = info->fake.fname;
			base_len = msdos_len = (msdos_len>8) ? 8 : msdos_len;
			/*
				There is no '.' any more so we know for a fact that
				the base length is the length.
			*/
			memcpy (info->fake.fname,fname,msdos_len);
			for (i=0; i<msdos_len; i++, pt++) *pt = lkp[(unsigned char)(*pt)];
			*pt = '\0';	/* GLU	C'est sur on a un 0 a la fin */
			info->msdos_reject = 1;
			/*
				The numeric extension is added only when we know
				the position in the EMD file, in umsdos_newentry(),
				umsdos_delentry(), and umsdos_findentry().
				See umsdos_manglename().
			*/
		}else{
			/* Conforming MSDOS file name */
			strncpy (info->fake.fname,fname,len);
			info->msdos_reject = 0;
			base_len = firstpt != NULL ? (int)(firstpt - fname) : len;
		}
		if (cardinal_per_size[base_len]){
			/* #Specification: file name / MSDOS devices / mangling
				To avoid unreachable file from MsDOS, any MsDOS conforming
				file with a basename equal to one of the MsDOS pseudo
				devices will be mangled.

				If a file such as "prn" was created, it would be unreachable
				under MsDOS because prn is assumed to be the printer, even
				if the file does have an extension.

				Since the extension is unimportant to MsDOS, we must patch
				the basename also. We simply insert a minus '-'. To avoid
				conflict with valid file with a minus in front (such as
				"-prn"), we add an mangled extension like any other
				mangled file name.

				Here is the list of DOS pseudo devices:

				#
					"prn","con","aux","nul",
					"lpt1","lpt2","lpt3","lpt4",
					"com1","com2","com3","com4",
					"clock$"
				#

				and some standard ones for common DOS programs

					"emmxxxx0","xmsxxxx0","setverxx"

				(Thanks to Chris Hall <[e-mail]>
				 for pointing these to me).

				Is there one missing ?
			*/
			/* This table must be ordered by length */
			static const char *tbdev[]={
				"prn","con","aux","nul",
				"lpt1","lpt2","lpt3","lpt4",
				"com1","com2","com3","com4",
				"clock$",
				"emmxxxx0","xmsxxxx0","setverxx"
			};
			/* Tell where to find in tbdev[], the first name of */
			/* a certain length */
			static const char start_ind_dev[9]={
				0, 0, 0, 4, 12, 12, 13, 13, 16 
			};
			char basen[9];
			int i;
			for (i=start_ind_dev[base_len-1]; i<start_ind_dev[base_len]; i++){
				if (memcmp(info->fake.fname,tbdev[i],base_len)==0){
					memcpy (basen,info->fake.fname,base_len);
					basen[base_len] = '\0';		/* GLU	C'est sur on a un 0 a la fin */
					/*
					GLU	On ne fait cela que si necessaire, on essaye d'etre le
					GLU	simple dans le cas general (le plus frequent).
					*/
					info->fake.fname[0] = '-';
					strcpy (info->fake.fname+1,basen);	/* GLU	C'est sur on a un 0 a la fin */
					msdos_len = (base_len==8) ? 8 : base_len + 1;
					info->msdos_reject = 1;
					break;
				}
			}
		}
		info->fake.fname[msdos_len] = '\0';	/* Help doing printk */
		/* GLU	Ce zero devrais deja y etre ! (invariant ?) */
		info->fake.len = msdos_len;
		/* Pourquoi ne pas utiliser info->fake.len partout ??? plus long ?*/
		memcpy (info->entry.name,fname,len);
		info->entry.name_len = len;
		ret = 0;
	}
	/*
		Evaluate how many record are needed to store this entry.
	*/
	info->recsize = umsdos_evalrecsize (len);
	return ret;
}

#ifdef TEST

struct MANG_TEST{
	char *fname;		/* Name to validate */
	int msdos_reject;	/* Expected msdos_reject flag */
	char *msname;		/* Expected msdos name */
};

struct MANG_TEST tb[]={
	"hello",		0,	"hello",
	"hello.1",		0,	"hello.1",
	"hello.1_",		0,	"hello.1_",
	"prm",			0,	"prm",

#ifdef PROPOSITION
	"HELLO",		1,	"hello",
	"Hello.1",		1,	"hello.1",
	"Hello.c",		1,	"hello.c",
#elseif
/*
	Je trouve les trois exemples ci-dessous tres "malheureux".
	Je propose de mettre en minuscule dans un passe preliminaire,
	et de tester apres si il y a d'autres caracters "mechants".
	Bon, je ne l'ai pas fait, parceque ce n'est pas si facilement
	modifiable que ca. Mais c'est pour le principe.
	Evidemment cela augmente les chances de "Collision",
	par exemple: entre "HELLO" et "Hello", mais ces problemes
	peuvent etre traiter ailleur avec les autres collisions.
*/
	"HELLO",		1,	"hello",
	"Hello.1",		1,	"hello_1",
	"Hello.c",		1,	"hello_c",
#endif

	"hello.{_1",		1,	"hello_{_",
	"hello\t",		1,	"hello#",
	"hello.1.1",		1,	"hello_1_",
	"hel,lo",		1,	"hel#lo",
	"Salut.Tu.vas.bien?",	1,	"salut_tu",
	".profile",		1,	"_profile",
	".xv",			1,	"_xv",
	"toto.",		1,	"toto_",
	"clock$.x",		1,	"-clock$",
	"emmxxxx0",		1,	"-emmxxxx",
	"emmxxxx0.abcd",	1,	"-emmxxxx",
	"aux",			1,	"-aux",
	"prn",			1,	"-prn",
	"prn.abc",		1,	"-prn",
	"PRN",			1,	"-prn",
/* 
GLU	ATTENTION : Le resultat de ceux-ci sont differents avec ma version
GLU	du mangle par rapport au mangle originale.
GLU	CAUSE: La maniere de calculer la variable baselen. 
GLU		Pour toi c'est toujours 3
GLU		Pour moi c'est respectivement 7, 8 et 8
*/
	"PRN.abc",		1,	"prn_abc",
	"Prn.abcd",		1,	"prn_abcd",
	"prn.abcd",		1,	"prn_abcd",
	"Prn.abcdefghij",	1,	"prn_abcd"
};

int main (int argc, char *argv[])
{
	int i,rold,rnew;
	printf ("Testing the umsdos_parse.\n");
	for (i=0; i<sizeof(tb)/sizeof(tb[0]); i++){
		struct MANG_TEST *pttb = tb+i;
		struct umsdos_info info;
		int ok = umsdos_parse (pttb->fname,strlen(pttb->fname),&info);
		if (strcmp(info.fake.fname,pttb->msname)!=0){
			printf ("**** %s -> ",pttb->fname);
			printf ("%s <> %s\n",info.fake.fname,pttb->msname);
		}else if (info.msdos_reject != pttb->msdos_reject){
			printf ("**** %s -> %s ",pttb->fname,pttb->msname);
			printf ("%d <> %d\n",info.msdos_reject,pttb->msdos_reject);
		}else{
			printf ("     %s -> %s %d\n",pttb->fname,pttb->msname
				,pttb->msdos_reject);
		}
	}
	printf ("Testing the new umsdos_evalrecsize.");
	for (i=0; i<UMSDOS_MAXNAME ; i++){
		rnew=umsdos_evalrecsize (i);
		rold=umsdos_evalrecsize_old (i);
		if (!(i%UMSDOS_REC_SIZE)){
			printf ("\n%d:\t",i);
		}
		if (rnew!=rold){
			printf ("**** %d newres: %d != %d \n", i, rnew, rold);
		}else{
			printf(".");
		}
	}
	printf ("\nEnd of Testing.\n");

	return 0;
}

#endif