dosfs.c revision 40005 
1/*
2 * Copyright (c) 1996, 1998 Robert Nordier
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS
16 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
21 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
23 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
25 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28/*
29 * Readonly filesystem for Microsoft FAT12/FAT16/FAT32 filesystems,
30 * also supports VFAT.
31 */
32
33#include <sys/types.h>
34#include <string.h>
35#include <stddef.h>
36
37#include "stand.h"
38
39#include "dosfs.h"
40
41
42static int	dos_open(const char *path, struct open_file *fd);
43static int	dos_close(struct open_file *fd);
44static int	dos_read(struct open_file *fd, void *buf, size_t size, size_t *resid);
45static off_t	dos_seek(struct open_file *fd, off_t offset, int whence);
46static int	dos_stat(struct open_file *fd, struct stat *sb);
47
48struct fs_ops dosfs_fsops = {
49    "dosfs", dos_open, dos_close, dos_read, null_write, dos_seek, dos_stat
50};
51
52#define SECSIZ  512             /* sector size */
53#define SSHIFT    9             /* SECSIZ shift */
54#define DEPSEC   16             /* directory entries per sector */
55#define DSHIFT    4             /* DEPSEC shift */
56#define LOCLUS    2             /* lowest cluster number */
57
58/* DOS "BIOS Parameter Block" */
59typedef struct {
60    u_char secsiz[2];           /* sector size */
61    u_char spc;                 /* sectors per cluster */
62    u_char ressec[2];           /* reserved sectors */
63    u_char fats;                /* FATs */
64    u_char dirents[2];          /* root directory entries */
65    u_char secs[2];             /* total sectors */
66    u_char media;               /* media descriptor */
67    u_char spf[2];              /* sectors per FAT */
68    u_char spt[2];              /* sectors per track */
69    u_char heads[2];            /* drive heads */
70    u_char hidsec[4];           /* hidden sectors */
71    u_char lsecs[4];            /* huge sectors */
72    u_char lspf[4];             /* huge sectors per FAT */
73    u_char xflg[2];             /* flags */
74    u_char vers[2];             /* filesystem version */
75    u_char rdcl[4];             /* root directory start cluster */
76    u_char infs[2];             /* filesystem info sector */
77    u_char bkbs[2];             /* backup boot sector */
78} DOS_BPB;
79
80/* Initial portion of DOS boot sector */
81typedef struct {
82    u_char jmp[3];              /* usually 80x86 'jmp' opcode */
83    u_char oem[8];              /* OEM name and version */
84    DOS_BPB bpb;                /* BPB */
85} DOS_BS;
86
87/* Supply missing "." and ".." root directory entries */
88static const char *const dotstr[2] = {".", ".."};
89static DOS_DE dot[2] = {
90    {".       ", "   ", FA_DIR, {0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}},
91     {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}},
92    {"..      ", "   ", FA_DIR, {0, 0, {0, 0}, {0, 0}, {0, 0}, {0, 0}},
93     {0, 0}, {0x21, 0}, {0, 0}, {0, 0, 0, 0}}
94};
95
96/* The usual conversion macros to avoid multiplication and division */
97#define bytsec(n)      ((n) >> SSHIFT)
98#define secbyt(s)      ((s) << SSHIFT)
99#define entsec(e)      ((e) >> DSHIFT)
100#define bytblk(fs, n)  ((n) >> (fs)->bshift)
101#define blkbyt(fs, b)  ((b) << (fs)->bshift)
102#define secblk(fs, s)  ((s) >> ((fs)->bshift - SSHIFT))
103#define blksec(fs, b)  ((b) << ((fs)->bshift - SSHIFT))
104
105/* Convert cluster number to offset within filesystem */
106#define blkoff(fs, b) (secbyt((fs)->lsndta) + blkbyt(fs, (b) - LOCLUS))
107
108/* Convert cluster number to logical sector number */
109#define blklsn(fs, b)  ((fs)->lsndta + blksec(fs, (b) - LOCLUS))
110
111/* Convert cluster number to offset within FAT */
112#define fatoff(sz, c)  ((sz) == 12 ? (c) + ((c) >> 1) :  \
113                        (sz) == 16 ? (c) << 1 :          \
114			(c) << 2)
115
116/* Does cluster number reference a valid data cluster? */
117#define okclus(fs, c)  ((c) >= LOCLUS && (c) <= (fs)->xclus)
118
119/* Get start cluster from directory entry */
120#define stclus(sz, de)  ((sz) != 32 ? cv2((de)->clus) :          \
121                         ((u_int)cv2((de)->dex.h_clus) << 16) |  \
122			 cv2((de)->clus))
123
124static int dosunmount(DOS_FS *);
125static int parsebs(DOS_FS *, DOS_BS *);
126static int namede(DOS_FS *, const char *, DOS_DE **);
127static int lookup(DOS_FS *, u_int, const char *, DOS_DE **);
128static void cp_xdnm(u_char *, DOS_XDE *);
129static void cp_sfn(u_char *, DOS_DE *);
130static off_t fsize(DOS_FS *, DOS_DE *);
131static int fatcnt(DOS_FS *, u_int);
132static int fatget(DOS_FS *, u_int *);
133static int fatend(u_int, u_int);
134static int ioread(DOS_FS *, u_int, void *, u_int);
135static int iobuf(DOS_FS *, u_int);
136static int ioget(struct open_file *, u_int, void *, u_int);
137
138/*
139 * Mount DOS filesystem
140 */
141static int
142dos_mount(DOS_FS *fs, struct open_file *fd)
143{
144    int err;
145
146    bzero(fs, sizeof(DOS_FS));
147    fs->fd = fd;
148    if ((err = !(fs->buf = malloc(SECSIZ)) ? errno : 0) ||
149        (err = ioget(fs->fd, 0, fs->buf, 1)) ||
150        (err = parsebs(fs, (DOS_BS *)fs->buf))) {
151        (void)dosunmount(fs);
152        return(err);
153    }
154    return 0;
155}
156
157/*
158 * Unmount mounted filesystem
159 */
160static int
161dos_unmount(DOS_FS *fs)
162{
163    int err;
164
165    if (fs->links)
166        return(EBUSY);
167    if ((err = dosunmount(fs)))
168        return(err);
169    return 0;
170}
171
172/*
173 * Common code shared by dos_mount() and dos_unmount()
174 */
175static int
176dosunmount(DOS_FS *fs)
177{
178    if (fs->buf)
179        free(fs->buf);
180    free(fs);
181    return(0);
182}
183
184/*
185 * Open DOS file
186 */
187static int
188dos_open(const char *path, struct open_file *fd)
189{
190    DOS_DE *de;
191    DOS_FILE *f;
192    DOS_FS *fs;
193    u_int size, clus;
194    int err = 0;
195
196    /* Allocate mount structure, associate with open */
197    fs = malloc(sizeof(DOS_FS));
198
199    if ((err = dos_mount(fs, fd)))
200	goto out;
201
202    if ((err = namede(fs, path, &de)))
203	goto out;
204
205    clus = stclus(fs->fatsz, de);
206    size = cv4(de->size);
207
208    if ((!(de->attr & FA_DIR) && (!clus != !size)) ||
209	((de->attr & FA_DIR) && size) ||
210	(clus && !okclus(fs, clus))) {
211        err = EINVAL;
212	goto out;
213    }
214    f = malloc(sizeof(DOS_FILE));
215    bzero(f, sizeof(DOS_FILE));
216    f->fs = fs;
217    fs->links++;
218    f->de = *de;
219    fd->f_fsdata = (void *)f;
220
221 out:
222    return(err);
223}
224
225/*
226 * Read from file
227 */
228static int
229dos_read(struct open_file *fd, void *buf, size_t nbyte, size_t *resid)
230{
231    off_t size;
232    u_int nb, off, clus, c, cnt, n;
233    DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
234    int err = 0;
235
236    nb = (u_int)nbyte;
237    if ((size = fsize(f->fs, &f->de)) == -1)
238	return EINVAL;
239    if (nb > (n = size - f->offset))
240        nb = n;
241    off = f->offset;
242    if ((clus = stclus(f->fs->fatsz, &f->de)))
243        off &= f->fs->bsize - 1;
244    c = f->c;
245    cnt = nb;
246    while (cnt) {
247        n = 0;
248        if (!c) {
249            if ((c = clus))
250                n = bytblk(f->fs, f->offset);
251        } else if (!off)
252            n++;
253        while (n--) {
254            if ((err = fatget(f->fs, &c)))
255		goto out;
256            if (!okclus(f->fs, c)) {
257		err = EINVAL;
258		goto out;
259	    }
260        }
261        if (!clus || (n = f->fs->bsize - off) > cnt)
262            n = cnt;
263        if ((err = ioread(f->fs, (c ? blkoff(f->fs, c) :
264				      secbyt(f->fs->lsndir)) + off,
265			  buf, n)))
266	    goto out;
267        f->offset += n;
268        f->c = c;
269        off = 0;
270        buf += n;
271        cnt -= n;
272    }
273 out:
274    if (resid)
275	*resid = nbyte - nb + cnt;
276    return(err);
277}
278
279/*
280 * Reposition within file
281 */
282static off_t
283dos_seek(struct open_file *fd, off_t offset, int whence)
284{
285    off_t off;
286    u_int size;
287    DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
288
289    size = cv4(f->de.size);
290    switch (whence) {
291    case SEEK_SET:
292        off = 0;
293        break;
294    case SEEK_CUR:
295        off = f->offset;
296        break;
297    case SEEK_END:
298        off = size;
299        break;
300    default:
301	return(-1);
302    }
303    off += offset;
304    if (off < 0 || off > size)
305        return(-1);
306    f->offset = (u_int)off;
307    f->c = 0;
308    return(off);
309}
310
311/*
312 * Close open file
313 */
314static int
315dos_close(struct open_file *fd)
316{
317    DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
318    DOS_FS *fs = f->fs;
319
320    f->fs->links--;
321    free(f);
322    dos_unmount(fs);
323    return 0;
324}
325
326/*
327 * Return some stat information on a file.
328 */
329static int
330dos_stat(struct open_file *fd, struct stat *sb)
331{
332    DOS_FILE *f = (DOS_FILE *)fd->f_fsdata;
333
334    /* only important stuff */
335    sb->st_mode = f->de.attr & FA_DIR ? S_IFDIR | 0555 : S_IFREG | 0444;
336    sb->st_nlink = 1;
337    sb->st_uid = 0;
338    sb->st_gid = 0;
339    if ((sb->st_size = fsize(f->fs, &f->de)) == -1)
340	return EINVAL;
341    return (0);
342}
343
344/*
345 * Parse DOS boot sector
346 */
347static int
348parsebs(DOS_FS *fs, DOS_BS *bs)
349{
350    u_int sc;
351
352    if ((bs->jmp[0] != 0x69 &&
353         bs->jmp[0] != 0xe9 &&
354         (bs->jmp[0] != 0xeb || bs->jmp[2] != 0x90)) ||
355        bs->bpb.media < 0xf0)
356        return EINVAL;
357    if (cv2(bs->bpb.secsiz) != SECSIZ)
358        return EINVAL;
359    if (!(fs->spc = bs->bpb.spc) || fs->spc & (fs->spc - 1))
360        return EINVAL;
361    fs->bsize = secbyt(fs->spc);
362    fs->bshift = ffs(fs->bsize) - 1;
363    if ((fs->spf = cv2(bs->bpb.spf))) {
364        if (bs->bpb.fats != 2)
365            return EINVAL;
366        if (!(fs->dirents = cv2(bs->bpb.dirents)))
367            return EINVAL;
368    } else {
369        if (!(fs->spf = cv4(bs->bpb.lspf)))
370            return EINVAL;
371        if (!bs->bpb.fats || bs->bpb.fats > 16)
372            return EINVAL;
373        if ((fs->rdcl = cv4(bs->bpb.rdcl)) < LOCLUS)
374            return EINVAL;
375    }
376    if (!(fs->lsnfat = cv2(bs->bpb.ressec)))
377        return EINVAL;
378    fs->lsndir = fs->lsnfat + fs->spf * bs->bpb.fats;
379    fs->lsndta = fs->lsndir + entsec(fs->dirents);
380    if (!(sc = cv2(bs->bpb.secs)) && !(sc = cv4(bs->bpb.lsecs)))
381        return EINVAL;
382    if (fs->lsndta > sc)
383        return EINVAL;
384    if ((fs->xclus = secblk(fs, sc - fs->lsndta) + 1) < LOCLUS)
385        return EINVAL;
386    fs->fatsz = fs->dirents ? fs->xclus < 0xff6 ? 12 : 16 : 32;
387    sc = (secbyt(fs->spf) << 1) / (fs->fatsz >> 2) - 1;
388    if (fs->xclus > sc)
389        fs->xclus = sc;
390    return 0;
391}
392
393/*
394 * Return directory entry from path
395 */
396static int
397namede(DOS_FS *fs, const char *path, DOS_DE **dep)
398{
399    char name[256];
400    DOS_DE *de;
401    char *s;
402    size_t n;
403    int err;
404
405    err = 0;
406    de = dot;
407    if (*path == '/')
408        path++;
409    while (*path) {
410        if (!(s = strchr(path, '/')))
411            s = strchr(path, 0);
412        if ((n = s - path) > 255)
413            return ENAMETOOLONG;
414        memcpy(name, path, n);
415        name[n] = 0;
416        path = s;
417        if (!(de->attr & FA_DIR))
418            return ENOTDIR;
419        if ((err = lookup(fs, stclus(fs->fatsz, de), name, &de)))
420            return err;
421        if (*path == '/')
422            path++;
423    }
424    *dep = de;
425    return 0;
426}
427
428/*
429 * Lookup path segment
430 */
431static int
432lookup(DOS_FS *fs, u_int clus, const char *name, DOS_DE **dep)
433{
434    static DOS_DIR dir[DEPSEC];
435    u_char lfn[261];
436    u_char sfn[13];
437    u_int nsec, lsec, xdn, chk, sec, ent, x;
438    int err, ok, i;
439
440    if (!clus)
441        for (ent = 0; ent < 2; ent++)
442            if (!strcasecmp(name, dotstr[ent])) {
443                *dep = dot + ent;
444                return 0;
445            }
446    if (!clus && fs->fatsz == 32)
447        clus = fs->rdcl;
448    nsec = !clus ? entsec(fs->dirents) : fs->spc;
449    lsec = 0;
450    xdn = chk = 0;
451    for (;;) {
452        if (!clus && !lsec)
453            lsec = fs->lsndir;
454        else if (okclus(fs, clus))
455            lsec = blklsn(fs, clus);
456        else
457            return EINVAL;
458        for (sec = 0; sec < nsec; sec++) {
459            if ((err = ioget(fs->fd, lsec + sec, dir, 1)))
460                return err;
461            for (ent = 0; ent < DEPSEC; ent++) {
462                if (!*dir[ent].de.name)
463                    return ENOENT;
464                if (*dir[ent].de.name != 0xe5)
465                    if ((dir[ent].de.attr & FA_MASK) == FA_XDE) {
466                        x = dir[ent].xde.seq;
467                        if (x & 0x40 || (x + 1 == xdn &&
468                                         dir[ent].xde.chk == chk)) {
469                            if (x & 0x40) {
470                                chk = dir[ent].xde.chk;
471                                x &= ~0x40;
472                            }
473                            if (x >= 1 && x <= 20) {
474                                cp_xdnm(lfn, &dir[ent].xde);
475                                xdn = x;
476                                continue;
477                            }
478                        }
479                    } else if (!(dir[ent].de.attr & FA_LABEL)) {
480                        if ((ok = xdn == 1)) {
481                            for (x = 0, i = 0; i < 11; i++)
482                                x = ((((x & 1) << 7) | (x >> 1)) +
483                                     dir[ent].de.name[i]) & 0xff;
484                            ok = chk == x &&
485                                !strcasecmp(name, (const char *)lfn);
486                        }
487                        if (!ok) {
488                            cp_sfn(sfn, &dir[ent].de);
489                            ok = !strcasecmp(name, (const char *)sfn);
490                        }
491                        if (ok) {
492                            *dep = &dir[ent].de;
493                            return 0;
494                        }
495                    }
496                xdn = 0;
497            }
498        }
499        if (!clus)
500            break;
501        if ((err = fatget(fs, &clus)))
502            return err;
503        if (fatend(fs->fatsz, clus))
504            break;
505    }
506    return ENOENT;
507}
508
509/*
510 * Copy name from extended directory entry
511 */
512static void
513cp_xdnm(u_char *lfn, DOS_XDE *xde)
514{
515    static struct {
516        u_int off;
517        u_int dim;
518    } ix[3] = {
519        {offsetof(DOS_XDE, name1), sizeof(xde->name1) / 2},
520        {offsetof(DOS_XDE, name2), sizeof(xde->name2) / 2},
521        {offsetof(DOS_XDE, name3), sizeof(xde->name3) / 2}
522    };
523    u_char *p;
524    u_int n, x, c;
525
526    lfn += 13 * ((xde->seq & ~0x40) - 1);
527    for (n = 0; n < 3; n++)
528        for (p = (u_char *)xde + ix[n].off, x = ix[n].dim; x;
529	     p += 2, x--) {
530            if ((c = cv2(p)) && (c < 32 || c > 127))
531                c = '?';
532            if (!(*lfn++ = c))
533                return;
534        }
535    if (xde->seq & 0x40)
536        *lfn = 0;
537}
538
539/*
540 * Copy short filename
541 */
542static void
543cp_sfn(u_char *sfn, DOS_DE *de)
544{
545    u_char *p;
546    int j, i;
547
548    p = sfn;
549    if (*de->name != ' ') {
550        for (j = 7; de->name[j] == ' '; j--);
551        for (i = 0; i <= j; i++)
552            *p++ = de->name[i];
553        if (*de->ext != ' ') {
554            *p++ = '.';
555            for (j = 2; de->ext[j] == ' '; j--);
556            for (i = 0; i <= j; i++)
557                *p++ = de->ext[i];
558        }
559    }
560    *p = 0;
561    if (*sfn == 5)
562        *sfn = 0xe5;
563}
564
565/*
566 * Return size of file in bytes
567 */
568static off_t
569fsize(DOS_FS *fs, DOS_DE *de)
570{
571   u_long size;
572   u_int c;
573   int n;
574
575   if (!(size = cv4(de->size)) && de->attr & FA_DIR)
576      if (!(c = cv2(de->clus)))
577         size = fs->dirents * sizeof(DOS_DE);
578      else {
579         if ((n = fatcnt(fs, c)) == -1)
580            return n;
581         size = blkbyt(fs, n);
582      }
583   return size;
584}
585
586/*
587 * Count number of clusters in chain
588 */
589static int
590fatcnt(DOS_FS *fs, u_int c)
591{
592   int n;
593
594   for (n = 0; okclus(fs, c); n++)
595      if (fatget(fs, &c))
596	  return -1;
597   return fatend(fs->fatsz, c) ? n : -1;
598}
599
600/*
601 * Get next cluster in cluster chain
602 */
603static int
604fatget(DOS_FS *fs, u_int *c)
605{
606    u_char buf[4];
607    u_int x;
608    int err;
609
610    err = ioread(fs, secbyt(fs->lsnfat) + fatoff(fs->fatsz, *c), buf,
611                 fs->fatsz != 32 ? 2 : 4);
612    if (err)
613        return err;
614    x = fs->fatsz != 32 ? cv2(buf) : cv4(buf);
615    *c = fs->fatsz == 12 ? *c & 1 ? x >> 4 : x & 0xfff : x;
616    return 0;
617}
618
619/*
620 * Is cluster an end-of-chain marker?
621 */
622static int
623fatend(u_int sz, u_int c)
624{
625    return c > (sz == 12 ? 0xff7U : sz == 16 ? 0xfff7U : 0xffffff7);
626}
627
628/*
629 * Offset-based I/O primitive
630 */
631static int
632ioread(DOS_FS *fs, u_int offset, void *buf, u_int nbyte)
633{
634    char *s;
635    u_int off, n;
636    int err;
637
638    s = buf;
639    if ((off = offset & (SECSIZ - 1))) {
640        offset -= off;
641        if ((err = iobuf(fs, bytsec(offset))))
642            return err;
643        offset += SECSIZ;
644        if ((n = SECSIZ - off) > nbyte)
645            n = nbyte;
646        memcpy(s, fs->buf + off, n);
647        s += n;
648        nbyte -= n;
649    }
650    n = nbyte & (SECSIZ - 1);
651    if (nbyte -= n) {
652        if ((err = ioget(fs->fd, bytsec(offset), s, bytsec(nbyte))))
653            return err;
654        offset += nbyte;
655        s += nbyte;
656    }
657    if (n) {
658        if ((err = iobuf(fs, bytsec(offset))))
659            return err;
660        memcpy(s, fs->buf, n);
661    }
662    return 0;
663}
664
665/*
666 * Buffered sector-based I/O primitive
667 */
668static int
669iobuf(DOS_FS *fs, u_int lsec)
670{
671    int err;
672
673    if (fs->bufsec != lsec) {
674        if ((err = ioget(fs->fd, lsec, fs->buf, 1)))
675            return err;
676        fs->bufsec = lsec;
677    }
678    return 0;
679}
680
681/*
682 * Sector-based I/O primitive
683 */
684static int
685ioget(struct open_file *fd, u_int lsec, void *buf, u_int nsec)
686{
687    int	err;
688
689    if ((err = (fd->f_dev->dv_strategy)(fd->f_devdata, F_READ, lsec,
690					secbyt(nsec), buf, NULL)))
691	return(err);
692    return(0);
693}
694