dossubs.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include <bio.h>
#include <auth.h>
#include <fcall.h>
#include "iotrack.h"
#include "dat.h"
#include "fns.h"

static uchar	isdos[256];

int
isdosfs(uchar *buf)
{
	/*
	 * When dynamic disc managers move the disc partition, 
	 * they make it start with 0xE9.
	 */
	if(buf[0] == 0xE9)
		return 1;

	/*
	 * Check if the jump displacement (magic[1]) is too short for a FAT.
	 */
	if(buf[0] == 0xEB && buf[2] == 0x90 && buf[1] >= 0x30)
		return 1;

	return 0;
}

int
dosfs(Xfs *xf)
{
	Iosect *p, *p1;
	Dosboot *b;
	Fatinfo *fi;
	Dosboot32 *b32;
	Dosbpb *bp;
	long fisec, extflags;
	int i;

	if(!isdos['a']){
		for(i = 'a'; i <= 'z'; i++)
			isdos[i] = 1;
		for(i = 'A'; i <= 'Z'; i++)
			isdos[i] = 1;
		for(i = '0'; i <= '9'; i++)
			isdos[i] = 1;
		isdos['$'] = 1;
		isdos['%'] = 1;
		isdos['''] = 1;
		isdos['-'] = 1;
		isdos['_'] = 1;
		isdos['@'] = 1;
		isdos['~'] = 1;
		isdos['`'] = 1;
		isdos['!'] = 1;
		isdos['('] = 1;
		isdos[')'] = 1;
		isdos['{'] = 1;
		isdos['}'] = 1;
		isdos['^'] = 1;
		isdos['#'] = 1;
		isdos['&'] = 1;
	}

	p = getsect(xf, 0);
	if(p == 0)
		return -1;

	b = (Dosboot*)p->iobuf;
	if(b->clustsize == 0 || isdosfs(p->iobuf) == 0){
		putsect(p);
		return -1;
	}

	bp = malloc(sizeof(Dosbpb));
	memset(bp, 0, sizeof(Dosbpb));	/* clear lock */
	xf->ptr = bp;
	xf->fmt = 1;

	bp->sectsize = GSHORT(b->sectsize);
	bp->clustsize = b->clustsize;
	bp->nresrv = GSHORT(b->nresrv);
	bp->nfats = b->nfats;
	bp->rootsize = GSHORT(b->rootsize);
	bp->volsize = GSHORT(b->volsize);
	if(bp->volsize == 0)
		bp->volsize = GLONG(b->bigvolsize);
	bp->mediadesc = b->mediadesc;
	bp->fatsize = GSHORT(b->fatsize);
	bp->fataddr = GSHORT(b->nresrv);

	bp->fatinfo = 0;

	if(bp->fatsize == 0){	/* is FAT32 */
		if(chatty)
			bootsecdump32(2, xf, (Dosboot32*)b);
		xf->isfat32 = 1;
		b32 = (Dosboot32*)b;
		bp->fatsize = GLONG(b32->fatsize32);
		if(bp->fatsize == 0){
			putsect(p);
			return -1;
		}
		bp->dataaddr = bp->fataddr + bp->nfats*bp->fatsize;
		bp->rootaddr = 0;
		bp->rootstart = GLONG(b32->rootstart);

		/*
		 * disable fat mirroring?
		 */
		extflags = GSHORT(b32->extflags);
		if(extflags & 0x0080){
			for(i = 0; i < 4; i++){
				if(extflags & (1 << i)){
					bp->fataddr += i * bp->fatsize;
					bp->nfats = 1;
					break;
				}
			}
		}

		/*
		 * fat free list info
		 */
		bp->freeptr = FATRESRV;
		fisec = GSHORT(b32->infospec);
		if(fisec != 0 && fisec < GSHORT(b32->nresrv)){
			p1 = getsect(xf, fisec);
			if(p1 != nil){
				fi = (Fatinfo*)p1->iobuf;
				if(GLONG(fi->sig1) == FATINFOSIG1 && GLONG(fi->sig) == FATINFOSIG){
					bp->fatinfo = fisec;
					bp->freeptr = GLONG(fi->nextfree);
					bp->freeclusters = GLONG(fi->freeclust);
					chat("fat info: %ld free clusters, next free %ld\n", bp->freeclusters, bp->freeptr);
				}
				putsect(p1);
			}
		}
	}else{
		if(chatty)
			bootdump(2, b);
		bp->rootaddr = bp->fataddr + bp->nfats*bp->fatsize;
		bp->rootstart = 0;
		i = bp->rootsize*DOSDIRSIZE + bp->sectsize-1;
		i /= bp->sectsize;
		bp->dataaddr = bp->rootaddr + i;
		bp->freeptr = FATRESRV;
	}
	bp->fatclusters = FATRESRV+(bp->volsize - bp->dataaddr)/bp->clustsize;

	if(xf->isfat32)
		bp->fatbits = 32;
	else if(bp->fatclusters < 4087)
		bp->fatbits = 12;
	else
		bp->fatbits = 16;

	chat("fatbits=%d (%d clusters)...", bp->fatbits, bp->fatclusters);
	for(i=0; i<b->nfats; i++)
		chat("fat %d: %ld...", i, bp->fataddr+i*bp->fatsize);
	chat("root: %ld...", bp->rootaddr);
	chat("data: %ld...", bp->dataaddr);
	putsect(p);
	return 0;
}

/*
 * initialize f to the root directory
 * this file has no Dosdir entry,
 * so we special case it all over.
 */
void
rootfile(Xfile *f)
{
	Dosptr *dp;

	dp = f->ptr;
	memset(dp, 0, sizeof(Dosptr));
	dp->prevaddr = -1;
}

int
isroot(ulong addr)
{
	return addr == 0;
}

int
getfile(Xfile *f)
{
	Dosptr *dp;
	Iosect *p;

	dp = f->ptr;
	if(dp->p)
		panic("getfile");
	p = getsect(f->xf, dp->addr);
	if(p == nil)
		return -1;

	/*
	 * we could also make up a Dosdir for the root
	 */
	dp->d = nil;
	if(!isroot(dp->addr)){
		if(f->qid.path != QIDPATH(dp)){
			chat("qid mismatch f=%#llux d=%#lux...", f->qid.path, QIDPATH(dp));
			putsect(p);
			errno = Enonexist;
			return -1;
		}
		dp->d = (Dosdir *)&p->iobuf[dp->offset];
	}
	dp->p = p;
	return 0;
}

void
putfile(Xfile *f)
{
	Dosptr *dp;

	dp = f->ptr;
	if(!dp->p)
		panic("putfile");
	putsect(dp->p);
	dp->p = nil;
	dp->d = nil;
}

long
getstart(Xfs *xf, Dosdir *d)
{
	long start;

	start = GSHORT(d->start);
	if(xf->isfat32)
		start |= GSHORT(d->hstart)<<16;
	return start;
}

void
putstart(Xfs *xf, Dosdir *d, long start)
{
	PSHORT(d->start, start);
	if(xf->isfat32)
		PSHORT(d->hstart, start>>16);
}

/*
 * return the disk cluster for the iclust cluster in f
 */
long
fileclust(Xfile *f, long iclust, int cflag)
{
	Dosbpb *bp;
	Dosptr *dp;
	Dosdir *d;
	long start, clust, nskip, next;

	bp = f->xf->ptr;
	dp = f->ptr;
	d = dp->d;
	next = 0;

	/* 
	 * asking for the cluster of the root directory
	 * is not a well-formed question, since the root directory
	 * does not begin on a cluster boundary.
	 */
	if(!f->xf->isfat32 && isroot(dp->addr))
		return -1;

	if(f->xf->isfat32 && isroot(dp->addr)){
		start = bp->rootstart;
	}else{
		start = getstart(f->xf, d);
		if(start == 0){
			if(!cflag)
				return -1;
			mlock(bp);
			start = falloc(f->xf);
			unmlock(bp);
			if(start <= 0)
				return -1;
			puttime(d, 0);
			putstart(f->xf, d, start);
			dp->p->flags |= BMOD;
			dp->clust = 0;
		}
	}
	if(dp->clust == 0 || iclust < dp->iclust){
		clust = start;
		nskip = iclust;
	}else{
		clust = dp->clust;
		nskip = iclust - dp->iclust;
	}
	if(chatty > 1 && nskip > 0)
		chat("clust %#lx, skip %ld...", clust, nskip);
	if(clust <= 0)
		return -1;
	if(nskip > 0){
		mlock(bp);
		while(--nskip >= 0){
			next = getfat(f->xf, clust);
			if(chatty > 1)
				chat("->%#lx", next);
			if(next > 0){
				clust = next;
				continue;
			}else if(!cflag)
				break;
			if(d && (d->attr&DSYSTEM)){
				next = cfalloc(f);
				if(next < 0)
					break;
				/* cfalloc will call putfat for us, since clust may change */
			} else {
				next = falloc(f->xf);
				if(next < 0)
					break;
				putfat(f->xf, clust, next);
			}
			clust = next;
		}
		unmlock(bp);
		if(next <= 0)
			return -1;
		dp->clust = clust;
		dp->iclust = iclust;
	}
	if(chatty > 1)
		chat(" clust(%#lx)=%#lx...", iclust, clust);
	return clust;
}

/*
 * return the disk sector for the isect disk sector in f 
 */
long
fileaddr(Xfile *f, long isect, int cflag)
{
	Dosbpb *bp;
	Dosptr *dp;
	long clust;

	bp = f->xf->ptr;
	dp = f->ptr;
	if(!f->xf->isfat32 && isroot(dp->addr)){
		if(isect*bp->sectsize >= bp->rootsize*DOSDIRSIZE)
			return -1;
		return bp->rootaddr + isect;
	}
	clust = fileclust(f, isect/bp->clustsize, cflag);
	if(clust < 0)
		return -1;

	return clust2sect(bp, clust) + isect%bp->clustsize;
}

/*
 * translate names
 */
void
fixname(char *buf)
{
	int c;
	char *p;

	p = buf;
	while(c = *p){
		if(c == ':' && trspaces)
			*p = ' ';
		p++;
	}
}

/*
 * classify the file name as one of 
 *	Invalid - contains a bad character
 *	Short - short valid 8.3 name, no lowercase letters
 *	ShortLower - short valid 8.3 name except for lowercase letters
 *	Long - long name 
 */
int
classifyname(char *buf)
{
	char *p, *dot;
	int c, isextended, is8dot3, islower, ndot;

	p = buf;
	isextended = 0;
	islower = 0;
	dot = nil;
	ndot = 0;
	while(c = (uchar)*p){
		if(c&0x80)	/* UTF8 */
			isextended = 1;
		else if(c == '.'){
			dot = p;
			ndot++;
		}else if(strchr("+,:;=[] ", c))
			isextended = 1;
		else if(!isdos[c])
			return Invalid;
		if('a' <= c && c <= 'z')
			islower = 1;
		p++;
	}

	is8dot3 = (ndot==0 && p-buf <= 8) || (ndot==1 && dot-buf <= 8 && p-(dot+1) <= 3);
	
	if(!isextended && is8dot3){
		if(islower)
			return ShortLower;
		return Short;
	}
	return Long;
}
		
/*
 * make an alias for a valid long file name
 */
void
mkalias(char *name, char *sname, int id)
{
	Rune r;
	char *s, *e, sid[10];
	int i, esuf, v;

	e = strrchr(name, '.');
	if(e == nil)
		e = strchr(name, '\0');

	s = name;
	i = 0;
	while(s < e && i < 6){
		if(isdos[(uchar)*s])
			sname[i++] = *s++;
		else
			s += chartorune(&r, s);
	}

	v = snprint(sid, 10, "%d", id);
	if(i + 1 + v > 8)
		i = 8 - 1 - v;
	sname[i++] = '~';
	strcpy(&sname[i], sid);
	i += v;

	sname[i++] = '.';
	esuf = i + 3;
	if(esuf > 12)
		panic("bad mkalias");
	while(*e && i < esuf){
		if(isdos[(uchar)*e])
			sname[i++] = *e++;
		else
			e += chartorune(&r, e);
	}
	if(sname[i-1] == '.')
		i--;
	sname[i] = '\0';
}

/*
 * check for valid plan 9 names,
 * rewrite ' ' to ':'
 */
char isfrog[256]={
	/*NUL*/	1, 1, 1, 1, 1, 1, 1, 1,
	/*BKS*/	1, 1, 1, 1, 1, 1, 1, 1,
	/*DLE*/	1, 1, 1, 1, 1, 1, 1, 1,
	/*CAN*/	1, 1, 1, 1, 1, 1, 1, 1,
/*	[' ']	1,	let's try this -rsc */
	['/']	1,
	[0x7f]	1,
};

int
nameok(char *elem)
{
	while(*elem) {
		if(*elem == ' ' && trspaces)
			*elem = ':';
		if(isfrog[*(uchar*)elem])
			return 0;
		elem++;
	}
	return 1;
}

/*
 * look for a directory entry matching name
 * always searches for long names which match a short name
 */
int
searchdir(Xfile *f, char *name, Dosptr *dp, int cflag, int longtype)
{
	Xfs *xf;
	Iosect *p;
	Dosbpb *bp;
	Dosdir *d;
	char buf[261], *bname;
	int isect, addr, o, addr1, addr2, prevaddr, prevaddr1, o1, islong, have, need, sum;

	xf = f->xf;
	bp = xf->ptr;
	addr1 = -1;
	addr2 = -1;
	prevaddr1 = -1;
	o1 = 0;
	islong = 0;
	sum = -1;

	need = 1;
	if(longtype!=Short && cflag)
		need += (utflen(name) + DOSRUNE-1) / DOSRUNE;

	memset(dp, 0, sizeof(Dosptr));
	dp->prevaddr = -1;
	dp->naddr = -1;
	dp->paddr = ((Dosptr *)f->ptr)->addr;
	dp->poffset = ((Dosptr *)f->ptr)->offset;

	have = 0;
	addr = -1;
	bname = nil;
	for(isect=0;; isect++){
		prevaddr = addr;
		addr = fileaddr(f, isect, cflag);
		if(addr < 0)
			break;
		p = getsect(xf, addr);
		if(p == 0)
			break;
		for(o=0; o<bp->sectsize; o+=DOSDIRSIZE){
			d = (Dosdir *)&p->iobuf[o];
			if(d->name[0] == 0x00){
				chat("end dir(0)...");
				putsect(p);
				if(!cflag)
					return -1;

				/*
				 * addr1 & o1 are the start of the dirs
				 * addr2 is the optional second cluster used if the long name
				 * entry does not fit within the addr1 cluster
				 *
				 * have tells us the number of contiguous free dirs
				 * starting at addr1.o1; need are necessary to hold the long name.
				 */
				if(addr1 < 0){
					addr1 = addr;
					prevaddr1 = prevaddr;
					o1 = o;
				}
				if(addr2 < 0 && (bp->sectsize-o)/DOSDIRSIZE + have < need){
					addr2 = fileaddr(f, isect+1, cflag);
					if(addr2 < 0)
						goto breakout;
				}else if(addr2 < 0)
					addr2 = addr;
				if(addr2 == addr1)
					addr2 = -1;
				dp->addr = addr1;
				dp->offset = o1;
				dp->prevaddr = prevaddr1;
				dp->naddr = addr2;
				return 0;
			}
			if(d->name[0] == DOSEMPTY){
				if(chatty)
					fprint(2, "empty dir\n");

				have++;
				if(addr1 == -1){
					addr1 = addr;
					o1 = o;
					prevaddr1 = prevaddr;
				}
				if(addr2 == -1 && have >= need)
					addr2 = addr;
				continue;
			}
			have = 0;
			if(addr2 == -1)
				addr1 = -1;

			dirdump(d);
			if((d->attr & 0xf) == 0xf){
				bname = getnamesect(buf, bname, p->iobuf + o, &islong, &sum, 1);
				continue;
			}
			if(d->attr & DVLABEL){
				islong = 0;
				continue;
			}
			if(islong != 1 || sum != aliassum(d) || cistrcmp(bname, name) != 0){
				bname = buf;
				getname(buf, d);
			}
			islong = 0;
			if(cistrcmp(bname, name) != 0)
				continue;
			if(chatty)
				fprint(2, "found\n");
			if(cflag){
				putsect(p);
				return -1;
			}
			dp->addr = addr;
			dp->prevaddr = prevaddr;
			dp->offset = o;
			dp->p = p;
			dp->d = d;
			return 0;
		}
		putsect(p);
	}
breakout:
	chat("end dir(1)...");
	return -1;
}

int
emptydir(Xfile *f)
{
	Xfs *xf = f->xf;
	Dosbpb *bp = xf->ptr;
	int isect, addr, o;
	Iosect *p;
	Dosdir *d;

	for(isect=0;; isect++){
		addr = fileaddr(f, isect, 0);
		if(addr < 0)
			break;
		p = getsect(xf, addr);
		if(p == 0)