paqfs.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 <auth.h>
#include <fcall.h>
#include <bio.h>
#include <mp.h>
#include <libsec.h>
#include <flate.h>

#include "paqfs.h"

enum
{
	OPERM	= 0x3,		/* mask of all permission types in open mode */
	OffsetSize = 4,		/* size in bytes of an offset */
};

typedef struct Fid Fid;
typedef struct Paq Paq;
typedef struct Block Block;

struct Fid
{
	short	busy;
	short	open;
	int	fid;
	char	*user;
	ulong	offset;		/* for directory reading */

	Paq	*paq;
	Fid	*next;
};

struct Paq
{	
	int ref;
	Paq *up;
	PaqDir *dir;
	Qid qid;
};

struct Block
{
	int ref;
	ulong addr;	/* block byte address */
	ulong age;
	uchar *data;
};

enum
{
	Pexec =		1,
	Pwrite = 	2,
	Pread = 	4,
	Pother = 	1,
	Pgroup = 	8,
	Powner =	64,
};

int	noauth;
Fid	*fids;
Fcall	rhdr, thdr;
int 	blocksize;
int 	cachesize = 20;
int	mesgsize = 8*1024 + IOHDRSZ;
Paq 	*root, *rootfile;
Block 	*cache;
ulong 	cacheage;
Biobuf	*bin;

Fid *	newfid(int);
void	paqstat(PaqDir*, char*);
void	io(int fd);
void	*erealloc(void*, ulong);
void	*emalloc(ulong);
void 	*emallocz(ulong n);
char 	*estrdup(char*);
void	usage(void);
ulong	getl(uchar *p);
int	gets(uchar *p);
char 	*getstr(uchar *p);
PaqDir	*getDir(uchar*);
void	getHeader(uchar *p, PaqHeader *b);
void	getBlock(uchar *p, PaqBlock *b);
void	getTrailer(uchar *p, PaqTrailer *b);
void	init(char*, int);
void	paqDirFree(PaqDir*);
Qid	paqDirQid(PaqDir *d);
Paq	*paqCpy(Paq *s);
Paq	*paqLookup(Paq *s, char *name);
void	paqFree(Paq*);
Paq	*paqWalk(Paq *s, char *name);
int	perm(PaqDir *s, char *user, int p);
int	dirRead(Fid*, uchar*, int);
Block	*blockLoad(ulong addr, int type);
void	blockFree(Block*);
int	checkDirSize(uchar *p, uchar *ep);
int	packDir(PaqDir*, uchar*, int);
int	blockRead(uchar *data, ulong addr, int type);
void	readHeader(PaqHeader *hdr, char *name, DigestState *ds);
void	readBlocks(char *name, DigestState *ds);
void	readTrailer(PaqTrailer *tlr, char *name, DigestState *ds);

char	*rflush(Fid*), *rversion(Fid*),
	*rauth(Fid*), *rattach(Fid*), *rwalk(Fid*),
	*ropen(Fid*), *rcreate(Fid*),
	*rread(Fid*), *rwrite(Fid*), *rclunk(Fid*),
	*rremove(Fid*), *rstat(Fid*), *rwstat(Fid*);

char 	*(*fcalls[])(Fid*) = {
	[Tflush]	rflush,
	[Tversion]	rversion,
	[Tattach]	rattach,
	[Tauth]		rauth,
	[Twalk]		rwalk,
	[Topen]		ropen,
	[Tcreate]	rcreate,
	[Tread]		rread,
	[Twrite]	rwrite,
	[Tclunk]	rclunk,
	[Tremove]	rremove,
	[Tstat]		rstat,
	[Twstat]	rwstat,
};

char	Eperm[] =	"permission denied";
char	Enotdir[] =	"not a directory";
char	Enoauth[] =	"authentication not required";
char	Enotexist[] =	"file does not exist";
char	Einuse[] =	"file in use";
char	Eexist[] =	"file exists";
char	Enotowner[] =	"not owner";
char	Eisopen[] = 	"file already open for I/O";
char	Excl[] = 	"exclusive use file already open";
char	Ename[] = 	"illegal name";
char	Erdonly[] = 	"read only file system";
char	Ebadblock[] = 	"bad block";
char	Eversion[] = 	"bad version of P9";
char	Edirtoobig[] = 	"directory entry too big";

int debug;

void
main(int argc, char *argv[])
{
	char *defmnt, *p;
	int pfd[2];
	int fd;
	int stdio = 0;
	int verify = 0;

	defmnt = "/n/paq";
	ARGBEGIN{
	case 'c':
		p = ARGF();
		if(p == nil)
			usage();
		cachesize = atoi(p);
		break;
	case 'a':
		noauth = 1;
		break;
	case 'v':
		verify = 1;
		break;
	case 'd':
		debug = 1;
		break;
	case 'i':
		defmnt = nil;
		stdio = 1;
		pfd[0] = 0;
		pfd[1] = 1;
		break;
	case 's':
		defmnt = nil;
		break;
	case 'm':
		defmnt = ARGF();
		if(defmnt == nil)
			usage();
		break;
	case 'M':
		p = ARGF();
		if(p == nil)
			usage();
		mesgsize = atoi(p);
		if(mesgsize < 512)
			mesgsize = 512;
		if(mesgsize > 128*1024)
			mesgsize = 128*1024;
		break;
	default:
		usage();
	}ARGEND

	if(argc != 1)
		usage();

	init(argv[0], verify);
	
	if(!stdio){
		if(pipe(pfd) < 0)
			sysfatal("pipe failed");
		if(defmnt == 0){
			fd = create("#s/paqfs", OWRITE, 0666);
			if(fd < 0)
				sysfatal("create of /srv/paqfs failed");
			if(fprint(fd, "%d", pfd[0]) < 0)
				sysfatal("writing /srv/paqfs");
		}
	}

	if(debug)
		fmtinstall('F', fcallfmt);
	switch(rfork(RFFDG|RFPROC|RFNAMEG|RFNOTEG)){
	case -1:
		sysfatal("fork");
	case 0:
		close(pfd[0]);
		io(pfd[1]);
		break;
	default:
		close(pfd[1]);	/* don't deadlock if child fails */
		if(defmnt && mount(pfd[0], -1, defmnt, MREPL|MCREATE, "") < 0)
			sysfatal("mount failed");
	}
	exits(0);
}

char*
rversion(Fid*)
{
	Fid *f;

	for(f = fids; f; f = f->next)
		if(f->busy)
			rclunk(f);
	if(rhdr.msize > mesgsize)
		thdr.msize = mesgsize;
	else
		thdr.msize = rhdr.msize;
	if(strcmp(rhdr.version, "9P2000") != 0)
		return Eversion;
	thdr.version = "9P2000";
	return 0;
}

char*
rauth(Fid*)
{
	return Enoauth;
}

char*
rflush(Fid *f)
{
	USED(f);
	return 0;
}

char*
rattach(Fid *f)
{
	/* no authentication! */
	f->busy = 1;
	f->paq = paqCpy(root);
	thdr.qid = f->paq->qid;
	if(rhdr.uname[0])
		f->user = estrdup(rhdr.uname);
	else
		f->user = "none";
	return 0;
}

char*
clone(Fid *f, Fid **res)
{
	Fid *nf;

	if(f->open)
		return Eisopen;
	if(f->busy == 0)
		return Enotexist;
	nf = newfid(rhdr.newfid);
	nf->busy = 1;
	nf->open = 0;
	nf->paq = paqCpy(f->paq);
	nf->user = strdup(f->user);
	*res = nf;
	return 0;
}

char*
rwalk(Fid *f)
{
	Paq *paq, *npaq;
	Fid *nf;
	int nqid, nwname;
	Qid qid;
	char *err;

	if(f->busy == 0)
		return Enotexist;
	nf = nil;
	if(rhdr.fid != rhdr.newfid){
		err = clone(f, &nf);
		if(err)
			return err;
		f = nf;	/* walk the new fid */
	}

	nwname = rhdr.nwname;

	/* easy case */
	if(nwname == 0) {
		thdr.nwqid = 0;
		return 0;
	}

	paq = paqCpy(f->paq);
	qid = paq->qid;
	err = nil;

	for(nqid = 0; nqid < nwname; nqid++){
		if((qid.type & QTDIR) == 0){
			err = Enotdir;
			break;
		}
		if(!perm(paq->dir, f->user, Pexec)) {
			err = Eperm;
			break;
		}
		npaq = paqWalk(paq, rhdr.wname[nqid]);
		if(npaq == nil) {
			err = Enotexist;
			break;
		}
		paqFree(paq);
		paq = npaq;
		qid = paq->qid;
		thdr.wqid[nqid] = qid;
	}

	thdr.nwqid = nqid;

	if(nqid == nwname){
		/* success */
		paqFree(f->paq);
		f->paq = paq;
		return 0;
	}

	paqFree(paq);
	if(nf != nil)
		rclunk(nf);

	/* only error on the first element */
	if(nqid == 0)
		return err;

	return 0;
}

char *
ropen(Fid *f)
{
	int mode, trunc;

	if(f->open)
		return Eisopen;
	if(f->busy == 0)
		return Enotexist;
	mode = rhdr.mode;
	if(f->paq->qid.type & QTDIR){
		if(mode != OREAD)
			return Eperm;
		thdr.qid = f->paq->qid;
		return 0;
	}
	if(mode & ORCLOSE)
		return Erdonly;
	trunc = mode & OTRUNC;
	mode &= OPERM;
	if(mode==OWRITE || mode==ORDWR || trunc)
		return Erdonly;
	if(mode==OREAD)
		if(!perm(f->paq->dir, f->user, Pread))
			return Eperm;
	if(mode==OEXEC)
		if(!perm(f->paq->dir, f->user, Pexec))
			return Eperm;
	thdr.qid = f->paq->qid;
	f->open = 1;
	return 0;
}

char *
rcreate(Fid *f)
{
	if(f->open)
		return Eisopen;
	if(f->busy == 0)
		return Enotexist;
	return Erdonly;
}

char *
readdir(Fid *f)
{
	PaqDir *pd;
	uchar *p, *ep;
	ulong off;
	int n, cnt, i;
	uchar *buf;
	Block *ptr, *b;

	buf = (uchar*)thdr.data;
	cnt = rhdr.count;
	if(rhdr.offset == 0)
		f->offset = 0;
	off = f->offset;

	if(rootfile && f->paq == root){
		if(off != 0){
			rhdr.count = 0;
			return nil;
		}
		n = packDir(rootfile->dir, buf, cnt);
		rhdr.count = n;
		return nil;
	}

	ptr = blockLoad(f->paq->dir->offset, PointerBlock);
	if(ptr == nil)
		return Ebadblock;
	i = off/blocksize;
	off -= i*blocksize;

	thdr.count = 0;
	b = blockLoad(getl(ptr->data + i*4), DirBlock);
	while(b != nil) {
		p = b->data + off;
		ep = b->data + blocksize;
		if(checkDirSize(p, ep)) {
			pd = getDir(p);
			n = packDir(pd, buf, cnt);
			paqDirFree(pd);
			if(n == 0) {
				blockFree(b);
				if(thdr.count == 0) {
					blockFree(ptr);
					return Edirtoobig;
				}
				break;
			}
			off += gets(p);
			cnt -= n;
			buf += n;
			thdr.count += n;
		} else {
			off = 0;
			i++;
			blockFree(b);
			b = blockLoad(getl(ptr->data + i*4), DataBlock);
		}
	}
	f->offset = i*blocksize + off;
	blockFree(ptr);

	return 0;
}

char*
rread(Fid *f)
{
	PaqDir *pd;
	uchar *buf;
	vlong off;
	ulong uoff;
	int n, cnt, i;
	Block *ptr, *b;

	if(f->busy == 0)
		return Enotexist;
	if(f->paq->qid.type & QTDIR)
		return readdir(f);
	pd = f->paq->dir;
	off = rhdr.offset;
	buf = (uchar*)thdr.data;
	cnt = rhdr.count;

	thdr.count = 0;
	if(off >= pd->length || cnt == 0)
		return 0;

	if(cnt > pd->length - off)
		cnt = pd->length - off;

	ptr = blockLoad(pd->offset, PointerBlock);
	if(ptr == nil)
		return Ebadblock;

	i = off/blocksize;
	uoff = off-i*blocksize;

	while(cnt > 0) {
		b = blockLoad(getl(ptr->data + i*4), DataBlock);
		if(b == nil) {
			blockFree(ptr);
			return Ebadblock;
		}
		n = blocksize - uoff;
		if(n > cnt)
			n = cnt;
		memmove(buf, b->data + uoff, n);
		cnt -= n;
		thdr.count += n;
		buf += n;
		uoff = 0;
		i++;
		blockFree(b);
	}
	blockFree(ptr);
	return 0;
}

char*
rwrite(Fid *f)
{
	if(f->busy == 0)
		return Enotexist;
	return Erdonly;
}

char *
rclunk(Fid *f)
{
	f->busy = 0;
	f->open = 0;
	free(f->user);
	paqFree(f->paq);
	return 0;
}

char *
rremove(Fid *f)
{
	rclunk(f);
	return Erdonly;
}

char *
rstat(Fid *f)
{
	if(f->busy == 0)
		return Enotexist;
	thdr.stat = (uchar*)thdr.data;
	thdr.nstat = packDir(f->paq->dir, thdr.stat, mesgsize);
	if(thdr.nstat == 0)
		return Edirtoobig;
	return 0;
}

char *
rwstat(Fid *f)
{
	if(f->busy == 0)
		return Enotexist;
	return Erdonly;
}

Paq*
paqCpy(Paq *s)
{
	s->ref++;
	return s;
}

void
paqFree(Paq *p)
{
	if(p == nil)
		return;
	p->ref--;
	if(p->ref > 0)
		return;
assert(p != root);
	paqFree(p->up);
	paqDirFree(p->dir);
	free(p);
}

void