ramfs.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>

/*
 * Rather than reading /adm/users, which is a lot of work for
 * a toy program, we assume all groups have the form
 *	NNN:user:user:
 * meaning that each user is the leader of his own group.
 */

enum
{
	OPERM	= 0x3,		/* mask of all permission types in open mode */
	Nram	= 2048,
	Maxsize	= 768*1024*1024,
	Maxfdata	= 8192,
};

typedef struct Fid Fid;
typedef struct Ram Ram;

struct Fid
{
	short	busy;
	short	open;
	short	rclose;
	int	fid;
	Fid	*next;
	char	*user;
	Ram	*ram;
};

struct Ram
{
	short	busy;
	short	open;
	long	parent;		/* index in Ram array */
	Qid	qid;
	long	perm;
	char	*name;
	ulong	atime;
	ulong	mtime;
	char	*user;
	char	*group;
	char	*muid;
	char	*data;
	long	ndata;
};

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

ulong	path;		/* incremented for each new file */
Fid	*fids;
Ram	ram[Nram];
int	nram;
int	mfd[2];
char	*user;
uchar	mdata[IOHDRSZ+Maxfdata];
uchar	rdata[Maxfdata];	/* buffer for data in reply */
uchar statbuf[STATMAX];
Fcall thdr;
Fcall	rhdr;
int	messagesize = sizeof mdata;

Fid *	newfid(int);
uint	ramstat(Ram*, uchar*, uint);
void	error(char*);
void	io(void);
void	*erealloc(void*, ulong);
void	*emalloc(ulong);
char	*estrdup(char*);
void	usage(void);
int	perm(Fid*, Ram*, int);

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*);

int needfid[] = {
	[Tversion] 0,
	[Tflush] 0,
	[Tauth] 0,
	[Tattach] 0,
	[Twalk] 1,
	[Topen] 1,
	[Tcreate] 1,
	[Tread] 1,
	[Twrite] 1,
	[Tclunk] 1,
	[Tremove] 1,
	[Tstat] 1,
	[Twstat] 1,
};

char 	*(*fcalls[])(Fid*) = {
	[Tversion]	rversion,
	[Tflush]	rflush,
	[Tauth]	rauth,
	[Tattach]	rattach,
	[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[] =	"ramfs: authentication not required";
char	Enotexist[] =	"file does not exist";
char	Einuse[] =	"file in use";
char	Eexist[] =	"file exists";
char	Eisdir[] =	"file is a directory";
char	Enotowner[] =	"not owner";
char	Eisopen[] = 	"file already open for I/O";
char	Excl[] = 	"exclusive use file already open";
char	Ename[] = 	"illegal name";
char	Eversion[] =	"unknown 9P version";
char	Enotempty[] =	"directory not empty";

int debug;
int private;

void
notifyf(void *a, char *s)
{
	USED(a);
	if(strncmp(s, "interrupt", 9) == 0)
		noted(NCONT);
	noted(NDFLT);
}

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

	service = "ramfs";
	defmnt = "/tmp";
	ARGBEGIN{
	case 'D':
		debug = 1;
		break;
	case 'i':
		defmnt = 0;
		stdio = 1;
		mfd[0] = 0;
		mfd[1] = 1;
		break;
	case 's':
		defmnt = 0;
		break;
	case 'm':
		defmnt = EARGF(usage());
		break;
	case 'p':
		private++;
		break;
	case 'S':
		defmnt = 0;
		service = EARGF(usage());
		break;
	default:
		usage();
	}ARGEND

	if(pipe(p) < 0)
		error("pipe failed");
	if(!stdio){
		mfd[0] = p[0];
		mfd[1] = p[0];
		if(defmnt == 0){
			char buf[64];
			snprint(buf, sizeof buf, "#s/%s", service);
			fd = create(buf, OWRITE|ORCLOSE, 0666);
			if(fd < 0)
				error("create failed");
			sprint(buf, "%d", p[1]);
			if(write(fd, buf, strlen(buf)) < 0)
				error("writing service file");
		}
	}

	user = getuser();
	notify(notifyf);
	nram = 1;
	r = &ram[0];
	r->busy = 1;
	r->data = 0;
	r->ndata = 0;
	r->perm = DMDIR | 0775;
	r->qid.type = QTDIR;
	r->qid.path = 0LL;
	r->qid.vers = 0;
	r->parent = 0;
	r->user = user;
	r->group = user;
	r->muid = user;
	r->atime = time(0);
	r->mtime = r->atime;
	r->name = estrdup(".");

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

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

	for(f = fids; f; f = f->next)
		if(f->busy)
			rclunk(f);
	if(thdr.msize > sizeof mdata)
		rhdr.msize = sizeof mdata;
	else
		rhdr.msize = thdr.msize;
	messagesize = rhdr.msize;
	if(strncmp(thdr.version, "9P2000", 6) != 0)
		return Eversion;
	rhdr.version = "9P2000";
	return 0;
}

char*
rauth(Fid*)
{
	return "ramfs: no authentication required";
}

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

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

char*
clone(Fid *f, Fid **nf)
{
	if(f->open)
		return Eisopen;
	if(f->ram->busy == 0)
		return Enotexist;
	*nf = newfid(thdr.newfid);
	(*nf)->busy = 1;
	(*nf)->open = 0;
	(*nf)->rclose = 0;
	(*nf)->ram = f->ram;
	(*nf)->user = f->user;	/* no ref count; the leakage is minor */
	return 0;
}

char*
rwalk(Fid *f)
{
	Ram *r, *fram;
	char *name;
	Ram *parent;
	Fid *nf;
	char *err;
	ulong t;
	int i;

	err = nil;
	nf = nil;
	rhdr.nwqid = 0;
	if(thdr.newfid != thdr.fid){
		err = clone(f, &nf);
		if(err)
			return err;
		f = nf;	/* walk the new fid */
	}
	fram = f->ram;
	if(thdr.nwname > 0){
		t = time(0);
		for(i=0; i<thdr.nwname && i<MAXWELEM; i++){
			if((fram->qid.type & QTDIR) == 0){
				err = Enotdir;
 				break;
			}
			if(fram->busy == 0){
				err = Enotexist;
				break;
			}
			fram->atime = t;
			name = thdr.wname[i];
			if(strcmp(name, ".") == 0){
    Found:
				rhdr.nwqid++;
				rhdr.wqid[i] = fram->qid;
				continue;
			}
			parent = &ram[fram->parent];
			if(!perm(f, parent, Pexec)){
				err = Eperm;
				break;
			}
			if(strcmp(name, "..") == 0){
				fram = parent;
				goto Found;
			}
			for(r=ram; r < &ram[nram]; r++)
				if(r->busy && r->parent==fram-ram && strcmp(name, r->name)==0){
					fram = r;
					goto Found;
				}
			break;
		}
		if(i==0 && err == nil)
			err = Enotexist;
	}
	if(nf != nil && (err!=nil || rhdr.nwqid<thdr.nwname)){
		/* clunk the new fid, which is the one we walked */
		f->busy = 0;
		f->ram = nil;
	}
	if(rhdr.nwqid > 0)
		err = nil;	/* didn't get everything in 9P2000 right! */
	if(rhdr.nwqid == thdr.nwname)	/* update the fid after a successful walk */
		f->ram = fram;
	return err;
}

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

	if(f->open)
		return Eisopen;
	r = f->ram;
	if(r->busy == 0)
		return Enotexist;
	if(r->perm & DMEXCL)
		if(r->open)
			return Excl;
	mode = thdr.mode;
	if(r->qid.type & QTDIR){
		if(mode != OREAD)
			return Eperm;
		rhdr.qid = r->qid;
		return 0;
	}
	if(mode & ORCLOSE){
		/* can't remove root; must be able to write parent */
		if(r->qid.path==0 || !perm(f, &ram[r->parent], Pwrite))
			return Eperm;
		f->rclose = 1;
	}
	trunc = mode & OTRUNC;
	mode &= OPERM;
	if(mode==OWRITE || mode==ORDWR || trunc)
		if(!perm(f, r, Pwrite))
			return Eperm;
	if(mode==OREAD || mode==ORDWR)
		if(!perm(f, r, Pread))
			return Eperm;
	if(mode==OEXEC)
		if(!perm(f, r, Pexec))
			return Eperm;
	if(trunc && (r->perm&DMAPPEND)==0){
		r->ndata = 0;
		if(r->data)
			free(r->data);
		r->data = 0;
		r->qid.vers++;
	}
	rhdr.qid = r->qid;
	rhdr.iounit = messagesize-IOHDRSZ;
	f->open = 1;
	r->open++;
	return 0;
}

char *
rcreate(Fid *f)
{
	Ram *r;
	char *name;
	long parent, prm;

	if(f->open)
		return Eisopen;
	if(f->ram->busy == 0)
		return Enotexist;
	parent = f->ram - ram;
	if((f->ram->qid.type&QTDIR) == 0)
		return Enotdir;
	/* must be able to write parent */
	if(!perm(f, f->ram, Pwrite))
		return Eperm;
	prm = thdr.perm;