1 #include <u.h>
2 #include <libc.h>
3 #include <fcall.h>
4 
5 /*
6  * Rather than reading /adm/users, which is a lot of work for
7  * a toy program, we assume all groups have the form
8  *	NNN:user:user:
9  * meaning that each user is the leader of his own group.
10  */
11 
12 enum
13 {
14 	OPERM	= 0x3,		/* mask of all permission types in open mode */
15 	Nram	= 2048,
16 	Maxsize	= 512*1024*1024,
17 	Maxfdata	= 8192
18 };
19 
20 typedef struct Fid Fid;
21 typedef struct Ram Ram;
22 
23 struct Fid
24 {
25 	short	busy;
26 	short	open;
27 	short	rclose;
28 	int	fid;
29 	Fid	*next;
30 	char	*user;
31 	Ram	*ram;
32 };
33 
34 struct Ram
35 {
36 	short	busy;
37 	short	open;
38 	long	parent;		/* index in Ram array */
39 	Qid	qid;
40 	long	perm;
41 	char	*name;
42 	ulong	atime;
43 	ulong	mtime;
44 	char	*user;
45 	char	*group;
46 	char	*muid;
47 	char	*data;
48 	long	ndata;
49 };
50 
51 enum
52 {
53 	Pexec =		1,
54 	Pwrite = 	2,
55 	Pread = 	4,
56 	Pother = 	1,
57 	Pgroup = 	8,
58 	Powner =	64
59 };
60 
61 ulong	path;		/* incremented for each new file */
62 Fid	*fids;
63 Ram	ram[Nram];
64 int	nram;
65 int	mfd[2];
66 char	*user;
67 uchar	mdata[IOHDRSZ+Maxfdata];
68 uchar	rdata[Maxfdata];	/* buffer for data in reply */
69 uchar statbuf[STATMAX];
70 Fcall thdr;
71 Fcall	rhdr;
72 int	messagesize = sizeof mdata;
73 
74 Fid *	newfid(int);
75 uint	ramstat(Ram*, uchar*, uint);
76 void	error(char*);
77 void	io(void);
78 void	*erealloc(void*, ulong);
79 void	*emalloc(ulong);
80 char	*estrdup(char*);
81 void	usage(void);
82 int	perm(Fid*, Ram*, int);
83 
84 char	*rflush(Fid*), *rversion(Fid*), *rauth(Fid*),
85 	*rattach(Fid*), *rwalk(Fid*),
86 	*ropen(Fid*), *rcreate(Fid*),
87 	*rread(Fid*), *rwrite(Fid*), *rclunk(Fid*),
88 	*rremove(Fid*), *rstat(Fid*), *rwstat(Fid*);
89 
90 char 	*(*fcalls[Tmax])(Fid*);
91 
92 static void
93 initfcalls(void)
94 {
95 	fcalls[Tversion]=	rversion;
96 	fcalls[Tflush]=	rflush;
97 	fcalls[Tauth]=	rauth;
98 	fcalls[Tattach]=	rattach;
99 	fcalls[Twalk]=		rwalk;
100 	fcalls[Topen]=		ropen;
101 	fcalls[Tcreate]=	rcreate;
102 	fcalls[Tread]=		rread;
103 	fcalls[Twrite]=	rwrite;
104 	fcalls[Tclunk]=	rclunk;
105 	fcalls[Tremove]=	rremove;
106 	fcalls[Tstat]=		rstat;
107 	fcalls[Twstat]=	rwstat;
108 }
109 
110 char	Eperm[] =	"permission denied";
111 char	Enotdir[] =	"not a directory";
112 char	Enoauth[] =	"ramfs: authentication not required";
113 char	Enotexist[] =	"file does not exist";
114 char	Einuse[] =	"file in use";
115 char	Eexist[] =	"file exists";
116 char	Eisdir[] =	"file is a directory";
117 char	Enotowner[] =	"not owner";
118 char	Eisopen[] = 	"file already open for I/O";
119 char	Excl[] = 	"exclusive use file already open";
120 char	Ename[] = 	"illegal name";
121 char	Eversion[] =	"unknown 9P version";
122 char	Enotempty[] =	"directory not empty";
123 char	Ebadfid[] =	"bad fid";
124 
125 int debug;
126 int private;
127 
128 void
129 notifyf(void *a, char *s)
130 {
131 	USED(a);
132 	if(strncmp(s, "interrupt", 9) == 0)
133 		noted(NCONT);
134 	noted(NDFLT);
135 }
136 
137 void
138 main(int argc, char *argv[])
139 {
140 	Ram *r;
141 	char *defmnt;
142 	int p[2];
143 	int stdio = 0;
144 	char *service;
145 
146 	initfcalls();
147 	service = "ramfs";
148 	defmnt = nil;
149 	ARGBEGIN{
150 	case 'D':
151 		debug = 1;
152 		break;
153 	case 'i':
154 		defmnt = 0;
155 		stdio = 1;
156 		mfd[0] = 0;
157 		mfd[1] = 1;
158 		break;
159 	case 's':
160 		defmnt = nil;
161 		break;
162 	case 'm':
163 		defmnt = ARGF();
164 		break;
165 	case 'p':
166 		private++;
167 		break;
168 	case 'S':
169 		defmnt = 0;
170 		service = EARGF(usage());
171 		break;
172 	default:
173 		usage();
174 	}ARGEND
175 	USED(defmnt);
176 
177 	if(pipe(p) < 0)
178 		error("pipe failed");
179 	if(!stdio){
180 		mfd[0] = p[0];
181 		mfd[1] = p[0];
182 		if(post9pservice(p[1], service, nil) < 0)
183 			sysfatal("post9pservice %s: %r", service);
184 	}
185 
186 	user = getuser();
187 	notify(notifyf);
188 	nram = 2;
189 	r = &ram[0];
190 	r->busy = 1;
191 	r->data = 0;
192 	r->ndata = 0;
193 	r->perm = DMDIR | 0775;
194 	r->qid.type = QTDIR;
195 	r->qid.path = 0;
196 	r->qid.vers = 0;
197 	r->parent = 0;
198 	r->user = user;
199 	r->group = user;
200 	r->muid = user;
201 	r->atime = time(0);
202 	r->mtime = r->atime;
203 	r->name = estrdup(".");
204 
205 	r = &ram[1];
206 	r->busy = 1;
207 	r->data = 0;
208 	r->ndata = 0;
209 	r->perm = 0666;
210 	r->qid.type = 0;
211 	r->qid.path = 1;
212 	r->qid.vers = 0;
213 	r->parent = 0;
214 	r->user = user;
215 	r->group = user;
216 	r->muid = user;
217 	r->atime = time(0);
218 	r->mtime = r->atime;
219 	r->name = estrdup("file");
220 
221 	if(debug)
222 		fmtinstall('F', fcallfmt);
223 	switch(rfork(RFFDG|RFPROC|RFNAMEG|RFNOTEG)){
224 	case -1:
225 		error("fork");
226 	case 0:
227 		close(p[1]);
228 		io();
229 		break;
230 	default:
231 		close(p[0]);	/* don't deadlock if child fails */
232 	}
233 	exits(0);
234 }
235 
236 char*
237 rversion(Fid *x)
238 {
239 	Fid *f;
240 
241 	USED(x);
242 	for(f = fids; f; f = f->next)
243 		if(f->busy)
244 			rclunk(f);
245 	if(thdr.msize > sizeof mdata)
246 		rhdr.msize = sizeof mdata;
247 	else
248 		rhdr.msize = thdr.msize;
249 	messagesize = rhdr.msize;
250 	if(strncmp(thdr.version, "9P2000", 6) != 0)
251 		return Eversion;
252 	rhdr.version = "9P2000";
253 	return 0;
254 }
255 
256 char*
257 rauth(Fid *x)
258 {
259 	if(x->busy)
260 		return Ebadfid;
261 	return "ramfs: no authentication required";
262 }
263 
264 char*
265 rflush(Fid *f)
266 {
267 	USED(f);
268 	return 0;
269 }
270 
271 char*
272 rattach(Fid *f)
273 {
274 	/* no authentication! */
275 	if(f->busy)
276 		return Ebadfid;
277 	f->busy = 1;
278 	f->rclose = 0;
279 	f->ram = &ram[0];
280 	rhdr.qid = f->ram->qid;
281 	if(thdr.uname[0])
282 		f->user = estrdup(thdr.uname);
283 	else
284 		f->user = "none";
285 	if(strcmp(user, "none") == 0)
286 		user = f->user;
287 	return 0;
288 }
289 
290 char*
291 xclone(Fid *f, Fid **nf)
292 {
293 	if(!f->busy)
294 		return Ebadfid;
295 	if(f->open)
296 		return Eisopen;
297 	if(f->ram->busy == 0)
298 		return Enotexist;
299 	*nf = newfid(thdr.newfid);
300 	(*nf)->busy = 1;
301 	(*nf)->open = 0;
302 	(*nf)->rclose = 0;
303 	(*nf)->ram = f->ram;
304 	(*nf)->user = f->user;	/* no ref count; the leakage is minor */
305 	return 0;
306 }
307 
308 char*
309 rwalk(Fid *f)
310 {
311 	Ram *r, *fram;
312 	char *name;
313 	Ram *parent;
314 	Fid *nf;
315 	char *err;
316 	ulong t;
317 	int i;
318 
319 	if(!f->busy)
320 		return Ebadfid;
321 	err = nil;
322 	nf = nil;
323 	rhdr.nwqid = 0;
324 	if(thdr.newfid != thdr.fid){
325 		err = xclone(f, &nf);
326 		if(err)
327 			return err;
328 		f = nf;	/* walk the new fid */
329 	}
330 	fram = f->ram;
331 	if(thdr.nwname > 0){
332 		t = time(0);
333 		for(i=0; i<thdr.nwname && i<MAXWELEM; i++){
334 			if((fram->qid.type & QTDIR) == 0){
335 				err = Enotdir;
336  				break;
337 			}
338 			if(fram->busy == 0){
339 				err = Enotexist;
340 				break;
341 			}
342 			fram->atime = t;
343 			name = thdr.wname[i];
344 			if(strcmp(name, ".") == 0){
345     Found:
346 				rhdr.nwqid++;
347 				rhdr.wqid[i] = fram->qid;
348 				continue;
349 			}
350 			parent = &ram[fram->parent];
351 			if(!perm(f, parent, Pexec)){
352 				err = Eperm;
353 				break;
354 			}
355 			if(strcmp(name, "..") == 0){
356 				fram = parent;
357 				goto Found;
358 			}
359 			for(r=ram; r < &ram[nram]; r++)
360 				if(r->busy && r->parent==fram-ram && strcmp(name, r->name)==0){
361 					fram = r;
362 					goto Found;
363 				}
364 			break;
365 		}
366 		if(i==0 && err == nil)
367 			err = Enotexist;
368 	}
369 	if(nf != nil && (err!=nil || rhdr.nwqid<thdr.nwname)){
370 		/* clunk the new fid, which is the one we walked */
371 fprint(2, "f %d zero busy\n", f->fid);
372 		f->busy = 0;
373 		f->ram = nil;
374 	}
375 	if(rhdr.nwqid == thdr.nwname)	/* update the fid after a successful walk */
376 		f->ram = fram;
377 	assert(f->busy);
378 	return err;
379 }
380 
381 char *
382 ropen(Fid *f)
383 {
384 	Ram *r;
385 	int mode, trunc;
386 
387 	if(!f->busy)
388 		return Ebadfid;
389 	if(f->open)
390 		return Eisopen;
391 	r = f->ram;
392 	if(r->busy == 0)
393 		return Enotexist;
394 	if(r->perm & DMEXCL)
395 		if(r->open)
396 			return Excl;
397 	mode = thdr.mode;
398 	if(r->qid.type & QTDIR){
399 		if(mode != OREAD)
400 			return Eperm;
401 		rhdr.qid = r->qid;
402 		return 0;
403 	}
404 	if(mode & ORCLOSE){
405 		/* can't remove root; must be able to write parent */
406 		if(r->qid.path==0 || !perm(f, &ram[r->parent], Pwrite))
407 			return Eperm;
408 		f->rclose = 1;
409 	}
410 	trunc = mode & OTRUNC;
411 	mode &= OPERM;
412 	if(mode==OWRITE || mode==ORDWR || trunc)
413 		if(!perm(f, r, Pwrite))
414 			return Eperm;
415 	if(mode==OREAD || mode==ORDWR)
416 		if(!perm(f, r, Pread))
417 			return Eperm;
418 	if(mode==OEXEC)
419 		if(!perm(f, r, Pexec))
420 			return Eperm;
421 	if(trunc && (r->perm&DMAPPEND)==0){
422 		r->ndata = 0;
423 		if(r->data)
424 			free(r->data);
425 		r->data = 0;
426 		r->qid.vers++;
427 	}
428 	rhdr.qid = r->qid;
429 	rhdr.iounit = messagesize-IOHDRSZ;
430 	f->open = 1;
431 	r->open++;
432 	return 0;
433 }
434 
435 char *
436 rcreate(Fid *f)
437 {
438 	Ram *r;
439 	char *name;
440 	long parent, prm;
441 
442 	if(!f->busy)
443 		return Ebadfid;
444 	if(f->open)
445 		return Eisopen;
446 	if(f->ram->busy == 0)
447 		return Enotexist;
448 	parent = f->ram - ram;
449 	if((f->ram->qid.type&QTDIR) == 0)
450 		return Enotdir;
451 	/* must be able to write parent */
452 	if(!perm(f, f->ram, Pwrite))
453 		return Eperm;
454 	prm = thdr.perm;
455 	name = thdr.name;
456 	if(strcmp(name, ".")==0 || strcmp(name, "..")==0)
457 		return Ename;
458 	for(r=ram; r<&ram[nram]; r++)
459 		if(r->busy && parent==r->parent)
460 		if(strcmp((char*)name, r->name)==0)
461 			return Einuse;
462 	for(r=ram; r->busy; r++)
463 		if(r == &ram[Nram-1])
464 			return "no free ram resources";
465 	r->busy = 1;
466 	r->qid.path = ++path;
467 	r->qid.vers = 0;
468 	if(prm & DMDIR)
469 		r->qid.type |= QTDIR;
470 	r->parent = parent;
471 	free(r->name);
472 	r->name = estrdup(name);
473 	r->user = f->user;
474 	r->group = f->ram->group;
475 	r->muid = f->ram->muid;
476 	if(prm & DMDIR)
477 		prm = (prm&~0777) | (f->ram->perm&prm&0777);
478 	else
479 		prm = (prm&(~0777|0111)) | (f->ram->perm&prm&0666);
480 	r->perm = prm;
481 	r->ndata = 0;
482 	if(r-ram >= nram)
483 		nram = r - ram + 1;
484 	r->atime = time(0);
485 	r->mtime = r->atime;
486 	f->ram->mtime = r->atime;
487 	f->ram = r;
488 	rhdr.qid = r->qid;
489 	rhdr.iounit = messagesize-IOHDRSZ;
490 	f->open = 1;
491 	if(thdr.mode & ORCLOSE)
492 		f->rclose = 1;
493 	r->open++;
494 	return 0;
495 }
496 
497 char*
498 rread(Fid *f)
499 {
500 	Ram *r;
501 	uchar *buf;
502 	long off;
503 	int n, m, cnt;
504 
505 	if(!f->busy)
506 		return Ebadfid;
507 	if(f->ram->busy == 0)
508 		return Enotexist;
509 	n = 0;
510 	rhdr.count = 0;
511 	off = thdr.offset;
512 	buf = rdata;
513 	cnt = thdr.count;
514 	if(cnt > messagesize)	/* shouldn't happen, anyway */
515 		cnt = messagesize;
516 	if(f->ram->qid.type & QTDIR){
517 		for(r=ram+1; off > 0; r++){
518 			if(r->busy && r->parent==f->ram-ram)
519 				off -= ramstat(r, statbuf, sizeof statbuf);
520 			if(r == &ram[nram-1])
521 				return 0;
522 		}
523 		for(; r<&ram[nram] && n < cnt; r++){
524 			if(!r->busy || r->parent!=f->ram-ram)
525 				continue;
526 			m = ramstat(r, buf+n, cnt-n);
527 			if(m == 0)
528 				break;
529 			n += m;
530 		}
531 		rhdr.data = (char*)rdata;
532 		rhdr.count = n;
533 		return 0;
534 	}
535 	r = f->ram;
536 	if(off >= r->ndata)
537 		return 0;
538 	r->atime = time(0);
539 	n = cnt;
540 	if(off+n > r->ndata)
541 		n = r->ndata - off;
542 	rhdr.data = r->data+off;
543 	rhdr.count = n;
544 	return 0;
545 }
546 
547 char*
548 rwrite(Fid *f)
549 {
550 	Ram *r;
551 	ulong off;
552 	int cnt;
553 
554 	r = f->ram;
555 	if(!f->busy)
556 		return Ebadfid;
557 	if(r->busy == 0)
558 		return Enotexist;
559 	off = thdr.offset;
560 	if(r->perm & DMAPPEND)
561 		off = r->ndata;
562 	cnt = thdr.count;
563 	if(r->qid.type & QTDIR)
564 		return Eisdir;
565 	if(off+cnt >= Maxsize)		/* sanity check */
566 		return "write too big";
567 	if(off+cnt > r->ndata)
568 		r->data = erealloc(r->data, off+cnt);
569 	if(off > r->ndata)
570 		memset(r->data+r->ndata, 0, off-r->ndata);
571 	if(off+cnt > r->ndata)
572 		r->ndata = off+cnt;
573 	memmove(r->data+off, thdr.data, cnt);
574 	r->qid.vers++;
575 	r->mtime = time(0);
576 	rhdr.count = cnt;
577 	return 0;
578 }
579 
580 static int
581 emptydir(Ram *dr)
582 {
583 	long didx = dr - ram;
584 	Ram *r;
585 
586 	for(r=ram; r<&ram[nram]; r++)
587 		if(r->busy && didx==r->parent)
588 			return 0;
589 	return 1;
590 }
591 
592 char *
593 realremove(Ram *r)
594 {
595 	if(r->qid.type & QTDIR && !emptydir(r))
596 		return Enotempty;
597 	r->ndata = 0;
598 	if(r->data)
599 		free(r->data);
600 	r->data = 0;
601 	r->parent = 0;
602 	memset(&r->qid, 0, sizeof r->qid);
603 	free(r->name);
604 	r->name = nil;
605 	r->busy = 0;
606 	return nil;
607 }
608 
609 char *
610 rclunk(Fid *f)
611 {
612 	char *e = nil;
613 
614 	if(f->open)
615 		f->ram->open--;
616 	if(f->rclose)
617 		e = realremove(f->ram);
618 fprint(2, "clunk fid %d busy=%d\n", f->fid, f->busy);
619 fprint(2, "f %d zero busy\n", f->fid);
620 	f->busy = 0;
621 	f->open = 0;
622 	f->ram = 0;
623 	return e;
624 }
625 
626 char *
627 rremove(Fid *f)
628 {
629 	Ram *r;
630 
631 	if(f->open)
632 		f->ram->open--;
633 fprint(2, "f %d zero busy\n", f->fid);
634 	f->busy = 0;
635 	f->open = 0;
636 	r = f->ram;
637 	f->ram = 0;
638 	if(r->qid.path == 0 || !perm(f, &ram[r->parent], Pwrite))
639 		return Eperm;
640 	ram[r->parent].mtime = time(0);
641 	return realremove(r);
642 }
643 
644 char *
645 rstat(Fid *f)
646 {
647 	if(!f->busy)
648 		return Ebadfid;
649 	if(f->ram->busy == 0)
650 		return Enotexist;
651 	rhdr.nstat = ramstat(f->ram, statbuf, sizeof statbuf);
652 	rhdr.stat = statbuf;
653 	return 0;
654 }
655 
656 char *
657 rwstat(Fid *f)
658 {
659 	Ram *r, *s;
660 	Dir dir;
661 
662 	if(!f->busy)
663 		return Ebadfid;
664 	if(f->ram->busy == 0)
665 		return Enotexist;
666 	convM2D(thdr.stat, thdr.nstat, &dir, (char*)statbuf);
667 	r = f->ram;
668 
669 	/*
670 	 * To change length, must have write permission on file.
671 	 */
672 	if(dir.length!=~0 && dir.length!=r->ndata){
673 	 	if(!perm(f, r, Pwrite))
674 			return Eperm;
675 	}
676 
677 	/*
678 	 * To change name, must have write permission in parent
679 	 * and name must be unique.
680 	 */
681 	if(dir.name[0]!='\0' && strcmp(dir.name, r->name)!=0){
682 	 	if(!perm(f, &ram[r->parent], Pwrite))
683 			return Eperm;
684 		for(s=ram; s<&ram[nram]; s++)
685 			if(s->busy && s->parent==r->parent)
686 			if(strcmp(dir.name, s->name)==0)
687 				return Eexist;
688 	}
689 
690 	/*
691 	 * To change mode, must be owner or group leader.
692 	 * Because of lack of users file, leader=>group itself.
693 	 */
694 	if(dir.mode!=~0 && r->perm!=dir.mode){
695 		if(strcmp(f->user, r->user) != 0)
696 		if(strcmp(f->user, r->group) != 0)
697 			return Enotowner;
698 	}
699 
700 	/*
701 	 * To change group, must be owner and member of new group,
702 	 * or leader of current group and leader of new group.
703 	 * Second case cannot happen, but we check anyway.
704 	 */
705 	if(dir.gid[0]!='\0' && strcmp(r->group, dir.gid)!=0){
706 		if(strcmp(f->user, r->user) == 0)
707 	/*	if(strcmp(f->user, dir.gid) == 0) */
708 			goto ok;
709 		if(strcmp(f->user, r->group) == 0)
710 		if(strcmp(f->user, dir.gid) == 0)
711 			goto ok;
712 		return Enotowner;
713 		ok:;
714 	}
715 
716 	/* all ok; do it */
717 	if(dir.mode != ~0){
718 		dir.mode &= ~DMDIR;	/* cannot change dir bit */
719 		dir.mode |= r->perm&DMDIR;
720 		r->perm = dir.mode;
721 	}
722 	if(dir.name[0] != '\0'){
723 		free(r->name);
724 		r->name = estrdup(dir.name);
725 	}
726 	if(dir.gid[0] != '\0')
727 		r->group = estrdup(dir.gid);
728 	if(dir.length!=~0 && dir.length!=r->ndata){
729 		r->data = erealloc(r->data, dir.length);
730 		if(r->ndata < dir.length)
731 			memset(r->data+r->ndata, 0, dir.length-r->ndata);
732 		r->ndata = dir.length;
733 	}
734 	ram[r->parent].mtime = time(0);
735 	return 0;
736 }
737 
738 uint
739 ramstat(Ram *r, uchar *buf, uint nbuf)
740 {
741 	int n;
742 	Dir dir;
743 
744 	dir.name = r->name;
745 	dir.qid = r->qid;
746 	dir.mode = r->perm;
747 	dir.length = r->ndata;
748 	dir.uid = r->user;
749 	dir.gid = r->group;
750 	dir.muid = r->muid;
751 	dir.atime = r->atime;
752 	dir.mtime = r->mtime;
753 	n = convD2M(&dir, buf, nbuf);
754 	if(n > 2)
755 		return n;
756 	return 0;
757 }
758 
759 Fid *
760 newfid(int fid)
761 {
762 	Fid *f, *ff;
763 
764 	ff = 0;
765 	for(f = fids; f; f = f->next)
766 		if(f->fid == fid)
767 			return f;
768 		else if(!ff && !f->busy)
769 			ff = f;
770 	if(ff){
771 		ff->fid = fid;
772 		return ff;
773 	}
774 	f = emalloc(sizeof *f);
775 	f->ram = nil;
776 	f->fid = fid;
777 	f->next = fids;
778 	fids = f;
779 	return f;
780 }
781 
782 void
783 io(void)
784 {
785 	char *err, buf[20];
786 	int n, pid, ctl;
787 
788 	pid = getpid();
789 	if(private){
790 		snprint(buf, sizeof buf, "/proc/%d/ctl", pid);
791 		ctl = open(buf, OWRITE);
792 		if(ctl < 0){
793 			fprint(2, "can't protect ramfs\n");
794 		}else{
795 			fprint(ctl, "noswap\n");
796 			fprint(ctl, "private\n");
797 			close(ctl);
798 		}
799 	}
800 
801 	for(;;){
802 		/*
803 		 * reading from a pipe or a network device
804 		 * will give an error after a few eof reads.
805 		 * however, we cannot tell the difference
806 		 * between a zero-length read and an interrupt
807 		 * on the processes writing to us,
808 		 * so we wait for the error.
809 		 */
810 		n = read9pmsg(mfd[0], mdata, messagesize);
811 		if(n < 0)
812 			error("mount read");
813 		if(n == 0)
814 			error("mount eof");
815 		if(convM2S(mdata, n, &thdr) == 0)
816 			continue;
817 
818 		if(debug)
819 			fprint(2, "ramfs %d:<-%F\n", pid, &thdr);
820 
821 		if(!fcalls[thdr.type])
822 			err = "bad fcall type";
823 		else
824 			err = (*fcalls[thdr.type])(newfid(thdr.fid));
825 		if(err){
826 			rhdr.type = Rerror;
827 			rhdr.ename = err;
828 		}else{
829 			rhdr.type = thdr.type + 1;
830 			rhdr.fid = thdr.fid;
831 		}
832 		rhdr.tag = thdr.tag;
833 		if(debug)
834 			fprint(2, "ramfs %d:->%F\n", pid, &rhdr);/**/
835 		n = convS2M(&rhdr, mdata, messagesize);
836 		if(n == 0)
837 			error("convS2M error on write");
838 		if(write(mfd[1], mdata, n) != n)
839 			error("mount write");
840 	}
841 }
842 
843 int
844 perm(Fid *f, Ram *r, int p)
845 {
846 	if((p*Pother) & r->perm)
847 		return 1;
848 	if(strcmp(f->user, r->group)==0 && ((p*Pgroup) & r->perm))
849 		return 1;
850 	if(strcmp(f->user, r->user)==0 && ((p*Powner) & r->perm))
851 		return 1;
852 	return 0;
853 }
854 
855 void
856 error(char *s)
857 {
858 	fprint(2, "%s: %s: %r\n", argv0, s);
859 	exits(s);
860 }
861 
862 void *
863 emalloc(ulong n)
864 {
865 	void *p;
866 
867 	p = malloc(n);
868 	if(!p)
869 		error("out of memory");
870 	memset(p, 0, n);
871 	return p;
872 }
873 
874 void *
875 erealloc(void *p, ulong n)
876 {
877 	p = realloc(p, n);
878 	if(!p)
879 		error("out of memory");
880 	return p;
881 }
882 
883 char *
884 estrdup(char *q)
885 {
886 	char *p;
887 	int n;
888 
889 	n = strlen(q)+1;
890 	p = malloc(n);
891 	if(!p)
892 		error("out of memory");
893 	memmove(p, q, n);
894 	return p;
895 }
896 
897 void
898 usage(void)
899 {
900 	fprint(2, "usage: %s [-is] [-m mountpoint]\n", argv0);
901 	exits("usage");
902 }