xref: /netbsd-src/sys/dev/md.c (revision deb6f0161a9109e7de9b519dc8dfb9478668dcdd) 
1 /*	$NetBSD: md.c,v 1.80 2018/03/03 19:26:12 christos Exp $	*/
2 
3 /*
4  * Copyright (c) 1995 Gordon W. Ross, Leo Weppelman.
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26  */
27 
28 /*
29  * This implements a general-purpose memory-disk.
30  * See md.h for notes on the config types.
31  *
32  * Note that this driver provides the same functionality
33  * as the MFS filesystem hack, but this is better because
34  * you can use this for any filesystem type you'd like!
35  *
36  * Credit for most of the kmem ramdisk code goes to:
37  *   Leo Weppelman (atari) and Phil Nelson (pc532)
38  * Credit for the ideas behind the "user space memory" code goes
39  * to the authors of the MFS implementation.
40  */
41 
42 #include <sys/cdefs.h>
43 __KERNEL_RCSID(0, "$NetBSD: md.c,v 1.80 2018/03/03 19:26:12 christos Exp $");
44 
45 #ifdef _KERNEL_OPT
46 #include "opt_md.h"
47 #else
48 #define MEMORY_DISK_SERVER 1
49 #endif
50 
51 #include <sys/param.h>
52 #include <sys/kernel.h>
53 #include <sys/malloc.h>
54 #include <sys/systm.h>
55 #include <sys/buf.h>
56 #include <sys/bufq.h>
57 #include <sys/device.h>
58 #include <sys/disk.h>
59 #include <sys/stat.h>
60 #include <sys/proc.h>
61 #include <sys/conf.h>
62 #include <sys/disklabel.h>
63 
64 #include <uvm/uvm_extern.h>
65 
66 #include <dev/md.h>
67 
68 #include "ioconf.h"
69 /*
70  * The user-space functionality is included by default.
71  * Use  `options MEMORY_DISK_SERVER=0' to turn it off.
72  */
73 #ifndef MEMORY_DISK_SERVER
74 #error MEMORY_DISK_SERVER should be defined by opt_md.h
75 #endif	/* MEMORY_DISK_SERVER */
76 
77 /*
78  * We should use the raw partition for ioctl.
79  */
80 #define MD_UNIT(unit)	DISKUNIT(unit)
81 
82 /* autoconfig stuff... */
83 
84 struct md_softc {
85 	device_t sc_dev;	/* Self. */
86 	struct disk sc_dkdev;	/* hook for generic disk handling */
87 	struct md_conf sc_md;
88 	kmutex_t sc_lock;	/* Protect self. */
89 	kcondvar_t sc_cv;	/* Wait here for work. */
90 	struct bufq_state *sc_buflist;
91 };
92 /* shorthand for fields in sc_md: */
93 #define sc_addr sc_md.md_addr
94 #define sc_size sc_md.md_size
95 #define sc_type sc_md.md_type
96 
97 static void	md_attach(device_t, device_t, void *);
98 static int	md_detach(device_t, int);
99 
100 static dev_type_open(mdopen);
101 static dev_type_close(mdclose);
102 static dev_type_read(mdread);
103 static dev_type_write(mdwrite);
104 static dev_type_ioctl(mdioctl);
105 static dev_type_strategy(mdstrategy);
106 static dev_type_size(mdsize);
107 
108 const struct bdevsw md_bdevsw = {
109 	.d_open = mdopen,
110 	.d_close = mdclose,
111 	.d_strategy = mdstrategy,
112 	.d_ioctl = mdioctl,
113 	.d_dump = nodump,
114 	.d_psize = mdsize,
115 	.d_discard = nodiscard,
116 	.d_flag = D_DISK | D_MPSAFE
117 };
118 
119 const struct cdevsw md_cdevsw = {
120 	.d_open = mdopen,
121 	.d_close = mdclose,
122 	.d_read = mdread,
123 	.d_write = mdwrite,
124 	.d_ioctl = mdioctl,
125 	.d_stop = nostop,
126 	.d_tty = notty,
127 	.d_poll = nopoll,
128 	.d_mmap = nommap,
129 	.d_kqfilter = nokqfilter,
130 	.d_discard = nodiscard,
131 	.d_flag = D_DISK
132 };
133 
134 static struct dkdriver mddkdriver = {
135 	.d_strategy = mdstrategy
136 };
137 
138 CFATTACH_DECL3_NEW(md, sizeof(struct md_softc),
139 	0, md_attach, md_detach, NULL, NULL, NULL, DVF_DETACH_SHUTDOWN);
140 
141 static kmutex_t md_device_lock;		/* Protect unit creation / deletion. */
142 extern size_t md_root_size;
143 
144 static void md_set_disklabel(struct md_softc *);
145 
146 /*
147  * This is called if we are configured as a pseudo-device
148  */
149 void
150 mdattach(int n)
151 {
152 
153 	mutex_init(&md_device_lock, MUTEX_DEFAULT, IPL_NONE);
154 	if (config_cfattach_attach(md_cd.cd_name, &md_ca)) {
155 		aprint_error("%s: cfattach_attach failed\n", md_cd.cd_name);
156 		return;
157 	}
158 }
159 
160 static void
161 md_attach(device_t parent, device_t self, void *aux)
162 {
163 	struct md_softc *sc = device_private(self);
164 
165 	sc->sc_dev = self;
166 	sc->sc_type = MD_UNCONFIGURED;
167 	mutex_init(&sc->sc_lock, MUTEX_DEFAULT, IPL_NONE);
168 	cv_init(&sc->sc_cv, "mdidle");
169 	bufq_alloc(&sc->sc_buflist, "fcfs", 0);
170 
171 	/* XXX - Could accept aux info here to set the config. */
172 #ifdef	MEMORY_DISK_HOOKS
173 	/*
174 	 * This external function might setup a pre-loaded disk.
175 	 * All it would need to do is setup the md_conf struct.
176 	 * See sys/dev/md_root.c for an example.
177 	 */
178 	md_attach_hook(device_unit(self), &sc->sc_md);
179 #endif
180 
181 	/*
182 	 * Initialize and attach the disk structure.
183 	 */
184 	disk_init(&sc->sc_dkdev, device_xname(self), &mddkdriver);
185 	disk_attach(&sc->sc_dkdev);
186 
187 	if (sc->sc_type != MD_UNCONFIGURED)
188 		md_set_disklabel(sc);
189 
190 	if (!pmf_device_register(self, NULL, NULL))
191 		aprint_error_dev(self, "couldn't establish power handler\n");
192 }
193 
194 static int
195 md_detach(device_t self, int flags)
196 {
197 	struct md_softc *sc = device_private(self);
198 	int rc;
199 
200 	rc = 0;
201 	mutex_enter(&sc->sc_dkdev.dk_openlock);
202 	if (sc->sc_dkdev.dk_openmask == 0 && sc->sc_type == MD_UNCONFIGURED)
203 		;	/* nothing to do */
204 	else if ((flags & DETACH_FORCE) == 0)
205 		rc = EBUSY;
206 	mutex_exit(&sc->sc_dkdev.dk_openlock);
207 
208 	if (rc != 0)
209 		return rc;
210 
211 	pmf_device_deregister(self);
212 	disk_detach(&sc->sc_dkdev);
213 	disk_destroy(&sc->sc_dkdev);
214 	bufq_free(sc->sc_buflist);
215 	mutex_destroy(&sc->sc_lock);
216 	cv_destroy(&sc->sc_cv);
217 	return 0;
218 }
219 
220 /*
221  * operational routines:
222  * open, close, read, write, strategy,
223  * ioctl, dump, size
224  */
225 
226 #if MEMORY_DISK_SERVER
227 static int	md_server_loop(struct md_softc *sc);
228 static int	md_ioctl_server(struct md_softc *sc, struct md_conf *umd,
229 		    struct lwp *l);
230 #endif	/* MEMORY_DISK_SERVER */
231 static int	md_ioctl_kalloc(struct md_softc *sc, struct md_conf *umd,
232 		    struct lwp *l);
233 
234 static int
235 mdsize(dev_t dev)
236 {
237 	struct md_softc *sc;
238 	int res;
239 
240 	sc = device_lookup_private(&md_cd, MD_UNIT(dev));
241 	if (sc == NULL)
242 		return 0;
243 
244 	mutex_enter(&sc->sc_lock);
245 	if (sc->sc_type == MD_UNCONFIGURED)
246 		res = 0;
247 	else
248 		res = sc->sc_size >> DEV_BSHIFT;
249 	mutex_exit(&sc->sc_lock);
250 
251 	return res;
252 }
253 
254 static int
255 mdopen(dev_t dev, int flag, int fmt, struct lwp *l)
256 {
257 	int unit;
258 	int part = DISKPART(dev);
259 	int pmask = 1 << part;
260 	cfdata_t cf;
261 	struct md_softc *sc;
262 	struct disk *dk;
263 #ifdef	MEMORY_DISK_HOOKS
264 	bool configured;
265 #endif
266 
267 	mutex_enter(&md_device_lock);
268 	unit = MD_UNIT(dev);
269 	sc = device_lookup_private(&md_cd, unit);
270 	if (sc == NULL) {
271 		if (part != RAW_PART) {
272 			mutex_exit(&md_device_lock);
273 			return ENXIO;
274 		}
275 		cf = malloc(sizeof(*cf), M_DEVBUF, M_WAITOK);
276 		cf->cf_name = md_cd.cd_name;
277 		cf->cf_atname = md_cd.cd_name;
278 		cf->cf_unit = unit;
279 		cf->cf_fstate = FSTATE_STAR;
280 		sc = device_private(config_attach_pseudo(cf));
281 		if (sc == NULL) {
282 			mutex_exit(&md_device_lock);
283 			return ENOMEM;
284 		}
285 	}
286 
287 	dk = &sc->sc_dkdev;
288 
289 	/*
290 	 * The raw partition is used for ioctl to configure.
291 	 */
292 	if (part == RAW_PART)
293 		goto ok;
294 
295 #ifdef	MEMORY_DISK_HOOKS
296 	/* Call the open hook to allow loading the device. */
297 	configured = (sc->sc_type != MD_UNCONFIGURED);
298 	md_open_hook(unit, &sc->sc_md);
299 	/* initialize disklabel if the device is configured in open hook */
300 	if (!configured && sc->sc_type != MD_UNCONFIGURED)
301 		md_set_disklabel(sc);
302 #endif
303 
304 	/*
305 	 * This is a normal, "slave" device, so
306 	 * enforce initialized.
307 	 */
308 	if (sc->sc_type == MD_UNCONFIGURED) {
309 		mutex_exit(&md_device_lock);
310 		return ENXIO;
311 	}
312 
313 ok:
314 	/* XXX duplicates code in dk_open().  Call dk_open(), instead? */
315 	mutex_enter(&dk->dk_openlock);
316 	/* Mark our unit as open. */
317 	switch (fmt) {
318 	case S_IFCHR:
319 		dk->dk_copenmask |= pmask;
320 		break;
321 	case S_IFBLK:
322 		dk->dk_bopenmask |= pmask;
323 		break;
324 	}
325 
326 	dk->dk_openmask = dk->dk_copenmask | dk->dk_bopenmask;
327 
328 	mutex_exit(&dk->dk_openlock);
329 	mutex_exit(&md_device_lock);
330 	return 0;
331 }
332 
333 static int
334 mdclose(dev_t dev, int flag, int fmt, struct lwp *l)
335 {
336 	int part = DISKPART(dev);
337 	int pmask = 1 << part;
338 	int error;
339 	cfdata_t cf;
340 	struct md_softc *sc;
341 	struct disk *dk;
342 
343 	sc = device_lookup_private(&md_cd, MD_UNIT(dev));
344 	if (sc == NULL)
345 		return ENXIO;
346 
347 	dk = &sc->sc_dkdev;
348 
349 	mutex_enter(&dk->dk_openlock);
350 
351 	switch (fmt) {
352 	case S_IFCHR:
353 		dk->dk_copenmask &= ~pmask;
354 		break;
355 	case S_IFBLK:
356 		dk->dk_bopenmask &= ~pmask;
357 		break;
358 	}
359 	dk->dk_openmask = dk->dk_copenmask | dk->dk_bopenmask;
360 	if (dk->dk_openmask != 0) {
361 		mutex_exit(&dk->dk_openlock);
362 		return 0;
363 	}
364 
365 	mutex_exit(&dk->dk_openlock);
366 
367 	mutex_enter(&md_device_lock);
368 	cf = device_cfdata(sc->sc_dev);
369 	error = config_detach(sc->sc_dev, DETACH_QUIET);
370 	if (! error)
371 		free(cf, M_DEVBUF);
372 	mutex_exit(&md_device_lock);
373 	return error;
374 }
375 
376 static int
377 mdread(dev_t dev, struct uio *uio, int flags)
378 {
379 	struct md_softc *sc;
380 
381 	sc = device_lookup_private(&md_cd, MD_UNIT(dev));
382 
383 	if (sc == NULL || sc->sc_type == MD_UNCONFIGURED)
384 		return ENXIO;
385 
386 	return (physio(mdstrategy, NULL, dev, B_READ, minphys, uio));
387 }
388 
389 static int
390 mdwrite(dev_t dev, struct uio *uio, int flags)
391 {
392 	struct md_softc *sc;
393 
394 	sc = device_lookup_private(&md_cd, MD_UNIT(dev));
395 
396 	if (sc == NULL || sc->sc_type == MD_UNCONFIGURED)
397 		return ENXIO;
398 
399 	return (physio(mdstrategy, NULL, dev, B_WRITE, minphys, uio));
400 }
401 
402 /*
403  * Handle I/O requests, either directly, or
404  * by passing them to the server process.
405  */
406 static void
407 mdstrategy(struct buf *bp)
408 {
409 	struct md_softc	*sc;
410 	void *	addr;
411 	size_t off, xfer;
412 	bool is_read;
413 
414 	sc = device_lookup_private(&md_cd, MD_UNIT(bp->b_dev));
415 
416 	if (sc == NULL || sc->sc_type == MD_UNCONFIGURED) {
417 		bp->b_error = ENXIO;
418 		goto done;
419 	}
420 
421 	mutex_enter(&sc->sc_lock);
422 
423 	switch (sc->sc_type) {
424 #if MEMORY_DISK_SERVER
425 	case MD_UMEM_SERVER:
426 		/* Just add this job to the server's queue. */
427 		bufq_put(sc->sc_buflist, bp);
428 		cv_signal(&sc->sc_cv);
429 		mutex_exit(&sc->sc_lock);
430 		/* see md_server_loop() */
431 		/* no biodone in this case */
432 		return;
433 #endif	/* MEMORY_DISK_SERVER */
434 
435 	case MD_KMEM_FIXED:
436 	case MD_KMEM_ALLOCATED:
437 		/* These are in kernel space.  Access directly. */
438 		is_read = ((bp->b_flags & B_READ) == B_READ);
439 		bp->b_resid = bp->b_bcount;
440 		off = (bp->b_blkno << DEV_BSHIFT);
441 		if (off >= sc->sc_size) {
442 			if (is_read)
443 				break;	/* EOF */
444 			goto set_eio;
445 		}
446 		xfer = bp->b_resid;
447 		if (xfer > (sc->sc_size - off))
448 			xfer = (sc->sc_size - off);
449 		addr = (char *)sc->sc_addr + off;
450 		disk_busy(&sc->sc_dkdev);
451 		if (is_read)
452 			memcpy(bp->b_data, addr, xfer);
453 		else
454 			memcpy(addr, bp->b_data, xfer);
455 		disk_unbusy(&sc->sc_dkdev, xfer, is_read);
456 		bp->b_resid -= xfer;
457 		break;
458 
459 	default:
460 		bp->b_resid = bp->b_bcount;
461 	set_eio:
462 		bp->b_error = EIO;
463 		break;
464 	}
465 	mutex_exit(&sc->sc_lock);
466 
467  done:
468 
469 	biodone(bp);
470 }
471 
472 static int
473 mdioctl(dev_t dev, u_long cmd, void *data, int flag, struct lwp *l)
474 {
475 	struct md_softc *sc;
476 	struct md_conf *umd;
477 	int error;
478 
479 	if ((sc = device_lookup_private(&md_cd, MD_UNIT(dev))) == NULL)
480 		return ENXIO;
481 
482 	mutex_enter(&sc->sc_lock);
483 	if (sc->sc_type != MD_UNCONFIGURED) {
484 		error = disk_ioctl(&sc->sc_dkdev, dev, cmd, data, flag, l);
485 		if (error != EPASSTHROUGH) {
486 			mutex_exit(&sc->sc_lock);
487 			return 0;
488 		}
489 	}
490 
491 	/* If this is not the raw partition, punt! */
492 	if (DISKPART(dev) != RAW_PART) {
493 		mutex_exit(&sc->sc_lock);
494 		return ENOTTY;
495 	}
496 
497 	umd = (struct md_conf *)data;
498 	error = EINVAL;
499 	switch (cmd) {
500 	case MD_GETCONF:
501 		*umd = sc->sc_md;
502 		error = 0;
503 		break;
504 
505 	case MD_SETCONF:
506 		/* Can only set it once. */
507 		if (sc->sc_type != MD_UNCONFIGURED)
508 			break;
509 		switch (umd->md_type) {
510 		case MD_KMEM_ALLOCATED:
511 			error = md_ioctl_kalloc(sc, umd, l);
512 			break;
513 #if MEMORY_DISK_SERVER
514 		case MD_UMEM_SERVER:
515 			error = md_ioctl_server(sc, umd, l);
516 			break;
517 #endif	/* MEMORY_DISK_SERVER */
518 		default:
519 			break;
520 		}
521 		break;
522 	}
523 	mutex_exit(&sc->sc_lock);
524 	return error;
525 }
526 
527 static void
528 md_set_disklabel(struct md_softc *sc)
529 {
530 	struct disk_geom *dg = &sc->sc_dkdev.dk_geom;
531 	struct disklabel *lp = sc->sc_dkdev.dk_label;
532 	struct partition *pp;
533 
534 	memset(lp, 0, sizeof(*lp));
535 
536 	lp->d_secsize = DEV_BSIZE;
537 	lp->d_secperunit = sc->sc_size / DEV_BSIZE;
538 	if (lp->d_secperunit >= (32*64)) {
539 		lp->d_nsectors = 32;
540 		lp->d_ntracks = 64;
541 		lp->d_ncylinders = lp->d_secperunit / (32*64);
542 	} else {
543 		lp->d_nsectors = 1;
544 		lp->d_ntracks = 1;
545 		lp->d_ncylinders = lp->d_secperunit;
546 	}
547 	lp->d_secpercyl = lp->d_ntracks*lp->d_nsectors;
548 
549 	strncpy(lp->d_typename, md_cd.cd_name, sizeof(lp->d_typename));
550 	lp->d_type = DKTYPE_MD;
551 	strncpy(lp->d_packname, "fictitious", sizeof(lp->d_packname));
552 	lp->d_rpm = 3600;
553 	lp->d_interleave = 1;
554 	lp->d_flags = 0;
555 
556 	pp = &lp->d_partitions[0];
557 	pp->p_offset = 0;
558 	pp->p_size = lp->d_secperunit;
559 	pp->p_fstype = FS_BSDFFS;
560 
561 	pp = &lp->d_partitions[RAW_PART];
562 	pp->p_offset = 0;
563 	pp->p_size = lp->d_secperunit;
564 	pp->p_fstype = FS_UNUSED;
565 
566 	lp->d_npartitions = RAW_PART+1;
567 	lp->d_magic = DISKMAGIC;
568 	lp->d_magic2 = DISKMAGIC;
569 	lp->d_checksum = dkcksum(lp);
570 
571 	memset(dg, 0, sizeof(*dg));
572 
573 	dg->dg_secsize = lp->d_secsize;
574 	dg->dg_secperunit = lp->d_secperunit;
575 	dg->dg_nsectors = lp->d_nsectors;
576 	dg->dg_ntracks = lp->d_ntracks = 64;;
577 	dg->dg_ncylinders = lp->d_ncylinders;
578 
579 	disk_set_info(sc->sc_dev, &sc->sc_dkdev, NULL);
580 }
581 
582 /*
583  * Handle ioctl MD_SETCONF for (sc_type == MD_KMEM_ALLOCATED)
584  * Just allocate some kernel memory and return.
585  */
586 static int
587 md_ioctl_kalloc(struct md_softc *sc, struct md_conf *umd,
588     struct lwp *l)
589 {
590 	vaddr_t addr;
591 	vsize_t size;
592 
593 	mutex_exit(&sc->sc_lock);
594 
595 	/* Sanity check the size. */
596 	size = umd->md_size;
597 	addr = uvm_km_alloc(kernel_map, size, 0, UVM_KMF_WIRED|UVM_KMF_ZERO);
598 
599 	mutex_enter(&sc->sc_lock);
600 
601 	if (!addr)
602 		return ENOMEM;
603 
604 	/* If another thread beat us to configure this unit:  fail. */
605 	if (sc->sc_type != MD_UNCONFIGURED) {
606 		uvm_km_free(kernel_map, addr, size, UVM_KMF_WIRED);
607 		return EINVAL;
608 	}
609 
610 	/* This unit is now configured. */
611 	sc->sc_addr = (void *)addr; 	/* kernel space */
612 	sc->sc_size = (size_t)size;
613 	sc->sc_type = MD_KMEM_ALLOCATED;
614 	md_set_disklabel(sc);
615 	return 0;
616 }
617 
618 #if MEMORY_DISK_SERVER
619 
620 /*
621  * Handle ioctl MD_SETCONF for (sc_type == MD_UMEM_SERVER)
622  * Set config, then become the I/O server for this unit.
623  */
624 static int
625 md_ioctl_server(struct md_softc *sc, struct md_conf *umd,
626     struct lwp *l)
627 {
628 	vaddr_t end;
629 	int error;
630 
631 	KASSERT(mutex_owned(&sc->sc_lock));
632 
633 	/* Sanity check addr, size. */
634 	end = (vaddr_t) ((char *)umd->md_addr + umd->md_size);
635 
636 	if (
637 #ifndef _RUMPKERNEL
638 	    /*
639 	     * On some architectures (e.g. powerpc) rump kernel provides
640 	     * "safe" low defaults which make this test fail since malloc
641 	     * does return higher addresses than the "safe" default.
642 	     */
643 	    (end >= VM_MAXUSER_ADDRESS) ||
644 #endif
645 	    (end < ((vaddr_t) umd->md_addr)))
646 		return EINVAL;
647 
648 	/* This unit is now configured. */
649 	sc->sc_addr = umd->md_addr; 	/* user space */
650 	sc->sc_size = umd->md_size;
651 	sc->sc_type = MD_UMEM_SERVER;
652 	md_set_disklabel(sc);
653 
654 	/* Become the server daemon */
655 	error = md_server_loop(sc);
656 
657 	/* This server is now going away! */
658 	sc->sc_type = MD_UNCONFIGURED;
659 	sc->sc_addr = 0;
660 	sc->sc_size = 0;
661 
662 	return (error);
663 }
664 
665 static int
666 md_server_loop(struct md_softc *sc)
667 {
668 	struct buf *bp;
669 	void *addr;	/* user space address */
670 	size_t off;	/* offset into "device" */
671 	size_t xfer;	/* amount to transfer */
672 	int error;
673 	bool is_read;
674 
675 	KASSERT(mutex_owned(&sc->sc_lock));
676 
677 	for (;;) {
678 		/* Wait for some work to arrive. */
679 		while ((bp = bufq_get(sc->sc_buflist)) == NULL) {
680 			error = cv_wait_sig(&sc->sc_cv, &sc->sc_lock);
681 			if (error)
682 				return error;
683 		}
684 
685 		/* Do the transfer to/from user space. */
686 		mutex_exit(&sc->sc_lock);
687 		error = 0;
688 		is_read = ((bp->b_flags & B_READ) == B_READ);
689 		bp->b_resid = bp->b_bcount;
690 		off = (bp->b_blkno << DEV_BSHIFT);
691 		if (off >= sc->sc_size) {
692 			if (is_read)
693 				goto done;	/* EOF (not an error) */
694 			error = EIO;
695 			goto done;
696 		}
697 		xfer = bp->b_resid;
698 		if (xfer > (sc->sc_size - off))
699 			xfer = (sc->sc_size - off);
700 		addr = (char *)sc->sc_addr + off;
701 		disk_busy(&sc->sc_dkdev);
702 		if (is_read)
703 			error = copyin(addr, bp->b_data, xfer);
704 		else
705 			error = copyout(bp->b_data, addr, xfer);
706 		disk_unbusy(&sc->sc_dkdev, (error ? 0 : xfer), is_read);
707 		if (!error)
708 			bp->b_resid -= xfer;
709 
710 	done:
711 		if (error) {
712 			bp->b_error = error;
713 		}
714 		biodone(bp);
715 		mutex_enter(&sc->sc_lock);
716 	}
717 }
718 #endif	/* MEMORY_DISK_SERVER */
719