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33 * @(#)spec_vnops.c 8.14 (Berkeley) 5/21/95
34 * $FreeBSD: src/sys/miscfs/specfs/spec_vnops.c,v 1.131.2.4 2001/02/26 04:23:20 jlemon Exp $
35 * $DragonFly: src/sys/vfs/specfs/spec_vnops.c,v 1.56 2007/08/21 17:26:48 dillon Exp $
38 #include <sys/param.h>
40 #include <sys/systm.h>
41 #include <sys/kernel.h>
44 #include <sys/device.h>
45 #include <sys/mount.h>
46 #include <sys/vnode.h>
48 #include <sys/fcntl.h>
49 #include <sys/vmmeter.h>
54 #include <vm/vm_object.h>
55 #include <vm/vm_page.h>
56 #include <vm/vm_pager.h>
58 #include <machine/limits.h>
62 #include <sys/thread2.h>
65 * Specfs chained debugging (bitmask)
67 * 0 - disable debugging
68 * 1 - report chained I/Os
69 * 2 - force 4K chained I/Os
71 #define SPEC_CHAIN_DEBUG 0
73 static int spec_advlock (struct vop_advlock_args *);
74 static int spec_bmap (struct vop_bmap_args *);
75 static int spec_close (struct vop_close_args *);
76 static int spec_freeblks (struct vop_freeblks_args *);
77 static int spec_fsync (struct vop_fsync_args *);
78 static int spec_getpages (struct vop_getpages_args *);
79 static int spec_inactive (struct vop_inactive_args *);
80 static int spec_ioctl (struct vop_ioctl_args *);
81 static int spec_open (struct vop_open_args *);
82 static int spec_poll (struct vop_poll_args *);
83 static int spec_kqfilter (struct vop_kqfilter_args *);
84 static int spec_print (struct vop_print_args *);
85 static int spec_read (struct vop_read_args *);
86 static int spec_strategy (struct vop_strategy_args *);
87 static int spec_write (struct vop_write_args *);
88 static void spec_strategy_done(struct bio *nbio);
90 struct vop_ops spec_vnode_vops = {
91 .vop_default = vop_defaultop,
92 .vop_access = (void *)vop_ebadf,
93 .vop_advlock = spec_advlock,
94 .vop_bmap = spec_bmap,
95 .vop_close = spec_close,
96 .vop_old_create = (void *)vop_panic,
97 .vop_freeblks = spec_freeblks,
98 .vop_fsync = spec_fsync,
99 .vop_getpages = spec_getpages,
100 .vop_inactive = spec_inactive,
101 .vop_ioctl = spec_ioctl,
102 .vop_old_link = (void *)vop_panic,
103 .vop_old_mkdir = (void *)vop_panic,
104 .vop_old_mknod = (void *)vop_panic,
105 .vop_open = spec_open,
106 .vop_pathconf = vop_stdpathconf,
107 .vop_poll = spec_poll,
108 .vop_kqfilter = spec_kqfilter,
109 .vop_print = spec_print,
110 .vop_read = spec_read,
111 .vop_readdir = (void *)vop_panic,
112 .vop_readlink = (void *)vop_panic,
113 .vop_reallocblks = (void *)vop_panic,
114 .vop_reclaim = (void *)vop_null,
115 .vop_old_remove = (void *)vop_panic,
116 .vop_old_rename = (void *)vop_panic,
117 .vop_old_rmdir = (void *)vop_panic,
118 .vop_setattr = (void *)vop_ebadf,
119 .vop_strategy = spec_strategy,
120 .vop_old_symlink = (void *)vop_panic,
121 .vop_write = spec_write
124 struct vop_ops *spec_vnode_vops_p = &spec_vnode_vops;
126 VNODEOP_SET(spec_vnode_vops);
128 extern int dev_ref_debug;
134 spec_vnoperate(struct vop_generic_args *ap)
136 return (VOCALL(&spec_vnode_vops, ap));
139 static void spec_getpages_iodone (struct bio *bio);
142 * Open a special file.
144 * spec_open(struct vnode *a_vp, int a_mode, struct ucred *a_cred,
149 spec_open(struct vop_open_args *ap)
151 struct vnode *vp = ap->a_vp;
157 * Don't allow open if fs is mounted -nodev.
159 if (vp->v_mount && (vp->v_mount->mnt_flag & MNT_NODEV))
161 if (vp->v_type == VBLK)
165 * Resolve the device. If the vnode is already open v_rdev may
166 * already be resolved. However, if the device changes out from
167 * under us we report it (and, for now, we allow it). Since
168 * v_release_rdev() zero's v_opencount, we have to save and restore
169 * it when replacing the rdev reference.
171 if (vp->v_rdev != NULL) {
172 dev = get_dev(vp->v_umajor, vp->v_uminor);
173 if (dev != vp->v_rdev) {
174 int oc = vp->v_opencount;
176 "Warning: spec_open: dev %s was lost",
177 vp->v_rdev->si_name);
179 error = v_associate_rdev(vp,
180 get_dev(vp->v_umajor, vp->v_uminor));
182 kprintf(", reacquisition failed\n");
184 vp->v_opencount = oc;
185 kprintf(", reacquisition successful\n");
191 error = v_associate_rdev(vp, get_dev(vp->v_umajor, vp->v_uminor));
197 * Prevent degenerate open/close sequences from nulling out rdev.
200 KKASSERT(dev != NULL);
203 * Make this field valid before any I/O in ->d_open. XXX the
204 * device itself should probably be required to initialize
205 * this field in d_open.
207 if (!dev->si_iosize_max)
208 dev->si_iosize_max = DFLTPHYS;
211 * XXX: Disks get special billing here, but it is mostly wrong.
212 * XXX: diskpartitions can overlap and the real checks should
213 * XXX: take this into account, and consequently they need to
214 * XXX: live in the diskslicing code. Some checks do.
216 if (vn_isdisk(vp, NULL) && ap->a_cred != FSCRED &&
217 (ap->a_mode & FWRITE)) {
219 * Never allow opens for write if the device is mounted R/W
221 if (vp->v_rdev && vp->v_rdev->si_mountpoint &&
222 !(vp->v_rdev->si_mountpoint->mnt_flag & MNT_RDONLY)) {
228 * When running in secure mode, do not allow opens
229 * for writing if the device is mounted
231 if (securelevel >= 1 && vfs_mountedon(vp)) {
237 * When running in very secure mode, do not allow
238 * opens for writing of any devices.
240 if (securelevel >= 2) {
246 /* XXX: Special casing of ttys for deadfs. Probably redundant */
247 if (dev_dflags(dev) & D_TTY)
248 vp->v_flag |= VISTTY;
251 * dev_dopen() is always called for each open. dev_dclose() is
252 * only called for the last close unless D_TRACKCLOSE is set.
255 error = dev_dopen(dev, ap->a_mode, S_IFCHR, ap->a_cred);
256 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
261 if (dev_dflags(dev) & D_TTY) {
266 kprintf("Warning:%s: no t_stop, using nottystop\n", devtoname(dev));
267 tp->t_stop = nottystop;
273 * If this is 'disk' or disk-like device, associate a VM object
276 if (vn_isdisk(vp, NULL)) {
277 if (!dev->si_bsize_phys)
278 dev->si_bsize_phys = DEV_BSIZE;
279 vinitvmio(vp, IDX_TO_OFF(INT_MAX));
281 if ((dev_dflags(dev) & D_DISK) == 0) {
284 kprintf("WARNING: driver %s should register devices with make_dev() (cdev_t = \"%s\")\n",
290 * If we were handed a file pointer we may be able to install a
291 * shortcut which issues device read and write operations directly
292 * from the fileops rather then having to go through spec_read()
296 vn_setspecops(ap->a_fp);
299 kprintf("spec_open: %s %d\n", dev->si_name, vp->v_opencount);
302 if (vp->v_opencount == 0)
313 * spec_read(struct vnode *a_vp, struct uio *a_uio, int a_ioflag,
314 * struct ucred *a_cred)
318 spec_read(struct vop_read_args *ap)
331 if (dev == NULL) /* device was revoked */
333 if (uio->uio_resid == 0)
337 error = dev_dread(dev, uio, ap->a_ioflag);
338 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
345 * spec_write(struct vnode *a_vp, struct uio *a_uio, int a_ioflag,
346 * struct ucred *a_cred)
350 spec_write(struct vop_write_args *ap)
363 KKASSERT(uio->uio_segflg != UIO_NOCOPY);
365 if (dev == NULL) /* device was revoked */
369 error = dev_dwrite(dev, uio, ap->a_ioflag);
370 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
375 * Device ioctl operation.
377 * spec_ioctl(struct vnode *a_vp, int a_command, caddr_t a_data,
378 * int a_fflag, struct ucred *a_cred)
382 spec_ioctl(struct vop_ioctl_args *ap)
386 if ((dev = ap->a_vp->v_rdev) == NULL)
387 return (EBADF); /* device was revoked */
389 return (dev_dioctl(dev, ap->a_command, ap->a_data,
390 ap->a_fflag, ap->a_cred));
394 * spec_poll(struct vnode *a_vp, int a_events, struct ucred *a_cred)
398 spec_poll(struct vop_poll_args *ap)
402 if ((dev = ap->a_vp->v_rdev) == NULL)
403 return (EBADF); /* device was revoked */
404 return (dev_dpoll(dev, ap->a_events));
408 * spec_kqfilter(struct vnode *a_vp, struct knote *a_kn)
412 spec_kqfilter(struct vop_kqfilter_args *ap)
416 if ((dev = ap->a_vp->v_rdev) == NULL)
417 return (EBADF); /* device was revoked */
418 return (dev_dkqfilter(dev, ap->a_kn));
422 * Synch buffers associated with a block device
424 * spec_fsync(struct vnode *a_vp, int a_waitfor)
428 spec_fsync(struct vop_fsync_args *ap)
430 struct vnode *vp = ap->a_vp;
433 if (!vn_isdisk(vp, NULL))
437 * Flush all dirty buffers associated with a block device.
439 error = vfsync(vp, ap->a_waitfor, 10000, NULL, NULL);
444 * spec_inactive(struct vnode *a_vp)
447 spec_inactive(struct vop_inactive_args *ap)
453 * Convert a vnode strategy call into a device strategy call. Vnode strategy
454 * calls are not limited to device DMA limits so we have to deal with the
457 * spec_strategy(struct vnode *a_vp, struct bio *a_bio)
460 spec_strategy(struct vop_strategy_args *ap)
462 struct bio *bio = ap->a_bio;
463 struct buf *bp = bio->bio_buf;
470 if (bp->b_cmd != BUF_CMD_READ &&
471 (LIST_FIRST(&bp->b_dep)) != NULL && bioops.io_start) {
472 (*bioops.io_start)(bp);
476 * Collect statistics on synchronous and asynchronous read
477 * and write counts for disks that have associated filesystems.
480 KKASSERT(vp->v_rdev != NULL); /* XXX */
481 if (vn_isdisk(vp, NULL) && (mp = vp->v_rdev->si_mountpoint) != NULL) {
482 if (bp->b_cmd == BUF_CMD_READ) {
483 if (bp->b_flags & B_ASYNC)
484 mp->mnt_stat.f_asyncreads++;
486 mp->mnt_stat.f_syncreads++;
488 if (bp->b_flags & B_ASYNC)
489 mp->mnt_stat.f_asyncwrites++;
491 mp->mnt_stat.f_syncwrites++;
496 * Device iosize limitations only apply to read and write. Shortcut
497 * the I/O if it fits.
499 if ((maxiosize = vp->v_rdev->si_iosize_max) == 0) {
500 kprintf("%s: si_iosize_max not set!\n", dev_dname(vp->v_rdev));
503 #if SPEC_CHAIN_DEBUG & 2
506 if (bp->b_bcount <= maxiosize ||
507 (bp->b_cmd != BUF_CMD_READ && bp->b_cmd != BUF_CMD_WRITE)) {
508 dev_dstrategy_chain(vp->v_rdev, bio);
513 * Clone the buffer and set up an I/O chain to chunk up the I/O.
515 nbp = kmalloc(sizeof(*bp), M_DEVBUF, M_INTWAIT|M_ZERO);
517 LIST_INIT(&nbp->b_dep);
519 BUF_LOCK(nbp, LK_EXCLUSIVE);
522 nbp->b_flags = B_PAGING | (bp->b_flags & B_BNOCLIP);
523 nbp->b_data = bp->b_data;
524 nbp->b_bio1.bio_done = spec_strategy_done;
525 nbp->b_bio1.bio_offset = bio->bio_offset;
526 nbp->b_bio1.bio_caller_info1.ptr = bio;
529 * Start the first transfer
531 if (vn_isdisk(vp, NULL))
532 chunksize = vp->v_rdev->si_bsize_phys;
534 chunksize = DEV_BSIZE;
535 chunksize = maxiosize / chunksize * chunksize;
536 #if SPEC_CHAIN_DEBUG & 1
537 kprintf("spec_strategy chained I/O chunksize=%d\n", chunksize);
539 nbp->b_cmd = bp->b_cmd;
540 nbp->b_bcount = chunksize;
541 nbp->b_bufsize = chunksize; /* used to detect a short I/O */
542 nbp->b_bio1.bio_caller_info2.index = chunksize;
544 #if SPEC_CHAIN_DEBUG & 1
545 kprintf("spec_strategy: chain %p offset %d/%d bcount %d\n",
546 bp, 0, bp->b_bcount, nbp->b_bcount);
549 dev_dstrategy(vp->v_rdev, &nbp->b_bio1);
554 * Chunked up transfer completion routine - chain transfers until done
558 spec_strategy_done(struct bio *nbio)
560 struct buf *nbp = nbio->bio_buf;
561 struct bio *bio = nbio->bio_caller_info1.ptr; /* original bio */
562 struct buf *bp = bio->bio_buf; /* original bp */
563 int chunksize = nbio->bio_caller_info2.index; /* chunking */
564 int boffset = nbp->b_data - bp->b_data;
566 if (nbp->b_flags & B_ERROR) {
568 * An error terminates the chain, propogate the error back
571 bp->b_flags |= B_ERROR;
572 bp->b_error = nbp->b_error;
573 bp->b_resid = bp->b_bcount - boffset +
574 (nbp->b_bcount - nbp->b_resid);
575 #if SPEC_CHAIN_DEBUG & 1
576 kprintf("spec_strategy: chain %p error %d bcount %d/%d\n",
577 bp, bp->b_error, bp->b_bcount,
578 bp->b_bcount - bp->b_resid);
580 kfree(nbp, M_DEVBUF);
582 } else if (nbp->b_resid) {
584 * A short read or write terminates the chain
586 bp->b_error = nbp->b_error;
587 bp->b_resid = bp->b_bcount - boffset +
588 (nbp->b_bcount - nbp->b_resid);
589 #if SPEC_CHAIN_DEBUG & 1
590 kprintf("spec_strategy: chain %p short read(1) bcount %d/%d\n",
591 bp, bp->b_bcount - bp->b_resid, bp->b_bcount);
593 kfree(nbp, M_DEVBUF);
595 } else if (nbp->b_bcount != nbp->b_bufsize) {
597 * A short read or write can also occur by truncating b_bcount
599 #if SPEC_CHAIN_DEBUG & 1
600 kprintf("spec_strategy: chain %p short read(2) bcount %d/%d\n",
601 bp, nbp->b_bcount + boffset, bp->b_bcount);
604 bp->b_bcount = nbp->b_bcount + boffset;
605 bp->b_resid = nbp->b_resid;
606 kfree(nbp, M_DEVBUF);
608 } else if (nbp->b_bcount + boffset == bp->b_bcount) {
610 * No more data terminates the chain
612 #if SPEC_CHAIN_DEBUG & 1
613 kprintf("spec_strategy: chain %p finished bcount %d\n",
618 kfree(nbp, M_DEVBUF);
624 boffset += nbp->b_bcount;
625 nbp->b_data = bp->b_data + boffset;
626 nbp->b_bcount = bp->b_bcount - boffset;
627 if (nbp->b_bcount > chunksize)
628 nbp->b_bcount = chunksize;
629 nbp->b_bio1.bio_done = spec_strategy_done;
630 nbp->b_bio1.bio_offset = bio->bio_offset + boffset;
632 #if SPEC_CHAIN_DEBUG & 1
633 kprintf("spec_strategy: chain %p offset %d/%d bcount %d\n",
634 bp, boffset, bp->b_bcount, nbp->b_bcount);
637 dev_dstrategy(nbp->b_vp->v_rdev, &nbp->b_bio1);
642 * spec_freeblks(struct vnode *a_vp, daddr_t a_addr, daddr_t a_length)
645 spec_freeblks(struct vop_freeblks_args *ap)
650 * XXX: This assumes that strategy does the deed right away.
651 * XXX: this may not be TRTTD.
653 KKASSERT(ap->a_vp->v_rdev != NULL);
654 if ((dev_dflags(ap->a_vp->v_rdev) & D_CANFREE) == 0)
656 bp = geteblk(ap->a_length);
657 bp->b_cmd = BUF_CMD_FREEBLKS;
658 bp->b_bio1.bio_offset = ap->a_offset;
659 bp->b_bcount = ap->a_length;
660 dev_dstrategy(ap->a_vp->v_rdev, &bp->b_bio1);
665 * Implement degenerate case where the block requested is the block
666 * returned, and assume that the entire device is contiguous in regards
667 * to the contiguous block range (runp and runb).
669 * spec_bmap(struct vnode *a_vp, off_t a_loffset,
670 * off_t *a_doffsetp, int *a_runp, int *a_runb)
673 spec_bmap(struct vop_bmap_args *ap)
675 if (ap->a_doffsetp != NULL)
676 *ap->a_doffsetp = ap->a_loffset;
677 if (ap->a_runp != NULL)
678 *ap->a_runp = MAXBSIZE;
679 if (ap->a_runb != NULL) {
680 if (ap->a_loffset < MAXBSIZE)
681 *ap->a_runb = (int)ap->a_loffset;
683 *ap->a_runb = MAXBSIZE;
689 * Device close routine
691 * spec_close(struct vnode *a_vp, int a_fflag)
693 * NOTE: the vnode may or may not be locked on call.
697 spec_close(struct vop_close_args *ap)
699 struct proc *p = curproc;
700 struct vnode *vp = ap->a_vp;
701 cdev_t dev = vp->v_rdev;
706 * Hack: a tty device that is a controlling terminal
707 * has a reference from the session structure.
708 * We cannot easily tell that a character device is
709 * a controlling terminal, unless it is the closing
710 * process' controlling terminal. In that case,
711 * if the reference count is 2 (this last descriptor
712 * plus the session), release the reference from the session.
714 * It is possible for v_opencount to be 0 or 1 in this case, 0
715 * because the tty might have been revoked.
719 if (vcount(vp) == 2 && vp->v_opencount <= 1 &&
720 p && vp == p->p_session->s_ttyvp) {
721 p->p_session->s_ttyvp = NULL;
726 * Vnodes can be opened and close multiple times. Do not really
727 * close the device unless (1) it is being closed forcibly,
728 * (2) the device wants to track closes, or (3) this is the last
729 * vnode doing its last close on the device.
731 * XXX the VXLOCK (force close) case can leave vnodes referencing
734 if (dev && ((vp->v_flag & VRECLAIMED) ||
735 (dev_dflags(dev) & D_TRACKCLOSE) ||
736 (vcount(vp) <= 1 && vp->v_opencount == 1))) {
738 if (vn_islocked(vp)) {
742 error = dev_dclose(dev, ap->a_fflag, S_IFCHR);
744 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
750 * Track the actual opens and closes on the vnode. The last close
751 * disassociates the rdev. If the rdev is already disassociated
752 * the vnode might have been revoked and no further opencount
756 /*KKASSERT(vp->v_opencount > 0);*/
758 kprintf("spec_close: %s %d\n",
759 dev->si_name, vp->v_opencount - 1);
761 if (vp->v_opencount == 1)
770 * Print out the contents of a special device vnode.
772 * spec_print(struct vnode *a_vp)
775 spec_print(struct vop_print_args *ap)
777 kprintf("tag VT_NON, dev %s\n", devtoname(ap->a_vp->v_rdev));
782 * Special device advisory byte-level locks.
784 * spec_advlock(struct vnode *a_vp, caddr_t a_id, int a_op,
785 * struct flock *a_fl, int a_flags)
789 spec_advlock(struct vop_advlock_args *ap)
791 return ((ap->a_flags & F_POSIX) ? EINVAL : EOPNOTSUPP);
795 spec_getpages_iodone(struct bio *bio)
797 bio->bio_buf->b_cmd = BUF_CMD_DONE;
798 wakeup(bio->bio_buf);
802 * spec_getpages() - get pages associated with device vnode.
804 * Note that spec_read and spec_write do not use the buffer cache, so we
805 * must fully implement getpages here.
808 spec_getpages(struct vop_getpages_args *ap)
816 int toff, nextoff, nread;
817 struct vnode *vp = ap->a_vp;
822 pcount = round_page(ap->a_count) / PAGE_SIZE;
825 * Calculate the offset of the transfer and do sanity check.
827 offset = IDX_TO_OFF(ap->a_m[0]->pindex) + ap->a_offset;
830 * Round up physical size for real devices. We cannot round using
831 * v_mount's block size data because v_mount has nothing to do with
832 * the device. i.e. it's usually '/dev'. We need the physical block
833 * size for the device itself.
835 * We can't use v_rdev->si_mountpoint because it only exists when the
836 * block device is mounted. However, we can use v_rdev.
839 if (vn_isdisk(vp, NULL))
840 blksiz = vp->v_rdev->si_bsize_phys;
844 size = (ap->a_count + blksiz - 1) & ~(blksiz - 1);
847 kva = (vm_offset_t)bp->b_data;
850 * Map the pages to be read into the kva.
852 pmap_qenter(kva, ap->a_m, pcount);
854 /* Build a minimal buffer header. */
855 bp->b_cmd = BUF_CMD_READ;
858 bp->b_runningbufspace = size;
859 runningbufspace += bp->b_runningbufspace;
861 bp->b_bio1.bio_offset = offset;
862 bp->b_bio1.bio_done = spec_getpages_iodone;
864 mycpu->gd_cnt.v_vnodein++;
865 mycpu->gd_cnt.v_vnodepgsin += pcount;
868 vn_strategy(ap->a_vp, &bp->b_bio1);
872 /* We definitely need to be at splbio here. */
873 while (bp->b_cmd != BUF_CMD_DONE)
874 tsleep(bp, 0, "spread", 0);
878 if (bp->b_flags & B_ERROR) {
886 * If EOF is encountered we must zero-extend the result in order
887 * to ensure that the page does not contain garabge. When no
888 * error occurs, an early EOF is indicated if b_bcount got truncated.
889 * b_resid is relative to b_bcount and should be 0, but some devices
890 * might indicate an EOF with b_resid instead of truncating b_bcount.
892 nread = bp->b_bcount - bp->b_resid;
893 if (nread < ap->a_count)
894 bzero((caddr_t)kva + nread, ap->a_count - nread);
895 pmap_qremove(kva, pcount);
898 for (i = 0, toff = 0; i < pcount; i++, toff = nextoff) {
899 nextoff = toff + PAGE_SIZE;
902 m->flags &= ~PG_ZERO;
904 if (nextoff <= nread) {
905 m->valid = VM_PAGE_BITS_ALL;
907 } else if (toff < nread) {
909 * Since this is a VM request, we have to supply the
910 * unaligned offset to allow vm_page_set_validclean()
911 * to zero sub-DEV_BSIZE'd portions of the page.
913 vm_page_set_validclean(m, 0, nread - toff);
919 if (i != ap->a_reqpage) {
921 * Just in case someone was asking for this page we
922 * now tell them that it is ok to use.
924 if (!error || (m->valid == VM_PAGE_BITS_ALL)) {
926 if (m->flags & PG_WANTED) {
929 vm_page_deactivate(m);
938 } else if (m->valid) {
941 * Since this is a VM request, we need to make the
942 * entire page presentable by zeroing invalid sections.
944 if (m->valid != VM_PAGE_BITS_ALL)
945 vm_page_zero_invalid(m, FALSE);
949 m = ap->a_m[ap->a_reqpage];
951 "spec_getpages:(%s) I/O read failure: (error=%d) bp %p vp %p\n",
952 devtoname(vp->v_rdev), error, bp, bp->b_vp);
954 " size: %d, resid: %d, a_count: %d, valid: 0x%x\n",
955 size, bp->b_resid, ap->a_count, m->valid);
957 " nread: %d, reqpage: %d, pindex: %lu, pcount: %d\n",
958 nread, ap->a_reqpage, (u_long)m->pindex, pcount);
960 * Free the buffer header back to the swap buffer pool.
963 return VM_PAGER_ERROR;
966 * Free the buffer header back to the swap buffer pool.