File:  [DragonFly] / src / sys / vfs / ufs / ufs_readwrite.c
Revision 1.10: download - view: text, annotated - select for diffs
Fri Apr 23 06:23:46 2004 UTC (9 years, 11 months ago) by dillon
Branches: MAIN
CVS tags: HEAD
msync(..., MS_INVALIDATE) will incorrectly remove dirty pages without
synchronizing them to their backing store under certain circumstances,
and can also cause struct buf's to become inconsistent.  This can be
particularly gruesome when MS_INVALIDATE is used on a range of memory that
is mmap()'d to be read-only.

Fix MS_INVALIDATE's operation (1) by making UFS honor the invalidation
request when flushing to backing store to destroy the related struct buf
and (2) by never removing pages wired into the buffer cache and never
removing pages that are found to still be dirty.

Note that NFS was already coded to honor invalidation requests in
nfs_write().  Filesystems other then NFS and UFS do not currently support
buffer-invalidation-on-write but all that means now is that the pages
will remain in cache, rather then be incorrectly removed and cause corruption.

Reported-by: Stephan Uphoff <ups@tree.com>, Julian Elischer <julian@elischer.org>

/*-
 * Copyright (c) 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)ufs_readwrite.c	8.11 (Berkeley) 5/8/95
 * $FreeBSD: src/sys/ufs/ufs/ufs_readwrite.c,v 1.65.2.14 2003/04/04 22:21:29 tegge Exp $
 * $DragonFly: src/sys/vfs/ufs/ufs_readwrite.c,v 1.10 2004/04/23 06:23:46 dillon Exp $
 */

#define	BLKSIZE(a, b, c)	blksize(a, b, c)
#define	FS			struct fs
#define	I_FS			i_fs

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_pager.h>
#include <vm/vm_map.h>
#include <vm/vnode_pager.h>
#include <sys/event.h>
#include <sys/vmmeter.h>
#include <vm/vm_page2.h>

#include "opt_directio.h"

#define VN_KNOTE(vp, b) \
	KNOTE((struct klist *)&vp->v_pollinfo.vpi_selinfo.si_note, (b))

#ifdef DIRECTIO
extern int ffs_rawread(struct vnode *vp, struct uio *uio, int *workdone);
#endif

/*
 * Vnode op for reading.
 */
/* ARGSUSED */
int
ffs_read(ap)
	struct vop_read_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int a_ioflag;
		struct ucred *a_cred;
	} */ *ap;
{
	struct vnode *vp;
	struct inode *ip;
	struct uio *uio;
	FS *fs;
	struct buf *bp;
	ufs_daddr_t lbn, nextlbn;
	off_t bytesinfile;
	long size, xfersize, blkoffset;
	int error, orig_resid;
	u_short mode;
	int seqcount;
	int ioflag;
	vm_object_t object;

	vp = ap->a_vp;
	seqcount = ap->a_ioflag >> 16;
	ip = VTOI(vp);
	mode = ip->i_mode;
	uio = ap->a_uio;
	ioflag = ap->a_ioflag;
#ifdef DIRECTIO
	if ((ioflag & IO_DIRECT) != 0) {
		int workdone;

		error = ffs_rawread(vp, uio, &workdone);
		if (error || workdone)
			return error;
	}
#endif

#ifdef DIAGNOSTIC
	if (uio->uio_rw != UIO_READ)
		panic("ffs_read: mode");

	if (vp->v_type == VLNK) {
		if ((int)ip->i_size < vp->v_mount->mnt_maxsymlinklen)
			panic("ffs_read: short symlink");
	} else if (vp->v_type != VREG && vp->v_type != VDIR)
		panic("ffs_read: type %d", vp->v_type);
#endif
	fs = ip->I_FS;
	if ((u_int64_t)uio->uio_offset > fs->fs_maxfilesize)
		return (EFBIG);

	orig_resid = uio->uio_resid;
	if (orig_resid <= 0)
		return (0);

	object = vp->v_object;

	bytesinfile = ip->i_size - uio->uio_offset;
	if (bytesinfile <= 0) {
		if ((vp->v_mount->mnt_flag & MNT_NOATIME) == 0)
			ip->i_flag |= IN_ACCESS;
		return 0;
	}

	if (object)
		vm_object_reference(object);

#ifdef ENABLE_VFS_IOOPT
	/*
	 * If IO optimisation is turned on,
	 * and we are NOT a VM based IO request, 
	 * (i.e. not headed for the buffer cache)
	 * but there IS a vm object associated with it.
	 */
	if ((ioflag & IO_VMIO) == 0 && (vfs_ioopt > 1) && object) {
		int nread, toread;

		toread = uio->uio_resid;
		if (toread > bytesinfile)
			toread = bytesinfile;
		if (toread >= PAGE_SIZE) {
			/*
			 * Then if it's at least a page in size, try 
			 * get the data from the object using vm tricks
			 */
			error = uioread(toread, uio, object, &nread);
			if ((uio->uio_resid == 0) || (error != 0)) {
				/*
				 * If we finished or there was an error
				 * then finish up (the reference previously
				 * obtained on object must be released).
				 */
				if ((error == 0 ||
				    uio->uio_resid != orig_resid) &&
				    (vp->v_mount->mnt_flag & MNT_NOATIME) == 0)
					ip->i_flag |= IN_ACCESS;

				if (object)
					vm_object_vndeallocate(object);
				return error;
			}
		}
	}
#endif

	/*
	 * Ok so we couldn't do it all in one vm trick...
	 * so cycle around trying smaller bites..
	 */
	for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
		if ((bytesinfile = ip->i_size - uio->uio_offset) <= 0)
			break;
#ifdef ENABLE_VFS_IOOPT
		if ((ioflag & IO_VMIO) == 0 && (vfs_ioopt > 1) && object) {
			/*
			 * Obviously we didn't finish above, but we
			 * didn't get an error either. Try the same trick again.
			 * but this time we are looping.
			 */
			int nread, toread;
			toread = uio->uio_resid;
			if (toread > bytesinfile)
				toread = bytesinfile;

			/*
			 * Once again, if there isn't enough for a
			 * whole page, don't try optimising.
			 */
			if (toread >= PAGE_SIZE) {
				error = uioread(toread, uio, object, &nread);
				if ((uio->uio_resid == 0) || (error != 0)) {
					/*
					 * If we finished or there was an 
					 * error then finish up (the reference
					 * previously obtained on object must 
					 * be released).
					 */
					if ((error == 0 ||
					    uio->uio_resid != orig_resid) &&
					    (vp->v_mount->mnt_flag &
					    MNT_NOATIME) == 0)
						ip->i_flag |= IN_ACCESS;
					if (object)
						vm_object_vndeallocate(object);
					return error;
				}
				/*
				 * To get here we didnt't finish or err.
				 * If we did get some data,
				 * loop to try another bite.
				 */
				if (nread > 0) {
					continue;
				}
			}
		}
#endif

		lbn = lblkno(fs, uio->uio_offset);
		nextlbn = lbn + 1;

		/*
		 * size of buffer.  The buffer representing the
		 * end of the file is rounded up to the size of
		 * the block type ( fragment or full block, 
		 * depending ).
		 */
		size = BLKSIZE(fs, ip, lbn);
		blkoffset = blkoff(fs, uio->uio_offset);
		
		/*
		 * The amount we want to transfer in this iteration is
		 * one FS block less the amount of the data before
		 * our startpoint (duh!)
		 */
		xfersize = fs->fs_bsize - blkoffset;

		/*
		 * But if we actually want less than the block,
		 * or the file doesn't have a whole block more of data,
		 * then use the lesser number.
		 */
		if (uio->uio_resid < xfersize)
			xfersize = uio->uio_resid;
		if (bytesinfile < xfersize)
			xfersize = bytesinfile;

		if (lblktosize(fs, nextlbn) >= ip->i_size) {
			/*
			 * Don't do readahead if this is the end of the file.
			 */
			error = bread(vp, lbn, size, &bp);
		} else if ((vp->v_mount->mnt_flag & MNT_NOCLUSTERR) == 0) {
			/* 
			 * Otherwise if we are allowed to cluster,
			 * grab as much as we can.
			 *
			 * XXX  This may not be a win if we are not
			 * doing sequential access.
			 */
			error = cluster_read(vp, ip->i_size, lbn,
				size, uio->uio_resid, seqcount, &bp);
		} else if (seqcount > 1) {
			/*
			 * If we are NOT allowed to cluster, then
			 * if we appear to be acting sequentially,
			 * fire off a request for a readahead
			 * as well as a read. Note that the 4th and 5th
			 * arguments point to arrays of the size specified in
			 * the 6th argument.
			 */
			int nextsize = BLKSIZE(fs, ip, nextlbn);
			error = breadn(vp, lbn,
			    size, &nextlbn, &nextsize, 1, &bp);
		} else {
			/*
			 * Failing all of the above, just read what the 
			 * user asked for. Interestingly, the same as
			 * the first option above.
			 */
			error = bread(vp, lbn, size, &bp);
		}
		if (error) {
			brelse(bp);
			bp = NULL;
			break;
		}

		/*
		 * If IO_DIRECT then set B_DIRECT for the buffer.  This
		 * will cause us to attempt to release the buffer later on
		 * and will cause the buffer cache to attempt to free the
		 * underlying pages.
		 */
		if (ioflag & IO_DIRECT)
			bp->b_flags |= B_DIRECT;

		/*
		 * We should only get non-zero b_resid when an I/O error
		 * has occurred, which should cause us to break above.
		 * However, if the short read did not cause an error,
		 * then we want to ensure that we do not uiomove bad
		 * or uninitialized data.
		 *
		 * XXX b_resid is only valid when an actual I/O has occured
		 * and may be incorrect if the buffer is B_CACHE or if the
		 * last op on the buffer was a failed write.  This KASSERT
		 * is a precursor to removing it from the UFS code.
		 */
		KASSERT(bp->b_resid == 0, ("bp->b_resid != 0"));
		size -= bp->b_resid;
		if (size < xfersize) {
			if (size == 0)
				break;
			xfersize = size;
		}

#ifdef ENABLE_VFS_IOOPT
		if (vfs_ioopt && object &&
		    (bp->b_flags & B_VMIO) &&
		    ((blkoffset & PAGE_MASK) == 0) &&
		    ((xfersize & PAGE_MASK) == 0)) {
			/*
			 * If VFS IO  optimisation is turned on,
			 * and it's an exact page multiple
			 * And a normal VM based op,
			 * then use uiomiveco()
			 */
			error =
				uiomoveco((char *)bp->b_data + blkoffset,
					(int)xfersize, uio, object);
		} else 
#endif
		{
			/*
			 * otherwise use the general form
			 */
			error =
				uiomove((char *)bp->b_data + blkoffset,
					(int)xfersize, uio);
		}

		if (error)
			break;

		if ((ioflag & (IO_VMIO|IO_DIRECT)) && 
		    (LIST_FIRST(&bp->b_dep) == NULL)) {
			/*
			 * If there are no dependencies, and it's VMIO,
			 * then we don't need the buf, mark it available
			 * for freeing. The VM has the data.
			 */
			bp->b_flags |= B_RELBUF;
			brelse(bp);
		} else {
			/*
			 * Otherwise let whoever
			 * made the request take care of
			 * freeing it. We just queue
			 * it onto another list.
			 */
			bqrelse(bp);
		}
	}

	/* 
	 * This can only happen in the case of an error
	 * because the loop above resets bp to NULL on each iteration
	 * and on normal completion has not set a new value into it.
	 * so it must have come from a 'break' statement
	 */
	if (bp != NULL) {
		if ((ioflag & (IO_VMIO|IO_DIRECT)) && 
		    (LIST_FIRST(&bp->b_dep) == NULL)) {
			bp->b_flags |= B_RELBUF;
			brelse(bp);
		} else {
			bqrelse(bp);
		}
	}

	if (object)
		vm_object_vndeallocate(object);
	if ((error == 0 || uio->uio_resid != orig_resid) &&
	    (vp->v_mount->mnt_flag & MNT_NOATIME) == 0)
		ip->i_flag |= IN_ACCESS;
	return (error);
}

/*
 * Vnode op for writing.
 */
int
ffs_write(ap)
	struct vop_write_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int a_ioflag;
		struct ucred *a_cred;
	} */ *ap;
{
	struct vnode *vp;
	struct uio *uio;
	struct inode *ip;
	FS *fs;
	struct buf *bp;
	ufs_daddr_t lbn;
	off_t osize;
	int seqcount;
	int blkoffset, error, extended, flags, ioflag, resid, size, xfersize;
	vm_object_t object;
	struct thread *td;

	extended = 0;
	seqcount = ap->a_ioflag >> 16;
	ioflag = ap->a_ioflag;
	uio = ap->a_uio;
	vp = ap->a_vp;
	ip = VTOI(vp);

	object = vp->v_object;
	if (object)
		vm_object_reference(object);

#ifdef DIAGNOSTIC
	if (uio->uio_rw != UIO_WRITE)
		panic("ffs_write: mode");
#endif

	switch (vp->v_type) {
	case VREG:
		if (ioflag & IO_APPEND)
			uio->uio_offset = ip->i_size;
		if ((ip->i_flags & APPEND) && uio->uio_offset != ip->i_size) {
			if (object)
				vm_object_vndeallocate(object);
			return (EPERM);
		}
		/* FALLTHROUGH */
	case VLNK:
		break;
	case VDIR:
		panic("ffs_write: dir write");
		break;
	default:
		panic("ffs_write: type %p %d (%d,%d)", vp, (int)vp->v_type,
			(int)uio->uio_offset,
			(int)uio->uio_resid
		);
	}

	fs = ip->I_FS;
	if (uio->uio_offset < 0 ||
	    (u_int64_t)uio->uio_offset + uio->uio_resid > fs->fs_maxfilesize) {
		if (object)
			vm_object_vndeallocate(object);
		return (EFBIG);
	}
	/*
	 * Maybe this should be above the vnode op call, but so long as
	 * file servers have no limits, I don't think it matters.
	 */
	td = uio->uio_td;
	if (vp->v_type == VREG && td && td->td_proc &&
	    uio->uio_offset + uio->uio_resid >
	    td->td_proc->p_rlimit[RLIMIT_FSIZE].rlim_cur) {
		psignal(td->td_proc, SIGXFSZ);
		if (object)
			vm_object_vndeallocate(object);
		return (EFBIG);
	}

	resid = uio->uio_resid;
	osize = ip->i_size;

	/*
	 * NOTE! These B_ flags are actually balloc-only flags, not buffer
	 * flags.  They are similar to the BA_ flags in -current.
	 */
	if (seqcount > B_SEQMAX)
		flags = B_SEQMAX << B_SEQSHIFT;
	else
		flags = seqcount << B_SEQSHIFT;
	if ((ioflag & IO_SYNC) && !DOINGASYNC(vp))
		flags |= B_SYNC;

	if (object && (object->flags & OBJ_OPT)) {
		vm_freeze_copyopts(object,
			OFF_TO_IDX(uio->uio_offset),
			OFF_TO_IDX(uio->uio_offset + uio->uio_resid + PAGE_MASK));
	}

	for (error = 0; uio->uio_resid > 0;) {
		lbn = lblkno(fs, uio->uio_offset);
		blkoffset = blkoff(fs, uio->uio_offset);
		xfersize = fs->fs_bsize - blkoffset;
		if (uio->uio_resid < xfersize)
			xfersize = uio->uio_resid;

		if (uio->uio_offset + xfersize > ip->i_size)
			vnode_pager_setsize(vp, uio->uio_offset + xfersize);

		/*      
		 * We must perform a read-before-write if the transfer
		 * size does not cover the entire buffer.
		 */
		if (fs->fs_bsize > xfersize)
			flags |= B_CLRBUF;
		else
			flags &= ~B_CLRBUF;
/* XXX is uio->uio_offset the right thing here? */
		error = VOP_BALLOC(vp, uio->uio_offset, xfersize,
		    ap->a_cred, flags, &bp);
		if (error != 0)
			break;
		/*
		 * If the buffer is not valid and we did not clear garbage
		 * out above, we have to do so here even though the write
		 * covers the entire buffer in order to avoid a mmap()/write
		 * race where another process may see the garbage prior to
		 * the uiomove() for a write replacing it.
		 */
		if ((bp->b_flags & B_CACHE) == 0 && fs->fs_bsize <= xfersize)
			vfs_bio_clrbuf(bp);
		if (ioflag & IO_DIRECT)
			bp->b_flags |= B_DIRECT;
		if (ioflag & IO_NOWDRAIN)
			bp->b_flags |= B_NOWDRAIN;
		if ((ioflag & (IO_SYNC|IO_INVAL)) == (IO_SYNC|IO_INVAL))
			bp->b_flags |= B_NOCACHE;

		if (uio->uio_offset + xfersize > ip->i_size) {
			ip->i_size = uio->uio_offset + xfersize;
			extended = 1;
		}

		size = BLKSIZE(fs, ip, lbn) - bp->b_resid;
		if (size < xfersize)
			xfersize = size;

		error =
		    uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
		if ((ioflag & (IO_VMIO|IO_DIRECT)) && 
		    (LIST_FIRST(&bp->b_dep) == NULL)) {
			bp->b_flags |= B_RELBUF;
		}

		/*
		 * If IO_SYNC each buffer is written synchronously.  Otherwise
		 * if we have a severe page deficiency write the buffer 
		 * asynchronously.  Otherwise try to cluster, and if that
		 * doesn't do it then either do an async write (if O_DIRECT),
		 * or a delayed write (if not).
		 */

		if (ioflag & IO_SYNC) {
			(void)bwrite(bp);
		} else if (vm_page_count_severe() || 
			    buf_dirty_count_severe() ||
			    (ioflag & IO_ASYNC)) {
			bp->b_flags |= B_CLUSTEROK;
			bawrite(bp);
		} else if (xfersize + blkoffset == fs->fs_bsize) {
			if ((vp->v_mount->mnt_flag & MNT_NOCLUSTERW) == 0) {
				bp->b_flags |= B_CLUSTEROK;
				cluster_write(bp, ip->i_size, seqcount);
			} else {
				bawrite(bp);
			}
		} else if (ioflag & IO_DIRECT) {
			bp->b_flags |= B_CLUSTEROK;
			bawrite(bp);
		} else {
			bp->b_flags |= B_CLUSTEROK;
			bdwrite(bp);
		}
		if (error || xfersize == 0)
			break;
		ip->i_flag |= IN_CHANGE | IN_UPDATE;
	}
	/*
	 * If we successfully wrote any data, and we are not the superuser
	 * we clear the setuid and setgid bits as a precaution against
	 * tampering.
	 */
	if (resid > uio->uio_resid && ap->a_cred && ap->a_cred->cr_uid != 0)
		ip->i_mode &= ~(ISUID | ISGID);
	if (resid > uio->uio_resid)
		VN_KNOTE(vp, NOTE_WRITE | (extended ? NOTE_EXTEND : 0));
	if (error) {
		if (ioflag & IO_UNIT) {
			(void)UFS_TRUNCATE(vp, osize,
			    ioflag & IO_SYNC, ap->a_cred, uio->uio_td);
			uio->uio_offset -= resid - uio->uio_resid;
			uio->uio_resid = resid;
		}
	} else if (resid > uio->uio_resid && (ioflag & IO_SYNC))
		error = UFS_UPDATE(vp, 1);

	if (object)
		vm_object_vndeallocate(object);

	return (error);
}


/*
 * get page routine
 */
int
ffs_getpages(ap)
	struct vop_getpages_args *ap;
{
	off_t foff, physoffset;
	int i, size, bsize;
	struct vnode *dp, *vp;
	vm_object_t obj;
	vm_pindex_t pindex, firstindex;
	vm_page_t mreq;
	int bbackwards, bforwards;
	int pbackwards, pforwards;
	int firstpage;
	int reqlblkno;
	daddr_t reqblkno;
	int poff;
	int pcount;
	int rtval;
	int pagesperblock;


	pcount = round_page(ap->a_count) / PAGE_SIZE;
	mreq = ap->a_m[ap->a_reqpage];
	firstindex = ap->a_m[0]->pindex;

	/*
	 * if ANY DEV_BSIZE blocks are valid on a large filesystem block,
	 * then the entire page is valid.  Since the page may be mapped,
	 * user programs might reference data beyond the actual end of file
	 * occuring within the page.  We have to zero that data.
	 */
	if (mreq->valid) {
		if (mreq->valid != VM_PAGE_BITS_ALL)
			vm_page_zero_invalid(mreq, TRUE);
		for (i = 0; i < pcount; i++) {
			if (i != ap->a_reqpage) {
				vm_page_free(ap->a_m[i]);
			}
		}
		return VM_PAGER_OK;
	}

	vp = ap->a_vp;
	obj = vp->v_object;
	bsize = vp->v_mount->mnt_stat.f_iosize;
	pindex = mreq->pindex;
	foff = IDX_TO_OFF(pindex) /* + ap->a_offset should be zero */;

	if (bsize < PAGE_SIZE)
		return vnode_pager_generic_getpages(ap->a_vp, ap->a_m,
						    ap->a_count,
						    ap->a_reqpage);

	/*
	 * foff is the file offset of the required page
	 * reqlblkno is the logical block that contains the page
	 * poff is the index of the page into the logical block
	 */
	reqlblkno = foff / bsize;
	poff = (foff % bsize) / PAGE_SIZE;

	if ( VOP_BMAP( vp, reqlblkno, &dp, &reqblkno,
		&bforwards, &bbackwards) || (reqblkno == -1)) {
		for(i = 0; i < pcount; i++) {
			if (i != ap->a_reqpage)
				vm_page_free(ap->a_m[i]);
		}
		if (reqblkno == -1) {
			if ((mreq->flags & PG_ZERO) == 0)
				vm_page_zero_fill(mreq);
			vm_page_undirty(mreq);
			mreq->valid = VM_PAGE_BITS_ALL;
			return VM_PAGER_OK;
		} else {
			return VM_PAGER_ERROR;
		}
	}

	physoffset = (off_t)reqblkno * DEV_BSIZE + poff * PAGE_SIZE;
	pagesperblock = bsize / PAGE_SIZE;
	/*
	 * find the first page that is contiguous...
	 * note that pbackwards is the number of pages that are contiguous
	 * backwards.
	 */
	firstpage = 0;
	if (ap->a_count) {
		pbackwards = poff + bbackwards * pagesperblock;
		if (ap->a_reqpage > pbackwards) {
			firstpage = ap->a_reqpage - pbackwards;
			for(i=0;i<firstpage;i++)
				vm_page_free(ap->a_m[i]);
		}

	/*
	 * pforwards is the number of pages that are contiguous
	 * after the current page.
	 */
		pforwards = (pagesperblock - (poff + 1)) +
			bforwards * pagesperblock;
		if (pforwards < (pcount - (ap->a_reqpage + 1))) {
			for( i = ap->a_reqpage + pforwards + 1; i < pcount; i++)
				vm_page_free(ap->a_m[i]);
			pcount = ap->a_reqpage + pforwards + 1;
		}

	/*
	 * number of pages for I/O corrected for the non-contig pages at
	 * the beginning of the array.
	 */
		pcount -= firstpage;
	}

	/*
	 * calculate the size of the transfer
	 */

	size = pcount * PAGE_SIZE;

	if ((IDX_TO_OFF(ap->a_m[firstpage]->pindex) + size) >
		obj->un_pager.vnp.vnp_size)
		size = obj->un_pager.vnp.vnp_size -
			IDX_TO_OFF(ap->a_m[firstpage]->pindex);

	physoffset -= foff;
	rtval = VOP_GETPAGES(dp, &ap->a_m[firstpage], size,
		(ap->a_reqpage - firstpage), physoffset);

	return (rtval);
}

/*
 * put page routine
 *
 * XXX By default, wimp out... note that a_offset is ignored (and always
 * XXX has been).
 */
int
ffs_putpages(ap)
	struct vop_putpages_args *ap;
{
	return vnode_pager_generic_putpages(ap->a_vp, ap->a_m, ap->a_count,
		ap->a_sync, ap->a_rtvals);
}