sys/nfsclient/nfs_bio.c

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Rick Macklem at The University of Guelph.
 *
 * 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.
 *
 *	@(#)nfs_bio.c	8.5 (Berkeley) 1/4/94
 * $FreeBSD: head/sys/nfsclient/nfs_bio.c 21673 1997-01-14 07:20:47Z jkh $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_extern.h>

#include <nfs/rpcv2.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>
#include <nfs/nfsmount.h>
#include <nfs/nqnfs.h>
#include <nfs/nfsnode.h>

static struct buf *nfs_getcacheblk __P((struct vnode *vp, daddr_t bn, int size,
					struct proc *p));

extern int nfs_numasync;
extern struct nfsstats nfsstats;

/*
 * Ifdefs for FreeBSD-current's merged VM/buffer cache. It is unfortunate
 * that this isn't done inside getblk() and brelse() so these calls
 * wouldn't need to be here.
 */
#ifdef B_VMIO
#define vnode_pager_uncache(vp)
#else
#define vfs_busy_pages(bp, f)
#define vfs_unbusy_pages(bp)
#define vfs_dirty_pages(bp)
#endif

/*
 * Vnode op for read using bio
 * Any similarity to readip() is purely coincidental
 */
int
nfs_bioread(vp, uio, ioflag, cred)
	register struct vnode *vp;
	register struct uio *uio;
	int ioflag;
	struct ucred *cred;
{
	register struct nfsnode *np = VTONFS(vp);
	register int biosize, diff, i;
	struct buf *bp = 0, *rabp;
	struct vattr vattr;
	struct proc *p;
	struct nfsmount *nmp = VFSTONFS(vp->v_mount);
	daddr_t lbn, rabn;
	int bufsize;
	int nra, error = 0, n = 0, on = 0, not_readin;

#ifdef DIAGNOSTIC
	if (uio->uio_rw != UIO_READ)
		panic("nfs_read mode");
#endif
	if (uio->uio_resid == 0)
		return (0);
	if (uio->uio_offset < 0)
		return (EINVAL);
	p = uio->uio_procp;
	if ((nmp->nm_flag & (NFSMNT_NFSV3 | NFSMNT_GOTFSINFO)) == NFSMNT_NFSV3)
		(void)nfs_fsinfo(nmp, vp, cred, p);
	biosize = vp->v_mount->mnt_stat.f_iosize;
	/*
	 * For nfs, cache consistency can only be maintained approximately.
	 * Although RFC1094 does not specify the criteria, the following is
	 * believed to be compatible with the reference port.
	 * For nqnfs, full cache consistency is maintained within the loop.
	 * For nfs:
	 * If the file's modify time on the server has changed since the
	 * last read rpc or you have written to the file,
	 * you may have lost data cache consistency with the
	 * server, so flush all of the file's data out of the cache.
	 * Then force a getattr rpc to ensure that you have up to date
	 * attributes.
	 * NB: This implies that cache data can be read when up to
	 * NFS_ATTRTIMEO seconds out of date. If you find that you need current
	 * attributes this could be forced by setting n_attrstamp to 0 before
	 * the VOP_GETATTR() call.
	 */
	if ((nmp->nm_flag & NFSMNT_NQNFS) == 0) {
		if (np->n_flag & NMODIFIED) {
			if (vp->v_type != VREG) {
				if (vp->v_type != VDIR)
					panic("nfs: bioread, not dir");
				nfs_invaldir(vp);
				error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
				if (error)
					return (error);
			}
			np->n_attrstamp = 0;
			error = VOP_GETATTR(vp, &vattr, cred, p);
			if (error)
				return (error);
			np->n_mtime = vattr.va_mtime.tv_sec;
		} else {
			error = VOP_GETATTR(vp, &vattr, cred, p);
			if (error)
				return (error);
			if (np->n_mtime != vattr.va_mtime.tv_sec) {
				if (vp->v_type == VDIR)
					nfs_invaldir(vp);
				error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
				if (error)
					return (error);
				np->n_mtime = vattr.va_mtime.tv_sec;
			}
		}
	}
	do {

	    /*
	     * Get a valid lease. If cached data is stale, flush it.
	     */
	    if (nmp->nm_flag & NFSMNT_NQNFS) {
		if (NQNFS_CKINVALID(vp, np, ND_READ)) {
		    do {
			error = nqnfs_getlease(vp, ND_READ, cred, p);
		    } while (error == NQNFS_EXPIRED);
		    if (error)
			return (error);
		    if (np->n_lrev != np->n_brev ||
			(np->n_flag & NQNFSNONCACHE) ||
			((np->n_flag & NMODIFIED) && vp->v_type == VDIR)) {
			if (vp->v_type == VDIR)
			    nfs_invaldir(vp);
			error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
			if (error)
			    return (error);
			np->n_brev = np->n_lrev;
		    }
		} else if (vp->v_type == VDIR && (np->n_flag & NMODIFIED)) {
		    nfs_invaldir(vp);
		    error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
		    if (error)
			return (error);
		}
	    }
	    if (np->n_flag & NQNFSNONCACHE) {
		switch (vp->v_type) {
		case VREG:
			return (nfs_readrpc(vp, uio, cred));
		case VLNK:
			return (nfs_readlinkrpc(vp, uio, cred));
		case VDIR:
			break;
		default:
			printf(" NQNFSNONCACHE: type %x unexpected\n",
				vp->v_type);
		};
	    }
	    switch (vp->v_type) {
	    case VREG:
		nfsstats.biocache_reads++;
		lbn = uio->uio_offset / biosize;
		on = uio->uio_offset & (biosize - 1);
		not_readin = 1;

		/*
		 * Start the read ahead(s), as required.
		 */
		if (nfs_numasync > 0 && nmp->nm_readahead > 0) {
		    for (nra = 0; nra < nmp->nm_readahead &&
			(off_t)(lbn + 1 + nra) * biosize < np->n_size; nra++) {
			rabn = lbn + 1 + nra;
			if (!incore(vp, rabn)) {
			    rabp = nfs_getcacheblk(vp, rabn, biosize, p);
			    if (!rabp)
				return (EINTR);
			    if ((rabp->b_flags & (B_CACHE|B_DELWRI)) == 0) {
				rabp->b_flags |= (B_READ | B_ASYNC);
				vfs_busy_pages(rabp, 0);
				if (nfs_asyncio(rabp, cred)) {
				    rabp->b_flags |= B_INVAL|B_ERROR;
				    vfs_unbusy_pages(rabp);
				    brelse(rabp);
				}
			    } else {
				brelse(rabp);
			    }
			}
		    }
		}

		/*
		 * If the block is in the cache and has the required data
		 * in a valid region, just copy it out.
		 * Otherwise, get the block and write back/read in,
		 * as required.
		 */
again:
		bufsize = biosize;
		if ((off_t)(lbn + 1) * biosize > np->n_size &&
		    (off_t)(lbn + 1) * biosize - np->n_size < biosize) {
			bufsize = np->n_size - lbn * biosize;
			bufsize = (bufsize + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
		}
		bp = nfs_getcacheblk(vp, lbn, bufsize, p);
		if (!bp)
			return (EINTR);
		if ((bp->b_flags & B_CACHE) == 0) {
			bp->b_flags |= B_READ;
			bp->b_flags &= ~(B_DONE | B_ERROR | B_INVAL);
			not_readin = 0;
			vfs_busy_pages(bp, 0);
			error = nfs_doio(bp, cred, p);
			if (error) {
			    brelse(bp);
			    return (error);
			}
		}
		if (bufsize > on) {
			n = min((unsigned)(bufsize - on), uio->uio_resid);
		} else {
			n = 0;
		}
		diff = np->n_size - uio->uio_offset;
		if (diff < n)
			n = diff;
		if (not_readin && n > 0) {
			if (on < bp->b_validoff || (on + n) > bp->b_validend) {
				bp->b_flags |= B_NOCACHE;
				if (bp->b_dirtyend > 0) {
				    if ((bp->b_flags & B_DELWRI) == 0)
					panic("nfsbioread");
				    if (VOP_BWRITE(bp) == EINTR)
					return (EINTR);
				} else
				    brelse(bp);
				goto again;
			}
		}
		vp->v_lastr = lbn;
		diff = (on >= bp->b_validend) ? 0 : (bp->b_validend - on);
		if (diff < n)
			n = diff;
		break;
	    case VLNK:
		nfsstats.biocache_readlinks++;
		bp = nfs_getcacheblk(vp, (daddr_t)0, NFS_MAXPATHLEN, p);
		if (!bp)
			return (EINTR);
		if ((bp->b_flags & B_CACHE) == 0) {
			bp->b_flags |= B_READ;
			vfs_busy_pages(bp, 0);
			error = nfs_doio(bp, cred, p);
			if (error) {
				bp->b_flags |= B_ERROR;
				brelse(bp);
				return (error);
			}
		}
		n = min(uio->uio_resid, NFS_MAXPATHLEN - bp->b_resid);
		on = 0;
		break;
	    case VDIR:
		nfsstats.biocache_readdirs++;
		lbn = uio->uio_offset / NFS_DIRBLKSIZ;
		on = uio->uio_offset & (NFS_DIRBLKSIZ - 1);
		bp = nfs_getcacheblk(vp, lbn, NFS_DIRBLKSIZ, p);
		if (!bp)
		    return (EINTR);
		if ((bp->b_flags & B_CACHE) == 0) {
		    bp->b_flags |= B_READ;
		    vfs_busy_pages(bp, 0);
		    error = nfs_doio(bp, cred, p);
		    if (error) {
		        vfs_unbusy_pages(bp);
			brelse(bp);
			while (error == NFSERR_BAD_COOKIE) {
			    nfs_invaldir(vp);
			    error = nfs_vinvalbuf(vp, 0, cred, p, 1);
			    /*
			     * Yuck! The directory has been modified on the
			     * server. The only way to get the block is by
			     * reading from the beginning to get all the
			     * offset cookies.
			     */
			    for (i = 0; i <= lbn && !error; i++) {
				bp = nfs_getcacheblk(vp, i, NFS_DIRBLKSIZ, p);
				if (!bp)
				    return (EINTR);
				if ((bp->b_flags & B_DONE) == 0) {
				    bp->b_flags |= B_READ;
				    vfs_busy_pages(bp, 0);
				    error = nfs_doio(bp, cred, p);
				    if (error) {
					vfs_unbusy_pages(bp);
					brelse(bp);
				    } else if (i < lbn)
					brelse(bp);
				}
			    }
			}
			if (error)
			    return (error);
		    }
		}

		/*
		 * If not eof and read aheads are enabled, start one.
		 * (You need the current block first, so that you have the
		 *  directory offset cookie of the next block.)
		 */
		if (nfs_numasync > 0 && nmp->nm_readahead > 0 &&
		    (np->n_direofoffset == 0 ||
		    (lbn + 1) * NFS_DIRBLKSIZ < np->n_direofoffset) &&
		    !(np->n_flag & NQNFSNONCACHE) &&
		    !incore(vp, lbn + 1)) {
			rabp = nfs_getcacheblk(vp, lbn + 1, NFS_DIRBLKSIZ, p);
			if (rabp) {
			    if ((rabp->b_flags & (B_CACHE|B_DELWRI)) == 0) {
				rabp->b_flags |= (B_READ | B_ASYNC);
				vfs_busy_pages(rabp, 0);
				if (nfs_asyncio(rabp, cred)) {
				    rabp->b_flags |= B_INVAL|B_ERROR;
				    vfs_unbusy_pages(rabp);
				    brelse(rabp);
				}
			    } else {
				brelse(rabp);
			    }
			}
		}
		n = min(uio->uio_resid, NFS_DIRBLKSIZ - bp->b_resid - on);
		break;
	    default:
		printf(" nfs_bioread: type %x unexpected\n",vp->v_type);
		break;
	    };

	    if (n > 0) {
		error = uiomove(bp->b_data + on, (int)n, uio);
	    }
	    switch (vp->v_type) {
	    case VREG:
		break;
	    case VLNK:
		n = 0;
		break;
	    case VDIR:
		if (np->n_flag & NQNFSNONCACHE)
			bp->b_flags |= B_INVAL;
		break;
	    default:
		printf(" nfs_bioread: type %x unexpected\n",vp->v_type);
	    }
 	    brelse(bp);
	} while (error == 0 && uio->uio_resid > 0 && n > 0);
	return (error);
}

/*
 * Vnode op for write using bio
 */
int
nfs_write(ap)
	struct vop_write_args /* {
		struct vnode *a_vp;
		struct uio *a_uio;
		int  a_ioflag;
		struct ucred *a_cred;
	} */ *ap;
{
	register int biosize;
	register struct uio *uio = ap->a_uio;
	struct proc *p = uio->uio_procp;
	register struct vnode *vp = ap->a_vp;
	struct nfsnode *np = VTONFS(vp);
	register struct ucred *cred = ap->a_cred;
	int ioflag = ap->a_ioflag;
	struct buf *bp;
	struct vattr vattr;
	struct nfsmount *nmp = VFSTONFS(vp->v_mount);
	daddr_t lbn;
	int bufsize;
	int n, on, error = 0, iomode, must_commit;

#ifdef DIAGNOSTIC
	if (uio->uio_rw != UIO_WRITE)
		panic("nfs_write mode");
	if (uio->uio_segflg == UIO_USERSPACE && uio->uio_procp != curproc)
		panic("nfs_write proc");
#endif
	if (vp->v_type != VREG)
		return (EIO);
	if (np->n_flag & NWRITEERR) {
		np->n_flag &= ~NWRITEERR;
		return (np->n_error);
	}
	if ((nmp->nm_flag & (NFSMNT_NFSV3 | NFSMNT_GOTFSINFO)) == NFSMNT_NFSV3)
		(void)nfs_fsinfo(nmp, vp, cred, p);
	if (ioflag & (IO_APPEND | IO_SYNC)) {
		if (np->n_flag & NMODIFIED) {
			np->n_attrstamp = 0;
			error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
			if (error)
				return (error);
		}
		if (ioflag & IO_APPEND) {
			np->n_attrstamp = 0;
			error = VOP_GETATTR(vp, &vattr, cred, p);
			if (error)
				return (error);
			uio->uio_offset = np->n_size;
		}
	}
	if (uio->uio_offset < 0)
		return (EINVAL);
	if (uio->uio_resid == 0)
		return (0);
	/*
	 * Maybe this should be above the vnode op call, but so long as
	 * file servers have no limits, i don't think it matters
	 */
	if (p && uio->uio_offset + uio->uio_resid >
	      p->p_rlimit[RLIMIT_FSIZE].rlim_cur) {
		psignal(p, SIGXFSZ);
		return (EFBIG);
	}
	/*
	 * I use nm_rsize, not nm_wsize so that all buffer cache blocks
	 * will be the same size within a filesystem. nfs_writerpc will
	 * still use nm_wsize when sizing the rpc's.
	 */
	biosize = vp->v_mount->mnt_stat.f_iosize;
	do {

		/*
		 * XXX make sure we aren't cached in the VM page cache
		 */
		/*
		 * Check for a valid write lease.
		 */
		if ((nmp->nm_flag & NFSMNT_NQNFS) &&
		    NQNFS_CKINVALID(vp, np, ND_WRITE)) {
			do {
				error = nqnfs_getlease(vp, ND_WRITE, cred, p);
			} while (error == NQNFS_EXPIRED);
			if (error)
				return (error);
			if (np->n_lrev != np->n_brev ||
			    (np->n_flag & NQNFSNONCACHE)) {
				error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
				if (error)
					return (error);
				np->n_brev = np->n_lrev;
			}
		}
		if ((np->n_flag & NQNFSNONCACHE) && uio->uio_iovcnt == 1) {
		    iomode = NFSV3WRITE_FILESYNC;
		    error = nfs_writerpc(vp, uio, cred, &iomode, &must_commit);
		    if (must_commit)
			nfs_clearcommit(vp->v_mount);
		    return (error);
		}
		nfsstats.biocache_writes++;
		lbn = uio->uio_offset / biosize;
		on = uio->uio_offset & (biosize-1);
		n = min((unsigned)(biosize - on), uio->uio_resid);
again:
		if (uio->uio_offset + n > np->n_size) {
			np->n_size = uio->uio_offset + n;
			vnode_pager_setsize(vp, (u_long)np->n_size);
		}
		bufsize = biosize;
		if ((lbn + 1) * biosize > np->n_size) {
			bufsize = np->n_size - lbn * biosize;
			bufsize = (bufsize + DEV_BSIZE - 1) & ~(DEV_BSIZE - 1);
		}
		bp = nfs_getcacheblk(vp, lbn, bufsize, p);
		if (!bp)
			return (EINTR);
		if (bp->b_wcred == NOCRED) {
			crhold(cred);
			bp->b_wcred = cred;
		}
		np->n_flag |= NMODIFIED;

		if ((bp->b_blkno * DEV_BSIZE) + bp->b_dirtyend > np->n_size) {
			bp->b_dirtyend = np->n_size - (bp->b_blkno * DEV_BSIZE);
		}

		/*
		 * If the new write will leave a contiguous dirty
		 * area, just update the b_dirtyoff and b_dirtyend,
		 * otherwise force a write rpc of the old dirty area.
		 */
		if (bp->b_dirtyend > 0 &&
		    (on > bp->b_dirtyend || (on + n) < bp->b_dirtyoff)) {
			bp->b_proc = p;
			if (VOP_BWRITE(bp) == EINTR)
				return (EINTR);
			goto again;
		}

		/*
		 * Check for valid write lease and get one as required.
		 * In case getblk() and/or bwrite() delayed us.
		 */
		if ((nmp->nm_flag & NFSMNT_NQNFS) &&
		    NQNFS_CKINVALID(vp, np, ND_WRITE)) {
			do {
				error = nqnfs_getlease(vp, ND_WRITE, cred, p);
			} while (error == NQNFS_EXPIRED);
			if (error) {
				brelse(bp);
				return (error);
			}
			if (np->n_lrev != np->n_brev ||
			    (np->n_flag & NQNFSNONCACHE)) {
				brelse(bp);
				error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
				if (error)
					return (error);
				np->n_brev = np->n_lrev;
				goto again;
			}
		}
		error = uiomove((char *)bp->b_data + on, n, uio);
		if (error) {
			bp->b_flags |= B_ERROR;
			brelse(bp);
			return (error);
		}
		if (bp->b_dirtyend > 0) {
			bp->b_dirtyoff = min(on, bp->b_dirtyoff);
			bp->b_dirtyend = max((on + n), bp->b_dirtyend);
		} else {
			bp->b_dirtyoff = on;
			bp->b_dirtyend = on + n;
		}
		if (bp->b_validend == 0 || bp->b_validend < bp->b_dirtyoff ||
		    bp->b_validoff > bp->b_dirtyend) {
			bp->b_validoff = bp->b_dirtyoff;
			bp->b_validend = bp->b_dirtyend;
		} else {
			bp->b_validoff = min(bp->b_validoff, bp->b_dirtyoff);
			bp->b_validend = max(bp->b_validend, bp->b_dirtyend);
		}

		/*
		 * Since this block is being modified, it must be written
		 * again and not just committed.
		 */
		bp->b_flags &= ~B_NEEDCOMMIT;

		/*
		 * If the lease is non-cachable or IO_SYNC do bwrite().
		 */
		if ((np->n_flag & NQNFSNONCACHE) || (ioflag & IO_SYNC)) {
			bp->b_proc = p;
			error = VOP_BWRITE(bp);
			if (error)
				return (error);
			if (np->n_flag & NQNFSNONCACHE) {
				error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
				if (error)
					return (error);
			}
		} else if ((n + on) == biosize &&
			(nmp->nm_flag & NFSMNT_NQNFS) == 0) {
			bp->b_proc = (struct proc *)0;
			bp->b_flags |= B_ASYNC;
			(void)nfs_writebp(bp, 0);
		} else
			bdwrite(bp);
	} while (uio->uio_resid > 0 && n > 0);
	return (0);
}

/*
 * Get an nfs cache block.
 * Allocate a new one if the block isn't currently in the cache
 * and return the block marked busy. If the calling process is
 * interrupted by a signal for an interruptible mount point, return
 * NULL.
 */
static struct buf *
nfs_getcacheblk(vp, bn, size, p)
	struct vnode *vp;
	daddr_t bn;
	int size;
	struct proc *p;
{
	register struct buf *bp;
	struct nfsmount *nmp = VFSTONFS(vp->v_mount);
	int biosize = vp->v_mount->mnt_stat.f_iosize;

	if (nmp->nm_flag & NFSMNT_INT) {
		bp = getblk(vp, bn, size, PCATCH, 0);
		while (bp == (struct buf *)0) {
			if (nfs_sigintr(nmp, (struct nfsreq *)0, p))
				return ((struct buf *)0);
			bp = getblk(vp, bn, size, 0, 2 * hz);
		}
	} else
		bp = getblk(vp, bn, size, 0, 0);

	if( vp->v_type == VREG)
		bp->b_blkno = (bn * biosize) / DEV_BSIZE;

	return (bp);
}

/*
 * Flush and invalidate all dirty buffers. If another process is already
 * doing the flush, just wait for completion.
 */
int
nfs_vinvalbuf(vp, flags, cred, p, intrflg)
	struct vnode *vp;
	int flags;
	struct ucred *cred;
	struct proc *p;
	int intrflg;
{
	register struct nfsnode *np = VTONFS(vp);
	struct nfsmount *nmp = VFSTONFS(vp->v_mount);
	int error = 0, slpflag, slptimeo;

	if ((nmp->nm_flag & NFSMNT_INT) == 0)
		intrflg = 0;
	if (intrflg) {
		slpflag = PCATCH;
		slptimeo = 2 * hz;
	} else {
		slpflag = 0;
		slptimeo = 0;
	}
	/*
	 * First wait for any other process doing a flush to complete.
	 */
	while (np->n_flag & NFLUSHINPROG) {
		np->n_flag |= NFLUSHWANT;
		error = tsleep((caddr_t)&np->n_flag, PRIBIO + 2, "nfsvinval",
			slptimeo);
		if (error && intrflg && nfs_sigintr(nmp, (struct nfsreq *)0, p))
			return (EINTR);
	}

	/*
	 * Now, flush as required.
	 */
	np->n_flag |= NFLUSHINPROG;
	error = vinvalbuf(vp, flags, cred, p, slpflag, 0);
	while (error) {
		if (intrflg && nfs_sigintr(nmp, (struct nfsreq *)0, p)) {
			np->n_flag &= ~NFLUSHINPROG;
			if (np->n_flag & NFLUSHWANT) {
				np->n_flag &= ~NFLUSHWANT;
				wakeup((caddr_t)&np->n_flag);
			}
			return (EINTR);
		}
		error = vinvalbuf(vp, flags, cred, p, 0, slptimeo);
	}
	np->n_flag &= ~(NMODIFIED | NFLUSHINPROG);
	if (np->n_flag & NFLUSHWANT) {
		np->n_flag &= ~NFLUSHWANT;
		wakeup((caddr_t)&np->n_flag);
	}
	return (0);
}

/*
 * Initiate asynchronous I/O. Return an error if no nfsiods are available.
 * This is mainly to avoid queueing async I/O requests when the nfsiods
 * are all hung on a dead server.
 */
int
nfs_asyncio(bp, cred)
	register struct buf *bp;
	struct ucred *cred;
{
	struct nfsmount *nmp;
	int i;
	int gotiod;
	int slpflag = 0;
	int slptimeo = 0;
	int error;

	if (nfs_numasync == 0)
		return (EIO);

	nmp = VFSTONFS(bp->b_vp->v_mount);
again:
	if (nmp->nm_flag & NFSMNT_INT)
		slpflag = PCATCH;
	gotiod = FALSE;

	/*
	 * Find a free iod to process this request.
	 */
	for (i = 0; i < NFS_MAXASYNCDAEMON; i++)
		if (nfs_iodwant[i]) {
			/*
			 * Found one, so wake it up and tell it which
			 * mount to process.
			 */
			NFS_DPF(ASYNCIO,
				("nfs_asyncio: waking iod %d for mount %p\n",
				 i, nmp));
			nfs_iodwant[i] = (struct proc *)0;
			nfs_iodmount[i] = nmp;
			nmp->nm_bufqiods++;
			wakeup((caddr_t)&nfs_iodwant[i]);
			gotiod = TRUE;
		}

	/*
	 * If none are free, we may already have an iod working on this mount
	 * point.  If so, it will process our request.
	 */
	if (!gotiod) {
		if (nmp->nm_bufqiods > 0) {
			NFS_DPF(ASYNCIO,
				("nfs_asyncio: %d iods are already processing mount %p\n",
				 nmp->nm_bufqiods, nmp));
			gotiod = TRUE;
		}
	}

	/*
	 * If we have an iod which can process the request, then queue
	 * the buffer.
	 */
	if (gotiod) {
		/*
		 * Ensure that the queue never grows too large.
		 */
		while (nmp->nm_bufqlen >= 2*nfs_numasync) {
			NFS_DPF(ASYNCIO,
				("nfs_asyncio: waiting for mount %p queue to drain\n", nmp));
			nmp->nm_bufqwant = TRUE;
			error = tsleep(&nmp->nm_bufq, slpflag | PRIBIO,
				       "nfsaio", slptimeo);
			if (error) {
				if (nfs_sigintr(nmp, NULL, bp->b_proc))
					return (EINTR);
				if (slpflag == PCATCH) {
					slpflag = 0;
					slptimeo = 2 * hz;
				}
			}
			/*
			 * We might have lost our iod while sleeping,
			 * so check and loop if nescessary.
			 */
			if (nmp->nm_bufqiods == 0) {
				NFS_DPF(ASYNCIO,
					("nfs_asyncio: no iods after mount %p queue was drained, looping\n", nmp));
				goto again;
			}
		}

		if (bp->b_flags & B_READ) {
			if (bp->b_rcred == NOCRED && cred != NOCRED) {
				crhold(cred);
				bp->b_rcred = cred;
			}
		} else {
			bp->b_flags |= B_WRITEINPROG;
			if (bp->b_wcred == NOCRED && cred != NOCRED) {
				crhold(cred);
				bp->b_wcred = cred;
			}
		}

		TAILQ_INSERT_TAIL(&nmp->nm_bufq, bp, b_freelist);
		nmp->nm_bufqlen++;
		return (0);
	}

	/*
	 * All the iods are busy on other mounts, so return EIO to
	 * force the caller to process the i/o synchronously.
	 */
	NFS_DPF(ASYNCIO, ("nfs_asyncio: no iods available, i/o is synchronous\n"));
	return (EIO);
}

/*
 * Do an I/O operation to/from a cache block. This may be called
 * synchronously or from an nfsiod.
 */
int
nfs_doio(bp, cr, p)
	register struct buf *bp;
	struct ucred *cr;
	struct proc *p;
{
	register struct uio *uiop;
	register struct vnode *vp;
	struct nfsnode *np;
	struct nfsmount *nmp;
	int error = 0, diff, len, iomode, must_commit = 0;
	struct uio uio;
	struct iovec io;

	vp = bp->b_vp;
	np = VTONFS(vp);
	nmp = VFSTONFS(vp->v_mount);
	uiop = &uio;
	uiop->uio_iov = &io;
	uiop->uio_iovcnt = 1;
	uiop->uio_segflg = UIO_SYSSPACE;
	uiop->uio_procp = p;

	/*
	 * Historically, paging was done with physio, but no more.
	 */
	if (bp->b_flags & B_PHYS) {
	    /*
	     * ...though reading /dev/drum still gets us here.
	     */
	    io.iov_len = uiop->uio_resid = bp->b_bcount;
	    /* mapping was done by vmapbuf() */
	    io.iov_base = bp->b_data;
	    uiop->uio_offset = ((off_t)bp->b_blkno) * DEV_BSIZE;
	    if (bp->b_flags & B_READ) {
		uiop->uio_rw = UIO_READ;
		nfsstats.read_physios++;
		error = nfs_readrpc(vp, uiop, cr);
	    } else {
		int com;

		iomode = NFSV3WRITE_DATASYNC;
		uiop->uio_rw = UIO_WRITE;
		nfsstats.write_physios++;
		error = nfs_writerpc(vp, uiop, cr, &iomode, &com);
	    }
	    if (error) {
		bp->b_flags |= B_ERROR;
		bp->b_error = error;
	    }
	} else if (bp->b_flags & B_READ) {
	    io.iov_len = uiop->uio_resid = bp->b_bcount;
	    io.iov_base = bp->b_data;
	    uiop->uio_rw = UIO_READ;
	    switch (vp->v_type) {
	    case VREG:
		uiop->uio_offset = ((off_t)bp->b_blkno) * DEV_BSIZE;
		nfsstats.read_bios++;
		error = nfs_readrpc(vp, uiop, cr);
		if (!error) {
		    bp->b_validoff = 0;
		    if (uiop->uio_resid) {
			/*
			 * If len > 0, there is a hole in the file and
			 * no writes after the hole have been pushed to
			 * the server yet.
			 * Just zero fill the rest of the valid area.
			 */
			diff = bp->b_bcount - uiop->uio_resid;
			len = np->n_size - (((u_quad_t)bp->b_blkno) * DEV_BSIZE
				+ diff);
			if (len > 0) {
			    len = min(len, uiop->uio_resid);
			    bzero((char *)bp->b_data + diff, len);
			    bp->b_validend = diff + len;
			} else
			    bp->b_validend = diff;
		    } else
			bp->b_validend = bp->b_bcount;
		}
		if (p && (vp->v_flag & VTEXT) &&
			(((nmp->nm_flag & NFSMNT_NQNFS) &&
			  NQNFS_CKINVALID(vp, np, ND_READ) &&
			  np->n_lrev != np->n_brev) ||
			 (!(nmp->nm_flag & NFSMNT_NQNFS) &&
			  np->n_mtime != np->n_vattr.va_mtime.tv_sec))) {
			uprintf("Process killed due to text file modification\n");
			psignal(p, SIGKILL);
#ifdef __NetBSD__
			p->p_holdcnt++;
#else
			p->p_flag |= P_NOSWAP;
#endif
		}
		break;
	    case VLNK:
		uiop->uio_offset = (off_t)0;
		nfsstats.readlink_bios++;
		error = nfs_readlinkrpc(vp, uiop, cr);
		break;
	    case VDIR:
		nfsstats.readdir_bios++;
		uiop->uio_offset = ((u_quad_t)bp->b_lblkno) * NFS_DIRBLKSIZ;
		if (nmp->nm_flag & NFSMNT_RDIRPLUS) {
			error = nfs_readdirplusrpc(vp, uiop, cr);
			if (error == NFSERR_NOTSUPP)
				nmp->nm_flag &= ~NFSMNT_RDIRPLUS;
		}
		if ((nmp->nm_flag & NFSMNT_RDIRPLUS) == 0)
			error = nfs_readdirrpc(vp, uiop, cr);
		break;
	    default:
		printf("nfs_doio:  type %x unexpected\n",vp->v_type);
		break;
	    };
	    if (error) {
		bp->b_flags |= B_ERROR;
		bp->b_error = error;
	    }
	} else {
	    if (((bp->b_blkno * DEV_BSIZE) + bp->b_dirtyend) > np->n_size)
		bp->b_dirtyend = np->n_size - (bp->b_blkno * DEV_BSIZE);

	    if (bp->b_dirtyend > bp->b_dirtyoff) {
		io.iov_len = uiop->uio_resid = bp->b_dirtyend
		    - bp->b_dirtyoff;
		uiop->uio_offset = ((off_t)bp->b_blkno) * DEV_BSIZE
		    + bp->b_dirtyoff;
		io.iov_base = (char *)bp->b_data + bp->b_dirtyoff;
		uiop->uio_rw = UIO_WRITE;
		nfsstats.write_bios++;
		if ((bp->b_flags & (B_ASYNC | B_NEEDCOMMIT | B_NOCACHE)) == B_ASYNC)
		    iomode = NFSV3WRITE_UNSTABLE;
		else
		    iomode = NFSV3WRITE_FILESYNC;
		bp->b_flags |= B_WRITEINPROG;
		error = nfs_writerpc(vp, uiop, cr, &iomode, &must_commit);
		if (!error && iomode == NFSV3WRITE_UNSTABLE)
		    bp->b_flags |= B_NEEDCOMMIT;
		else
		    bp->b_flags &= ~B_NEEDCOMMIT;
		bp->b_flags &= ~B_WRITEINPROG;

		/*
		 * For an interrupted write, the buffer is still valid
		 * and the write hasn't been pushed to the server yet,
		 * so we can't set B_ERROR and report the interruption
		 * by setting B_EINTR. For the B_ASYNC case, B_EINTR
		 * is not relevant, so the rpc attempt is essentially
		 * a noop.  For the case of a V3 write rpc not being
		 * committed to stable storage, the block is still
		 * dirty and requires either a commit rpc or another
		 * write rpc with iomode == NFSV3WRITE_FILESYNC before
		 * the block is reused. This is indicated by setting
		 * the B_DELWRI and B_NEEDCOMMIT flags.
		 */
    		if (error == EINTR
		    || (!error && (bp->b_flags & B_NEEDCOMMIT))) {
			bp->b_flags &= ~(B_INVAL|B_NOCACHE);
			bp->b_flags |= B_DELWRI;

		/*
		 * Since for the B_ASYNC case, nfs_bwrite() has reassigned the
		 * buffer to the clean list, we have to reassign it back to the
		 * dirty one. Ugh.
		 */
			if (bp->b_flags & B_ASYNC)
				reassignbuf(bp, vp);
			else
				bp->b_flags |= B_EINTR;
	    	} else {
			if (error) {
				bp->b_flags |= B_ERROR;
				bp->b_error = np->n_error = error;
				np->n_flag |= NWRITEERR;
			}
			bp->b_dirtyoff = bp->b_dirtyend = 0;
		}
	    } else {
		bp->b_resid = 0;
		biodone(bp);
		return (0);
	    }
	}
	bp->b_resid = uiop->uio_resid;
	if (must_commit)
		nfs_clearcommit(vp->v_mount);
	biodone(bp);
	return (error);
}