Index: head/sys/compat/cloudabi/cloudabi_file.c
===================================================================
--- head/sys/compat/cloudabi/cloudabi_file.c
+++ head/sys/compat/cloudabi/cloudabi_file.c
@@ -287,7 +287,8 @@
 
 	/* Install vnode operations if no custom operations are provided. */
 	if (fp->f_ops == &badfileops) {
-		fp->f_seqcount = 1;
+		fp->f_seqcount[UIO_READ] = 1;
+		fp->f_seqcount[UIO_WRITE] = 1;
 		finit(fp, (fflags & FMASK) | (fp->f_flag & FHASLOCK),
 		    DTYPE_VNODE, vp, &vnops);
 	}
Index: head/sys/fs/devfs/devfs_vnops.c
===================================================================
--- head/sys/fs/devfs/devfs_vnops.c
+++ head/sys/fs/devfs/devfs_vnops.c
@@ -1305,7 +1305,7 @@
 	td->td_fpop = fpop;
 	dev_relthread(dev, ref);
 
-	foffset_unlock_uio(fp, uio, flags | FOF_NOLOCK | FOF_NEXTOFF);
+	foffset_unlock_uio(fp, uio, flags | FOF_NOLOCK | FOF_NEXTOFF_R);
 	return (error);
 }
 
@@ -1802,7 +1802,7 @@
 	td->td_fpop = fpop;
 	dev_relthread(dev, ref);
 
-	foffset_unlock_uio(fp, uio, flags | FOF_NOLOCK | FOF_NEXTOFF);
+	foffset_unlock_uio(fp, uio, flags | FOF_NOLOCK | FOF_NEXTOFF_W);
 	return (error);
 }
 
Index: head/sys/kern/kern_descrip.c
===================================================================
--- head/sys/kern/kern_descrip.c
+++ head/sys/kern/kern_descrip.c
@@ -795,7 +795,7 @@
 		if (arg >= 0) {
 			bsize = fp->f_vnode->v_mount->mnt_stat.f_iosize;
 			arg = MIN(arg, INT_MAX - bsize + 1);
-			fp->f_seqcount = MIN(IO_SEQMAX,
+			fp->f_seqcount[UIO_READ] = MIN(IO_SEQMAX,
 			    (arg + bsize - 1) / bsize);
 			atomic_set_int(&fp->f_flag, FRDAHEAD);
 		} else {
Index: head/sys/kern/vfs_syscalls.c
===================================================================
--- head/sys/kern/vfs_syscalls.c
+++ head/sys/kern/vfs_syscalls.c
@@ -1124,7 +1124,8 @@
 	 */
 	if (fp->f_ops == &badfileops) {
 		KASSERT(vp->v_type != VFIFO, ("Unexpected fifo."));
-		fp->f_seqcount = 1;
+		fp->f_seqcount[UIO_READ] = 1;
+		fp->f_seqcount[UIO_WRITE] = 1;
 		finit(fp, (flags & FMASK) | (fp->f_flag & FHASLOCK),
 		    DTYPE_VNODE, vp, &vnops);
 	}
@@ -4442,7 +4443,8 @@
 	td->td_dupfd = 0;
 #endif
 	fp->f_vnode = vp;
-	fp->f_seqcount = 1;
+	fp->f_seqcount[UIO_READ] = 1;
+	fp->f_seqcount[UIO_WRITE] = 1;
 	finit(fp, (fmode & FMASK) | (fp->f_flag & FHASLOCK), DTYPE_VNODE, vp,
 	    &vnops);
 	VOP_UNLOCK(vp);
Index: head/sys/kern/vfs_vnops.c
===================================================================
--- head/sys/kern/vfs_vnops.c
+++ head/sys/kern/vfs_vnops.c
@@ -489,10 +489,13 @@
 static int
 sequential_heuristic(struct uio *uio, struct file *fp)
 {
+	enum uio_rw rw;
 
 	ASSERT_VOP_LOCKED(fp->f_vnode, __func__);
+
+	rw = uio->uio_rw;
 	if (fp->f_flag & FRDAHEAD)
-		return (fp->f_seqcount << IO_SEQSHIFT);
+		return (fp->f_seqcount[rw] << IO_SEQSHIFT);
 
 	/*
 	 * Offset 0 is handled specially.  open() sets f_seqcount to 1 so
@@ -501,8 +504,8 @@
 	 * unless previous seeks have reduced f_seqcount to 0, in which
 	 * case offset 0 is not special.
 	 */
-	if ((uio->uio_offset == 0 && fp->f_seqcount > 0) ||
-	    uio->uio_offset == fp->f_nextoff) {
+	if ((uio->uio_offset == 0 && fp->f_seqcount[rw] > 0) ||
+	    uio->uio_offset == fp->f_nextoff[rw]) {
 		/*
 		 * f_seqcount is in units of fixed-size blocks so that it
 		 * depends mainly on the amount of sequential I/O and not
@@ -513,20 +516,20 @@
 		 * to any block size used by software.
 		 */
 		if (uio->uio_resid >= IO_SEQMAX * 16384)
-			fp->f_seqcount = IO_SEQMAX;
+			fp->f_seqcount[rw] = IO_SEQMAX;
 		else {
-			fp->f_seqcount += howmany(uio->uio_resid, 16384);
-			if (fp->f_seqcount > IO_SEQMAX)
-				fp->f_seqcount = IO_SEQMAX;
+			fp->f_seqcount[rw] += howmany(uio->uio_resid, 16384);
+			if (fp->f_seqcount[rw] > IO_SEQMAX)
+				fp->f_seqcount[rw] = IO_SEQMAX;
 		}
-		return (fp->f_seqcount << IO_SEQSHIFT);
+		return (fp->f_seqcount[rw] << IO_SEQSHIFT);
 	}
 
 	/* Not sequential.  Quickly draw-down sequentiality. */
-	if (fp->f_seqcount > 1)
-		fp->f_seqcount = 1;
+	if (fp->f_seqcount[rw] > 1)
+		fp->f_seqcount[rw] = 1;
 	else
-		fp->f_seqcount = 0;
+		fp->f_seqcount[rw] = 0;
 	return (0);
 }
 
@@ -734,8 +737,10 @@
 
 	if ((flags & FOF_NOUPDATE) == 0)
 		atomic_store_long(&fp->f_offset, val);
-	if ((flags & FOF_NEXTOFF) != 0)
-		fp->f_nextoff = val;
+	if ((flags & FOF_NEXTOFF_R) != 0)
+		fp->f_nextoff[UIO_READ] = val;
+	if ((flags & FOF_NEXTOFF_W) != 0)
+		fp->f_nextoff[UIO_WRITE] = val;
 
 	if ((flags & FOF_NOLOCK) != 0)
 		return;
@@ -788,8 +793,10 @@
 	mtx_lock(mtxp);
 	if ((flags & FOF_NOUPDATE) == 0)
 		fp->f_offset = val;
-	if ((flags & FOF_NEXTOFF) != 0)
-		fp->f_nextoff = val;
+	if ((flags & FOF_NEXTOFF_R) != 0)
+		fp->f_nextoff[UIO_READ] = val;
+	if ((flags & FOF_NEXTOFF_W) != 0)
+		fp->f_nextoff[UIO_WRITE] = val;
 	if ((flags & FOF_NOLOCK) == 0) {
 		KASSERT((fp->f_vnread_flags & FOFFSET_LOCKED) != 0,
 		    ("Lost FOFFSET_LOCKED"));
@@ -878,7 +885,7 @@
 	if (error == 0)
 #endif
 		error = VOP_READ(vp, uio, ioflag, fp->f_cred);
-	fp->f_nextoff = uio->uio_offset;
+	fp->f_nextoff[UIO_READ] = uio->uio_offset;
 	VOP_UNLOCK(vp);
 	if (error == 0 && advice == POSIX_FADV_NOREUSE &&
 	    orig_offset != uio->uio_offset)
@@ -953,7 +960,7 @@
 	if (error == 0)
 #endif
 		error = VOP_WRITE(vp, uio, ioflag, fp->f_cred);
-	fp->f_nextoff = uio->uio_offset;
+	fp->f_nextoff[UIO_WRITE] = uio->uio_offset;
 	VOP_UNLOCK(vp);
 	if (vp->v_type != VCHR)
 		vn_finished_write(mp);
Index: head/sys/sys/file.h
===================================================================
--- head/sys/sys/file.h
+++ head/sys/sys/file.h
@@ -81,7 +81,8 @@
 
 #define	FOF_OFFSET	0x01	/* Use the offset in uio argument */
 #define	FOF_NOLOCK	0x02	/* Do not take FOFFSET_LOCK */
-#define	FOF_NEXTOFF	0x04	/* Also update f_nextoff */
+#define	FOF_NEXTOFF_R	0x04	/* Also update f_nextoff[UIO_READ] */
+#define	FOF_NEXTOFF_W	0x08	/* Also update f_nextoff[UIO_WRITE] */
 #define	FOF_NOUPDATE	0x10	/* Do not update f_offset */
 off_t foffset_lock(struct file *fp, int flags);
 void foffset_lock_uio(struct file *fp, struct uio *uio, int flags);
@@ -187,10 +188,10 @@
 	 *  DTYPE_VNODE specific fields.
 	 */
 	union {
-		int16_t	f_seqcount;	/* (a) Count of sequential accesses. */
+		int16_t	f_seqcount[2];	/* (a) Count of seq. reads and writes. */
 		int	f_pipegen;
 	};
-	off_t		f_nextoff;	/* next expected read/write offset. */
+	off_t		f_nextoff[2];	/* next expected read/write offset. */
 	union {
 		struct cdev_privdata *fvn_cdevpriv;
 					/* (d) Private data for the cdev. */