Index: head/stand/libsa/cd9660.c
===================================================================
--- head/stand/libsa/cd9660.c
+++ head/stand/libsa/cd9660.c
@@ -66,7 +66,7 @@
 static int	cd9660_close(struct open_file *f);
 static int	cd9660_read(struct open_file *f, void *buf, size_t size,
 		    size_t *resid);
-static int	cd9660_write(struct open_file *f, void *buf, size_t size,
+static int	cd9660_write(struct open_file *f, const void *buf, size_t size,
 		    size_t *resid);
 static off_t	cd9660_seek(struct open_file *f, off_t offset, int where);
 static int	cd9660_stat(struct open_file *f, struct stat *sb);
@@ -557,7 +557,8 @@
 }
 
 static int
-cd9660_write(struct open_file *f __unused, void *start __unused, size_t size __unused, size_t *resid __unused)
+cd9660_write(struct open_file *f __unused, const void *buf __unused,
+    size_t size __unused, size_t *resid __unused)
 {
 	return EROFS;
 }
Index: head/stand/libsa/nfs.c
===================================================================
--- head/stand/libsa/nfs.c
+++ head/stand/libsa/nfs.c
@@ -126,7 +126,6 @@
 int		nfs_open(const char *path, struct open_file *f);
 static int	nfs_close(struct open_file *f);
 static int	nfs_read(struct open_file *f, void *buf, size_t size, size_t *resid);
-static int	nfs_write(struct open_file *f, void *buf, size_t size, size_t *resid);
 static off_t	nfs_seek(struct open_file *f, off_t offset, int where);
 static int	nfs_stat(struct open_file *f, struct stat *sb);
 static int	nfs_readdir(struct open_file *f, struct dirent *d);
@@ -138,7 +137,7 @@
 	nfs_open,
 	nfs_close,
 	nfs_read,
-	nfs_write,
+	null_write,
 	nfs_seek,
 	nfs_stat,
 	nfs_readdir
@@ -713,15 +712,6 @@
 		*resid = size;
 
 	return (0);
-}
-
-/*
- * Not implemented.
- */
-int
-nfs_write(struct open_file *f, void *buf, size_t size, size_t *resid)
-{
-	return (EROFS);
 }
 
 off_t
Index: head/stand/libsa/nullfs.c
===================================================================
--- head/stand/libsa/nullfs.c
+++ head/stand/libsa/nullfs.c
@@ -83,7 +83,7 @@
 	return EIO;
 }
 
-int	null_write (struct open_file *f, void *buf, size_t size, size_t *resid)
+int	null_write (struct open_file *f, const void *buf, size_t size, size_t *resid)
 {
 	return EIO;
 }
Index: head/stand/libsa/stand.h
===================================================================
--- head/stand/libsa/stand.h
+++ head/stand/libsa/stand.h
@@ -105,7 +105,7 @@
     int		(*fo_close)(struct open_file *f);
     int		(*fo_read)(struct open_file *f, void *buf,
 			   size_t size, size_t *resid);
-    int		(*fo_write)(struct open_file *f, void *buf,
+    int		(*fo_write)(struct open_file *f, const void *buf,
 			    size_t size, size_t *resid);
     off_t	(*fo_seek)(struct open_file *f, off_t offset, int where);
     int		(*fo_stat)(struct open_file *f, struct stat *sb);
@@ -383,7 +383,7 @@
 extern int	null_open(const char *path, struct open_file *f);
 extern int	null_close(struct open_file *f);
 extern int	null_read(struct open_file *f, void *buf, size_t size, size_t *resid);
-extern int	null_write(struct open_file *f, void *buf, size_t size, size_t *resid);
+extern int	null_write(struct open_file *f, const void *buf, size_t size, size_t *resid);
 extern off_t	null_seek(struct open_file *f, off_t offset, int where);
 extern int	null_stat(struct open_file *f, struct stat *sb);
 extern int	null_readdir(struct open_file *f, struct dirent *d);
Index: head/stand/libsa/tftp.c
===================================================================
--- head/stand/libsa/tftp.c
+++ head/stand/libsa/tftp.c
@@ -69,7 +69,8 @@
 static int	tftp_close(struct open_file *f);
 static int	tftp_parse_oack(struct tftp_handle *h, char *buf, size_t len);
 static int	tftp_read(struct open_file *f, void *buf, size_t size, size_t *resid);
-static int	tftp_write(struct open_file *f, void *buf, size_t size, size_t *resid);
+static int	tftp_write(struct open_file *f, const void *buf, size_t size,
+		size_t *resid);
 static off_t	tftp_seek(struct open_file *f, off_t offset, int where);
 static int	tftp_set_blksize(struct tftp_handle *h, const char *str);
 static int	tftp_stat(struct open_file *f, struct stat *sb);
@@ -574,8 +575,8 @@
 }
 
 static int
-tftp_write(struct open_file *f __unused, void *start __unused, size_t size __unused,
-    size_t *resid __unused /* out */)
+tftp_write(struct open_file *f __unused, const void *start __unused,
+    size_t size __unused, size_t *resid __unused /* out */)
 {
 	return (EROFS);
 }
Index: head/stand/libsa/ufs.c
===================================================================
--- head/stand/libsa/ufs.c
+++ head/stand/libsa/ufs.c
@@ -84,7 +84,8 @@
 #include "string.h"
 
 static int	ufs_open(const char *path, struct open_file *f);
-static int	ufs_write(struct open_file *f, void *buf, size_t size, size_t *resid);
+static int	ufs_write(struct open_file *f, const void *buf, size_t size,
+		size_t *resid);
 static int	ufs_close(struct open_file *f);
 static int	ufs_read(struct open_file *f, void *buf, size_t size, size_t *resid);
 static off_t	ufs_seek(struct open_file *f, off_t offset, int where);
@@ -131,7 +132,7 @@
 static int	read_inode(ino_t, struct open_file *);
 static int	block_map(struct open_file *, ufs2_daddr_t, ufs2_daddr_t *);
 static int	buf_read_file(struct open_file *, char **, size_t *);
-static int	buf_write_file(struct open_file *, char *, size_t *);
+static int	buf_write_file(struct open_file *, const char *, size_t *);
 static int	search_directory(char *, struct open_file *, ino_t *);
 static int	ufs_use_sa_read(void *, off_t, void **, int);
 
@@ -306,7 +307,7 @@
 static int
 buf_write_file(f, buf_p, size_p)
 	struct open_file *f;
-	char *buf_p;
+	const char *buf_p;
 	size_t *size_p;		/* out */
 {
 	struct file *fp = (struct file *)f->f_fsdata;
@@ -770,14 +771,14 @@
 static int
 ufs_write(f, start, size, resid)
 	struct open_file *f;
-	void *start;
+	const void *start;
 	size_t size;
 	size_t *resid;	/* out */
 {
 	struct file *fp = (struct file *)f->f_fsdata;
 	size_t csize;
 	int rc = 0;
-	char *addr = start;
+	const char *addr = start;
 
 	csize = size;
 	while ((size != 0) && (csize != 0)) {
Index: head/stand/libsa/write.c
===================================================================
--- head/stand/libsa/write.c
+++ head/stand/libsa/write.c
@@ -69,7 +69,7 @@
 ssize_t
 write(fd, dest, bcount)
 	int fd;
-	void *dest;
+	const void *dest;
 	size_t bcount;
 {
 	struct open_file *f = &files[fd];
@@ -82,7 +82,8 @@
 	if (f->f_flags & F_RAW) {
 		twiddle(4);
 		errno = (f->f_dev->dv_strategy)(f->f_devdata, F_WRITE,
-			btodb(f->f_offset), bcount, dest, &resid);
+			btodb(f->f_offset), bcount, __DECONST(void *, dest),
+			&resid);
 		if (errno)
 			return (-1);
 		f->f_offset += resid;
Index: head/stand/userboot/userboot/host.c
===================================================================
--- head/stand/userboot/userboot/host.c
+++ head/stand/userboot/userboot/host.c
@@ -74,16 +74,6 @@
 	return (CALLBACK(read, f->f_fsdata, start, size, resid));
 }
 
-/*
- * Don't be silly - the bootstrap has no business writing anything.
- */
-static int
-host_write(struct open_file *f, void *start, size_t size, size_t *resid)
-{
-
-	return (EROFS);
-}
-
 static off_t
 host_seek(struct open_file *f, off_t offset, int where)
 {
@@ -183,7 +173,7 @@
 	host_open,
 	host_close,
 	host_read,
-	host_write,
+	null_write,
 	host_seek,
 	host_stat,
 	host_readdir
Index: head/stand/zfs/zfs.c
===================================================================
--- head/stand/zfs/zfs.c
+++ head/stand/zfs/zfs.c
@@ -53,7 +53,6 @@
 #define		ZFS_BE_LAST	8
 
 static int	zfs_open(const char *path, struct open_file *f);
-static int	zfs_write(struct open_file *f, void *buf, size_t size, size_t *resid);
 static int	zfs_close(struct open_file *f);
 static int	zfs_read(struct open_file *f, void *buf, size_t size, size_t *resid);
 static off_t	zfs_seek(struct open_file *f, off_t offset, int where);
@@ -69,7 +68,7 @@
 	zfs_open,
 	zfs_close,
 	zfs_read,
-	zfs_write,
+	null_write,
 	zfs_seek,
 	zfs_stat,
 	zfs_readdir
@@ -171,16 +170,6 @@
 		*resid = size - n;
 
 	return (0);
-}
-
-/*
- * Don't be silly - the bootstrap has no business writing anything.
- */
-static int
-zfs_write(struct open_file *f, void *start, size_t size, size_t *resid	/* out */)
-{
-
-	return (EROFS);
 }
 
 static off_t