Index: sys/amd64/amd64/minidump_machdep.c
===================================================================
--- sys/amd64/amd64/minidump_machdep.c
+++ sys/amd64/amd64/minidump_machdep.c
@@ -56,7 +56,6 @@
 int vm_page_dump_size;
 
 static struct kerneldumpheader kdh;
-static off_t dumplo;
 
 /* Handle chunked writes. */
 static size_t fragsz;
@@ -93,8 +92,7 @@
 	if (fragsz == 0)
 		return (0);
 
-	error = dump_write(di, dump_va, 0, dumplo, fragsz);
-	dumplo += fragsz;
+	error = dump_append(di, dump_va, 0, fragsz);
 	fragsz = 0;
 	return (error);
 }
@@ -177,10 +175,9 @@
 		wdog_kern_pat(WD_LASTVAL);
 
 		if (ptr) {
-			error = dump_write(di, ptr, 0, dumplo, len);
+			error = dump_append(di, ptr, 0, len);
 			if (error)
 				return (error);
-			dumplo += len;
 			ptr += len;
 			sz -= len;
 		} else {
@@ -333,7 +330,7 @@
 	printf("Dumping %llu out of %ju MB:", (long long)dumpsize >> 20,
 	    ptoa((uintmax_t)physmem) / 1048576);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -419,7 +416,7 @@
 	if (error)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/arm/arm/minidump_machdep.c
===================================================================
--- sys/arm/arm/minidump_machdep.c
+++ sys/arm/arm/minidump_machdep.c
@@ -58,8 +58,6 @@
 
 static struct kerneldumpheader kdh;
 
-static off_t dumplo;
-
 /* Handle chunked writes. */
 static size_t fragsz;
 static void *dump_va;
@@ -89,8 +87,7 @@
 	if (fragsz == 0)
 		return (0);
 
-	error = dump_write(di, dump_va, 0, dumplo, fragsz);
-	dumplo += fragsz;
+	error = dump_append(di, dump_va, 0, fragsz);
 	fragsz = 0;
 	return (error);
 }
@@ -141,10 +138,9 @@
 		wdog_kern_pat(WD_LASTVAL);
 #endif
 		if (ptr) {
-			error = dump_write(di, ptr, 0, dumplo, len);
+			error = dump_append(di, ptr, 0, len);
 			if (error)
 				return (error);
-			dumplo += len;
 			ptr += len;
 			sz -= len;
 		} else {
@@ -251,7 +247,7 @@
 	printf("Physical memory: %u MB\n", ptoa((uintmax_t)physmem) / 1048576);
 	printf("Dumping %llu MB:", (long long)dumpsize >> 20);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -329,7 +325,7 @@
 	if (error)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/arm64/arm64/minidump_machdep.c
===================================================================
--- sys/arm64/arm64/minidump_machdep.c
+++ sys/arm64/arm64/minidump_machdep.c
@@ -62,7 +62,6 @@
 int vm_page_dump_size;
 
 static struct kerneldumpheader kdh;
-static off_t dumplo;
 
 /* Handle chunked writes. */
 static size_t fragsz;
@@ -96,8 +95,7 @@
 	if (fragsz == 0)
 		return (0);
 
-	error = dump_write(di, dump_va, 0, dumplo, fragsz);
-	dumplo += fragsz;
+	error = dump_append(di, dump_va, 0, fragsz);
 	fragsz = 0;
 	return (error);
 }
@@ -183,10 +181,9 @@
 		wdog_kern_pat(WD_LASTVAL);
 
 		if (ptr) {
-			error = dump_write(di, ptr, 0, dumplo, len);
+			error = dump_append(di, ptr, 0, len);
 			if (error)
 				return (error);
-			dumplo += len;
 			ptr += len;
 			sz -= len;
 		} else {
@@ -295,7 +292,7 @@
 	printf("Dumping %llu out of %ju MB:", (long long)dumpsize >> 20,
 	    ptoa((uintmax_t)physmem) / 1048576);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -395,7 +392,7 @@
 	if (error)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/i386/i386/minidump_machdep.c
===================================================================
--- sys/i386/i386/minidump_machdep.c
+++ sys/i386/i386/minidump_machdep.c
@@ -54,7 +54,6 @@
 int vm_page_dump_size;
 
 static struct kerneldumpheader kdh;
-static off_t dumplo;
 
 /* Handle chunked writes. */
 static size_t fragsz;
@@ -86,8 +85,7 @@
 	if (fragsz == 0)
 		return (0);
 
-	error = dump_write(di, dump_va, 0, dumplo, fragsz);
-	dumplo += fragsz;
+	error = dump_append(di, dump_va, 0, fragsz);
 	fragsz = 0;
 	return (error);
 }
@@ -135,10 +133,9 @@
 		wdog_kern_pat(WD_LASTVAL);
 
 		if (ptr) {
-			error = dump_write(di, ptr, 0, dumplo, len);
+			error = dump_append(di, ptr, 0, len);
 			if (error)
 				return (error);
-			dumplo += len;
 			ptr += len;
 			sz -= len;
 		} else {
@@ -258,7 +255,7 @@
 	printf("Physical memory: %ju MB\n", ptoa((uintmax_t)physmem) / 1048576);
 	printf("Dumping %llu MB:", (long long)dumpsize >> 20);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -334,7 +331,7 @@
 	if (error)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/kern/kern_dump.c
===================================================================
--- sys/kern/kern_dump.c
+++ sys/kern/kern_dump.c
@@ -51,8 +51,6 @@
 
 #define	MD_ALIGN(x)	roundup2((off_t)(x), PAGE_SIZE)
 
-off_t dumplo;
-
 /* Handle buffered writes. */
 static size_t fragsz;
 
@@ -122,11 +120,9 @@
 	while (sz > 0) {
 		nbytes = MIN(sz, sizeof(buf));
 
-		error = dump_write(di, buf, 0, dumplo, nbytes);
+		error = dump_append(di, buf, 0, nbytes);
 		if (error)
 			return (error);
-		dumplo += nbytes;
-
 		sz -= nbytes;
 	}
 
@@ -148,11 +144,9 @@
 		ptr += len;
 		sz -= len;
 		if (fragsz == di->blocksize) {
-			error = dump_write(di, di->blockbuf, 0, dumplo,
-			    di->blocksize);
+			error = dump_append(di, di->blockbuf, 0, di->blocksize);
 			if (error)
 				return (error);
-			dumplo += di->blocksize;
 			fragsz = 0;
 		}
 	}
@@ -167,8 +161,7 @@
 	if (fragsz == 0)
 		return (0);
 
-	error = dump_write(di, di->blockbuf, 0, dumplo, di->blocksize);
-	dumplo += di->blocksize;
+	error = dump_append(di, di->blockbuf, 0, di->blocksize);
 	fragsz = 0;
 	return (error);
 }
@@ -216,11 +209,10 @@
 		wdog_kern_pat(WD_LASTVAL);
 #endif
 
-		error = dump_write(di, va, 0, dumplo, sz);
+		error = dump_append(di, va, 0, sz);
 		dumpsys_unmap_chunk(pa, chunk, va);
 		if (error)
 			break;
-		dumplo += sz;
 		pgs -= chunk;
 		pa += sz;
 
@@ -347,7 +339,7 @@
 	printf("Dumping %ju MB (%d chunks)\n", (uintmax_t)dumpsize >> 20,
 	    ehdr.e_phnum - DUMPSYS_NUM_AUX_HDRS);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -369,19 +361,18 @@
 	 * All headers are written using blocked I/O, so we know the
 	 * current offset is (still) block aligned. Skip the alignement
 	 * in the file to have the segment contents aligned at page
-	 * boundary. We cannot use MD_ALIGN on dumplo, because we don't
-	 * care and may very well be unaligned within the dump device.
+	 * boundary.
 	 */
 	error = dumpsys_buf_seek(di, (size_t)hdrgap);
 	if (error)
 		goto fail;
 
-	/* Dump memory chunks (updates dumplo) */
+	/* Dump memory chunks. */
 	error = dumpsys_foreach_chunk(dumpsys_cb_dumpdata, di);
 	if (error < 0)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/kern/kern_shutdown.c
===================================================================
--- sys/kern/kern_shutdown.c
+++ sys/kern/kern_shutdown.c
@@ -157,7 +157,6 @@
 	uint8_t			kdc_iv[KERNELDUMP_IV_MAX_SIZE];
 	keyInstance		kdc_ki;
 	cipherInstance		kdc_ci;
-	off_t			kdc_nextoffset;
 	uint32_t		kdc_dumpkeysize;
 	struct kerneldumpkey	kdc_dumpkey[];
 };
@@ -931,8 +930,6 @@
 		goto out;
 	}
 
-	kdc->kdc_nextoffset = 0;
-
 	kdk = kdc->kdc_dumpkey;
 	memcpy(kdk->kdk_iv, kdc->kdc_iv, sizeof(kdk->kdk_iv));
 out:
@@ -1024,24 +1021,20 @@
 		    (uintmax_t)length, (intmax_t)di->mediasize);
 		return (ENOSPC);
 	}
+	if (length % di->blocksize != 0) {
+		printf("Attempt to write partial block of length %ju.\n",
+		    (uintmax_t)length);
+		return (EINVAL);
+	}
+	if (offset % di->blocksize != 0) {
+		printf("Attempt to write at unaligned offset %jd.\n",
+		    (intmax_t)offset);
+		return (EINVAL);
+	}
 
 	return (0);
 }
 
-/* Call dumper with bounds checking. */
-static int
-dump_raw_write(struct dumperinfo *di, void *virtual, vm_offset_t physical,
-    off_t offset, size_t length)
-{
-	int error;
-
-	error = dump_check_bounds(di, offset, length);
-	if (error != 0)
-		return (error);
-
-	return (di->dumper(di->priv, virtual, physical, offset, length));
-}
-
 #ifdef EKCD
 static int
 dump_encrypt(struct kerneldumpcrypto *kdc, uint8_t *buf, size_t size)
@@ -1067,40 +1060,16 @@
 
 /* Encrypt data and call dumper. */
 static int
-dump_encrypted_write(struct dumperinfo *di, void *virtual, vm_offset_t physical,
-    off_t offset, size_t length)
+dump_encrypted_append(struct dumperinfo *di, void *virtual,
+    vm_offset_t physical, size_t length)
 {
 	static uint8_t buf[KERNELDUMP_BUFFER_SIZE];
 	struct kerneldumpcrypto *kdc;
 	int error;
 	size_t nbytes;
-	off_t nextoffset;
 
 	kdc = di->kdc;
 
-	error = dump_check_bounds(di, offset, length);
-	if (error != 0)
-		return (error);
-
-	/* Signal completion. */
-	if (virtual == NULL && physical == 0 && offset == 0 && length == 0) {
-		return (di->dumper(di->priv, virtual, physical, offset,
-		    length));
-	}
-
-	/* Data have to be aligned to block size. */
-	if ((length % di->blocksize) != 0)
-		return (EINVAL);
-
-	/*
-	 * Data have to be written continuously becase we're encrypting using
-	 * CBC mode which has this assumption.
-	 */
-	if (kdc->kdc_nextoffset != 0 && kdc->kdc_nextoffset != offset)
-		return (EINVAL);
-
-	nextoffset = offset + (off_t)length;
-
 	while (length > 0) {
 		nbytes = MIN(length, sizeof(buf));
 		bcopy(virtual, buf, nbytes);
@@ -1108,17 +1077,14 @@
 		if (dump_encrypt(kdc, buf, nbytes) != 0)
 			return (EIO);
 
-		error = di->dumper(di->priv, buf, physical, offset, nbytes);
+		error = dump_append(di, buf, physical, nbytes);
 		if (error != 0)
 			return (error);
 
-		offset += nbytes;
 		virtual = (void *)((uint8_t *)virtual + nbytes);
 		length -= nbytes;
 	}
 
-	kdc->kdc_nextoffset = nextoffset;
-
 	return (0);
 }
 
@@ -1131,26 +1097,11 @@
 	if (kdc == NULL)
 		return (0);
 
-	return (dump_raw_write(di, kdc->kdc_dumpkey, physical, offset,
+	return (dump_write(di, kdc->kdc_dumpkey, physical, offset,
 	    kdc->kdc_dumpkeysize));
 }
 #endif /* EKCD */
 
-int
-dump_write(struct dumperinfo *di, void *virtual, vm_offset_t physical,
-    off_t offset, size_t length)
-{
-
-#ifdef EKCD
-	if (di->kdc != NULL) {
-		return (dump_encrypted_write(di, virtual, physical, offset,
-		    length));
-	}
-#endif
-
-	return (dump_raw_write(di, virtual, physical, offset, length));
-}
-
 static int
 dump_write_header(struct dumperinfo *di, struct kerneldumpheader *kdh,
     vm_offset_t physical, off_t offset)
@@ -1170,7 +1121,7 @@
 		memcpy(buf, kdh, hdrsz);
 	}
 
-	return (dump_raw_write(di, buf, physical, offset, di->blocksize));
+	return (dump_write(di, buf, physical, offset, di->blocksize));
 }
 
 /*
@@ -1179,10 +1130,9 @@
  * key.
  */
 int
-dump_start(struct dumperinfo *di, struct kerneldumpheader *kdh, off_t *dumplop)
+dump_start(struct dumperinfo *di, struct kerneldumpheader *kdh)
 {
 	uint64_t dumpsize;
-	off_t dumplo;
 	uint32_t keysize;
 	int error;
 
@@ -1199,35 +1149,62 @@
 	if (di->mediasize < KERNELDUMP_METADATA_SIZE + dumpsize)
 		return (E2BIG);
 
-	dumplo = di->mediaoffset + di->mediasize - dumpsize;
+	di->dumpoff = di->mediaoffset + di->mediasize - dumpsize;
 
-	error = dump_write_header(di, kdh, 0, dumplo);
+	error = dump_write_header(di, kdh, 0, di->dumpoff);
 	if (error != 0)
 		return (error);
-	dumplo += di->blocksize;
+	di->dumpoff += di->blocksize;
 
 #ifdef EKCD
-	error = dump_write_key(di, 0, *dumplop);
+	error = dump_write_key(di, 0, di->dumpoff);
 	if (error != 0)
 		return (error);
-	dumplo += keysize;
+	di->dumpoff += keysize;
 #endif
 
-	*dumplop = dumplo;
-
 	return (0);
 }
 
+int
+dump_append(struct dumperinfo *di, void *virtual, vm_offset_t physical,
+    size_t length)
+{
+	int error;
+
+#ifdef EKCD
+	if (di->kdc != NULL)
+		error = dump_encrypted_append(di, virtual, physical, length);
+	else
+#endif
+		error = dump_write(di, virtual, physical, di->dumpoff, length);
+	if (error == 0)
+		di->dumpoff += length;
+	return (error);
+}
+
+int
+dump_write(struct dumperinfo *di, void *virtual, vm_offset_t physical,
+    off_t offset, size_t length)
+{
+	int error;
+
+	error = dump_check_bounds(di, offset, length);
+	if (error != 0)
+		return (error);
+	return (di->dumper(di->priv, virtual, physical, offset, length));
+}
+
 /*
  * Write the trailing kernel dump header and signal to the lower layers that the
  * dump has completed.
  */
 int
-dump_finish(struct dumperinfo *di, struct kerneldumpheader *kdh, off_t dumplo)
+dump_finish(struct dumperinfo *di, struct kerneldumpheader *kdh)
 {
 	int error;
 
-	error = dump_write_header(di, kdh, 0, dumplo);
+	error = dump_write_header(di, kdh, 0, di->dumpoff);
 	if (error != 0)
 		return (error);
 
Index: sys/mips/mips/minidump_machdep.c
===================================================================
--- sys/mips/mips/minidump_machdep.c
+++ sys/mips/mips/minidump_machdep.c
@@ -56,7 +56,6 @@
 int vm_page_dump_size;
 
 static struct kerneldumpheader kdh;
-static off_t dumplo;
 
 /* Handle chunked writes. */
 static uint64_t counter, progress, dumpsize;
@@ -166,10 +165,9 @@
 		wdog_kern_pat(WD_LASTVAL);
 
 		if (ptr) {
-			error = dump_write(di, ptr, 0, dumplo, len);
+			error = dump_append(di, ptr, 0, len);
 			if (error)
 				return (error);
-			dumplo += len;
 			ptr += len;
 			sz -= len;
 		} else {
@@ -267,7 +265,7 @@
 	printf("Dumping %llu out of %ju MB:", (long long)dumpsize >> 20,
 	    ptoa((uintmax_t)physmem) / 1048576);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -335,7 +333,7 @@
 		}
 	}
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/sparc64/sparc64/dump_machdep.c
===================================================================
--- sys/sparc64/sparc64/dump_machdep.c
+++ sys/sparc64/sparc64/dump_machdep.c
@@ -49,7 +49,6 @@
 
 static off_t fileofs;
 
-extern off_t dumplo;
 extern struct dump_pa dump_map[DUMPSYS_MD_PA_NPAIRS];
 
 int do_minidump = 0;
@@ -99,7 +98,7 @@
 
 	printf("Dumping %lu MB (%d chunks)\n", (u_long)(size >> 20), nreg);
 
-	error = dump_start(di, &kdh, &dumplo);
+	error = dump_start(di, &kdh);
 	if (error != 0)
 		goto fail;
 
@@ -128,7 +127,7 @@
 	if (error < 0)
 		goto fail;
 
-	error = dump_finish(di, &kdh, dumplo);
+	error = dump_finish(di, &kdh);
 	if (error != 0)
 		goto fail;
 
Index: sys/sys/conf.h
===================================================================
--- sys/sys/conf.h
+++ sys/sys/conf.h
@@ -336,21 +336,23 @@
 	off_t	mediaoffset;	/* Initial offset in bytes. */
 	off_t	mediasize;	/* Space available in bytes. */
 	void	*blockbuf;	/* Buffer for padding shorter dump blocks */
+	off_t	dumpoff;	/* Offset of ongoing kernel dump. */
 	struct kerneldumpcrypto	*kdc; /* Kernel dump crypto. */
 };
 
+extern int dumping;		/* system is dumping */
+
+int doadump(boolean_t);
 int set_dumper(struct dumperinfo *di, const char *devname, struct thread *td,
     uint8_t encrypt, const uint8_t *key, uint32_t encryptedkeysize,
     const uint8_t *encryptedkey);
+
+int dump_start(struct dumperinfo *di, struct kerneldumpheader *kdh);
+int dump_append(struct dumperinfo *, void *, vm_offset_t, size_t);
+int dump_write(struct dumperinfo *, void *, vm_offset_t, off_t, size_t);
+int dump_finish(struct dumperinfo *di, struct kerneldumpheader *kdh);
 void dump_init_header(const struct dumperinfo *di, struct kerneldumpheader *kdh,
     char *magic, uint32_t archver, uint64_t dumplen);
-int dump_start(struct dumperinfo *di, struct kerneldumpheader *kdh,
-    off_t *dumplop);
-int dump_finish(struct dumperinfo *di, struct kerneldumpheader *kdh,
-    off_t dumplo);
-int dump_write(struct dumperinfo *, void *, vm_offset_t, off_t, size_t);
-int doadump(boolean_t);
-extern int dumping;		/* system is dumping */
 
 #endif /* _KERNEL */