diff --git a/apps/ed/README.md b/apps/ed/README.md
index 2ea0bf9..6db9de6 100644
--- a/apps/ed/README.md
+++ b/apps/ed/README.md
@@ -22,8 +22,9 @@ not listed here are either bugs or simply aren't implemented yet.
 
 ## Usage
 
-`ed` is invoked from the shell with no argument. ed takes no argument.
-It reads from the currently selected blkdev and writes to it.
+`ed` is invoked from the shell with a single argument: the name of the file to
+edit. If the file doesn't exist, `ed` errors out. If it exists, a prompt is
+shown.
 
 In normal mode, `ed` waits for a command and executes it. If the command is
 invalid, a line with `?` is printed and `ed` goes back to waiting for a command.
diff --git a/apps/ed/buf.asm b/apps/ed/buf.asm
index 65cc517..f5226e1 100644
--- a/apps/ed/buf.asm
+++ b/apps/ed/buf.asm
@@ -40,8 +40,8 @@ bufInit:
 	ld	ix, BUF_LINES
 	ld	bc, 0		; line count
 .loop:
-	call	blkTell		; --> HL
-	call	blkGetC
+	call	ioTell		; --> HL
+	call	ioGetC
 	jr	nz, .loopend
 	ld	(ix), l
 	inc	ix
diff --git a/apps/ed/io.asm b/apps/ed/io.asm
index 4e582d4..eecd5ec 100644
--- a/apps/ed/io.asm
+++ b/apps/ed/io.asm
@@ -6,11 +6,62 @@
 .equ	IO_MAXLEN	0x7f
 
 ; *** Variables ***
+; Handle of the target file
+.equ	IO_FILE_HDL	IO_RAMSTART
+; block device targeting IO_FILE_HDL
+.equ	IO_BLK		IO_FILE_HDL+FS_HANDLE_SIZE
 ; Buffer for lines read from I/O.
-.equ	IO_LINE		IO_RAMSTART
+.equ	IO_LINE		IO_BLK+BLOCKDEV_SIZE
 .equ	IO_RAMEND	IO_LINE+IO_MAXLEN+1	; +1 for null
 ; *** Code ***
 
+; Given a file name in (HL), open that file in (IO_FILE_HDL) and open a blkdev
+; on it at (IO_BLK).
+ioInit:
+	call	fsFindFN
+	ret	nz
+	ld	ix, IO_FILE_HDL
+	call	fsOpen
+	ld	de, IO_BLK
+	ld	hl, .blkdev
+	jp	blkSet
+.fsGetC:
+	ld	ix, IO_FILE_HDL
+	jp	fsGetC
+.fsPutC:
+	ld	ix, IO_FILE_HDL
+	jp	fsPutC
+.blkdev:
+	.dw	.fsGetC, .fsPutC
+
+ioGetC:
+	push	ix
+	ld	ix, IO_BLK
+	call	_blkGetC
+	pop	ix
+	ret
+
+ioPutC:
+	push	ix
+	ld	ix, IO_BLK
+	call	_blkPutC
+	pop	ix
+	ret
+
+ioSeek:
+	push	ix
+	ld	ix, IO_BLK
+	call	_blkSeek
+	pop	ix
+	ret
+
+ioTell:
+	push	ix
+	ld	ix, IO_BLK
+	call	_blkTell
+	pop	ix
+	ret
+
 ; Given an offset HL, read the line in IO_LINE, without LF and null terminates
 ; it. Make HL point to IO_LINE.
 ioGetLine:
@@ -19,11 +70,11 @@ ioGetLine:
 	push	bc
 	ld	de, 0		; limit ourselves to 16-bit for now
 	xor	a		; absolute seek
-	call	blkSeek
+	call	ioSeek
 	ld	hl, IO_LINE
 	ld	b, IO_MAXLEN
 .loop:
-	call	blkGetC
+	call	ioGetC
 	jr	nz, .loopend
 	or	a		; null? hum, weird. same as LF
 	jr	z, .loopend
diff --git a/apps/ed/main.asm b/apps/ed/main.asm
index 5582b01..5e8acad 100644
--- a/apps/ed/main.asm
+++ b/apps/ed/main.asm
@@ -31,11 +31,17 @@
 ;
 ; *** Requirements ***
 ; BLOCKDEV_SIZE
+; FS_HANDLE_SIZE
+; _blkGetC
+; _blkPutC
+; _blkSeek
+; _blkTell
 ; addHL
-; blkGetC
-; blkSeek
-; blkTell
 ; cpHLDE
+; fsFindFN
+; fsOpen
+; fsGetC
+; fsPutC
 ; intoHL
 ; printstr
 ; printcrlf
@@ -49,6 +55,9 @@
 .equ	ED_RAMEND	ED_CURLINE+2
 
 edMain:
+	; because ed only takes a single string arg, we can use HL directly
+	call	ioInit
+	ret	nz
 	; diverge from UNIX: start at first line
 	ld	hl, 0
 	ld	(ED_CURLINE), hl
diff --git a/tools/emul/shell/shell_.asm b/tools/emul/shell/shell_.asm
index 74ef5f5..a522124 100644
--- a/tools/emul/shell/shell_.asm
+++ b/tools/emul/shell/shell_.asm
@@ -27,6 +27,7 @@
 	jp	fsFindFN
 	jp	fsOpen
 	jp	fsGetC
+	jp	fsPutC
 	jp	cpHLDE
 	jp	parseArgs
 	jp	printstr
@@ -37,9 +38,6 @@
 	jp	printcrlf
 	jp	stdioPutC
 	jp	stdioReadLine
-	jp	blkGetC
-	jp	blkSeek
-	jp	blkTell
 
 #include "core.asm"
 #include "err.h"
diff --git a/tools/emul/shell/user.h b/tools/emul/shell/user.h
index 2eab1c8..c2d1379 100644
--- a/tools/emul/shell/user.h
+++ b/tools/emul/shell/user.h
@@ -20,16 +20,14 @@
 .equ	fsFindFN		0x2a
 .equ	fsOpen			0x2d
 .equ	fsGetC			0x30
-.equ	cpHLDE			0x33
-.equ	parseArgs		0x36
-.equ	printstr		0x39
-.equ	_blkGetC		0x3c
-.equ	_blkPutC		0x3f
-.equ	_blkSeek		0x42
-.equ	_blkTell		0x45
-.equ	printcrlf		0x48
-.equ	stdioPutC		0x4b
-.equ	stdioReadLine	0x4e
-.equ	blkGetC			0x51
-.equ	blkSeek			0x54
-.equ	blkTell			0x57
+.equ	fsPutC			0x33
+.equ	cpHLDE			0x36
+.equ	parseArgs		0x39
+.equ	printstr		0x3c
+.equ	_blkGetC		0x3f
+.equ	_blkPutC		0x42
+.equ	_blkSeek		0x45
+.equ	_blkTell		0x48
+.equ	printcrlf		0x4b
+.equ	stdioPutC		0x4e
+.equ	stdioReadLine	0x51