This is a patch for tftpd. It does 2 things:

1. adds an '-u' option for tftpd

With this option I can run tftpd as current user - no switch to user none.
Then I don't need to create world writable dir for tftp write requests.
It is useful for QEMU with the user network stack and redirected ports.
I can exchange files between my host OS and Plan9 guest in QEMU
with tftp client in my host OS. 
I start tftpd in my working dir, send/receive files, kill tftpd.

Example of batch file for starting QEMU in MS-Windows:

set QEMU=C:/Program Files/QEMU
"%QEMU%/qemu.exe" -hda plan9.10G.qcow2 -m 256 -net nic,model=rtl8139 -net user -redir udp:69::69 -redir tcp:567::567 -redir tcp:17010::17010 -L "%QEMU%"

2. it was impossible to send file to tftpd server (write request) due to an error. I corrected it.

Reference: /n/sources/patch/maybe/tftpd-error
Date: Thu Sep 11 21:13:18 CES 2008
Signed-off-by: antonin.vecera@gmail.com

--- /sys/src/cmd/ip/tftpd.c	Thu Sep 11 21:35:24 2008
+++ /sys/src/cmd/ip/tftpd.c	Thu Sep 11 21:25:26 2008
@@ -13,6 +13,7 @@
 
 int 	dbg;
 int	restricted;
+int	user;
 void	sendfile(int, char*, char*);
 void	recvfile(int, char*, char*);
 void	nak(int, int, char*);
@@ -72,6 +73,9 @@
 	case 's':
 		svc = EARGF(usage());
 		break;
+	case 'u':
+		user = 1;
+		break;
 	case 'x':
 		p = ARGF();
 		if(p == nil)
@@ -107,7 +111,8 @@
 	if (cfd < 0)
 		sysfatal("announcing on %s: %r", buf);
 	syslog(dbg, flog, "tftpd started on %s dir %s", buf, adir);
-	setuser();
+	if(!user)
+		setuser();
 	for(;;) {
 		lcfd = listen(adir, ldir);
 		if(lcfd < 0)
@@ -306,11 +311,11 @@
 		if(op == Tftp_ERROR)
 			goto error;
 
-		n -= 4;
 		inblock = buf[2]<<8|buf[3];
+		n -= 4;
 		if(op == Tftp_DATA) {
 			if(inblock == block) {
-				ret = write(file, buf, n);
+				ret = write(file, buf+4, n);
 				if(ret < 0) {
 					errstr(errbuf, sizeof errbuf);
 					nak(fd, 0, errbuf);
@@ -318,8 +323,8 @@
 				}
 				ack(fd, block);
 				block++;
-			}
-			ack(fd, 0xffff);
+			} else
+				ack(fd, 0xffff);
 		}
 	}
 error:
--- /sys/man/8/dhcpd	Thu Sep 11 21:36:10 2008
+++ /sys/man/8/dhcpd	Thu Sep 11 21:26:06 2008
@@ -28,7 +28,7 @@
 .IR netmtpt ]
 .PP
 .B ip/tftpd
-.RB [ -dr ]
+.RB [ -dru ]
 .RB [ -h
 .IR homedir ]
 .RB [ -x
@@ -252,6 +252,9 @@
 .TP
 .B d
 Print debugging to standard output.
+.TP
+.B u
+Don't switch to user none, run as current user.
 .TP
 .B x
 The IP stack to use is mounted at