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ip/tftpd: add -m argument for name substitution using regular expressions

This allows mapping incoming filenames to a different name
using regular expressions, followed by subtitutions
of the %[ICE] format strings.

I needed this to have individual cmdline.txt files for
netbooted raspberry pi's. In this example, i map cmdline.txt
to %C, which gets substituted for /cfg/pxe/$ether of the client.

--- a/sys/man/8/dhcpd

+++ b/sys/man/8/dhcpd

@@ -43,7 +43,9 @@

 .RB [ -x

 .IR netmtpt ]

 .RB [ -n

-.IR namespace-file ]

+.IR nsfile ]

+.RB [ -m

+.IR mapfile ]

 .SH DESCRIPTION

 These programs support booting over the Internet.

 They should all be run on the same server to

@@ -323,6 +325,26 @@

 .TP

 .B n

 Sets the namespace file (default /lib/namespace).

+.TP

+.B m

+Loads name substitutions from

+.IR mapfile .

+The format is a space or tab separated two-column text

+with the first column being a regular expression

+(see

+.IR regexp (6))

+that is matched against the requested file name

+and the second column contains a subsitution.

+Lines starting with

+.B #

+are ignored.

+Occurances in the resulting filename of

+.BR %I ,

+.B %C

+or

+.B %E

+are replaced with the ip, cfgpxe name or ether MAC of

+of the client.

 .PD

 .SH FILES

 .BR /lib/ndb/dhcp "    directory of dynamic address files

--- a/sys/src/cmd/ip/tftpd.c

+++ b/sys/src/cmd/ip/tftpd.c

@@ -6,6 +6,7 @@

 #include <auth.h>

 #include <bio.h>

 #include <ip.h>

+#include <regexp.h>

 enum

 {

@@ -63,6 +64,13 @@

 	int	max;

 };

+typedef struct Map Map;

+struct Map {

+	Reprog	*re;

+	char	*sub;

+	Map	*next;

+};

+

 int 	dbg;

 int	restricted;

 int	pid;

@@ -85,6 +93,7 @@

 void	clrcon(void);

 void	setuser(void);

 void	remoteaddr(char*, char*, int);

+void	readmapfile(char*);

 void	doserve(int);

 char	bigbuf[32768];

@@ -94,6 +103,7 @@

 int	dirsllen;

 char	*homedir = "/";

 char	*nsfile = nil;

+Map	*namemap = nil;

 char	flog[] = "ipboot";

 char	net[Maxpath];

@@ -109,7 +119,7 @@

 void

 usage(void)

 {

-	fprint(2, "usage: %s [-dr] [-h homedir] [-s svc] [-x netmtpt]\n",

+	fprint(2, "usage: %s [-dr] [-h homedir] [-s svc] [-x netmtpt] [-n nsfile] [-m mapfile]\n",

 		argv0);

 	exits("usage");

 }

@@ -142,6 +152,9 @@

 	case 'n':

 		nsfile = EARGF(usage());

 		break;

+	case 'm':

+		readmapfile(EARGF(usage()));

+		break;

 	default:

 		usage();

 	}ARGEND

@@ -177,7 +190,6 @@

 	if (cfd < 0)

 		sysfatal("announcing on %s: %r", buf);

 	syslog(dbg, flog, "tftpd started on %s dir %s", buf, adir);

-//	setuser();

 	for(;;) {

 		lcfd = listen(adir, ldir);

 		if(lcfd < 0)

@@ -368,6 +380,7 @@

 }

 /*

+ * substitute name from namemap file and

  * replace one occurrence of %[ICE] with ip, cfgpxe name, or ether mac, resp.

  * we can't easily use $ because u-boot has stranger quoting rules than sh.

  */

@@ -374,11 +387,21 @@

 char *

 mapname(char *file)

 {

-	int nf;

-	char *p, *newnm, *cur, *arpf, *ln, *remip, *bang;

-	char *fields[4];

+	char sub[1024], *p, *newnm, *cur, *arpf, *ln, *remip, *bang;

 	Biobuf *arp;

+	Map *map;

+	for(map = namemap; map != nil; map = map->next){

+		Resub subs[16];

+

+		memset(subs, 0, sizeof(subs));

+		if(regexec(map->re, file, subs, nelem(subs))){

+			regsub(map->sub, sub, sizeof(sub), subs, nelem(subs));

+			file = sub;

+			break;

+		}

+	}

+

 	p = strchr(file, '%');

 	if (p == nil || p[1] == '\0')

 		return strdup(file);

@@ -411,6 +434,9 @@

 			break;

 		/* read lines looking for remip in 3rd field of 4 */

 		while ((ln = Brdline(arp, '\n')) != nil) {

+			char *fields[4];

+			int nf;

+

 			ln[Blinelen(arp)-1] = 0;

 			nf = tokenize(ln, fields, nelem(fields));

 			if (nf >= 4 && strcmp(fields[2], remip) == 0) {

@@ -448,8 +474,12 @@

 	while(*p && dlen--)

 		p++;

+	syslog(dbg, flog, "tftpd %d mode %s file %s", pid, mode, file);

+

 	file = mapname(file);	/* we don't free the result; minor leak */

+	syslog(dbg, flog, "tftpd %d file -> %s", pid, file);

+

 	if(dlen == 0) {

 		nak(fd, 0, "bad tftpmode");

 		close(fd);

@@ -771,4 +801,52 @@

 	if(n > 0)

 		n--;

 	raddr[n] = 0;

+}

+

+void

+readmapfile(char *file)

+{

+	Map **link, *map;

+	Biobuf *bio;

+	char *s, *p, *d;

+	int line;

+

+	/* go to last entry */

+	for(link = &namemap; *link; link = &(*link)->next)

+		;

+

+	if((bio = Bopen(file, OREAD)) == nil)

+		sysfatal("open: %r");

+

+	for(line = 1; (s = Brdstr(bio, '\n', 1)) != nil; free(s), line++){

+		p = s;

+		while(strchr("\t ", *p))

+			p++;

+

+		if(*p == '#')

+			continue;

+

+		if(d = strchr(p, '\t'))

+			*d++ = '\0';

+		else if(d = strchr(p, ' '))

+			*d++ = '\0';

+		else {

+			fprint(2, "%s:%d: ignored: %s\n", file, line, p);

+			continue;

+		}

+		while(strchr("\t ", *d))

+			d++;

+		map = malloc(sizeof(Map));

+		map->re = regcomp(p);

+		if(map->re == nil){

+			fprint(2, "%s:%d: syntax error: %s\n", file, line, p);

+			free(map);

+			continue;

+		}

+		map->sub = strdup(d);

+		map->next = nil;

+		*link = map;

+		link = &map->next;

+	}

+	Bterm(bio);

 }