Adds usage diag. to du, and option -m, to find
files newer than a given time. This depends on the
fossil patch to enable the mtime propagation.
The man page also rewrites the synopsis in a more
compact way.

Reference: /n/sources/patch/saved/du
Date: Sun Feb 24 00:53:38 CET 2008

--- /sys/src/cmd/du.c	Sun Feb 24 00:53:38 2008
+++ /sys/src/cmd/du.c	Sun Feb 24 00:53:38 2008
@@ -15,10 +15,18 @@
 int	tflag;
 int	uflag;
 int	qflag;
+ulong	mtime;
 char	*fmt = "%llud\t%q\n";
 vlong	blocksize = 1024LL;
 
 void
+usage(void)
+{
+	fprint(2, "usage: %s [-asfntuq] [-m time] [-b bsz] [file...]\n", argv0);
+	exits("usage");
+}
+
+void
 main(int argc, char *argv[])
 {
 	int i;
@@ -37,6 +45,12 @@
 	case 'f':	/* ignore errors */
 		fflag = 1;
 		break;
+	case 'm':	/* all files, modified after time */
+		aflag = 1;
+		s = EARGF(usage());
+		if (s)
+			mtime = strtoul(s, nil, 10);
+		break;
 	case 'n':	/* all files, number of bytes */
 		aflag = 1;
 		nflag = 1;
@@ -52,7 +66,7 @@
 		qflag = 1;
 		break;
 	case 'b':	/* block size */
-		s = ARGF();
+		s = EARGF(usage());
 		if(s) {
 			blocksize = strtoul(s, &ss, 0);
 			if(s == ss)
@@ -61,6 +75,8 @@
 				blocksize *= 1024;
 		}
 		break;
+	default:
+		usage();
 	} ARGEND
 	if(argc==0)
 		print(fmt, du(".", dirstat(".")), ".");
@@ -95,7 +111,8 @@
 				if((d->qid.type&QTDIR) == 0) {
 					t = k(d->length);
 					nk += t;
-					if(aflag) {
+					if(aflag)
+					if(!mtime || d->mtime >= mtime){
 						file = s_copy(name);
 						s_append(file, "/");
 						s_append(file, d->name);
@@ -114,6 +131,8 @@
 				if(strcmp(d->name, ".") == 0 ||
 				   strcmp(d->name, "..") == 0 ||
 				   seen(d))
+					continue;
+				if (mtime && d->mtime < mtime)
 					continue;
 				file = s_copy(name);
 				s_append(file, "/");
--- /sys/man/1/du	Sun Feb 24 00:53:38 2008
+++ /sys/man/1/du	Sun Feb 24 00:53:38 2008
@@ -4,25 +4,10 @@
 .SH SYNOPSIS
 .B du
 [
-.B -a
+.B -asfntuq
 ]
 [
-.B -f
-]
-[
-.B -n
-]
-[
-.B -q
-]
-[
-.B -s
-]
-[
-.B -t
-]
-[
-.B -u
+.B -m time
 ]
 [
 .BI -b size
@@ -85,6 +70,12 @@
 .BR -n ,
 the QID of
 each file rather than the size.
+.PP
+The
+.B -m
+option instructs
+.I du
+to ignore any file with modified time less than the one given.
 .PP
 Finally, the
 .B -s