libdraw: use multiple read() calls in openfont() to read .font file

font files might be bigger than the i/o unit, so do multiple reads
until eof to read it.

sys/src/libdraw/openfont.c

@@ -2,36 +2,43 @@
 #include <libc.h>
 #include <draw.h>
 
+static char*
+readfile(char *name)
+{
+	enum { HUNK = 8*1024, };
+	int f, n, r;
+	char *s, *p;
+
+	n = 0;
+	r = -1;
+	if((s = malloc(HUNK)) != nil){
+		if((f = open(name, OREAD)) >= 0){
+			while((r = read(f, s+n, HUNK)) > 0){
+				n += r;
+				r = -1;
+				if((p = realloc(s, n+HUNK)) == nil)
+					break;
+				s = p;
+			}
+			close(f);
+		}
+	}
+	if(r < 0 || (p = realloc(s, n+1)) == nil){
+		free(s);
+		return nil;
+	}
+	p[n] = 0;
+	return p;
+}
+
 Font*
 openfont(Display *d, char *name)
 {
 	Font *fnt;
-	int fd, i, n;
 	char *buf;
-	Dir *dir;
 
-	fd = open(name, OREAD);
+	if((buf = readfile(name)) == nil)
-	if(fd < 0)
+		return nil;
-		return 0;
-
-	dir = dirfstat(fd);
-	if(dir == nil){
-    Err0:
-		close(fd);
-		return 0;
-	}
-	n = dir->length;
-	free(dir);
-	buf = malloc(n+1);
-	if(buf == 0)
-		goto Err0;
-	buf[n] = 0;
-	i = read(fd, buf, n);
-	close(fd);
-	if(i != n){
-		free(buf);
-		return 0;
-	}
 	fnt = buildfont(d, buf, name);
 	free(buf);
 	return fnt;