libbio: add Breadn

sys/src/libbio/breadn.c

@@ -0,0 +1,26 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+
+long
+Breadn(Biobufhdr *bp, void *data, long len)
+{
+	char *e, *p;
+	int n;
+
+	p = data;
+	e = p + len;
+	if(e < p){
+		Berror(bp, "invalid read length");
+		return -1;
+	}
+	while(p < e){
+		if((n = Bread(bp, p, e - p)) <= 0){
+			if(n < 0 && p == data)
+				return -1;
+			break;
+		}
+		p += n;
+	}
+	return p - (char*)data;
+}

sys/src/libbio/mkfile

@@ -17,6 +17,7 @@ OFILES=\
 	brdline.$O\
 	brdstr.$O\
 	bread.$O\
+	breadn.$O\
 	bseek.$O\
 	bwrite.$O\
 	bvprint.$O\