minimal plan9port to cross-build Jehanne

lib/lib9/read9pmsg.c

@@ -0,0 +1,31 @@
+#include <u.h>
+#include <libc.h>
+#include <fcall.h>
+
+int
+read9pmsg(int fd, void *abuf, uint n)
+{
+	int m, len;
+	uchar *buf;
+
+	buf = abuf;
+
+	/* read count */
+	m = readn(fd, buf, BIT32SZ);
+	if(m != BIT32SZ){
+		if(m < 0)
+			return -1;
+		return 0;
+	}
+
+	len = GBIT32(buf);
+	if(len <= BIT32SZ || len > n){
+		werrstr("bad length in 9P2000 message header");
+		return -1;
+	}
+	len -= BIT32SZ;
+	m = readn(fd, buf+BIT32SZ, len);
+	if(m < len)
+		return 0;
+	return BIT32SZ+m;
+}