xread/xwrite: do not worry about EINTR at calling sites.

We had errno==EINTR check after read(2)/write(2) sprinkled all
over the places, always doing continue.  Consolidate them into
xread()/xwrite() wrapper routines.

Credits for suggestion goes to HPA -- bugs are mine.

Signed-off-by: Junio C Hamano <junkio@cox.net>

copy.c

@@ -6,32 +6,27 @@ int copy_fd(int ifd, int ofd)
 		int len;
 		char buffer[8192];
 		char *buf = buffer;
-		len = read(ifd, buffer, sizeof(buffer));
+		len = xread(ifd, buffer, sizeof(buffer));
 		if (!len)
 			break;
 		if (len < 0) {
 			int read_error;
-			if (errno == EAGAIN)
-				continue;
 			read_error = errno;
 			close(ifd);
 			return error("copy-fd: read returned %s",
 				     strerror(read_error));
 		}
-		while (1) {
-			int written = write(ofd, buf, len);
+		while (len) {
+			int written = xwrite(ofd, buf, len);
 			if (written > 0) {
 				buf += written;
 				len -= written;
-				if (!len)
-					break;
 			}
-			if (!written)
+			else if (!written)
 				return error("copy-fd: write returned 0");
-			if (errno == EAGAIN || errno == EINTR)
-				continue;
-			return error("copy-fd: write returned %s",
-				     strerror(errno));
+			else
+				return error("copy-fd: write returned %s",
+					     strerror(errno));
 		}
 	}
 	close(ifd);