Cleaup read() and write() variants, plus a couple of new functions like

xlseek and fdlength() for the new mkswap.

libbb/xfuncs.c

@@ -120,40 +120,55 @@ int bb_xopen3(const char *pathname, int flags, int mode)
 #endif
 
 #ifdef L_xread
-ssize_t bb_xread(int fd, void *buf, size_t count)
+
+// Die with an error message if we can't read the entire buffer.
+
+void xread(int fd, void *buf, size_t count)
 {
-	ssize_t size;
-
-	size = read(fd, buf, count);
-	if (size < 0) {
-		bb_perror_msg_and_die(bb_msg_read_error);
-	}
-	return(size);
-}
-#endif
-
-#ifdef L_xread_all
-void bb_xread_all(int fd, void *buf, size_t count)
-{
-	ssize_t size;
-
 	while (count) {
-		if ((size = bb_xread(fd, buf, count)) == 0) {	/* EOF */
+		ssize_t size;
+
+		if ((size = safe_read(fd, buf, count)) < 1)
 			bb_error_msg_and_die("Short read");
-		}
 		count -= size;
 		buf = ((char *) buf) + size;
 	}
-	return;
+}
+#endif
+
+#ifdef L_xwrite
+
+// Die with an error message if we can't write the entire buffer.
+
+void xwrite(int fd, void *buf, size_t count)
+{
+	while (count) {
+		ssize_t size;
+
+		if ((size = safe_write(fd, buf, count)) < 1)
+			bb_error_msg_and_die("Short write");
+		count -= size;
+		buf = ((char *) buf) + size;
+	}
+}
+#endif
+
+#ifdef L_xlseek
+
+// Die if we can't lseek to the right spot.
+
+void xlseek(int fd, off_t offset, int whence)
+{
+	if (whence != lseek(fd, offset, whence)) bb_error_msg_and_die("lseek");
 }
 #endif
 
 #ifdef L_xread_char
-unsigned char bb_xread_char(int fd)
+unsigned char xread_char(int fd)
 {
 	char tmp;
 
-	bb_xread_all(fd, &tmp, 1);
+	xread(fd, &tmp, 1);
 
 	return(tmp);
 }
@@ -294,3 +309,41 @@ void xsetuid(uid_t uid)
 	if (setuid(uid)) bb_error_msg_and_die("setuid");
 }
 #endif
+
+#ifdef L_fdlength
+off_t fdlength(int fd)
+{
+	off_t bottom = 0, top = 0, pos;
+	long size;
+
+	// If the ioctl works for this, return it.
+
+	if (ioctl(fd, BLKGETSIZE, &size) >= 0) return size*512;
+
+	// If not, do a binary search for the last location we can read.
+
+	do {
+		char temp;
+
+		pos = bottom + (top - bottom) / 2;;
+
+		// If we can read from the current location, it's bigger.
+
+		if (lseek(fd, pos, 0)>=0 && safe_read(fd, &temp, 1)==1) {
+			if (bottom == top) bottom = top = (top+1) * 2;
+			else bottom = pos;
+
+		// If we can't, it's smaller.
+
+		} else {
+			if (bottom == top) {
+				if (!top) return 0;
+				bottom = top/2;
+			}
+			else top = pos;
+		}
+	} while (bottom + 1 != top);
+
+	return pos + 1;
+}
+#endif