fix and improve tftp_read.

ChangeLog

@@ -1,3 +1,14 @@
+2000-02-25  OKUJI Yoshinori  <okuji@gnu.org>
+
+	* netboot/fsys_tftp.c (tftp_read): Set BUF_READ to zero if
+	FILEPOS is less than SAVED_FILEPOS, before calling buf_fill.
+	Don't discard all of the copied data so that we can move FILEPOS
+	backwards cheaply. Now SAVED_FILEPOS indicates the file position
+	corresponding to the first byte of BUF. If (FILEPOS -
+	SAVED_FILEPOS) is greater than (FSYS_BUFLEN / 2), move the data
+	forwards and add (FSYS_BUFLEN / 2) into SAVED_FILEPOS and
+	subtract the same value from BUF_READ.
+	
 2000-02-24  OKUJI Yoshinori  <okuji@gnu.org>
 
 	* stage2/disk_io.c [!STAGE1_5] (print_fsys_type): Mask

netboot/fsys_tftp.c

@@ -290,6 +290,7 @@ tftp_read (char *addr, int size)
   if (filepos < saved_filepos)
     {
       /* Uggh.. FILEPOS has been moved backwards. So reopen the file.  */
+      buf_read = 0;
       buf_fill (1);
       grub_memmove ((char *) &tp, (char *) &saved_tp, saved_len);
       len = saved_len;
@@ -331,18 +332,16 @@ tftp_read (char *addr, int size)
 	  size -= amt;
 	  addr += amt;
 	  filepos += amt;
-	  saved_filepos = filepos;
 	  ret += amt;
-
-	  /* Move the unused data forwards.  */
-	  grub_memmove (buf, buf + amt, buf_read - amt);
-	  buf_read -= amt;
 	}
-      else
+
+      /* If the size of the empty space becomes small, move the unused
+	 data forwards.  */
+      if (filepos - saved_filepos > FSYS_BUFLEN / 2)
 	{
-	  /* Reset the reading offset.  */
+	  grub_memmove (buf, buf + FSYS_BUFLEN / 2, FSYS_BUFLEN / 2);
-	  saved_filepos += buf_read;
+	  buf_read -= FSYS_BUFLEN / 2;
-	  buf_read = 0;
+	  saved_filepos += FSYS_BUFLEN / 2;
 	}
 
       /* Read the data.  */