[ext2resize] [PATCH] Endless loop in ext2_move_blocks()?

[Petter R. <pe...@hu...>]

When building ext2resize 1.1.19 with -W and -Wall, I see this warning:

  ext2.c: I funktionen 'ext2_move_blocks':
  ext2.c:137: advarsel: comparison of unsigned expression >= 0 is always true

This is the code in question:

	blk_t i;
        [...]
	} else if (src > dest)
		for (i = 0; i < num; i++)
			ext2_copy_block(fs, src + i, dest + i);
	else
		for (i = num - 1; i >= 0; i--)
			ext2_copy_block(fs, src + i, dest + i);

As i is unsigned, it will always be 0 or higher, and this the else
block is an endless loop.

What is the best way to fix this?  My suggestion is to run i from num
to 0 instead of trying to run from num-1 to -1:

--- ext2resize-1.1.19.orig/src/ext2.c
+++ ext2resize-1.1.19/src/ext2.c
@@ -131,8 +131,8 @@
                for (i = 0; i < num; i++)
                        ext2_copy_block(fs, src + i, dest + i);
        else
-               for (i = num - 1; i >= 0; i--)
-                       ext2_copy_block(fs, src + i, dest + i);
+               for (i = num; i > 0; i--)
+                       ext2_copy_block(fs, src + i - 1, dest + i - 1);
 }

 void ext2_read_blocks(struct ext2_fs *fs, void *ptr, blk_t block, blk_t num)

Can the default build be changed to include -W in addition to -Wall?
It show quite a lot of signed/unsigned issues, and I suspect it is
better to expose those to more people.  I suggest adding code like
this to configure.in just before the "dnl Checks for libraries." line.

  if eval "test x$GCC = xyes"; then
     CFLAGS="$CFLAGS -W -Wall"
  fi

Friendly,
-- 
Petter Reinholdtsen