Btrfs devel - Aug 2009 - [PATCH] Btrfs: improve the BIO_RW_DISCARD conditional compile func definition

The conditional compile func definition shall better not be defined this way:
static int btrfs_issue_discard()
{
#ifdef BIO_RW_DISCARD
	...
#else
	return 0;
#endif
}

instead, can be better done this way:

#ifndef BIO_RW_DISCARD
static int btrfs_issue_discard()
{
	return 0;
}
#endif

#ifdef BIO_RW_DISCARD
static int btrfs_issue_discard()
{ 
	...
}
#endif