vfs_syscalls.c:

vfs_syscalls.c:
Changed rename(2) to follow the letter of the POSIX spec.  POSIX
requires rename() to have no effect if its args "resolve to the same
existing file".  I think "file" can only reasonably be read as referring
to the inode, although the rationale and "resolve" seem to say that
sameness is at the level of (resolved) directory entries.

ext2fs_vnops.c, ufs_vnops.c:
Replaced code that gave the historical BSD behaviour of removing one
link name by checks that this code is now unreachable.  This fixes
some races.  All vnodes needed to be unlocked for the removal, and
locking at another level using something like IN_RENAME was not even
attempted, so it was possible for rename(x, y) to return with both x
and y removed even without any unlink(2) syscalls (one process can
remove x using rename(x, y) and another process can remove y using
rename(y, x)).

Prodded by:	alfred
MFC after:	8 weeks
PR:		42617