Vitez Gabor wrote:

Hi,

It would be really great if ext4 supported an xfs_freeze like operation. 
On xfs it spared me a lot of headaches when I was playing with unstable 
kernel features.

  thanks
    Gabor

Right now ext3 and ext4 -can- be frozen, but only via devicemapper,
because the call to freeze_bdev is only exposed via

<dm ioctl>
  dev_suspend
    do_suspend
      dm_suspend
        lock_fs
          freeze_bdev <-- generic, exported kernel function

on an lvm volume.  So, I think ext[34] are perfectly capable of being
frozen, there's just no generic userspace utility to point at a generic
block device to do that freezing.  xfs's collection of ioctls to do this
directly got grandfathered in, I guess.  :)

-Eric