Re: Getting FS access events

[Anton Altaparmakov <aia21@cam.ac.uk>]

At 08:13 15/05/01, Linus Torvalds wrote:
>On Tue, 15 May 2001, Richard Gooch wrote:
> > So what happens if I dd from the block device and also from a file on
> > the mounted FS, where that file overlaps the bnums I dd'ed? Do we get
> > two copies in the page cache? One for the block device access, and one
> > for the file access?
>
>Yup. And never the two shall meet.
>
>Why should they? Why would you ever do something like that, or care about
>the fact?

They shouldn't, but maybe some stupid utility or a typo will do it creating 
two incoherent copies of the same block on the device. -> Bad Things can 
happen.

Can't we simply stop people from doing it by say having mount lock the 
device from further opens (and vice versa of course, doing a "dd" should 
result in lock of device preventing a mount during the duration of "dd"). - 
Wouldn't this be a good thing, guaranteeing that problems cannot happen 
while not incurring any overhead except on device open/close? Or is this a 
matter of "give the user enough rope"? - If proper rw locking is 
implemented it could allow simultaneous -o ro mount with a dd from the 
device but do exclusive write locking, for example, for maximum flexibility.

Just my 2p.

Anton


-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Linux NTFS Maintainer / WWW: http://sourceforge.net/projects/linux-ntfs/
ICQ: 8561279 / WWW: http://www-stu.christs.cam.ac.uk/~aia21/