Re: bdflush (was: corrupt inode)

[Seth Mos <knuffie@xs4all.nl>]

At 22:13 9-8-2001 +0800, Federico Sevilla III wrote:
>On Thu, 9 Aug 2001 at 08:58, yocum@fnal.gov wrote:
> > Nope. If the machine dies while there's still data in the buffer (in
> > local memory cache) that data is gone.
>
>And it's possible to get files filled with binary zeroes, which is
>explained in the FAQ. Right?

Explanation will follow soon, a bit tied up at the moment. Tonight perhaps.

>I am still unclear as to whether the actions of bdflush are equivalent to
>those of sync, though, at least with XFS. (I am not sure whether this is
>filesystem-specific or not)

I don't think defining it per filesystem would be efficient. I guess this 
goes for all filesystems

>Also: let's say I modify a small file, then leave the system active for 30
>seconds. Theoretically that means the data would have been flushed to disk
>already, right?

It does on my system.

>  Assuming write cache is turned off, of course. Then will
>turning off the machine (or it dying for some reason) cause a file filled
>with binary zeroes?

No, it will only do that if the program in question would actually truncate 
the file IIRC.

>  It shouldn't, at least by my limited understanding. I
>hope I am correct.

A email spool would probably not be affected since those programs are a lot 
more secure in making sure that the data goes to disk.

http://marc.theaimsgroup.com/?l=linux-xfs&m=99535721114156&w=4

vi -r <file>

Seems to be the right way to do it. Pico does not exhibit this problem, 
better yet it seems this clients calls a sync after saving and exiting. I 
was real fast but it got it's data to disk.
So i would say this is a "safe" editor ;-)

The journaling fs is not to blame, it does it's work correctly. The 
application needs to have some form of modern day filesystems. Does anybody 
have a ReiserFS or JFS filesystem to test this with?

I also tried this trick with vi and sure thing the file got filled with 
nulls. Somebody should patch vi to have a "fsync" operation mode. Otherwise 
you should put an alias in your .profile like:
alias vi='vi -r'

Or something resembling that.

Cheers
--
Seth
Every program has two purposes one for which
it was written and another for which it wasn't
I use the last kind.