Re: [PATCH] nanosecond resolution for stat(2)

Re: [PATCH] nanosecond resolution for stat(2)

[Linus Torvalds]

On Mon, 23 Sep 2002, Andi Kleen wrote:
> 
> Some drivers (like mouse drivers or tty) do dubious inode [mac] time 
> accesses of the on disk inode and without even marking it dirty. This is 
> likely a bug.

No, it is intentional. At least some versions of "w" (maybe all) will use
the tty access times to judge how long the tty has been idle. The point is
that this is all information that is interesting (and useful), but not
worth sending to disk - it is useful only as long as the inode remains
locked in-core for other reasons, ie being in use.

(It's not only "not worth it" to send to disk, but it would be positively 
wrong to even _try_ updating the disk with the access times, since we want 
these things to work even with a read-only /dev).

		Linus

Re: [PATCH] nanosecond resolution for stat(2)

[Andi Kleen]

On Mon, Sep 23, 2002 at 08:57:32PM +0200, Linus Torvalds wrote:
> 
> On Mon, 23 Sep 2002, Andi Kleen wrote:
> > 
> > Some drivers (like mouse drivers or tty) do dubious inode [mac] time 
> > accesses of the on disk inode and without even marking it dirty. This is 
> > likely a bug.
> 
> No, it is intentional. At least some versions of "w" (maybe all) will use
> the tty access times to judge how long the tty has been idle. The point is
> that this is all information that is interesting (and useful), but not
> worth sending to disk - it is useful only as long as the inode remains
> locked in-core for other reasons, ie being in use.
> 
> (It's not only "not worth it" to send to disk, but it would be positively 
> wrong to even _try_ updating the disk with the access times, since we want 
> these things to work even with a read-only /dev).

Ok. But it is surely not needed for mouse drivers, isn't it ? 
(I removed a few updates in them) 

I didn't change tty in this regard anyways.

Would you consider to merge the patch ? 

-Andi

Re: [PATCH] nanosecond resolution for stat(2)

[Kai Henningsen]

torvalds@transmeta.com (Linus Torvalds)  wrote on 23.09.02 in <Pine.LNX.4.33.0209231154520.3512-100000@penguin.transmeta.com>:

> On Mon, 23 Sep 2002, Andi Kleen wrote:
> >
> > Some drivers (like mouse drivers or tty) do dubious inode [mac] time
> > accesses of the on disk inode and without even marking it dirty. This is
> > likely a bug.
>
> No, it is intentional. At least some versions of "w" (maybe all) will use
> the tty access times to judge how long the tty has been idle. The point is
> that this is all information that is interesting (and useful), but not
> worth sending to disk - it is useful only as long as the inode remains
> locked in-core for other reasons, ie being in use.
>
> (It's not only "not worth it" to send to disk, but it would be positively
> wrong to even _try_ updating the disk with the access times, since we want
> these things to work even with a read-only /dev).

Should there perhaps be a special function for this - say  
device_atime_update_nowrite() or something like that, to make it clearer  
what happens? You could put something like you just wrote as a comment  
before that function ...

MfG Kai