Re: mnotify: mixing nonotify & simple mount watching (Was: Re: [RFC/PATCH] Nonotify...)



Hi,

Am Freitag, den 13.08.2004, 22:14 +0200 schrieb nf:

> Maybe it would be sufficient to store the file modification dates not
> only in the parent directories but also in a field in the device
> superblock: The userspace client would only have to poll the
> 'mcontents_mtime' [1] of the mounted devices and, only if it has
> changed, poll the 'dcontents_mtime' [2] of the directories on the
> device. That would also reduce the idle activity to almost zero, but
> without the need of a complex event queuing and grouping mechanism
> inside the kernel. (But to be honest, i don't know how that kernel event
> stuff works).
> 
> [1] Mountpoint contents modification time
> [2] Directory contents modification time
^-- hmm...

Keep in mind that directory mtimes have pretty unexpected semantics. If
you have a directory "a" which in turn has a directory "b" which in turn
contains file "c", if you change file "c", for some reason *only* the
mtime of the directory "b" get updated. 
(I'd either think that it would be *supposed* to be either: 1) *only*
the mtime of the file be updated or 2) the mtime of the directory "b" be
updated, that would trigger updating the mtime of the directory "a")

a     <-- 3. mtime, unchanged
+--b  <-- 2. mtime, changed
   +-- c <-- 1. file, changed

At least I think it is that way, but I have to say that I never quite
understood that kind of inconsistency so I might be wrong.

[...]

cheers,
   Danny

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