Re: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)

[Linus Torvalds]

On Sat, 19 May 2001, Alexander Viro wrote:
> 
> On Sun, 20 May 2001, Edgar Toernig wrote:
> 
> > That assumption is totally bogus.  Even for regular files you have side
> > effects (atime); for anything else they're unpredictable.
> 
> That means only one thing: safe backups are possible only in single-user
> mode.

There are some strong arguments that we should have filesystem
"backdoors" for maintenance purposes, including backup. 

You can, of course, so parts of this on a LVM level, and doing backups
with "disk snapshots" may be a valid approach. However, even that is
debatable: there is very little that says that the disk image has to be
up-to-date at any particular point in time, so even with a disk snapshot
capability (which is not necessarily reasonable under all circumstances)
there are arguments for maintenance interfaces.

Thinks like "lazy fsck" (ie fsck while already running the filesystem) and
defragmentation simply is not feasible on a LVM level.

                Linus

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