Re: linux-2.4.10-pre5

[H. Peter Anvin]

Followup to:  <[e-mail]>
By author:    Linus Torvalds <[e-mail]>
In newsgroup: linux.dev.kernel
> 
> I agree that coherency wrt fsck is something that theoretically would be a
> GoodThing(tm). And this is, in fact, why I believe that filesystem
> management _must_ have a good interface to the low-level filesystem.
> Because you cannot do it any other way.
> 
> This is not a fsck-only issue. I am a total non-believer in the "dump"
> program, for example. I always found it to be a totally ridiculous and
> idiotic way to make backups. It would be much better to have good
> (filesystem-independent) interfaces to do what "dump" wants to do (ie have
> ways of explicitly bypassing the accessed bits and get the full inode
> information etc).
> 
> Nobody does a "read()" on directories any more to parse the directory
> structure. Similarly, nobody should have done a "dump" on the raw device
> any more for the last 20 years or so. But some backwards places still do.
> 

The main reason people seems to still justify use dump/restore is --
believe it or not -- the inability to set atime.  One would think this
would be a trivial extension to the VFS, even if protected by a
capability (CAP_BACKUP?).

The ideal way to run backups I have found is on filesystems which
support atomic snapshots -- that way, your backup set becomes not only
safe (since it goes through the kernel etc. etc.) but totally
coherent, since it is guaranteed to be unchanging.  This is a major
win for filesystems which can do atomic snapshots, and I'd highly
encourage filesystem developers to consider this feature.

	-hpa

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