Re: ext4 features

From: Jeffrey V. Merkey
Date: Wed Jul 05 2006 - 01:39:15 EST


H. Peter Anvin wrote:

Bill Davidsen wrote:


DC> Easily doable in userspace, why bother with kernel programming

In userspace you can't automatically delete the files when the space
becomes needed. The LD_PRELOAD/glibc methods also have the
disadvantage of having to figure out where a file goes when it's
deleted, depending on which device it happens to reside on. Demanding
read access to /proc/mounts just to do rm could cause problems.

Userspace has had 10 years to invent a good solution. If it was so
easy, it would probably have been done.

Actually, if it were so important it WOULD have been done. I suspect that the issue is not lack of a good solution, but lack of a good problem. The behavior you propose requires a lot of kernel cleverness, including make the inodes seem to go away, so the count is "right" for what the user sees.


The real solution for it is snapshots.


Peter,

Explain what you are thinking here. What I proposed, I have already implemented in NetWare, it's very easy to do. Snapshotting is not complex for FS's but does require a lot of space for meta-data to manage it. EXT is not architecteced for something this complex. A simple hidden mv is much easier to do.

Jeff


-hpa
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