Messages in this thread | | | Date | Thu, 18 Feb 1999 02:19:36 -0500 (EST) | From | Alexander Viro <> | Subject | Re: fsync on large files |
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On Wed, 17 Feb 1999, Linus Torvalds wrote:
> Now, as it is, the linux dentry cache would be confused by having > potentially multiple aliases for the same path, but that's something that > I consider to be a misfeature - but one that wasn't worth fixing > considering that we didn't have any serious filesystems that could take > advantage of it anyway (I think the only two filesystems we support right > now that can do it at all are AFFS and iso9660, and for the latter I don't > actuall yknow of anybody who does that kind of disks). > > But being able to handle hardlinked directories would actually be really > nice: if you avoid loops (which is easy to do), it goes from being a ^^^^^^^^^^^^^^ mkdir a mkdir b mkdir a/c ln a/c b/c mkdir a/c/d mv b a/c/d
If you have a way to deal with that... BTW, I strongly suspect that any solution involving scanning potential ancestors is *not* good - you can construct very unpleasant DoS that way.
> dangerous feature to a really nice one.
> > Basically, I used to think that hardlinked directories are evil, and > horrible. What changed my opinion was that (a) I found a few cases where I > really wanted to use them and (b) I noticed that most of the reason for > hating them was because they were hard to do right rather than anything > fundamentally wrong with the concept. > > We can't do them right as is, but getting rid of ".." in the on-disk > directory structure would be one step, and I think I can handle the dentry > aliasing issue too.
Could you elaborate? I am trying to figure out the way to do that and for the case of multiple links *from the same directory* I have a kinda-sorta solution. For generic thing... I would really like to hear your variant. > Imagine, for example, a directory tree with a shared component. Wouldn't > it be nice to just link it into the tree at multiple points? Imagine a > chroot() environment, for a moment - symlinks don't work to the outside, > but hardlinking does.
nullfs. It was invented for such things and we can do it. With *very* small overhead - dcache helps big way here. Cheers, Al
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