|From:||Erez Zadok <ezk-AT-cs.sunysb.edu>|
|To:||Christoph Hellwig <hch-AT-infradead.org>|
|Subject:||Re: [UNIONFS] 00/29 Unionfs and related patches pre-merge review (v2)|
|Date:||Thu, 10 Jan 2008 10:57:46 -0500|
|Cc:||Erez Zadok <ezk-AT-cs.sunysb.edu>, torvalds-AT-linux-foundation.org, akpm-AT-linux-foundation.org, viro-AT-ftp.linux.org.uk, linux-kernel-AT-vger.kernel.org, linux-fsdevel-AT-vger.kernel.org|
In message <20080110150808.GA32080@infradead.org>, Christoph Hellwig writes: > On Thu, Jan 10, 2008 at 09:59:19AM -0500, Erez Zadok wrote: > > > > Dear Linus, Al, Christoph, and Andrew, > > > > As per your request, I'm posting for review the unionfs code (and related > > code) that's in my korg tree against mainline (v2.6.24-rc7-71-gfd0b45d). > > This is in preparation for merge in 2.6.25. > > Huh? There's still aboslutely not fix to the underlying problems of > the whole idea. I think we made it pretty clear that unionfs is not > the way to go, and that we'll get the union mount patches clear once > the per-mountpoint r/o and unprivilegued mount patches series are in > and stable. I'll reiterate what I've said before: unionfs is used today by many users, it works, and is stable. After years of working with unionfs, we've settled on a set of features that users actually use. This functionality can be in mainline today. Unioning at the VFS level, will take a long time to reach the same level of maturity and support the same set of features. Based on my years of practical experience with it, unioning directories seems like a simple idea, but in practice it's quite hard no matter the approach taken to implement it. Existing users of unioning aren't likely to switch to Union Mounts unless it supports the same set of features. How long will it realistically take to get whiteout support in every lower file system that's used by Unionfs users? How will Union Mounts support persistent inode numbers at the VFS level? Those are just a few of the questions. I think a better approach would be to start with Unionfs (a standalone file system that doesn't touch the rest of the kernel). And as Linux gradually starts supporting more and more features that help unioning/stacking in general, to change Unionfs to use those features (e.g., native whiteout support). Eventually there could be basic unioning support at the VFS level, and concurrently a file-system which offers the extra features (e.g., persistency). This can be done w/o affecting user-visible APIs. Cheers, Erez. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html
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