Messages in this thread |  | | Subject | Re: undelete in user space? | Date | Thu, 04 Jul 1996 17:15:11 -0500 | From | "Larry 'Daffy' Daffner" <> |
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Kevin M Bealer writes: -> On Sun, 30 Jun 1996, Ian Main wrote: -> -> > I suppose I'm a bit late on this one but.. Wouldn't it be best to -> > implement undelete in user space using a new rm? One could write it so -> -> Yes ... but there are more ways to delete than just "rm". Lots of programs -> can delete. rm, cp, mv, redirection of output, any compiled program that -> contains code to open a file in write mode. -> -> Which brings another point: how widely interpreted would the "undelete" -> thing be? If I have a database program which modifies a file, should it be -> backed up? What if I open a file, lseek to the beginning and start writing?
Well, the solution that I have experience with (which seemed to work pretty well when I was using it) is a package developed at Purdue called entomb. I'm looking at the design docs for it right now, and basically what it entails is creating a library 'libtomb', which contains replacements for creat, open, rename, truncate and unlink, which call an 'entomb' program to save the file off to a directory owned by an entomb user which is exempt from quotas. Users can then get back files clobbered by programs which use these libraries by using a program called unrm. The system seemed to work well (and still does, I assume) for a large number of users, and it doesn't require any changes to the kernel. Looks like it will run on Linux fairly trivially, but I haven't checked. Anyways, if anyone is interested, it's at ftp.cc.purdue.edu as /pucc/entomb-3.5.tar.gz. -> BTW what is meant by a journaling filesystem? Is this a filesystem that can -> be "unwound" to the state it was in at some previous time, or is this a -> filesystem that stores enough info on what it is doing beforehand to -> recover from any error?
I believe that a journalling filesystem is one that can be rewound to a sane state at any point in time. So merely far enough to recover from errors.
-Larry -- Larry Daffner | Linux: Unleash the workstation in your PC! vizzie@airmail.net | http://www.linux.org/ Never underestimate the bandwidth of a station wagon full of mag tapes -- Dennis Ritchie
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