Messages in this thread | | | Date | Thu, 26 Aug 2004 13:40:06 -0500 | From | David Masover <> | Subject | Re: silent semantic changes with reiser4 |
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Christophe Saout wrote:
| Yes, the main compound stream unaware applications would see would just | be a writable view of its contents. Probably not trivial to implement | but doable.
Not the main stream, I think, but we do need a way to make "eight-stream octopus" files portable. But there needs to be a copy(2) syscall, and apps need to start supporting it. After all, copy-on-write was planned for Reiser4, now 4.1*. And don't anyone dare suggest "userland library".
| It should be a simple format. Something simliar to tar. The worst thing
Simple, yes. Similar to tar, no.
How about a serializer plugin? foo.mp3/serialize (say) should return some single stream which contains all of foo.mp3. It could work for directories as well, recursively, at least on the same filesystem -- you'd back up by doing
cp /serialize /backup/20040826
This has two potential problems. One is security -- I want to be able to serialize foo.mp3 without being root, but root doesn't want me to be able to serialize /etc and thus get access to shadow.
The second problem is that in order to actually be used for backup, we need snapshots, which are not done yet*. Currently, it'd have to lock the file/directory (recursively), which you don't want to do to entire live filesystems... So, no massive backups of live systems yet, but definitely useful for sending around mp3s and such.
| that can happen is people start writing plugins for every existing | compound format out there. It should be the other way around, agree on a | simple compound format and encourage applications to use this one if the | want to use this advantage.
For the format, I vote for whatever format we're using at the storage layer. It'd be a lot faster that way, both in execution time (I think) and in development time (I'm sure). Plus, imagine the restore:
cat /backup/20040826 > /dev/hda5 resizefs_reiser4 /dev/hda5
* Disclaimer -- all this is "I think, last I checked".
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