Re: reiser4 plugins

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On Jun 27, 2005, at 17:19:21, David Masover wrote:
Precisely. Come back when you have a good sturdy set of arguments. See the FUSE project (Also discussed in this thread), for better ideas on how
to add strange filesystem semantics.

If I didn't care about performance.  I will read up on how FUSE works,
though, to see if there's anything in the _kernel_ code that would be
useful.

A number of projects do their performance critical things in userspace,
including real-time audio and video editing.  The kernel is *NOT* for
performance-critical things, unless they cannot be done efficiently in
userspace. It is for _security_critical_ and _stability_critical_ things,
and even then, some of those are pushed to userspace as well.

NOTE:  Even the FUSE project,  which
is in _userspace_ (as opposed to the massive kernelspace mess of reiser4), is taking a lot of flak for changing UNIX semantics, so I see no reason
why Reiser4 should be special.

Right.  Kernel people hate change.  Got it.

No, seriously, I have to respect the history involved, which is why I'm
not pretending to know more than I do.

There is a good reason to hate change (at least without thorough evidence to back it up). Even small changes can break things in subtle ways. Big changes can tend to wreak kernel-global (and even userspace-global) havoc.

Ok, good.  That's one of the first issues.  A _lot_ of applications
would get themselves thoroughly confused at that '...' interface, not
to  mention a lot of sysadmins :-D.


Not as much as you think.  Unless a lot of applications can't handle
opening or saving files that have '...' in the pathname?

If those files are as special as you lead me to believe, even a simple
"tar -cjvf foo.tar.bz2 foo" would break horribly, because it would tar up
all sorts of strange special files that shouldn't be included.  Worse,
when I untar that archive on the filesystem, it will overwrite those files, which probably should be overwritten even less than they should be stored
in an archive.

The sysadmin problem doesn't worry me so much.

Personally, I know several sysadmins who, never having heard of Reiser4
but using it anyways, would get scared when all of the '...' directories
started showing up, thinking that some cracker had gotten a module loaded in their kernel. If you can, please avoid overloading existing semantics
in filesystems.  You can either claim that your filesystem is POSIXy,
(similar to ext3, xfs, etc), or you can claim that it's not compatible by
design (AFS, Coda) or you can claim that it's a completely virtualized
interface (procfs, sysfs, CKRM fs, etc) and doesn't care about POSIX in
any case. Reiser4 definitely isn't the third, but neither is it either of
the first two, because it would break standard operations.

Agreed. I don't know enough about VFS to propose one, though. I think
others are working on that, finally.

When the VFS work gets done, this discussion can move on, otherwise, we
are stuck at an impasse.

Not too much, I hope.

Although being able to use different keys on a per-file basis would be
nice.  I'm not sure if that would work in the existing system.  Not to
mention that keys would also be handlable with '...', if/when it happens.

I think the '...' is just a bad idea in general, because it breaks tar
and such.  An interface like this might be simpler to design and use:

# mkdir /attr
# mount -t attrfs attrfs /attr

/attr/fd/$FD_NUM              == '...' directory for a filedescriptor
/attr/fs/$DEV_NUM/$INODE_NUM  == '...' directory for an inode

It would be usable from a shell with a simple "getattrpath" command
which returns "fs/$DEV_NUM/$INODE_NUM" by stat-ing any given path.

Cheers,
Kyle Moffett

--
There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies.
 -- C.A.R. Hoare

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