Re: Carrying Attributes too Far

[Bennett Todd <bet@rahul.net>]

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2003-09-18T17:44:13 Alexander G. M. Smith:
> They need to be hidden sometimes. [...] Or be prepared for them to
> make a mess, like storing all their e-mail inside an attribute on
> an e-mail icon.

And that thought provoked some pondering in me.

I've been thinking about these new semantics in Reiserfs v4 in terms
of the ability to take a file, and attach some addenda on it by
viewing it as a directory instead.

As a Maildir user, your above comment turned that view upside down
--- you're saying someone will attach an icon to the directory that
happens to be their Maildir folder. Viewing directories (non-leaf
nodes of the tree) as files is the dual, the same concept viewed
backwards, as viewing files (leaves) as directories.

There's a nice satisfying generality to this vision, but I'm sorta
pondering, what semantics are right to show in the POSIX API?

For attributes like owner/group/perm, clearly they get projected
into the pretend inode structure for the file they're attached to,
the file shows up as a file, not a directory, when you stat it, so
archivers like tar, tree-walkers like find, directory listers like
ls, etc. see what they expect.

If someone were to want to attach an icon to a directory describing
what it contained, that'd be an opposite case; stat should still
report the internal node as a directory, you shouldn't see the icon
unless you explicitly tried to open that internal node with a file
open syscall.

Perhaps this distinction makes it a little more concrete what sorts
of uses of this file/directory duality are going to be good
engineering? Or is it just that only a subset of Reiserfs V4's
brilliant new semantics will remain a good, comfortable fit for
POSIX semantic expectations, able to be cleanly and pleasantly
reflected back through a compatibility layer; more daring
applications will depart more pervasively from POSIX.

If both sorts of operations I described above are going to be
permissible and possible, its at least easy to distinguish which
view should be reflected back through the compatibility api --- that
would be, whichever view was created first. If you create a file
then attach attributes to it, it'll show up as a file. If you create
a directory then attach a file to it, it'll show up as a directory.

-Bennett

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