Re: [9fans] rewriting paths [was: mv vs cp]

Re: [9fans] rewriting paths [was: mv vs cp]

[Fco.J.Ballesteros]

One thing I like in Plan 9 is that by keeping the fs alive,
you can survive crashes on any other machine. The renamefs 
would make you more dependent on crashes not happening 
in the machine w/ renamefs before it moves everything around.

The other question I have: is all this worth just to avoid mv
doing a cp+rm? Beware that even if you could move, the
worm would burn a copy unless you also modify it.

Re: [9fans] rewriting paths [was: mv vs cp]

[George Michaelson]

Something maybe not covered so far is what mv etc do with sparce files,
if memory serves me right some operations are 'safe' and some have a habit
of filling the empty extent with data, having unforseen consequences for
the real size of used disk.

Of course, if 9 doesn't have them, it doesn't have the problem either.

-George

Re: [9fans] rewriting paths [was: mv vs cp]

[Douglas A. Gwyn]

George Michaelson wrote:
> Something maybe not covered so far is what mv etc do with sparce files,
> if memory serves me right some operations are 'safe' and some have a habit
> of filling the empty extent with data, having unforseen consequences for
> the real size of used disk.
> Of course, if 9 doesn't have them, it doesn't have the problem either.

It wouldn't much matter, since it's just an optimization issue and
could be "fixed".

Re: [9fans] rewriting paths [was: mv vs cp]

[Richard]

Fco.J.Ballesteros writes:
>One thing I like in Plan 9 is that by keeping the fs alive,
>you can survive crashes on any other machine. The renamefs 
>would make you more dependent on crashes not happening 
>in the machine w/ renamefs before it moves everything around.

I see your point.

In renamefs's defense, I note that most users most of the time are
working on their own stuff, not making any chanages to the parts of the
network that everyone relies on.  If the renamefs is running on your own
terminal or cpued to some cpu server, and your working on your own
stuff, a crash of the renamefs will not affect the other users.

Ie, do not use renamefs when you are adminning the network.

Re: [9fans] useful language extension, or no?

[rob pike, esq.]

> Suppose I'm not saying "why," but "why not."  IMO it's cleaner and
> quite possibly more efficient (without getting into a usec argument,
> please).  Do you disagree?

Yes.  The benefit is minor, too small to justify changing the language.
You're trying to formalize an idiom; just using the idiom suits me fine.

The type inclusion feature, I think, did a lot more, since it trigged type
conversion and promotion: a much bigger deal.

-rob

Re: [9fans] useful language extension, or no?

[Sam]

Ok, I'll bite and play devil's advocate.

What about the promotion of a structure from itself
to one of its members in a function call simply because
it makes locking a structure easier?  Surely passing in
a pointer to a function and having the in-func pointer completely
different violates some standard of programming languages.

Why was it worthwhile to change the language in this respect,
for the idiom of "always having to make sure the lock is the
first item in the structure for pointer coersion is a pain?"

Sam

On Tue, 16 Jul 2002, rob pike,
esq. wrote:

> > Suppose I'm not saying "why," but "why not."  IMO it's cleaner and
> > quite possibly more efficient (without getting into a usec argument,
> > please).  Do you disagree?
>
> Yes.  The benefit is minor, too small to justify changing the language.
> You're trying to formalize an idiom; just using the idiom suits me fine.
>
> The type inclusion feature, I think, did a lot more, since it trigged type
> conversion and promotion: a much bigger deal.
>
> -rob
>

[9fans] more extensions

[FJ Ballesteros]

Including tuples (perhaps as an instance of nameless structs) would
simplify many interfaces, right? that's one thing I learned using
Limbo.

The extension would probably be not too complex, also. 

I don't have time to implement this during this semester, but would
be willing to do so in the future if people from the Labs agree.

Is there agreement on this?

Re: [9fans] more extensions

[Sam]

My next thought, but I figured I'd used all my contribution
credits today.

Sam

On Tue, 16 Jul
2002, FJ Ballesteros wrote:

>
> Including tuples (perhaps as an instance of nameless structs) would
> simplify many interfaces, right? that's one thing I learned using
> Limbo.
>
> The extension would probably be not too complex, also.
>
> I don't have time to implement this during this semester, but would
> be willing to do so in the future if people from the Labs agree.
>
> Is there agreement on this?
>

[9fans] more extensions

[Howard Trickey]

This is tempting.  Tuples are one of my favorite things
about Limbo.

However, I'm biased, as I was the one that pushed for tuples
in Limbo, I think.

But adding them to C's already delicate grammar might
be harder than it appears.  And  there comes a point
where an extension changes the flavor of a language
a little too much, and I think this one might be over
that line.

- Howard Trickey

> Including tuples (perhaps as an instance of nameless structs) would
> simplify many interfaces, right? that's one thing I learned using
> Limbo.

[9fans] New language?

[Sam]

> be harder than it appears.  And  there comes a point
> where an extension changes the flavor of a language
> a little too much, and I think this one might be over
> that line.

Too true.  What then, a new language based on C pulling the
yummy stuff out of limbo?  One that's not interpreted, without
a garbage collector, and no atend >:), but that has tuples, array bounds
checking, etc?  At this point should we just considering loosening up
Oberon a little and making a few additions?

I'd be willing to help so long as we fix the BCPL inherited '&'
precedence.

Sam

Re: [9fans] New language?

[GBA]

Don't know much about Limbo, but have you seen this?

http://www.digitalmars.com/d/index.html


> Too true.  What then, a new language based on C pulling the
> yummy stuff out of limbo?  One that's not interpreted, without
> a garbage collector, and no atend >:), but that has tuples, array bounds
> checking, etc?  At this point should we just considering loosening up
> Oberon a little and making a few additions?
> 
> I'd be willing to help so long as we fix the BCPL inherited '&'
> precedence.
> 
> Sam
> 
> 

Re: [9fans] New language?

[Lucio De Re]

On Tue, Jul 16, 2002 at 10:45:02PM -0700, GBA wrote:
> 
> Don't know much about Limbo, but have you seen this?
> 
> http://www.digitalmars.com/d/index.html
> 
What, no tuples?!

More seriously, I'm happy to work further on Alef, but I have long
ago accepted Bell Labs' view that maintaing the libraries is a
disaster.

I see the "D" people mention "versioning".  I'm insufficiently
knowledgeable to decide whether that is something I would appreciate
or despise.  I know NetBSD is hooked on it (in the sense that meat
hangs from hooks in refrigerators, sadly) because of their use of
dynamic libraries.

I guess that makes it a useful solution, if you can't get rid of
the problem in the first place.

++L

Re: [9fans] more extensions

[Scott Schwartz]

| Including tuples (perhaps as an instance of nameless structs) would
| simplify many interfaces, right? that's one thing I learned using
| Limbo.

Yeah, but limbo has bounds checked arrays, which are even more useful.

Re: [9fans] more extensions

[Dan Cross]

> | Including tuples (perhaps as an instance of nameless structs) would
> | simplify many interfaces, right? that's one thing I learned using
> | Limbo.
> 
> Yeah, but limbo has bounds checked arrays, which are even more useful.

Has anyone ever wondered, ``why not just port limbo?''  Surely the
runtime environment provided by Dis can be emulated using a library.

Not in response to Scott's comment, but in general, I'm not a big fan
of changing C; C is what C is.  If you want something else, use
something else, but don't try to morph C into another language.

	- Dan C.

Re: [9fans] more extensions

[Jon Snader]

On Tue, Jul 16, 2002 at 02:47:27PM -0400, Dan Cross wrote:
> 
> Not in response to Scott's comment, but in general, I'm not a big fan
> of changing C; C is what C is.  If you want something else, use
> something else, but don't try to morph C into another language.
> 

As a wise man once said (sort of): ``If you want limbo, you know
where to get it.''

Re: [9fans] more extensions

[Douglas A. Gwyn]

FJ Ballesteros wrote:
> Including tuples ...

Tuples are truly useful.  There are some syntactic issues to solve
when adding them to C, but assuming they're dealt with I would
welcome this experiment.  It would provide some leverage in arguing
for standardization of the feature for C0x.

Re: [9fans] mv vs cp

[jmk]

As Dave points out, there are a lot of balls in the air during
an atomic 'rename'. 4.2BSD introduced the 'rename' system call,
and as an alpha/beta tester for 4.1[abc] and 4.2BSD I can testify
to how long it took to get it right and how much ugly code was
involved.

--jim

[9fans] rewriting paths [was: mv vs cp]

[Richard Uhtenwoldt]

I was thinking about this in the bathtub just now.  One could interpose
a filesystem between the user and kfs --or wherever one's files are
really stored-- called renamefs, which rewrites paths before forwarding
them to kfs.  9P requests do not really contain paths, but you get the
idea: the new file server, renamefs, maintains a rewrite table
containing the paths specified by past move commands (2 paths per move
command to be precise).  This state is used to rewrite certain 9P
requests (eg, some walk requests) before relaying them to the 
server that really stores files.

To increase the usefulness of renamefs, we allow it to store 2 types of
records.  Specifically, a record can take the form

  D<path>

, which means that the string <path> "no longer lives here"
(ie, renamefs will act as if <path> does not exist), or it can
take the form

  A<path><path2>

, which means that <path2> will get rewritten as <path> and does not
carry the implication that <path> no longer lives here.  (Yes, yes, I
know: between <path> and <path2> you need some lexeme that does not
occur in paths.)

Then,

  Mv <path> <path2> 

can be implemented by adding two records, A<path><path2> and D<path>, and
something resembling Unix's

  Ln -s <path> <path2>

is implementable by adding one record, A<path><path2>, to the rewrite
table inside renamefs.  The main socioeconomic purpose of these features
is to make Unix users feel more at home by providing means to move
directories, means to do inter-directory moves and symlinks.  Moreover,

  Del <path>

which just adds D<path> to the rewrite table, is a delete that supports
undelete (via removal of the D record).  And resource forks can be
implemented via ... --Just kidding.

No need to modify 9P of course: just have renamefs listen on a specific
file like /foo/rename where foo might be mnt (sorry for my unfamiliarity
with Plan9 file naming conventions) and have mv write requests
(candidates already in the form of strings for entry into the rewrite
table) to /foo/rename (rather than having mv send rename or copy and
delete requests like it does now).

When everyone is sleeping, or when the user says so, renamefs can empty
the rewrite table by actually copying and deleting files in the
underlying filesystem.  Call this operation "update".

There are multiple ways I'm sure to create pathological situations with
renamefs, and I do not know enough about Plan 9 to address them, except
to point out that one way to recover from pathology --assuming the
update operation has not run yet-- is simply to delete the rewrite table
via, eg, echo clear >>/foo/rename or, if the namespace is so screwed up
that that impossible, to reboot without mounting renamefs.

Advantages of my design:

Users who do not need the functionality do not pay any cost: the code
for renamefs and it's clients (eg, the new mv command) lie dormant on
the hard drive where they cannot cause problems.  No modification
of extant code is required.

Makes Plan 9 look more like Unix for those who want want that sort
of thing, and yes I hear loud and clear that many here do not.