[Toybox] getfattr is insane

[Rob Landley]

On 08/20/2016 10:54 PM, enh wrote:
> On Sat, Aug 20, 2016 at 6:52 PM, Rob Landley <rob at landley.net> wrote:
>> (Extended attributes make me irritable. They're just so thoroughly NOT
>> throught through. The querying API puts a gap between "tell me how much
>> memory to allocate" and the actual query for data, meaning the size can
>> change between them so you have to LOOP with a realloc, and yet libc
>> doesn't do this for you.
> 
> (arguably that's a very unix attitude. or at least BSD. SEE ALSO:
> readlink(2).

Doing it wrong, or being mad about it done wrong? :)

Moore's Law can be phrased as "your hardware depreciates 50% every 18
months", and way back I noticed a software-side corollary which is 50%
of what you know about how to program the hardware becomes obsolete
every 18 months.

The main strength of unix has always been that it's mostly the same 50%
cycling out over and over. Now that the S-curve of Moore's Law is
flattening out I'm not sure that's still true, but I'm at least trying
to establish a unixish baseline on the phone side of things before
moving on to the next problem.

> at least as we expose these in higher-level languages for
> the younger generation we can paper over these cracks.

It's not so much "the younger generation" as "there's two orders of
magnitude more people programming but only one order of magnitude more
system programmers". Our slice didn't get smaller, the pie got huge. I
recently read Linus Torvalds estimate there are ten thousand active
kernel developers who are _public_ about it.

People have been trying to do systems programming in higher-level
abstractions since multics and the i432. Fuchsia is yet another attempt
at making microkernels combine with an MMU, because clearly nobody's
ever tried that before. (Sure the amiga had a mirokernel os that could
handle multimedia, but what it _didn't_ have was an MMU.)

And yet it turns out no matter how many layers you add you can never
abstract away the hardware entirely, and somehow breaking up your single
point of failure into a bunch of vital services always winds up giving
you _multiple_ single points of failure.

Funny that. But sure, let's have another go.

> [he says, while
> filing a bug in another tab to fix getxattr in the same way we fixed
> readlink in the android.system.Os API.])
>
>> And of course the magic in-band-signaling
>> prefixes so "setfattr -n walrus filename" is denied, because magic name.)
>>
>> Also, the f in setfattr stands for "filesystem". As opposed to...? You'd
>> think it would be setxattr, but no. There isn't one. Would anyone have
>> any interest if I MADE one that takes keyword=value pairs to set the
>> data, prepends "user." by default if you didn't provide a prefix, lets
>> you set more than one in a given call, and the get version behaves like
>> a %*(#&%& unix program?
>>
>> No?
> 
> i hate everything about them too, right down to their stupid names.
> the Mac alternative seemed more sensible from its man page
> (https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/xattr.1.html)
> but i've never used it, so i don't know what it's like in practice.

I have a mac laptop (SEI gave me one). I don't use it all that much, but
I can fire it up and check mac command line stuff.

> i did consider writing something more like that, but i assumed that
> sooner or later someone would ask for setfattr/getfattr (which are the
> only Linux tools i've ever come across for this), and didn't want to
> start the "now we have (n+1) standards" race.

While I'm sympathetic with this point of view, the old one is crap.

The tricky part is I've now accepted the old crappy one into toybox, and
promoted half of it out of pending, and in order to _not_ have two I'd
either not implement the better way, or have to delete the old one.

> and i was wary of adding something supposed to be Mac-like, not having
> a Mac and so not able to test what interoperability problems i'd be
> introducing by misreading the man page/hitting gaps in the man page.
> maybe something for the TODO list though.

I've got one. And I'm willing to accept bug reports from people who
would notice a difference.

The problem is I don't want to support two commands to do the same thing
if I can help it. (Unless they share code and one's a trivial reskin of
the other.)

> [as for the "f" for "filesystem"... the wikipedia page doesn't even
> understand the difference between POSIX extended attributes and ext2
> file system attributes. confusion abounds.]

I have _opinions_ about Wikipedia[citation needed].

>> Sigh. The hard part of cleaning this up is figuring out what "clean"
>> looks like. I promoted the set command already, but this is just... ow.
> 
> (i think you're forgetting to push again.)

Yeah, I was. Fixed it.

I've now had thismessage sitting open on my desktop for several days
without actually getting a chance to starting on an xattr program. Sigh.
Press send already...

Rob