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Re: How to stack libtrivfs-based translators

From: Sergiu Ivanov
Subject: Re: How to stack libtrivfs-based translators
Date: Thu, 17 Jul 2008 15:33:13 +0300


On Wed, Jul 16, 2008 at 2:32 AM, <olafBuddenhagen@gmx.net> wrote:
On Tue, Jul 15, 2008 at 06:10:02PM +0300, Sergiu Ivanov wrote:
> I have written a libtrivfs-based translator (the source code is
> supplied in the attachment), however I have problems with stacking it
> upon itself.
> If I now try to stack mangle upon foo again, using the command:
>   settrans -L foo mangle
> I receive the following error message:
>   settrans: foo: Operation not supported

This requires certain RPCs in fs.defs (and probably fsys.defs) to be
implemented, most notably file_set_translator. A quick look at
file-set-translator.c from libtrivfs shows us that
trivfs_S_file_set_translator() is "implemented" as

  { return EOPNOTSUPP; }

i.e. it's not implemented at all.

In other words, libtrivfs doesn't seem to support setting further
translators on the translated node out of the box. (I think you could
implement it manually, though...)

OK, thanks a lot. I'll keep that in mind.

> When I try fsysopts on the translated node foo in the following way:
>   fsysopts foo
> I get a similar error:
>   fsysopts: foo: Operation not supported

You need to implement the trivfs_append_args() callback -- see the hello
translator for a trivial example, or others like pfinet for more complex

Oh, I've forgotten this thing already, although I've once studied the
code of hello translator thouroughly... Thank you, I'll keep this in
mind, too.


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