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Re: How to stack libtrivfs-based translators

From: olafBuddenhagen
Subject: Re: How to stack libtrivfs-based translators
Date: Wed, 16 Jul 2008 01:32:02 +0200
User-agent: Mutt/1.5.18 (2008-05-17)


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...)

I must admit that this surprises me quite a bit. I wonder whether there
is any good reason for that...

> 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


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