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Subject: [bug#34863] [WIP] syscalls: Add loop device interface.
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From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
References: <20190314220823.30769-1-dannym@scratchpost.org>
	<20190315171306.777c88bd@scratchpost.org>
Date: Sat, 16 Mar 2019 11:18:12 +0100
In-Reply-To: <20190315171306.777c88bd@scratchpost.org> (Danny Milosavljevic's
	message of "Fri, 15 Mar 2019 17:13:06 +0100")
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To: Danny Milosavljevic <dannym@scratchpost.org>
Cc: 34863@debbugs.gnu.org

Hi!

Danny Milosavljevic <dannym@scratchpost.org> skribis:

>> +(define (set-loop-device-status loop-file status)
>> +  (let ((buf (make-bytevector sizeof-loop-info64)))
>> +    (apply write-loop-info64! buf status) ; TODO: Be more user-friendly.
>
> I don't know how instantiate a C structure given an assoc list.  Help?

You have to extract the fields from STATUS and then pass them in the
right order to =E2=80=98write-loop-info64!=E2=80=99:

  (let-syntax ((field (syntax-rules ()
                        ((_ field) (assoc-ref status 'field)))))
    (write-loop-info64! buf (field lo-device) (field lo-inode)
                        (field lo-rdevice) =E2=80=A6))

However, given the number of fields, you might want to define a Scheme
record type, as is done for =E2=80=98%statfs=E2=80=99 and <file-system>.

HTH!

Ludo=E2=80=99.