From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <b554ab3d58d82e0786362357907ebace@rei2.9hal>
Date: Mon, 25 Mar 2013 08:19:45 +0100
From: cinap_lenrek@gmx.de
To: 9fans@9fans.net
In-Reply-To: <CCCB7481-E1C0-4DA7-8A4E-1F2331F265F1@ar.aichi-u.ac.jp>
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Subject: Re: [9fans] Disk backup?
Topicbox-Message-UUID: 3417ba00-ead8-11e9-9d60-3106f5b1d025

the block bitmap on a fakeworm is at the end of the sub
device/partition. see fworm.c:

int
fwormread(Device *d, Off b, void *c)
{
	Iobuf *p;
	Device *fdev;
	Devsize l;

	if(chatty > 1)
		fprint(2, "fworm read  %lld\n", (Wideoff)b);
	fdev = FDEV(d);
	l = devsize(fdev);
	l -= l/(BUFSIZE*8) + 1;
	if(b >= l)
		panic("fworm: rbounds %lld", (Wideoff)b);
	l += b/(BUFSIZE*8);

	p = getbuf(fdev, l, Brd|Bres);
	if(!p || checktag(p, Tvirgo, l))
		panic("fworm: checktag %lld", (Wideoff)l);
	l = b % (BUFSIZE*8);
	if(!(p->iobuf[l/8] & (1<<(l%8)))) {
		putbuf(p);
		fprint(2, "fworm: read %lld\n", (Wideoff)b);
		return 1;
	}
	putbuf(p);
	return devread(fdev, b, c);
}

the block tags do not really matter for the backup. you use the
fakeworm only as a backend for the cw device so you can just
copy all the blocks that got ther bit set in the bitmap compared
to the backup.

--
cinap