Re: fsck -C -p: NO WRITE ACCESS

From: John-Mark Gurney <jmg_at_funkthat.com>
Date: Fri, 18 Feb 2022 02:08:21 UTC 
Andriy Gapon wrote this message on Tue, Feb 15, 2022 at 08:44 +0200:
> On 15/02/2022 01:17, John-Mark Gurney wrote:
> > Andriy Gapon wrote this message on Mon, Feb 07, 2022 at 14:15 +0200:
> >> I've got a problem where fsck behaves differently from my expectations.
> >> The problem happens with a filesystem on a GELI encrypted ZVOL.
> >> The volume has 4K block size and that's the GELI's sector size as well.
> >> FreeBSD is stable/13 from mid January.
> > 
> > Did you put a ffs filesystem that was formatted on a 512 byte sector disk
> > onto this geli device?
> 
> As far as I can recall, no.  I created it with newsfs on the geli device.

Looks like it's a bug in newfs, as I just reproduced this myself:
fsbtodb           int32_t          0x00000003

and manually specifying a sector size of 4096 to newfs does not fix the
issue.

This is the issue:
https://cgit.freebsd.org/src/blame/sbin/newfs/newfs.c#n399

It changes the sectorsize back down to 512 from whatever it should
be, which means that the calculation in mkfs.c becomes off.  I'd file
a bug report and get someone who knows FFS to look at it.  I tried to
change mkfs.c to use realsectorsize isntead, so fsbtodb is set to 0, but
then it break ffsinfo, because it's calculations are likely wrong.

> > fsck calculates the sector size via (/sbin/fsck_ffs/setup.c):
> > 	dev_bsize = sblock.fs_fsize / fsbtodb(&sblock, 1);
> > 
> > and fsbtodb:
> > ../../sys/ufs/ffs/fs.h:#define	fsbtodb(fs, b)	((daddr_t)(b) << (fs)->fs_fsbtodb)
> > 
> >> fsize   4096    shift   12      mask    0xfffff000
> >> frag    8       shift   3       fsbtodb 3
> > 
> > fsize / (1 << 3) == 4096 / 8 == 512.
> > 
> > so, likely updating fsbtodb to be 0 instead of 3 would fix this.  I'm not
> > sure how to do this though, as tunefs and fsdb don't seem to have options
> > to do this, and likely you'll want to update all the superblocks w/ this
> > new value.

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."