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Date: Mon, 21 Apr 2003 23:44:40 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: David Schultz <das@freebsd.org>
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cc: Robert Watson <rwatson@freebsd.org>
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Subject: Re: HEADS UP: UFS2 now the default creation type on 5.0-CURRENT
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On Mon, 21 Apr 2003, David Schultz wrote:

> The cgbase hack should only limit the size of the filesystem, not
> the disk location.  It occurs to me that with a little more
> hackery, we can avoid the limitation entirely.  If we revert to
> the 64-bit cgbase() and un-inline it, boot2 goes from 19 bytes
> available to -9 bytes.  Add a kludge to factor out a few 64-bit
> multiply-adds and we're back to 3 bytes available.  (I'm sure
> there are cleaner ways to save 9 bytes.)  An untested unpolished
> diff follows.

I played with similar changes, but didn't finish them.

> Index: ufsread.c
> ===================================================================
> RCS file: /cvs/src/sys/boot/common/ufsread.c,v
> retrieving revision 1.11
> diff -u -r1.11 ufsread.c
> --- ufsread.c	25 Feb 2003 00:10:20 -0000	1.11
> +++ ufsread.c	21 Apr 2003 10:10:01 -0000
> ...
> @@ -47,11 +59,11 @@
>  ...
> -#define FS_TO_VBA(fs, fsb, off) (fsbtodb(fs, fsb) + \
> -    ((off) / VBLKSIZE) * DBPERVBLK)
> +#define FS_TO_VBA(fs, fsb, off)	ma((off) / VBLKSIZE, DBPERVBLK, \
> +	fsbtodb((fs), (fsb)))

The division by VBLKSIZE should probably be a shift.  ufsread.c has
VBLKSHIFT and uses it for all multiplications and divisions by VBLKSIZE
except this one.  gcc can't optimize to just a shift since all the
types are signed and C99 specifies that division of negative integers
by positive ones has the usual hardware brokenness.

Bruce