Hello!
On Wed, 15 Mar 2006, Oliver Fromme wrote:
> # bsdlabel ad0s1 | fgrep b:
> b: 2097152 0 swap
>
> Previously, on a 4.11 system, swapinfo said that swap size was less than
> size of b: partition on a slice - it was ok, as boot sectors are
> located at beginning of slice. But now, sizes match exactly. What
> changed and is it dangerous nowadays to have swap partition at offset 0 ?
The code in sys/swap_pager.c does not touch the first two
blocks, where blocks are measured in PAGE_SIZE units.
The smallest page size supported on FreeBSD architectures
is 4 KB (on i386), so that's at least 2 * 4k, which is 16
sectors on the disk. That's enough to skip MBR, disklabel
and boot blocks.
You're right about RELENG_5 (and CURRENT). I've found this code (though not
from the first attempt ;) in /sys/vm/swap_pager.c, at start of
swaponsomething():
/*
* Do not free the first two block in order to avoid overwriting
* any bsd label at the front of the partition
*/
blist_free(sp->sw_blist, 2, nblks - 2);
However I don't see any equivalent code in RELENG_4. Neither can I find where
it's documented, and thus any guarantees that it won't disappear tomorrow ;(
In other words: You're save. No danger. No need to worry.
In this particular case - yes.
Sincerely, Dmitry
--
Atlantis ISP, System Administrator
e-mail: [EMAIL PROTECTED]
nic-hdl: LYNX-RIPE
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