latest 8.0-BETA2 lost my zfs

[Danny Braniss]

> it seems that the latest changes to zfs prevents zpool to see/find
> the pool in /dev/ad0p4 (BTW, the pool was created under 8.0)
> 
> # gpart show
> =>        34  1953525101  ad0  GPT  (932G)
>           34         128    1  freebsd-boot  (64K)
>          162     4194304    2  freebsd-ufs  (2.0G)
>      4194466     8388608    3  freebsd-swap  (4.0G)
>     12583074  1940942061    4  freebsd-zfs  (926G)
> 
> # zpool list
> no pools available
> # zpool import -a
> # 
> 
> under 7.2, the pool is still there:
> 
> pundit-2> zfs list
> NAME     USED  AVAIL  REFER  MOUNTPOINT
> z       5.27G   900G    18K  /z
> z/home  5.21G   900G  5.21G  /home
> z/var   59.7M   900G  59.7M  /var
> pundit-2> zpool list
> NAME   SIZE   USED  AVAIL    CAP  HEALTH  ALTROOT
> z      920G  5.27G   915G     0%  ONLINE  -

running 'truss zpool import -a' reveals the problem:

open("ad0p4",O_RDONLY,00)                        ERR#2 'No such file or directory'
open("/dev/ad0p4",O_RDONLY,05003312752)          = 5 (0x5)
ioctl(5,DIOCGSECTORSIZE,0xbfbfa1f4)              = 0 (0x0)
fstat(5,{ mode=crw-r----- ,inode=75,size=0,blksize=4096 }) = 0 (0x0)
pread(0x5,0x2834a000,0x40000,0x0,0x0,0x805ab64)  = 262144 (0x40000)
pread(0x5,0x2834a000,0x40000,0x40000,0x0,0x1bfd8) = 262144 (0x40000)
pread(0x5,0x2834a000,0x40000,0xfff80000,0xffffffff,0x1bfd8) ERR#5 'Input/output error'
                             ********** offset is a bit too big :-) 
pread(0x5,0x2834a000,0x40000,0xfffc0000,0xffffffff,0x1bfd8) ERR#5 'Input/output error'