illumos gate

This seems to have materialized not so long ago, at least I don't remember encountering this problem more than a year ago. What appears to happen is zdb, while it scans labels, given for example a command as follows, reports that it failed to read last two labels.

zdb -lu c2t0d0s0

What zdb reports, given above command.

------------------------------------
LABEL 2
------------------------------------
failed to read label 2
------------------------------------
LABEL 3
------------------------------------
failed to read label 3

This snippet suggests that last two addresses are miscalculated. I am fairly sure they cannot exist, given sizes of disks with which I have been getting these numbers. In fact, I am seeing same values no matter what the size of the actual disk is. This is certainly a problem.

psize: 0x0 l: 0x0 offset: 0x0 return: 0x0
psize: 0x0 l: 0x1 offset: 0x0 return: 0x40000
psize: 0x0 l: 0x2 offset: 0x0 return: 0xfffffffffff80000
psize: 0x0 l: 0x3 offset: 0x0 return: 0xfffffffffffc0000

Problem is likely related to using `stat64` to get information about the disk. At least as far as I can tell, stat is where things go wrong in the dump_label function in zdb.c.

This snippet makes it apparent that addresses for labels 2 and 3 are most certainly bogus.

dtrace -qn 'pid$target:::entry
    /probefunc=="vdev_label_offset"/ {
        /* Trace three arguments to vdev_label_offset */

        psize = (uint64_t)arg0 ; lbl = arg1 ; off = (uint64_t)arg2 ;
        }
    pid$target:::return /probefunc=="vdev_label_offset"/ {
        printf("psize: 0x%x l: 0x%x offset: 0x%x return: 0x%x\n",
            psize, lbl, off, arg1); 
    }' -c 'zdb -lu c2t0d0s0'