Re: strange ld(4) behavior when reading off end of disk

[txt.file%txtfile.eu@localhost]

To find disk trouble I would prefer badblocks(8).

The first command is with 1 MB blocksize the latter with 512 byte. Have 
you tried running "dd if=/dev/rld0c of=/dev/null iseek=31166974 bs=1M"? 
What happens then?

kind regards
txt.file

On 9/10/20 10:14 PM, Greg Troxel wrote:
> I have a RPI3 with a 32G uSD, running netbsd-9.  It's pretty normal.  On
> all of my machines, I run dd from the disk to /dev/null, usually bs=1m,
> every couple of months, to proactively find disk trouble.
>
> On one machine I ran "dd if=/dev/ld0c of=/dev/null bs=1m".
> I got an I/O error indication form dd, and in dmesg (boot, and just now):
>
> [     1.708641] ld0 at sdmmc0: <0x03:0x5344:SL32G:0x80:0x241f2b31:0x118>
> [     1.718247] ld0: 30436 MB, 7729 cyl, 128 head, 63 sec, 512 bytes/sect x 62333952 sectors
> [     1.728247] ld0: 4-bit width, High-Speed/SDR25, 50.000 MHz
> [     6.831184] boot device: ld0
> [     6.841186] root on ld0a dumps on ld0b
>
> [ 1367984.030787] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28), retrying
> [ 1367984.850821] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28), retrying
> [ 1367985.670855] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28), retrying
> [ 1367986.490890] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28), retrying
> [ 1367987.310922] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28), retrying
> [ 1367988.130956] ld0c: error reading fsbn 62333948 of 62333948-62333951 (ld0 bn 62333948; cn 30436 tn 31 sn 28)
>
> I realize I'm going to get a short read, but I expect a short read, not
> an error to dd, and not an error in the kernel.
>
> When I try to read from the  suspect address I get normal behavior:
>
>    $ dd if=/dev/rld0c of=/dev/null iseek=62333948
>    4+0 records in
>    4+0 records out
>    2048 bytes transferred in 0.004 secs (512000 bytes/sec)
>
> My c partition size is 62333952, so it seems ok.
>
> The machine is otherwise ok.
>
>
> Is there some missing bounds checking in ld, perhaps?
> Am I confused?
> Other ideas?