On Mon, Oct 31, 2016 at 02:32:53PM +0800, Qu Wenruo wrote:
>
>
> At 10/31/2016 02:25 PM, Marc MERLIN wrote:
> >On Mon, Oct 31, 2016 at 02:04:10PM +0800, Qu Wenruo wrote:
> >>>Sorry for asking, am I doing this wrong?
> >>>myth:~# dd if=/dev/mapper/crypt_bcache0 of=/tmp/dump1 bs=512 count=32
> >>>skip=26367830208
> >>>dd: reading `/dev/mapper/crypt_bcache0': Invalid argument
> >>>0+0 records in
> >>>0+0 records out
> >>>0 bytes (0 B) copied, 0.000401393 s, 0.0 kB/s
> >>
> >>So, the underlying MD RAID5 are complaining about some wrong data, and
> >>refuse to read out.
> >>
> >>It seems that btrfs-progs can't handle read failure?
> >>Maybe dm-error could emulate it.
> >>
> >>And what about the 2nd range?
> >
> >they both fail the same, but I wasn' tsure if I typed the wrong dd command
> >or not.
>
> Strange, your command seems OK to me.
>
> Does it has anything to do with your security setup or something like that?
> Or is it related to dm-crypt or bcache?
>
>
> But this reminds me, if dd can't read it, maybe btrfs-progs is the same.
>
> Maybe only kernel can read dm-crypt device while user space tools can't
> access dm-crypt devices directly?
It can, it's just the offset seems wrong:
myth:~# dd if=/dev/mapper/crypt_bcache0 of=/tmp/dump1 bs=512 count=32
skip=26367830208
dd: reading `/dev/mapper/crypt_bcache0': Invalid argument
0+0 records in
0+0 records out
0 bytes (0 B) copied, 0.000421662 s, 0.0 kB/s
If I divide by 1000, it works:
myth:~# dd if=/dev/mapper/crypt_bcache0 of=/tmp/dump1 bs=512 count=32
skip=26367830
32+0 records in
32+0 records out
16384 bytes (16 kB) copied, 0.139005 s, 118 kB/s
so that's why I was asking you if I counted the offset wrong. I took the
value you asked and divided by 512, but it seems too big
13500329066496 / 512 = 26367830208
Marc
--
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
.... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/
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