Re: btrfs send ioctl failed with -5: Input/output error

[Michael Welsh Duggan <mwd@md5i.com>]

Michael Welsh Duggan <mwd@md5i.com> writes:

> I am now getting the following error when trying to do a btrfs send:
>
> root@maru2:/usr/local/src/btrfs-progs# ./btrfs send
> /usr/local/snapshots/2014-05-15 > /backup/intermediate
> At subvol /usr/local/snapshots/2014-05-15
> ERROR: send ioctl failed with -5: Input/output error
>
> I'm running a 3.14.4 kernel, and Btrfs progs v3.14.1.
>
> root@maru2:/usr/local/src/btrfs-progs# uname -a
> Linux maru2 3.14-1-amd64 #1 SMP Debian 3.14.4-1 (2014-05-13) x86_64 GNU/Linux
>
> root@maru2:/usr/local/src/btrfs-progs# ./btrfs --version
> Btrfs v3.14.1
>
> Is there anything I can do to help debug this issue?

I'd like to find out what is happening here.  I am an experienced C
programmer, but have not dealt with kernel hacking before.  I _do_ know
how to build and install a kernel.  I'd like some hints on what logging,
etc., I could add in order to determine where in the send ioctl
processing the IO error is coming from.  From there, I hope to move to
"why."  Ideally I'd be able to run gdb on this, but nothing I have read
online about kernel debugging with gdb sounds promising.

I'd make an image, but the amount of data is enough to make this
prohibitive.

-- 
Michael Welsh Duggan
(md5i@md5i.com)