Re: ceph kernel client orientation

[Ilya Dryomov <idryomov@gmail.com>]

On Tue, May 19, 2020 at 3:44 PM <Michal.Plsek@seznam.cz> wrote:
>
> Hello,
>
> I am trying to get to functions responsible for reading/writing to/opening RBD blocks in ceph client kernel module (alternatives to librbd’s rbd_read(), rbd_write() etc.). I presume it should be located somewhere around drivers/block/, but until now I’ve been without luck. My idea is to edit these functions, rebuild the ceph kernel ‘rbd’ module and replace it. Since comments are pretty much missing everywhere, it would be nice to narrow my searching area.
>
> If you know anything about it, please let me know. Thanks, M.

Hi Michal,

Everything is in drivers/block/rbd.c.  The entry point is
rbd_queue_rq(), this is where all rbd requests are dispatched from.
After setting up where data is to be written from (for writes) or read
to (for reads), the details specific to each type of request (read,
write, discard or zeroout) are handled in __rbd_img_fill_request()
and then later on the respective state machine is kicked off.

The job of the state machine is to submit requests to the OSDs and
handle replies from the OSDs.  As in librbd, satisfying a single
user I/O request can require sending multiple OSDs requests, in some
cases sequentially.

Unfortunately, there is no one function to edit.  I might be able
to help more if you explain what you are trying to achieve.

Thanks,

                Ilya