Re: [PATCH 18/19] ib_srp: Remove SCSI devices upon port down event

On 11/12/12 23:40, Or Gerlitz wrote:

Bart Van Assche [off-list ref] wrote:

quoted

This patch is a modified version of a patch from Karandeep Chahal
that was posted on May 29, 2012 on the linux-rdma mailing list
(http://www.mail-archive.com/linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg11796.html)

If you want your patch to land upstream, I would expect here a
change-log that explains why we want to do that... e.g what happens if
someone mounts a file system on this block device, do we want to pull
the rug behind the FS legs, why? what's special in port down even from
any other loss of IB connectivity that we have to give it special
treatment? why its needed to react on IB events and not just on
connectivity loss?

This patch is not an essential part of this patch series. All it does
is to trigger failover more quickly if a port down event has been
received. Without this patch, if an IB cable has been disconnected long
enough, a QP error will be generated anyway and that event will trigger
the path failure logic introduced in the earlier patches of this series.

Regarding file system behavior: if a file system should be shielded
from path failures in a multipath setup then it should be mounted on
top of a multipath device instead of using the SCSI host directly
created by ib_srp. In the file system tests I ran I have been using
the following multipathd options:

defaults {
    queue_without_daemon no
}
devices {
    device {
        ...
        features          "3 queue_if_no_path pg_init_retries 50"
        fast_io_fail_tmo  15
        dev_loss_tmo      60
    }
}

Are you perhaps worrying about what will happen in a setup with a single
path between initiator and target and where the IB connection disappears
and reappears quickly ? Shouldn't multipath be used even in such a setup
to avoid that the filesystem encounters an I/O error if the path disappears
for a longer time than what is tolerated by the SCSI error handler in order
to recover gracefully ?

Thanks,

Bart.
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