[Libguestfs] [PATCH nbdkit 0/2] Add new retry filter.
Martin Kletzander
mkletzan at redhat.com
Thu Sep 19 12:04:30 UTC 2019
On Thu, Sep 19, 2019 at 01:47:45PM +0200, Nenad Peric wrote:
>A theoretical way to test this against any other protocol is to have a
>firewall rule which can be triggered locally which just drops the traffic
>and then re-enables the traffic in a while (short or long, can be
>decided/tweaked).
>This way, there is no need to think about which protocol is used, when we
>kill the connectivity.
>The only consideration could probably be that the dropped connections would
>cover only the ports we need.
>To reduce the size of the hammer :)
>
Good idea, you just need to keep in mind that the underlying protocols might
have their own keep-alive methods, which should be removed or at least minimised
when testing this.
>
>*Nenad Perić*
>
>PRINCIPAL SOFTWARE ENGINEER
>
>Red Hat - Migration Engineering
>
>nenad at redhat.com
>
><http://redhat.com>
>
>
>On Thu, Sep 19, 2019 at 1:34 PM Richard W.M. Jones <rjones at redhat.com>
>wrote:
>
>> This is a retry filter implementation as outlined here:
>> https://www.redhat.com/archives/libguestfs/2019-September/msg00167.html
>>
>> It is only lightly tested. One way to test it is to try an SSH copy
>> (see the commit message for patch 2/2), and in the middle of the copy
>> kill the per-connection sshd on the remote machine. You will see that
>> the copy recovers after a few seconds. Add the nbdkit -v option to
>> see some useful messages from the filter:
>>
>> ...
>> nbdkit: ssh[1]: debug: ssh: pread count=2097152 offset=216006656
>> nbdkit: ssh[1]: error: read failed: Socket error: Connection reset by
>> peer (-1)
>> nbdkit: ssh[1]: debug: retry 1: original errno = 5
>> nbdkit: ssh[1]: debug: waiting 2 seconds before retrying
>> nbdkit: ssh[1]: debug: ssh: reopen
>> nbdkit: ssh[1]: debug: close
>> nbdkit: ssh[1]: error: cannot close file: Socket error: Connection reset
>> by peer
>> nbdkit: ssh[1]: debug: ssh: open readonly=0
>> nbdkit: ssh[1]: debug: opened libssh handle
>> nbdkit: ssh[1]: debug: ssh: pread count=2097152 offset=216006656
>> ...
>>
>> It really needs an actual test, which is tricky to implement. My
>> thinking currently is that a custom (sh) plugin is the way to go, but
>> it would also be nice to test curl/ssh/vddk with this filter -- if
>> anyone has any suggestions on how to do that ...
>>
>> This patch will probably conflict with Eric's series here:
>> https://www.redhat.com/archives/libguestfs/2019-September/msg00180.html
>> but that shouldn't be too hard to fix up.
>>
>> Rich.
>>
>>
>>
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