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Re: [Qemu-block] RFC block/iscsi command timeout


From: Peter Lieven
Subject: Re: [Qemu-block] RFC block/iscsi command timeout
Date: Tue, 26 May 2015 11:30:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

Am 26.05.2015 um 11:01 schrieb Kevin Wolf:
Am 22.05.2015 um 09:30 hat Peter Lieven geschrieben:
Hi,

next libiscsi version will allow to define command timeouts. At least for sync 
commands this
was in fact possible since somewhen in 2013. Per default this timeout is 
disabled.

I would like to at least define a timeout for the sync commands (login, 
readcapacity, inquiry, logout etc)
of about 5000msec.
You should probably make the timeout an integer option rather than a
boolean one. Then we don't need to discuss whether 5000 msec are
appropriate...

The chance to the iSCSI driver of qemu would be minimal for that. The timeout
handling is done in the sync event loop of libiscsi.

My question is if it would be a good idea to have timeout (fairly high of 
course) for all other commands as well?
...and what "fairly high" actually means.

Following your idea to introduce an option I would do the following:

Default:
 sync commands: 5000msec (this should be far, far enough for login, logout, 
etc.) These are all calls in iscsi_open / iscsi_close, not called during normal 
operation.
 async commands: no timeout

Secifying a timeout will then set the timeout for sync and async commands with
the option to specify 0 to disable timeouts at all.

If we run into a timeout we theoretically have the following options:
 - reconnect
 - retry
 - error

I would reconnect as Ronnie proposed.

Peter




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