Re: [PATCH 3/4] pnfs-obj: autologin: Add support for protocol autologin

[Boaz Harrosh <bharrosh@panasas.com>]

On 03/16/2012 02:40 PM, Myklebust, Trond wrote:
> On Thu, 2012-03-15 at 23:23 -0700, Boaz Harrosh wrote:
>> From: Sachin Bhamare <sbhamare@panasas.com>
>>
>> The pnfs-objects protocol mandates that we autologin into devices not
>> present in the system, according to information specified in the
>> get_device_info returned from the server.
>>
>> The Protocol specifies two login hints.
>> 1. An IP address:port combination
>> 2. A string URI which is constructed as a URL with a protocol prefix
>>    followed by :// and a string as address. For each  protocol prefix
>>    the string-address format might be different.
>>
>> We only support the second option. The first option is just redundant
>> to the second one.
>> NOTE: The Kernel part of autologin does not parse the URI string. It
>> just channels it to a user-mode script. So any new login protocols should
>> only update the user-mode script which is a part of the nfs-utils package,
>> but the Kernel need not change.
>>
>> We implement the autologin by using the call_usermodehelper() API.
>> (Thanks to Steve Dickson <steved@redhat.com> for pointing it out)
>> So there is no running daemon needed, and or special setup.
>>
>> All is needed is that "/sbin/osd_login" script exists.
>> TODO:
>>   "osd_login" is an hard coded name. If not present we will rate_limit
>>   print to dmsg and keep failing. In such cases we should stop trying
>>   and provide sysfs interface for re-enabling autologin. For example,
>>   we could ZERO out the script name and let user-mode set a new script
>>   name.
>>   [Q] Where in sysfs should a layout-driver put its things?
> 
> Please see fs/nfs/cache_lib.c, which already does this sort of thing.
> The right thing to do is not sysfs, but a kernel module parameter.
> 

I have a question about the "kernel module parameter" is that an hot
affair. I mean if the module is loaded, does it have to be unloaded
before I can specify a new "module parameter" on load. Or it will
update globally even if the module is already loaded?

The reason I'm asking is because the layout-driver is referenced
by nfs-core on mount. And will not release until unmount, of the
last pnf-objects mount-point.

That's why I thought of a /sys so all mount-points need not be unmounted
before admin can fix the problem.

> 

Thanks
Boaz