Re: Adding a new FC disk to a linux host

[Steven Dake <sdake@mvista.com>]

Suresh,

The locking of the SCSI devices is not correct in the SCSI midlayer, 
resulting in potential linked list walk-offs during insertion on one 
processor and removal on another processor in the system.  There are 
other problems even for single-processor configurations.

I have partially fixed this, but my patch is incomplete and i've not had 
time to revise it so it is correct.

If you want to insert by FibreChannel WWN, you can look at
www.sourceforge.net/projects/atca-hotswap.

This allows insertion by a FC WWN via a kernel patch and provides a 
userspace library to do the same.  This patch was mainly made for 2.4 
where there was no way to correlate a FibreChannel WWN with a scsi 
target ID.  Since sysfs in linux scsi has added FibreChannel IEEE ID 
support (wwns), I will eventually change the userspace library to do the 
correct thing when you request an insertion on a fibrechannel id by 
scanning the scsi list in sysfs and finding the correct 
host/channel/id/lun on which to insert and doing the insert 
automatically.  If you want to write that hotswap library code, i'll put 
it in to the sourceforge project.

It would also be possible to request that the fibrehcannel device list 
out its supproted scsi target ids, and compare that to the SCSI layer's 
view, and automatically insert those that are not in the scsi midlayer. 
 Exercise for the reader.

Thanks!
-steve

Suresh Kr N wrote:

>ok , i see this in scsi.c .
>Is this safe in a Fibre channel SAN scenario ? could it corrupt an ongoing
>data tranfer in a fibre channel SAN scenario ?
>and also are there are easier ways to achieve this ( without you supplying a
>scsi id etc ).
>
>suresh
>
>  /*
>         * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
>         * with  "0 1 2 3" replaced by your "Host Channel Id Lun".
>         * Consider this feature BETA.
>         *     CAUTION: This is not for hotplugging your peripherals. As
>         *     SCSI was not designed for this you could damage your
>         *     hardware !
>         * However perhaps it is legal to switch on an
>         * already connected device. It is perhaps not
>         * guaranteed this device doesn't corrupt an ongoing data transfer.
>         */
>
>-----Original Message-----
>From: linux-scsi-owner@vger.kernel.org
>[mailto:linux-scsi-owner@vger.kernel.org]On Behalf Of Suresh Kr N
>Sent: Thursday, February 13, 2003 11:01 PM
>To: Steven Dake
>Cc: linux-scsi@vger.kernel.org
>Subject: RE: Adding a new FC disk to a linux host
>
>
>This works for me ( by the way is this still BETA ? i dont see this comment
>in the kernel scsi sources anymore ).
>But then i need to deduce the these input parameters of target no , lun no
>etc , as i need to do this from a userland san management app.
>
>I figured that the HBA apis give you the new target number , and probably i
>could do a report luns or something to get the lun numbers as well. So this
>way could work for me .
>
>Is there a way to ask the midlayer for a full rescan ( so that i wont have
>to find out these parameters )
>
>suresh
>
>
>-----Original Message-----
>From: linux-scsi-owner@vger.kernel.org
>[mailto:linux-scsi-owner@vger.kernel.org]On Behalf Of Steven Dake
>Sent: Thursday, February 13, 2003 5:05 AM
>To: Suresh Kr N
>Cc: linux-scsi@vger.kernel.org
>Subject: Re: Adding a new FC disk to a linux host
>
>
>you can scan specific scsi ids.  read scsi_proc.c search for
>add-single-device
>
>         * Usage: echo "scsi add-single-device 0 1 2 3" >/proc/scsi/scsi
>         * with  "0 1 2 3" replaced by your "Host Channel Id Lun".
>         * Consider this feature BETA.
>
>
>Good luck
>-steve
>
>Suresh Kr N wrote:
>
>  
>
>>sorry about the wrong thread name in the previous post. updated now
>>
>>
>>hi everyone
>>
>>I am working on a san management application for a linux. My application
>>sends zoning commands to the fabric to zone in a disk to a host ,  so i
>>    
>>
>need
>  
>
>>to have that disk acessible to the host without a reboot of the host.
>>
>>I need to do this from the user space. Is there a way to ask the scsi
>>midlayer for a rescan ?
>>In solaris , i invoke a command called "drvconfig" to achieve this.
>>
>>I have seen in the linux-scsi archive that this is kind of possible,  but
>>the discussion didnt seem to state how.
>>I am attaching the above thread here in the mail.
>>
>>I have verified that echo "scsi add-single-device a b c d" >
>>    
>>
>/proc/scsi/scsi
>  
>
>>works fine . But this does involve parameters which cant be found out
>>programmatically.
>>
>>Also a side question here :In a FC world, to get the target number for
>>    
>>
>above
>  
>
>>command , can i find out the current maximum target number of the scsi
>>devices, and increase it by one ? or  does the FC devices have actually a
>>preknown target no , which would be collected by the FC card driver ?
>>
>>Could someone please help ? ( even a "non-standard" way should be good
>>enough" )
>>
>>Thanks
>>Suresh
>>
>>
>>
>>--------------------------------------------------------
>>Message 2 in thread
>>From: Alan Cox (alan@lxorguk.ukuu.org.uk)
>>Subject: Re: Hot plugging a disk in runtime
>>View this article only
>>Newsgroups: mlist.linux.scsi
>>Date: 2002-05-20 05:32:38 PST
>>
>>
>>
>>
>>    
>>
>>>1.. How is it possible to signal SCSI mid-layer (or other layers) of a
>>>presence of a newly hot-plugged disk ?
>>>
>>>
>>>      
>>>
>>aacraid is one example that does this, but via its config tools.
>>
>>
>>
>>    
>>
>>>2.. Can an adapter's device driver trigger SCSI subsystem to scan
>>>channels for new LUNs / Targets ?
>>>
>>>
>>>      
>>>
>>It is designed so user space can do so - so yes
>>
>>
>>
>>    
>>
>>>3.. Is this can be handled in a kernel level ? is there a user space
>>>application that can be triggered to start scanning adapters (obviously
>>>through SCSI subsystem) and registering new LUNs / Targets etc... ?
>>>
>>>
>>>      
>>>
>>echo "scsi-add-single-device a b c d" /proc/scsi/scsi
>>
>>if I remember it right
>>
>>
>>entire thread is at
>>
>>http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=linux.scsi.20020
>>    
>>
>5
>  
>
>>201420.g4KEK3x01892%40localhost.localdomain&rnum=7&prev=/groups%3Fq%3Dhot%2
>>    
>>
>B
>  
>
>>plug%2B%2BSCSI%2Bfibre-channel%2BLinux%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sel
>>    
>>
>m
>  
>
>>%3Dlinux.scsi.200205201420.g4KEK3x01892%2540localhost.localdomain%26rnum%3D
>>    
>>
>7
>  
>
>>-
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>>
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