From:	MERC::"uunet!WKUVX1.BITNET!MacroMan" 29-MAR-1993 17:07:32.51
To:	MACRO32@WKUVX1.BITNET
CC:	
Subj:	Re: SHOW DEVICE and mounted status.

In article <1993Mar28.144910.1367@dmc.com>, munroe@dmc.com (Dick Munroe) writes:
> How does SHOW DEVICE get its information about the device being
> mounted?  I have a cluster, a disk mounted on one node, but not
> cluster wide.  Mount counts are what you would expect, 0 on all
> nodes except the one having the mounted device.  The unexpected
> thing is that the DEVCHAR bit indicating mounted is clear on all
> nodes except the one having the mounted device (according to
> F$GETDVI).  The reason it's unexpected is because SHOW
> DEVICE/FULL show that the device IS mounted on all other nodes on
> the cluster.
>
> So how does SHOW DEVICE get the mounted information?  By looking
> at the UCBs directly?
> --
> Dick Munroe                           Internet: munroe@dmc.com
> Doyle Munroe Consultants, Inc.                UUCP: ...uunet!thehulk!munroe
> 267 Cox St.                           Office: (508) 568-1618
> Hudson, Ma.                           FAX: (508) 562-1133
>
> GET CONNECTED!!! Send mail to info@dmc.com to find out about DMConnection.
--

This information is maintained in locks.  There will be a lock named
"SYS$_device" for each disk.  For example, "SYS$_$1$DUA11:".  Each node that
has this disk mounted will have a CR-mode (concurrent read) lock queued to the
lock.  "SHOW DEVICE" queues a null-mode lock request to this lock, then uses a
$GETLKI to find out what other locks on the resource.

There is an undocumented logical name that may prove useful to you.  Define
"SHOW$DEBUG" to be some value.  The "SHOW DEVICE" command will then show you
a bunch of useful information which you can either pass along to DEC or use
yourself with SDA to try and figure out what went wrong.

-Bob Longo
=======================================+======================================
Bob Longo (longo@sfpp.com)             | "I am not gonna raise taxes on the
Santa Fe Pacific Pipelines             | middle class to pay for these
Los Angeles, CA                        | programs." - Bill Clinton