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VMLINK Automounter

Description

A VMLINK-like automounter script combining the function of vmcp link, chccwdev, and mount in one fell swoop.

Use /etc/auto.net as a starting reference. vmcp link may fail (e.g., if the virtual machine attempting the link is not authorized). mount may fail (e.g., if there is no filesystem or is not a known filesystem).

The automount point should be identified by

  • vmid of the owning virtual machine
  • address of the disk on the owning virtual machine, and optionally
  • partition, if the disk has multiple partitions

Note that a 3390 CKD volume in "compatible layout" can have 1, 2, or 3 partitions. Other layouts can have 1 partition or 0 (meaning the entire disk from the starting block, offset zero).

Note that a 9336 or 3370 FBA volume can have a PC-like partition table and can therefore have zero (full disk) up to (at least) 15 partitions.

Additional Information

See the vmlink command in the CMS Commands and Utilities Reference SC24-6166 (various revisions).

https://www.ibm.com/support/knowledgecenter/SSB27U_6.4.0/com.ibm.zvm.v640.dmsb4/vmlink.htm

(The link will go 404, but hopefully not before this project is completed.)

Desirable Skills

Mostly shell scripting.

Familiarity with the mount command (or acquired during the project) is a must. Familiarity with vmcp link needed too, but can be learned.

Expected Outcome

Users should be able to cd /vmlink/vmid.addr or cd /vmlink/vmid.addr.part and have access to the filesystem(s) available on the linked virtual disk.

Difficultly

Medium

Mentors

Additional Comments

In one shop, we did a lot of sharing of disks among virtual machines. Doing a vmcp link was no big deal for the VMers. Use of mount was second nature for the Linux guys. The combination was always a mental stretch. Eventually we coaxed the automounter into doing it all for us.

Most Linux distributions include /etc/auto.net which serves as an example. (Usually also /etc/auto.smb if you like.) For this project, create /etc/auto.vmlink to handle linking, varying online, and mounting of disks owned by other virtual machines (assuming your v-machine has the rights to read the disk(s), which is a whole other story).

Partitioning is another matter. If a disk has one (or zero) partitions, the script could just figure things out. If the disk has multiple partitions, maybe tack-on an extra dotted indicator for the partition of interest.

I call it "VMLINK-like" because in CMS there is the vmlink command which provides a similar effect.