[gsoc15] dynamically discover bes

[Prasad Joshi]

Week 3 status
==========
After understanding on disk representation of snapshots and clones, I
have been able to find names of the BEs created using beadm command. I
could print the BE names on console.

The next task would be to convert BE names to object numbers, create
list of BEs.

Thanks and Regards,
Prasad

On Tue, Jun 9, 2015 at 6:36 AM, Prasad Joshi
<prasadjoshi.linux at gmail.com> wrote:
> Last week I mostly worked on understanding beadm and gptzfsboot code
>
> beadm create prepares new BE by creating a snapshot and clone of that
> snapshot. beadm activate command sets bootfs property of the POOL.
> bootfs property contains object number of active dataset object.
> During bootup gptzfsboot probes all the disks, creating SPA for any
> valid pool. gptzfsboot assumes the first pool it finds as a primary
> pool, it then reads meta object set, then tries to find object nunber
> of active dataset object either through
> a. bootfs - it would be set if BE was already created
> b. mos->properties_zap->root_dataset->dd_head_dataset_obj (through
> root_datasets bonus buffer)
> Once the object number is obtaind gptzfsboot mounts the dataset.
>
> After mounting, few files are looked up like /boot/config or
> /boot.config for presense of boot command (did not went into details
> of this). Then (if keyboard is not hit), gptzfsboot execs
> /boot/zfsloader. If gptzfsboot is interrupted by keyboard, then it
> displays default BE or POOL it is trying to boot from (using
> zfs_rlookup() to map active dataset object to string BE name). Though
> I haven't checked this but through serial console user would be
> allowed to enter other pool or BE to boot from.
>
> I could not go into details of how gptzfsboot reads /boot/zfsloader from disk.
>
> Pending Tasks
> =============
> 1. Understand upon keyboard interruption, how user entered zfs paths
> (format [zfs:pool/filesystem:][/path/to/loader]) are converted in
> object numbers?
> 2. Learn ZFS on disk format in more details so as to identify active
> dataset object numbers of all BEs. Once the object numbers are
> available, I can use zfs_rlookup() function to map object number to
> printable pool name.
> 3. Prepare library for console based menu.
>
> Plan for next week
> ==================
> Pending task 2 above