I'm submitting the following fast-track on behalf of Jan Setje-Eilers.
The project believes this qualifies for automatic approval and I've
filed it as such, but can promote to a full fast-track if anyone
prefers.
The proposal is to add a command-line -u option to installboot and
installgrub with Consolidation Private commitment and minor release
binding.
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1) Summary
Updating the boot block on a pool with multiple zfs boot
environments during upgrades should involve a check to avoid
potentially downgrading the boot block.
2) Technical Details
2.0) Background
With the advent of zfs boot, multiple versions of the OS
can reside in a single area of a device (entire device, partition
or slice). This forces them to share a single boot loader which
imposes the following issues:
a) Newer boot loaders must be able to load older versions
of the OS.
This is ultimately an implementation issue and
is not part of this case.
b) During upgrade care must be taken to avoid replacing
what might be a newer copy of a boot loader with an
older one.
This issue can arise if a BE is cloned and
updated to a newer version and is subsequently
fallen back to and then again cloned and updated
to an intermediate version.
2.1) Current state
2.1.1) SPARC
In order to avoid potentially downgrading the loader on SPARC
it is simply never updated. This is poor.
2.1.2) x86
On x86 the private concept of a capability file was
introduced to attempt to capture both a version and
features a specific copy of GRUB might supply. This
relied on being able to see all the capability files
of available BEs. It also required manual updates of
the file.
2.2 Proposed Solution
2.2.1) Mechanism
A version string is embedded into the installed boot block
when it is installed. That string can then be parsed and
compared against a potentially newer string on subsequent
installs.
2.2.2) Implementation details
The string is supplied by the packaging information and is
ultimately a consolidation private bit of information that
is generated in the same place that the tools to parse and
compare it are built.
For the sake of the current bits this will be the package
fmri which will gain minor and micro version numbers
to allow some manual control in addition to the release
and build numbers as well as time-stamps.
However the SVR4 package version could have been used
just as well, and the tool could explicitly handle a
transition to a new type of string if the need were to
arise.
For the sake of this case package fmris are treated
as external and may evolve.
However at the moment an fmri might look like this:
pkg://opensolaris.org/system/boot/[email protected],5.11-0.136:20100316T170914Z
In this example each of the following are tested to
be greater, equal or lower. A result of greater (newer) will
force an install (update). A result of equal will move on to
the next check (or in the final case result in no install).
A result of lower will block an install.
0.97 external version
123 minor version (Solaris specific features)
456 micro version (Solaris specific changes/fixes)
5 major OS version
11 minor OS version
0 release number
136 build number
20100316T170914Z time stamp
The publisher is ignored when computing newerness, but
is written to the installed boot block.
Lack of an embedded version (or complete lack of a booter)
is treated as an event worthy of getting the booter onto
a more supportable train and loader is installed and the
version string is written. This covers situations such
as a developer modification (bfu, manual installboot
invocation) of one BE followed by falling back to another
and then updating from there.
The version string is validated to be parsable and comparable
and the entire operation returns failure if the string
can not be worked with. This is done to avoid creating
a situation where installed bits can not be updated from.
3) Consolidation Private Interfaces
This interface is being developed for libbe which is bound for
the OS/Net consolidation, so the commitment level is consolidation
private.
Both installboot and installgrub gain a -u option that
takes the version string.
3.1) installboot
installboot [-F fstype] [-u<version>] bootblk raw-device
3.2) installgrub
installgrub [-fm] [-u<version>] stage1 stage2 raw-device
Both check the version against a version supplied by a previously
installed boot block and will only update the boot block if the
install is deemed to be an upgrade.
Lack of an embedded version (or complete lack of a booter) will
result in an install.
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