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pkg-gate / doc / scripting.txt

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        Getting rid of install/upgrade scripting

The design of SVR4 packaging relies heavily on the use of scripting to
achieve common packaging operations.  These scripts are delivered by
the package developers, and run in multiple installation contexts, 
which may include install, alternate roots, zones, cross architecture 
and cross OS versions.  This has caused a host of complex and thorny
issues, and led directly to the IPS team's decision to eliminate the
use of scripting in IPS.

Instead, the IPS architecture requires software to be largely
self-assembling; changes in configuration are either detected at boot
time or the appropriate SMF services are restarted in the case of live
installation of packages.  [In the few cases when this is not possible
due to assembly being needed for boot, the required support is being
built into IPS directly; such cases are actually rare].

Some concrete examples of how such "self-assembly" can be realized may
be worthwhile:

The recent hostid project moved the storage of the hostid information
on i386 architecture machines from the sysinit kernel module (which
was bpatch'd during install) into the /etc/hostid file.  The initial
design for handling upgrade added code to both BFU and the installer,
which decoded the hostid from the sysinit module and created the
hostid file during upgrade.  Freshly installed systems had no hostid
file, so the kernel generated one dyanmically and a SMF service
created the /etc/hostid file after boot.  Since neither bfu nor
install code runs during IPS image-update operations, this strategy
did not work on OpenSolaris and the hostid was not preserved on
upgrade.

To fix this, the kernel was modified to search for a sysinit module
and read the hostid from that if /etc/hostid didn't already exist.
Only if that was not present did the kernel generate a new hostid.  As
a result of this change, the upgrade code could be eliminated from
both BFU and upgrade, and the system upgrade process just works the
same in all cases.

The key design pattern here is to have the consumer of the
configuration file (here, genunix) handle the old file format/location
if the new file doeesn't exist; writing out the new file resolves the
upgrade process and completes the self-assembly.

Another common problem is the configuration file management problem.
A canonical example might be /etc/security/exec_attr.  Here many
different packages contribute lines into this file.  With SVR4
packages, a package's file fragments are merged in by the class action
script i.rbac during installation or upgrade.  Removal is problematic
on uninstall and is not attempted.

For IPS, the proposed solution is to have each package deliver its
portion of this file into a separate directory, using the name of the
package (suitably escaped, of course) as the file name.  A service
that runs at boot determines whether or not the file needs to be
re-composited from the file fragments.  This cleanly handles both
install and uninstall.

The key design pattern here is to have packages deliver their
components as files, which is something the packaging system is
designed to do.  Assembly of the composited file is left to boot time
and an SMF service, which deals with older package fragments, etc.

Another approach to the configuration file problem is to change the
format of the file.  A classic problem is the management of
/etc/driver_aliases, which is "maintained" by add_drv and update_drv.
This file maintains a mapping between a PCI id and the driver that
supports that device.  Note that rather than maintaining a text file
which would be read in by the kernel at boot, an alternate approach
would be to encode the same information as a directory of symbolic
links from the PCI id to the name of the driver.  This would eliminate
the potential confusion of two different drivers trying to own the
same PCI id, the need for locking the file during updates, and the
need to run programs on install and uninstall to manage this file
since the links would be simply installed and uninstalled as part of
the normal packaging operations.

The design pattern here is also simple - the filesystem already
maintains a single namespace, locking, conflict detection, etc;
reusing these attributes saves time and effort.

Another common problem is moving files, links and directories around
the filesystem and between packages; this is often handled via
scripting in the case of SVR4 packages.  In IPS, normal (not editable)
files can simply move between packages; this results in their removal
from the original location and then their re-installation in their new
location.  To insure that editable files retain their customizations,
the receiving package must annotate the actions that deliver the new
file name/location with an attribute that defines the original owning
packages and location. This looks like this:

original_name=SUNWfoo:etc/foo.txt

indicating that the name of original owning package was SUNWfoo and
that the original path was etc/foo.txt.  Note that no matter where
this file moves to subsequently, it should always maintain this
identifier.

Directories in IPS are automatically reference counted, and are
deleted when there are no longer any explicit declarations of
those directories or no files under packaging system control in
the directory.  Left-over files & directories not under packaging 
control are moved to a lost-and-found directory under var/pkg;
this is needed to support changing directories to symbolic links,
etc., w/o scripting.

There is not yet a simple method to move unpackaged files, etc
from an old location to a new one; developers facing this problem
should move those files as part of their self-assembly at first
boot and avoid removing the references to the original directories
to prevent their movement to lost-and-found during upgrade.  
We are considering various solutions to this problem.

In the short term, those developers working on OpenSolaris have a 
foot in both worlds - since OpenSolaris is built from Nevada SVR4
packages, their code needs to work in both environments.  With
the exception of driver post-install scripts (which are converted
by the folks working on OpenSolaris to IPS driver actions) the goal
is to remove all post-install/class action processing other than
SMF service restarting on live systems using the patterns shown
here.
 
 
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