Re: [RFC] grub-install C rewrite

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

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On 26.09.2013 16:44, Lennart Sorensen wrote:
>> windows is low priority and more of a bonus. The problems of handling
>> anything that looks like a list (e.g. list of devices where / resides on
>> in case of btrfs) and code becoming hairy to handle those cases is
>> bigger reason.
> 
> Sure lists can be a hassle.
> 
> I didn't check lately, but does grub-install understand a list of devices
> to install to yet?
> 
> ie:  grub-install /dev/sda /dev/sdb
> 
> After all if I have software raid, both those devices contain /boot and
> are valid to boot from.  And since on things like IBM powerpc,
> grub-install likes to update the firmware with the list of boot devices,
> they do all have to be specified at once or you end up with the wrong
> list (which so far I have worked around by manually fixing the firmware
> settings after updating grub, which doesn't happen very often lately).
> 
> So calling grub-install for each device in turn (as I believe Debian
> does on x86 if you tell it multiple boot devices), does not actually
> give the correct result.
> 
This is interesting testcase which wasn't brought before. This would
potentially involve creating several core.img or forcing UUID when using
multiple devices. Again, pretty easy in C and hairy in bash due to list
handling.
> So really my main objection is that it is much harder to debug and fix
> C code than it is to fix a script calling a bunch of external commands.
> 
> At the very least a C version of grub-install must have an option to
> list every command it is attempting to execute externally.  Certainly
> adding 'set -x' to grub-install has often been helpful.

It's surely sth we can do. grub-install does only following that is
affecting system:
1) mkdir -p
2) copy files. We can write exact copy commands
3) grub-mkimage. We can do the same.
4) grub-setup. Ditto
5) Create load.cfg. Ditto.
6) calling external commands.
 We can have 4 levels of verbosity:
0) quiet,
1) write to stderr the commands
2) like 1 but show grub_util_info
3) additionally show grub_dprintf

It's also possible to have options --dry-run (doesn't really do the
changes, except, perhaps, "mkdir -p") and --gen-script which would
generate a list of commands which when executed would do exactly as if
grub-install was run. So you can do
grub-install --dry-run --gen-script=/tmp/myinstall ...
<change /tmp/myinstall to will>
/tmp/myinstall
This has additional advantage of see which commands are really executed
without having to understand the whole command flow.


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