On 06/02/2014 09:37 AM, Nikolai Kondrashov wrote:
On 05/31/2014 04:45 AM, Dmitri Pal wrote:
I reworked the design based on the feedback provided.
It is a completely rewritten version.
Please take a look.
https://fedorahosted.org/sssd/wiki/DesignDocs/ding-libs/INIConfigMerge
I'm likely awfully under-informed (I haven't seen any prior
discussion or
requirements, never used the library), but I'd like to give my
opinion anyway,
if only as an exercise.
I wouldn't like to steal much of anyone's time so please ignore me if
I'm
entirely missing the point. I've likely missed some requirements and
the below
needs details figured out, but I think this general approach would be
better
for both end-users and developers.
First of all, the proposal sounds terribly complicated.
Hm. I think it is significantly simplified in comparison to the
previous version.
The function is not SSSD specific. It is a part of the generic
library, it is up to application developer to use different aspects of
it.
I would rather implement a complex function and have a simplified use
of it than have a simplified function and then several month later
realize that we need to have more flexibility and a break ABI or have
function augment2, augment3 etc - ugly.
Both in merging logic
and in permission requirements. What's worse, this complexity is
hidden from
system administrators (users) in the code. It means that all the
parameters
passed to "ini_config_augment" will need to be documented somewhere.
The function is for developers not for admins. It is a tool. It is up
to the developer to use it in such a way that admin can understand.
As in: "you can put these and these sections in these files and the
files will
need to have these and these permissions and be owned by such and
such user
and group, etc.".
This is an application choice. SSSD might not required to use it (at
first) up until it realizes that overwriting some sections is not a
good idea.
This will be needed for every application using this feature
and it will need to be updated with the code. And all hell will break
loose
when someone decides to adjust ini_config_augment arguments based on
previously read keys/sections. Just because it can be done, you know.
I do not think it is a valid concern. You can shoot yourself into the
head in so many different ways.
Assigning special treatment to "augmenting" configuration, and adding
ability
to ignore erros there specifically, also doesn't seem right. Given the
overwriting feature is provided, the *whole* of the actual
configuration can
be placed there, and thus it seems better to give equal treatment
both to the
"main" and to the "augmented" configuration. I.e. either provide a
way to
ignore/enforce errors in both or in none.
I disagree. Overwriting is much more dangerous than augmenting.
From my, once again, entirely uninformed view as a potential user and an
administrator I would have liked to see the following instead.
Allow both sections and keys appear more than once in a configuration
file.
Ini library support this but it is application's choice to allow it or
not.
SSSD does not allow it while GSS proxy does.
Repeated keys would overwrite previous value. New keys in repeated
sections
would add keys. Missing keys in repeated sections wouldn't change
anything.
I assume this is the way it works currently, as some QA tests use it.
You are not testing the library itself. SSSD reads the config with a
special flag indicating what you described but there are all sorts of
different modes that can be specified that would treat duplicates as
errors or preserve the original value.
Again library provides flexibility, application decides on the best
option to use.
Adjust the configuration language to add syntax to remove sections
and keys.
NO. No language. That adds much more complexity then needed.
Something which can be understood with little or no documentation. For
example:
[section_a]
key_a = 1
key_b = 2
[section_b]
key_c = 3
; Add "key_d" to "section_b"
[section_b]
key_d = 4
; Remove "section_a"
-[section_a]
; Start "section_a" anew
[section_a]
key_d = 42
; Remove "key_c" from "section_b" and overwrite "key_c"
[section_b]
-key_d
key_c = 2
Add configuration language syntax to include files/directories of files,
optionally specifying file permission requirements and section
modification
permissions. With this amount of features the need for documentation
to read
them would be inevitable, but we can at least try:
[section_a]
key_a = 1
key_b = 2
[section_b]
key_c = 3
; Include an application configuration file, only allowed to add
some
; sections
<application.conf add section_c_*,
user application,
group application,
mode 640>
; Include a subdirectory of configuration files, allowed to add any
; and modify/remove some sections
<service.d add *,
modify section_a_*,
user root,
group service,
mode 660>
; Include another configuration file keeping the permissions intact
<additional.conf>
I am strongly apposed any kind of the include directives.
Having include directives means someone needs to insert them.
The use case we are trying to solve is to be able to augment config
files without changing the main config file.
Included files would be processed as if read at the spot of the
directive
without any other requirements.
This is a significant rewrite of the parser because of the language of
the INI file change. Now any config file is a config file. As soon as
you introduce language you have a "proper" ini file and one that needs
to be merged and processed. It is just way more complex than suggested.
I.e. they can continue existing or start new
sections. The usual ordering of files in directories would apply. Nested
includes should be possible allowing applications to sub-delegate
some of
their configuration. Includes should not be allowed to relax section
addition/modification permissions, only to make them stricter. File
permission
requirements should probably be changeable, though.
The ideas is to avoid the includes and have any config file be a valid
config file.
The support for the extended syntax may be configurable via the API.
Which API?
This way there might be no need to add another function, although a
feature
for merging many files from the code would be useful.
There is already a way to merge snippets in the library. The function
is proposed to have a one tool instead of implementing the same
functionality in different places.
This way everything is visible to and controllable by the
administrator and
doesn't need application-specific documentation, only the configuration
language documentation, which may be borrowed from the library and would
rarely change. More complicated include statements would need some
comments,
but at least those would be close to the actual logic.
If someone want to implement it be my guest. Having spent some time in
the area I would say it is power of magnitude more complex than the
original "more complex" design that was proposed (you can read it in
the page history).
Nick
