Re: [PATCH 6/6] doc/technical_overview: Describe binary cache

[Alexander Smirnov <asmirnov@ilbers.de>]

> This should be done along the way in every single patch, not afterwards.

I don't think that it really should. The requirement to documentation is 
to describe current code state in repo. So if something has been changed 
in design - HEAD of branch should contain relevant documentation, what 
could be achieved by dedicate patch. Moreover this single patch 
explicitly describes the influence of whole series to current design.

> 
> Henning
> 
> Am Sun, 27 Aug 2017 18:13:39 +0300
> schrieb Alexander Smirnov <asmirnov@ilbers.de>:
> 
>> Describe Isar binary cache feature.
>>
>> Signed-off-by: Alexander Smirnov <asmirnov@ilbers.de>
>> ---
>>   doc/technical_overview.md | 59
>> +++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 55
>> insertions(+), 4 deletions(-)
>>
>> diff --git a/doc/technical_overview.md b/doc/technical_overview.md
>> index 20e08b4..b3265dc 100644
>> --- a/doc/technical_overview.md
>> +++ b/doc/technical_overview.md
>> @@ -100,6 +100,43 @@ Target filesystem lifecycle can be described as
>> following:
>>    - According to the list of custom packages in bitbake recipes, the
>> initial filesystem will be populated by successfully built packages.
>>   
>> +## 2.5 Binary Cache
>> +
>> +As mentioned above, apart from fetching binary packages from
>> upstream apt +repositories, Isar is able to build custom packages
>> from sources. To simplify +further custom packages management, Isar
>> implements binary caching. +
>> +Binary cache is a typical apt repository created by Isar to store
>> newly built +packages. This repository has mainly two goals:
>> +
>> + - Simplify image filesystem populating and distributing binary
>> packages to
>> +   other systems.
>> +
>> + - Reuse these binaries in next builds to avoid re-building from the
>> +   scratch everytime.
>> +
>> +Current Isar tree provides default cache repository: `meta-isar-bin`.
>> +Isar binary cache is described by the following files:
>> +
>> + - `meta-isar-bin/conf/layer.conf`
>> +
>> + - `meta-isar-bin/files/distributions.in`
>> +
>> +After system build is complete, this repo contains binary packages
>> for all the +distros and architectures, requested in multiconfig. So
>> this folder can be +published and used as apt repo for already
>> installed systems. +
>> +An important note, that Isar creates local repositories using
>> dedicated Debian +tool reprepro. This tool takes care about:
>> +
>> + - Maintenance of multiple architectures and distros.
>> +
>> + - Internal packages database management.
>> +
>> + - Repo signatures management.
>> +
>> + - Requests about available packages in repo (name, version etc...).
>> +
>>   # 3 Isar Internal Processes
>>   
>>   ## 3.1 General Overview
>> @@ -174,10 +211,17 @@ contain debian folder. The build process is
>> implemented in
>>      3. Run dpkg-buildpackage
>>   
>> -4. Task `do_install`: install successfully built packages
>> +4. Further package processing depends on binary cache option:
>> +
>> +   1. Task `do_install_to_deploy`: install successfully built
>> packages if
>> +   binary cache is disabled:
>>      `${BUILDCHROOT_DIR}/home/build/${PN}/*.deb` to deploy directory
>>      `${DEPLOY_DIR_DEB}`
>>   
>> +   2. Task `do_install_to_cache`: install successfully built
>> packages to
>> +   binary cache repository:
>> +   `${BUILDCHROOT_DIR}/home/build/${PN}/*.deb` to `${DIR_CACHE}`
>> +
>>   ## 3.5 Populate Target Filesystem
>>   
>>   Each target image can be extended by custom packages listed in
>> IMAGE_INSTALL @@ -185,11 +229,18 @@ variable. Task `do_populate`
>> performs the following:
>>   1. Parse IMAGE_INSTALL variable.
>>   
>> -2. Find respective packages in `${DEPLOY_DIR_DEB}`.
>> +2. Further steps depends in binary cache option.
>> +If binary cache is disabled:
>> +
>> +   1. Find respective packages in `${DEPLOY_DIR_DEB}`.
>> +
>> +   2. Copy packages to deb folder in dedicated target filesystem.
>> +
>> +   3. Execute dpkg command in chroot for all the copied packages.
>>   
>> -3. Copy them to deb folder in dedicated target filesystem.
>> +If binary cache is enabled:
>>   
>> -4. Execute dpkg command in chroot for all the copied packages.
>> +   1. Call apt-get install in chroot in target image filesystem.
>>   
>>   ## 3.6 Generate Bootable Image
>>   
>