FAQ entry about why no binary packages

Hello All!

Now and then, someone will ask why Buildroot has no support for generating binary packages.

Rather than re-hash the same answer every time, add a section in the FAQ in the manual, that we can point users to.

This is an RFC, the text is not complete/accurate, and just a copy-paste of a mail I sent a bit earlier on the list. The goal is that people start adding to this section, to make it simple and complete, and not too long.

[PATCH] manual/faq: add section about why no binary packages

Regards,
Yann E. MORIN.

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| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
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From: "Yann E. MORIN" <[email protected]>

It somes up evry now and then on the list, so better be prepared to point at the manual, rather than rehash the same evry time.

---
 docs/manual/faq-troubleshooting.txt | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

index 4e0612b..e97457a 100644
@@ -111,3 +111,24 @@ directory as the new root, will most likely fail.
 If you want to run the target filesystem inside a chroot, or as an NFS
 root, then use the tarball image generated in +images/+ and extract it
 as root.
+
+[[faq-no-binary-packages]]
+Why doesn't Buildroot generate binary packages (.deb, .ipkg...)?
+----------------------------------------------------------------
+
+Buildroot explicitly avoids generating binary packages, on purpose.
+
+Buildroot strive at making it easy to generate a root filesystem (hence
+the name, by the way). That is what we want to make Buildroot good at:
+building root filesystems.
+
+Buildroot is not meant to be a distribution (or rather, a distribution
+generator). It is the opinion of most Buildroot developpers (me included)
+that this is not a goal we should pursue. We believe that there are other
+tools better suited to generate a distro than Buildroot is. For example,
+http://openembedded.org/[Open Embedded], or https://openwrt.org/[openWRT],
+are such tools.
+
+Rather, we prefer to push Buildroot in a direction that makes it easy
+(or even easier) to generate complete root filesystems. This is what
+makes Buildroot stands out in the crowd (among other things, of course!).

1.8.1.2

Hi Yann, all,

2014/1/5 Yann E. MORIN <[email protected]>

s/evry/every/ (twice)
hmm... you typed faster than your keyboard can handle? ;-)

I think i have something roughly about this and other in one of my doc-branches, but i lack time to work on it :-/ Meanwhile, an entry in the FAQ is good enough to me.

Regards,

Samuel
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Hi Yann,

     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -

Dear Baruch Siach,

I would go even further, and explain why tracking what files each package installs is by far not sufficient to support binary packages. Several people have showed up throughout the project history, willing to add support binary packages by assuming that simply tracking which files "make install" installs will be sufficient. But that's forgetting all the optional dependencies problems, and various other things.

We had a write-up about this in some report of a past Buildroot Developers Meeting, with some good arguments. Would be nice to dig that up and summarize these arguments in the doc.

Best regards,

Thomas

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Hello,

The report at
http://lists.busybox.net/pipermail/buildroot/2011-November/047229.html
has the details I was referring to. I'm copy/pasting them here:

===

Package management
------------------

On the feature that is often discussed on the Buildroot list, and which was on the agenda for this meeting was the general topic of "package management". To summarize, the idea would be to add some tracking of which Buildroot package installs what files, with the goals of :

* Being able to remove files installed by a package when this package gets unselected from the menuconfig ;

* Ultimately, be able to generate binary packages (ipk or other format) that can be installed on the target without re-generating a new root filesystem image.

In general, most people think it is easy to do: just track which package installed what and remove it when the package is unselected. However, it is much more complicated than that:

* It is not only about the target/ directory, but also the sysroot in host/usr/<tuple>/sysroot and the host directory itself. All files installed in those directories by various packages must be tracked.

* When a package is removed, it is not sufficient to remove just the files it installed. One must also remove all its reverse dependencies (i.e packages relying on it) and rebuild all those packages. For example, package A depends optionally on the OpenSSL library. Both are selected, and Buildroot is built. Package A is built with crypto support using OpenSSL. Later on, OpenSSL gets unselected from the configuration, but package A remains (since OpenSSL is an optional dependency, this is possible). If you just remove the OpenSSL files, then the files installed by package A are
broken: they use a library that is no longer present on the target. Technically, it is possible to do this (the prototype that Lionel Landwerlin and Thomas Petazzoni have worked on started to do this), but it is difficult and adds a fair bit of complexity.

* In addition to the previous problem, there is the case where the optional dependency is not even known to Buildroot. For example, package A in version 1.0 never used OpenSSL, but in version 2.0 it automatically uses OpenSSL if available. If the Buildroot .mk file hasn't been updated to take this into account, then package A will not be part of the reverse dependencies of OpenSSL and will not be removed and rebuilt when OpenSSL is removed. For sure, the .mk file of package A should be fixed to mention this optional dependency, but in the mean time, you can have non-reproducible behaviors.

* The whole idea is also to allow changes in the menuconfig to be applied on the output directory without having to rebuild everything from scratch. However, this is very difficult to achieve in a reliable way: what happens when the suboptions of a package are changed (we would have to detect this, and rebuild the package from scratch and potentially all its reverse dependencies), what happens if toolchain options are changed, etc. At the moment, what Buildroot does is clear and simple so its behaviour is very reliable and it is easy to support users. If we start telling users that the configuration changes done in menuconfig are applied after the next make, then it has to work correctly and properly in all situations, and not have some bizarre corner cases. We fear bug reports like "I have enabled package A, B and C, then ran make, then disabled package C and enabled package D and ran make, then re-enabled package C and enabled package E and then there is a build failure". Or worse "I did some configuration, then built, then did some changes, built, some more changes, built, some more changes, built, and now it fails, but I don't remember all the changes I did and in which order". This will be impossible to support.

For all these reasons, the conclusion of the Buildroot Developer Day was that adding tracking of installed files to remove them when the package is unselected is something that is very hard to achieve reliably and will add a lot of complexity.

In the morning, we had some discussion with Robert Schwebel about how PTXdist does package management. They only do it for files installed in the target filesystem. So for example the libraries/headers are never removed from their sysroot, so you quickly end up with inconsistencies. This is something we would like to avoid in Buildroot, because it creates confusing behaviors in our opinion. Esben from OE-lite also said that package management is very difficult to do reliably and that it would add a lot of complexity to a currently relatively simple Buildroot.

Buildroot focus is on simplicity and building relatively small systems, and this is definitely something we want to preserve. Moving away from this principle would make Buildroot more similar to existing more complicated build systems and therefore less interesting.

For the time being, we'd prefer not to add such mechanisms in Buildroot and keep its behavior as simple and easy to understand as it is today. We think it's better to focus on other features than trying to implement something that will never be completely reliable and will add a very significant complexity to Buildroot.

===

Thomas

Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com