Hi folks, As most of you know within the Yocto Project and OpenEmbedded we've been trying to figure out how to improve the OE developer workflow. This potentially covers a lot of different areas, but one in particular I where think we can have some impact is helping application developers - people who are working on some application or component of the system, rather than the OS as a whole.
Currently, what we provide is an installable SDK containing the toolchain, libraries and headers; we also have the ADT which additionally provides some Eclipse integration (which I'll leave aside for the moment) and has some ability to be extended / updated using opkg only. The pros: * Self contained, no extra dependencies * Relocatable, can be installed anywhere * Runs on lots of different systems * Mostly pre-configured for the desired target machine The cons: * No ability to migrate into the build environment * No helper scripts/tools beyond the basic environment setup * No real upgrade workflow (package feed upgrade possible in theory, but no tools to help manage the feeds and difficult to scale with multiple releases and targets) As the ADT/SDK stand, they do provide an easy way to run the cross-compilation on a separate machine; but that's about it - you're somewhat on your own as far as telling whatever build system your application / some third-party library you need uses to use that toolchain, and completely on your own as far as getting your changes that code into your image or getting those changes integrated into the build system is concerned. We can do better. Bridging the gap ================ We have a lot of power in the build system - e.g. the cross-compilation tools and helper classes. I think it would help a lot if we could give the developer access to some of this power, but in a manner that does not force the developer to have to deal with the pain of actually setting up the build system and keeping it running. I think there is a path forward where we can integrate the build system into the SDK and wrap it in some helper scripts in such a way that we: * Avoid the need to configure the build system - it comes pre-configured. The developer is not expected to need to touch the configuration files at all. * Avoid building anything on the developer's machine that we don't need to - lock the sstate signatures such that only components that the developer ends up building are the ones that they've selected to work on, which are tracked by the tools, and the rest comes from sstate - and perhaps a portion of the sstate is already part of the downloaded SDK to avoid too much fetching during builds, either in the form of sstate packages or already populated into the target sysroot and other places within the internal copy of the build system. This should reduce the likelihood of the system breaking on the developer's machine as well as reduce the number of host dependencies. * Provide tools to add new software - in practical terms this means creating a new recipe in an automated/guided manner (figuring out as much as we can looking at the source tree) and then configuring the build to use the developer's external source tree rather than SRC_URI, by making use of the externalsrc class. This also gives a head start when it comes to integrating the new software into the build - you already have a recipe, even if some additional tweaking is required. * Provide tools to allow modifying software for which a recipe already exists. If the user has an external source tree we use that, otherwise we can fetch the source, apply any patches and place the result in an external source tree, possibly managed with git. (It's fair to say this is perhaps less of an application developer type task, but still an important one and fairly simple to add once we have the rest of the tooling.) * Provide tools to get your changes onto the target in order to test them. With access to the build system, rebuilding the image with changes to a target component is fairly trivial; but we can go further - assuming a network connection to the target is available we can provide tools to simply deploy the files installed by the changed recipe onto the running device (using an "sstate-like" mechanism - remove the old list of files and then install the new ones). * Provide tools to get your changes to the code or the metadata into a form that you can submit somewhere. For compilation, this would mean that we use the normal native / cross tools instead of nativesdk; the only parts that remain as nativesdk are those that we need to provide to isolate the SDK from differences in the host system (such as Python / libc). We'll need to do some additional loader tricks on top of what we currently do for nativesdk so that the native / cross tools can make use of the nativesdk libc in the SDK, but this shouldn't be a serious barrier. Example workflow ================ I won't give a workflow for every possible usage, but just to give a basic example - let's assume you want to build a "new" piece of software for which you have your own source tree on your machine. The rough set of steps required would be something like this (rough, e.g. the command names given shouldn't be read as final): 1. Install the SDK 2. Run a setup script to make the SDK tools available 3. Add a new recipe with "sdktool add <recipename>" - interactive process. The tool records that <recipename> is being worked on, creates a recipe that can be used to build the software using your external source tree, and places the recipe where it will be used automatically by other steps. 4. Build the recipe with "sdktool build <recipename>". This probably only goes as far as do_install or possibly do_package_qa; in any case the QA process would be less stringent than with the standard build system however in order to avoid putting too many barriers in the way of testing on the target. 5. Fix any failures and repeat from the previous step as necessary. 6. Deploy changes to target with "sdktool deploy-target <ip address>" assuming SSH is available on the target. Alternatively "sdktool build-image <imagename>" can be used to regenerate an image with the changes in it; "sdktool runqemu" could do that (if necessary) and then run the result within QEMU with the appropriate options set. Construction & Updating ======================= At some point, you need to update the installed SDK after changes on the build system side. Our current SDK has no capability to do this - you just install a new one and delete the old. The ADT supports opkg, but then you have another set of feeds to maintain and we don't really provide any tools to help with that. If we're already talking about replacing the SDK's target sysroot and most of the host part by using the build system + pre-built components from sstate, then it would perhaps make sense to construct the new SDK itself from sstate packages and add some tools around filtering and publishing the sstate cache at the same time. (We can even look at ways to compare the contents of two sstate packages which have different signatures to see if the output really has changed, and simply not publish the new sstate package and preserve the locked signature for those have not.) We can then have a simple update tool shipped with the SDK along with a manifest of the components + their signatures. The update tool downloads the new manifest from the server and removes / extracts sstate packages until the result matches the manifest. Where to from here? =================== I'd like to get some feedback on the above. Within the Yocto Project we've committed to doing something to improve the developer experience in the 1.7 timeframe, so I'd hope that if there are no violent objections we could at least have enough of this working for 1.7 so that the concept can be put to the test. [Note: we would preserve the ability to produce the existing SDK as-is - we wouldn't be outright replacing that, at least not just yet; it will likely replace the ADT more immediately however.] Cheers, Paul -- Paul Eggleton Intel Open Source Technology Centre -- _______________________________________________ Openembedded-core mailing list Openembedded-core@lists.openembedded.org http://lists.openembedded.org/mailman/listinfo/openembedded-core
