Difference between revisions of "Using devtool to modify recipes in Yocto"

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== Creating Using devtool to modify recipes in Yocto ==
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== Using devtool to modify recipes in Yocto ==
  
 
Suppose you have a requirement of customizing an existing sources for a recipe, <code>devtool</code> will be the best option to go, as it will do all the steps required to create a patch, <code>bbappend</code> file etc.
 
Suppose you have a requirement of customizing an existing sources for a recipe, <code>devtool</code> will be the best option to go, as it will do all the steps required to create a patch, <code>bbappend</code> file etc.
 +
<br />
  
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As part of building a recipe, Yocto/OE creates a tmp/work/<architecture>/<recipe>/<version> directory, known as the "work directory".  
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As part of building a recipe, Yocto/OE creates a <code>tmp/work/<architecture>/<recipe>/<version></code> directory, known as the "work directory". <br /><br />
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This is where all of the work done to build a recipe takes place.  
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This is where all of the work done to build a recipe takes place. <br /><br />
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One of the things you'll find in this directory is the source, usually under a subdirectory named <recipename>-<version> or "git" (depending on how the fetched source is provided).  
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One of the things you'll find in this directory is the source, usually under a subdirectory named <code><recipename>-<version></code> or "git" (depending on how the fetched source is provided). <br /><br />
 
The temptation (and what people used to do in the past) is to simply make changes here and then recompile, but there are several reasons why that's not a good idea:
 
The temptation (and what people used to do in the past) is to simply make changes here and then recompile, but there are several reasons why that's not a good idea:
  
 
* It's awkward - you have to use <code>bitbake -c compile -f</code> or <code>bitbake -C compile</code> to force recompilation, since the build system doesn't know that you've made any changes
 
* It's awkward - you have to use <code>bitbake -c compile -f</code> or <code>bitbake -C compile</code> to force recompilation, since the build system doesn't know that you've made any changes
 
* You can easily lose your changes if you're not careful e.g. running <code>bitbake -c clean</code> will wipe the directory out
 
* You can easily lose your changes if you're not careful e.g. running <code>bitbake -c clean</code> will wipe the directory out
 +
 +
<br />
  
 
Luckily there's a much better method using the <code>devtool</code> command:
 
Luckily there's a much better method using the <code>devtool</code> command:
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 +
# Run <code>devtool modify &lt;recipename&gt;</code>. This will fetch the sources for the recipe and unpack them to a workspace/sources/<recipename> directory and initialise it as a git repository if it isn't already one. If you prefer you can specify your own path, or if you already have your own existing source tree you can specify the path along with the -n option to use that instead of unpacking a new one.
 +
# Make the changes you want to make to the source
 +
# Run a build to test your changes - you can just <code>bitbake &lt;recipename&gt;</code> or even build an entire image incorporating the changes assuming a package produced by the recipe is part of an image. There's no need to force anything - the build system will detect changes to the source and recompile as necessary.
 +
# If you wish, test your changes on the target. There's a "devtool deploy-target" command which will copy the files installed at do_install over to the target machine assuming it has network access, and any dependencies are already present in the image.
 +
# Repeat from step 2 as needed until you're happy with the results.
 +
# At this point you will almost certainly want to place your changes in the form of a patch to be applied from the metadata - devtool provides help with this as well. Commit your changes using "git commit" (as many or as few commits as you'd like) and then run either:
 +
#* <code>devtool update-recipe &lt;recipename&gt;</code> to update the original recipe - usually appropriate if it's your own recipe or you're submitting the changes back to the upstream layer
 +
#* <code>devtool update-recipe -a &lt;layerpath&gt; &lt;recipename&gt;</code> to put your changes in the form of a bbappend to be applied by a different layer. This is usually the desired method if your changes are customisations rather than bugfixes.
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# If you're finished working on the recipe, run <code>devtool reset &lt;recipename&gt;</code>.
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 +
<br />
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 +
This is just one of the things that devtool can do - it provides some powerful tools to help you maintain recipes and make changes to source code.
 +
 +
<br />
 +
 +
-----
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== Using devtool to modify the linux kernel recipes in Yocto ==
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 +
Modifying the kernel inside Yocto/OE
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# From your build directory run
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devtool modify virtual/kernel
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It will create a workspace directory containing the kernel sources in build directory
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<br />
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Now discover the package-name (PN) of the virtual/kernel
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 +
devtool status
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  NOTE: Starting bitbake server...
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  linux-yocto: /home/tux/yocto-bbb-dunfell/poky/build/workspace/sources/linux-yocto
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edit manually what you need (.c and .dts) in <code>workspace/sources/linux-yocto/</code>
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devtool build linux-yocto
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now you have your kernel and DeviceTree in <code>tmp/deploy/images/beaglebone-yocto/</code>
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then deploy them on the target board and test them.
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 +
<br />
 +
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Once you are satisfied, add this git repository to your fork.<br />
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This will add your patches to the original recipe
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git add .
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git commit -m "my linux modifications"
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devtool update-recipe linux-yocto
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 +
<br />

Revision as of 16:21, 30 November 2020

Using devtool to modify recipes in Yocto

Suppose you have a requirement of customizing an existing sources for a recipe, devtool will be the best option to go, as it will do all the steps required to create a patch, bbappend file etc.

As part of building a recipe, Yocto/OE creates a tmp/work/<architecture>/<recipe>/<version> directory, known as the "work directory".

This is where all of the work done to build a recipe takes place.

One of the things you'll find in this directory is the source, usually under a subdirectory named <recipename>-<version> or "git" (depending on how the fetched source is provided).

The temptation (and what people used to do in the past) is to simply make changes here and then recompile, but there are several reasons why that's not a good idea:

  • It's awkward - you have to use bitbake -c compile -f or bitbake -C compile to force recompilation, since the build system doesn't know that you've made any changes
  • You can easily lose your changes if you're not careful e.g. running bitbake -c clean will wipe the directory out


Luckily there's a much better method using the devtool command:

  1. Run devtool modify <recipename>. This will fetch the sources for the recipe and unpack them to a workspace/sources/<recipename> directory and initialise it as a git repository if it isn't already one. If you prefer you can specify your own path, or if you already have your own existing source tree you can specify the path along with the -n option to use that instead of unpacking a new one.
  2. Make the changes you want to make to the source
  3. Run a build to test your changes - you can just bitbake <recipename> or even build an entire image incorporating the changes assuming a package produced by the recipe is part of an image. There's no need to force anything - the build system will detect changes to the source and recompile as necessary.
  4. If you wish, test your changes on the target. There's a "devtool deploy-target" command which will copy the files installed at do_install over to the target machine assuming it has network access, and any dependencies are already present in the image.
  5. Repeat from step 2 as needed until you're happy with the results.
  6. At this point you will almost certainly want to place your changes in the form of a patch to be applied from the metadata - devtool provides help with this as well. Commit your changes using "git commit" (as many or as few commits as you'd like) and then run either:
    • devtool update-recipe <recipename> to update the original recipe - usually appropriate if it's your own recipe or you're submitting the changes back to the upstream layer
    • devtool update-recipe -a <layerpath> <recipename> to put your changes in the form of a bbappend to be applied by a different layer. This is usually the desired method if your changes are customisations rather than bugfixes.
  7. If you're finished working on the recipe, run devtool reset <recipename>.


This is just one of the things that devtool can do - it provides some powerful tools to help you maintain recipes and make changes to source code.


Using devtool to modify the linux kernel recipes in Yocto

Modifying the kernel inside Yocto/OE

  1. From your build directory run 
devtool modify virtual/kernel

It will create a workspace directory containing the kernel sources in build directory


Now discover the package-name (PN) of the virtual/kernel 

devtool status
 NOTE: Starting bitbake server...
 linux-yocto: /home/tux/yocto-bbb-dunfell/poky/build/workspace/sources/linux-yocto

edit manually what you need (.c and .dts) in workspace/sources/linux-yocto/ 

devtool build linux-yocto

now you have your kernel and DeviceTree in tmp/deploy/images/beaglebone-yocto/ then deploy them on the target board and test them.


Once you are satisfied, add this git repository to your fork.
This will add your patches to the original recipe 

git add .
git commit -m "my linux modifications"
devtool update-recipe linux-yocto


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