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overview-manual, ref-manual: Moved "Shared State Cache" to overview manual

Browse Source 
Fixes [YOCTO #12370]

The section on shared state cache needed to be in the overview manual
and not in the ref-manual.  I moved it.  Some links were affected,
which I fixed.

(From yocto-docs rev: 1c4e5207bdde19d4b48ef42b1de81390d8a02d64)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2018-01-11 10:01:23 -08:00
committed by Richard Purdie
parent 937b66e9d1
commit 00f87f8416
9 changed files with 656 additions and 620 deletions
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6
documentation/dev-manual/dev-manual-common-tasks.xml
View File

@@ -7346,7 +7346,7 @@ Some notes from Cal:
<para>
Because the OpenEmbedded build system uses
"<ulink url='&YOCTO_DOCS_REF_URL;#checksums'>signatures</ulink>",
"<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#overview-checksums'>signatures</ulink>",
which are unique to a given build, the build system
knows when to rebuild packages.
All the inputs into a given task are represented by a
@@ -7450,8 +7450,8 @@ Some notes from Cal:
<para>
For more information on shared state, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#shared-state-cache'>Shared State Cache</ulink>"
section in the Yocto Project Reference Manual.
"<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>Shared State Cache</ulink>"
section in the Yocto Project Overview Manual.
</para>
</note>
</section>

635
documentation/overview-manual/overview-concepts.xml
View File

@@ -471,6 +471,641 @@
</note>
</section>
<section id="shared-state-cache">
<title>Shared State Cache</title>
<para>
By design, the OpenEmbedded build system builds everything from
scratch unless BitBake can determine that parts do not need to be
rebuilt.
Fundamentally, building from scratch is attractive as it means all
parts are built fresh and there is no possibility of stale data
causing problems.
When developers hit problems, they typically default back to
building from scratch so they know the state of things from the
start.
</para>
<para>
Building an image from scratch is both an advantage and a
disadvantage to the process.
As mentioned in the previous paragraph, building from scratch
ensures that everything is current and starts from a known state.
However, building from scratch also takes much longer as it
generally means rebuilding things that do not necessarily need
to be rebuilt.
</para>
<para>
The Yocto Project implements shared state code that supports
incremental builds.
The implementation of the shared state code answers the following
questions that were fundamental roadblocks within the OpenEmbedded
incremental build support system:
<itemizedlist>
<listitem><para>
What pieces of the system have changed and what pieces have
not changed?
</para></listitem>
<listitem><para>
How are changed pieces of software removed and replaced?
</para></listitem>
<listitem><para>
How are pre-built components that do not need to be rebuilt
from scratch used when they are available?
</para></listitem>
</itemizedlist>
</para>
<para>
For the first question, the build system detects changes in the
"inputs" to a given task by creating a checksum (or signature) of
the task's inputs.
If the checksum changes, the system assumes the inputs have changed
and the task needs to be rerun.
For the second question, the shared state (sstate) code tracks
which tasks add which output to the build process.
This means the output from a given task can be removed, upgraded
or otherwise manipulated.
The third question is partly addressed by the solution for the
second question assuming the build system can fetch the sstate
objects from remote locations and install them if they are deemed
to be valid.
<note>
The OpenEmbedded build system does not maintain
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
information as part of the shared state packages.
Consequently, considerations exist that affect maintaining
shared state feeds.
For information on how the OpenEmbedded build system
works with packages and can track incrementing
<filename>PR</filename> information, see the
"<ulink url='&YOCTO_DOCS_DEV_URL;#automatically-incrementing-a-binary-package-revision-number'>Automatically Incrementing a Binary Package Revision Number</ulink>"
section in the Yocto Project Development Tasks Manual.
</note>
</para>
<para>
The rest of this section goes into detail about the overall
incremental build architecture, the checksums (signatures), shared
state, and some tips and tricks.
</para>
<section id='overall-architecture'>
<title>Overall Architecture</title>
<para>
When determining what parts of the system need to be built,
BitBake works on a per-task basis rather than a per-recipe
basis.
You might wonder why using a per-task basis is preferred over
a per-recipe basis.
To help explain, consider having the IPK packaging backend
enabled and then switching to DEB.
In this case, the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
task outputs are still valid.
However, with a per-recipe approach, the build would not
include the <filename>.deb</filename> files.
Consequently, you would have to invalidate the whole build and
rerun it.
Rerunning everything is not the best solution.
Also, in this case, the core must be "taught" much about
specific tasks.
This methodology does not scale well and does not allow users
to easily add new tasks in layers or as external recipes
without touching the packaged-staging core.
</para>
</section>
<section id='overview-checksums'>
<title>Checksums (Signatures)</title>
<para>
The shared state code uses a checksum, which is a unique
signature of a task's inputs, to determine if a task needs to
be run again.
Because it is a change in a task's inputs that triggers a
rerun, the process needs to detect all the inputs to a given
task.
For shell tasks, this turns out to be fairly easy because
the build process generates a "run" shell script for each task
and it is possible to create a checksum that gives you a good
idea of when the task's data changes.
</para>
<para>
To complicate the problem, there are things that should not be
included in the checksum.
First, there is the actual specific build path of a given
task - the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>.
It does not matter if the work directory changes because it
should not affect the output for target packages.
Also, the build process has the objective of making native
or cross packages relocatable.
<note>
Both native and cross packages run on the build host.
However, cross packages generate output for the target
architecture.
</note>
The checksum therefore needs to exclude
<filename>WORKDIR</filename>.
The simplistic approach for excluding the work directory is to
set <filename>WORKDIR</filename> to some fixed value and
create the checksum for the "run" script.
</para>
<para>
Another problem results from the "run" scripts containing
functions that might or might not get called.
The incremental build solution contains code that figures out
dependencies between shell functions.
This code is used to prune the "run" scripts down to the
minimum set, thereby alleviating this problem and making the
"run" scripts much more readable as a bonus.
</para>
<para>
So far we have solutions for shell scripts.
What about Python tasks?
The same approach applies even though these tasks are more
difficult.
The process needs to figure out what variables a Python
function accesses and what functions it calls.
Again, the incremental build solution contains code that first
figures out the variable and function dependencies, and then
creates a checksum for the data used as the input to the task.
</para>
<para>
Like the <filename>WORKDIR</filename> case, situations exist
where dependencies should be ignored.
For these cases, you can instruct the build process to
ignore a dependency by using a line like the following:
<literallayout class='monospaced'>
PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
</literallayout>
This example ensures that the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCHS'><filename>PACKAGE_ARCHS</filename></ulink>
variable does not depend on the value of
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
even if it does reference it.
</para>
<para>
Equally, there are cases where we need to add dependencies
BitBake is not able to find.
You can accomplish this by using a line like the following:
<literallayout class='monospaced'>
PACKAGE_ARCHS[vardeps] = "MACHINE"
</literallayout>
This example explicitly adds the <filename>MACHINE</filename>
variable as a dependency for
<filename>PACKAGE_ARCHS</filename>.
</para>
<para>
Consider a case with in-line Python, for example, where
BitBake is not able to figure out dependencies.
When running in debug mode (i.e. using
<filename>-DDD</filename>), BitBake produces output when it
discovers something for which it cannot figure out dependencies.
The Yocto Project team has currently not managed to cover
those dependencies in detail and is aware of the need to fix
this situation.
</para>
<para>
Thus far, this section has limited discussion to the direct
inputs into a task.
Information based on direct inputs is referred to as the
"basehash" in the code.
However, there is still the question of a task's indirect
inputs - the things that were already built and present in the
<ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>.
The checksum (or signature) for a particular task needs to add
the hashes of all the tasks on which the particular task
depends.
Choosing which dependencies to add is a policy decision.
However, the effect is to generate a master checksum that
combines the basehash and the hashes of the task's
dependencies.
</para>
<para>
At the code level, there are a variety of ways both the
basehash and the dependent task hashes can be influenced.
Within the BitBake configuration file, we can give BitBake
some extra information to help it construct the basehash.
The following statement effectively results in a list of
global variable dependency excludes - variables never
included in any checksum:
<literallayout class='monospaced'>
BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
</literallayout>
The previous example excludes
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
since that variable is actually constructed as a path within
<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>,
which is on the whitelist.
</para>
<para>
The rules for deciding which hashes of dependent tasks to
include through dependency chains are more complex and are
generally accomplished with a Python function.
The code in <filename>meta/lib/oe/sstatesig.py</filename> shows
two examples of this and also illustrates how you can insert
your own policy into the system if so desired.
This file defines the two basic signature generators
<ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OE-Core</ulink>
uses: "OEBasic" and "OEBasicHash".
By default, there is a dummy "noop" signature handler enabled
in BitBake.
This means that behavior is unchanged from previous versions.
OE-Core uses the "OEBasicHash" signature handler by default
through this setting in the <filename>bitbake.conf</filename>
file:
<literallayout class='monospaced'>
BB_SIGNATURE_HANDLER ?= "OEBasicHash"
</literallayout>
The "OEBasicHash" <filename>BB_SIGNATURE_HANDLER</filename>
is the same as the "OEBasic" version but adds the task hash to
the stamp files.
This results in any
<ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>
change that changes the task hash, automatically
causing the task to be run again.
This removes the need to bump
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
values, and changes to Metadata automatically ripple across
the build.
</para>
<para>
It is also worth noting that the end result of these
signature generators is to make some dependency and hash
information available to the build.
This information includes:
<itemizedlist>
<listitem><para>
<filename>BB_BASEHASH_task-</filename><replaceable>taskname</replaceable>:
The base hashes for each task in the recipe.
</para></listitem>
<listitem><para>
<filename>BB_BASEHASH_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
The base hashes for each dependent task.
</para></listitem>
<listitem><para>
<filename>BBHASHDEPS_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
The task dependencies for each task.
</para></listitem>
<listitem><para>
<filename>BB_TASKHASH</filename>:
The hash of the currently running task.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='shared-state'>
<title>Shared State</title>
<para>
Checksums and dependencies, as discussed in the previous
section, solve half the problem of supporting a shared state.
The other part of the problem is being able to use checksum
information during the build and being able to reuse or rebuild
specific components.
</para>
<para>
The
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-sstate'><filename>sstate</filename></ulink>
class is a relatively generic implementation of how to
"capture" a snapshot of a given task.
The idea is that the build process does not care about the
source of a task's output.
Output could be freshly built or it could be downloaded and
unpacked from somewhere - the build process does not need to
worry about its origin.
</para>
<para>
There are two types of output, one is just about creating a
directory in
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>.
A good example is the output of either
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>.
The other type of output occurs when a set of data is merged
into a shared directory tree such as the sysroot.
</para>
<para>
The Yocto Project team has tried to keep the details of the
implementation hidden in <filename>sstate</filename> class.
From a user's perspective, adding shared state wrapping to a task
is as simple as this
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-deploy'><filename>do_deploy</filename></ulink>
example taken from the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-deploy'><filename>deploy</filename></ulink>
class:
<literallayout class='monospaced'>
DEPLOYDIR = "${WORKDIR}/deploy-${PN}"
SSTATETASKS += "do_deploy"
do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
do_deploy[dirs] = "${DEPLOYDIR} ${B}"
</literallayout>
The following list explains the previous example:
<itemizedlist>
<listitem><para>
Adding "do_deploy" to <filename>SSTATETASKS</filename>
adds some required sstate-related processing, which is
implemented in the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-sstate'><filename>sstate</filename></ulink>
class, to before and after the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-deploy'><filename>do_deploy</filename></ulink>
task.
</para></listitem>
<listitem><para>
The
<filename>do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"</filename>
declares that <filename>do_deploy</filename> places its
output in <filename>${DEPLOYDIR}</filename> when run
normally (i.e. when not using the sstate cache).
This output becomes the input to the shared state cache.
</para></listitem>
<listitem><para>
The
<filename>do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"</filename>
line causes the contents of the shared state cache to be
copied to <filename>${DEPLOY_DIR_IMAGE}</filename>.
<note>
If <filename>do_deploy</filename> is not already in
the shared state cache or if its input checksum
(signature) has changed from when the output was
cached, the task will be run to populate the shared
state cache, after which the contents of the shared
state cache is copied to
<filename>${DEPLOY_DIR_IMAGE}</filename>.
If <filename>do_deploy</filename> is in the shared
state cache and its signature indicates that the
cached output is still valid (i.e. if no
relevant task inputs have changed), then the
contents of the shared state cache will be copied
directly to
<filename>${DEPLOY_DIR_IMAGE}</filename> by the
<filename>do_deploy_setscene</filename> task
instead, skipping the
<filename>do_deploy</filename> task.
</note>
</para></listitem>
<listitem><para>
The following task definition is glue logic needed to
make the previous settings effective:
<literallayout class='monospaced'>
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
</literallayout>
<filename>sstate_setscene()</filename> takes the flags
above as input and accelerates the
<filename>do_deploy</filename> task through the
shared state cache if possible.
If the task was accelerated,
<filename>sstate_setscene()</filename> returns True.
Otherwise, it returns False, and the normal
<filename>do_deploy</filename> task runs.
For more information, see the
"<ulink url='&YOCTO_DOCS_BB_URL;#setscene'>setscene</ulink>"
section in the BitBake User Manual.
</para></listitem>
<listitem><para>
The <filename>do_deploy[dirs] = "${DEPLOYDIR} ${B}"</filename>
line creates <filename>${DEPLOYDIR}</filename> and
<filename>${B}</filename> before the
<filename>do_deploy</filename> task runs, and also sets
the current working directory of
<filename>do_deploy</filename> to
<filename>${B}</filename>.
For more information, see the
"<ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'>Variable Flags</ulink>"
section in the BitBake User Manual.
<note>
In cases where
<filename>sstate-inputdirs</filename> and
<filename>sstate-outputdirs</filename> would be the
same, you can use
<filename>sstate-plaindirs</filename>.
For example, to preserve the
<filename>${PKGD}</filename> and
<filename>${PKGDEST}</filename> output from the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
task, use the following:
<literallayout class='monospaced'>
do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
</literallayout>
</note>
</para></listitem>
<listitem><para>
<filename>sstate-inputdirs</filename> and
<filename>sstate-outputdirs</filename> can also be used
with multiple directories.
For example, the following declares
<filename>PKGDESTWORK</filename> and
<filename>SHLIBWORK</filename> as shared state
input directories, which populates the shared state
cache, and <filename>PKGDATA_DIR</filename> and
<filename>SHLIBSDIR</filename> as the corresponding
shared state output directories:
<literallayout class='monospaced'>
do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
</literallayout>
</para></listitem>
<listitem><para>
These methods also include the ability to take a
lockfile when manipulating shared state directory
structures, for cases where file additions or removals
are sensitive:
<literallayout class='monospaced'>
do_package[sstate-lockfile] = "${PACKAGELOCK}"
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<para>
Behind the scenes, the shared state code works by looking in
<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></ulink>
for shared state files.
Here is an example:
<literallayout class='monospaced'>
SSTATE_MIRRORS ?= "\
file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \
file://.* file:///some/local/dir/sstate/PATH"
</literallayout>
<note>
The shared state directory
(<filename>SSTATE_DIR</filename>) is organized into
two-character subdirectories, where the subdirectory
names are based on the first two characters of the hash.
If the shared state directory structure for a mirror has the
same structure as <filename>SSTATE_DIR</filename>, you must
specify "PATH" as part of the URI to enable the build system
to map to the appropriate subdirectory.
</note>
</para>
<para>
The shared state package validity can be detected just by
looking at the filename since the filename contains the task
checksum (or signature) as described earlier in this section.
If a valid shared state package is found, the build process
downloads it and uses it to accelerate the task.
</para>
<para>
The build processes use the <filename>*_setscene</filename>
tasks for the task acceleration phase.
BitBake goes through this phase before the main execution
code and tries to accelerate any tasks for which it can find
shared state packages.
If a shared state package for a task is available, the
shared state package is used.
This means the task and any tasks on which it is dependent
are not executed.
</para>
<para>
As a real world example, the aim is when building an IPK-based
image, only the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></ulink>
tasks would have their shared state packages fetched and
extracted.
Since the sysroot is not used, it would never get extracted.
This is another reason why a task-based approach is preferred
over a recipe-based approach, which would have to install the
output from every task.
</para>
</section>
<section id='tips-and-tricks'>
<title>Tips and Tricks</title>
<para>
The code in the build system that supports incremental builds
is not simple code.
This section presents some tips and tricks that help you work
around issues related to shared state code.
</para>
<section id='overview-debugging'>
<title>Debugging</title>
<para>
Seeing what metadata went into creating the input signature
of a shared state (sstate) task can be a useful debugging
aid.
This information is available in signature information
(<filename>siginfo</filename>) files in
<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>.
For information on how to view and interpret information in
<filename>siginfo</filename> files, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</ulink>"
section in the Yocto Project Reference Manual.
</para>
</section>
<section id='invalidating-shared-state'>
<title>Invalidating Shared State</title>
<para>
The OpenEmbedded build system uses checksums and shared
state cache to avoid unnecessarily rebuilding tasks.
Collectively, this scheme is known as "shared state code."
</para>
<para>
As with all schemes, this one has some drawbacks.
It is possible that you could make implicit changes to your
code that the checksum calculations do not take into
account.
These implicit changes affect a task's output but do not
trigger the shared state code into rebuilding a recipe.
Consider an example during which a tool changes its output.
Assume that the output of <filename>rpmdeps</filename>
changes.
The result of the change should be that all the
<filename>package</filename> and
<filename>package_write_rpm</filename> shared state cache
items become invalid.
However, because the change to the output is
external to the code and therefore implicit,
the associated shared state cache items do not become
invalidated.
In this case, the build process uses the cached items
rather than running the task again.
Obviously, these types of implicit changes can cause
problems.
</para>
<para>
To avoid these problems during the build, you need to
understand the effects of any changes you make.
Realize that changes you make directly to a function
are automatically factored into the checksum calculation.
Thus, these explicit changes invalidate the associated
area of shared state cache.
However, you need to be aware of any implicit changes that
are not obvious changes to the code and could affect
the output of a given task.
</para>
<para>
When you identify an implicit change, you can easily
take steps to invalidate the cache and force the tasks
to run.
The steps you can take are as simple as changing a
function's comments in the source code.
For example, to invalidate package shared state files,
change the comment statements of
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
or the comments of one of the functions it calls.
Even though the change is purely cosmetic, it causes the
checksum to be recalculated and forces the OpenEmbedded
build system to run the task again.
<note>
For an example of a commit that makes a cosmetic
change to invalidate shared state, see this
<ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54'>commit</ulink>.
</note>
</para>
</section>
</section>
</section>
<section id='x32'>
<title>x32 psABI</title>

2
documentation/overview-manual/overview-development-environment.xml
View File

@@ -2490,7 +2490,7 @@
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAMP'><filename>STAMP</filename></ulink>
variable, and the end of the name consists of the task's name
and current
<ulink url='&YOCTO_DOCS_BB_URL;#checksums'>input checksum</ulink>.
<link linkend='overview-checksums'>input checksum</link>.
<note>
This naming scheme assumes that
<ulink url='&YOCTO_DOCS_BB_URL;#var-BB_SIGNATURE_HANDLER'><filename>BB_SIGNATURE_HANDLER</filename></ulink>

6
documentation/ref-manual/ref-bitbake.xml
View File

@@ -348,8 +348,10 @@
If doing so results in unnecessary rebuilds of tasks, you can whitelist the
variable so that the shared state code ignores the dependency when it creates
checksums.
For information on this process, see the <filename>BB_HASHBASE_WHITELIST</filename>
example in the "<link linkend='checksums'>Checksums (Signatures)</link>" section.
For information on this process, see the
<filename>BB_HASHBASE_WHITELIST</filename> example in the
"<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#overview-checksums'>Checksums (Signatures)</ulink>"
section in the Yocto Project Overview Manual.
</note>
</section>

4
documentation/ref-manual/ref-classes.xml
View File

@@ -3182,8 +3182,8 @@ This check was removed for YP 2.3 release
<para>
For more information on sstate, see the
"<link linkend='shared-state-cache'>Shared State Cache</link>"
section.
"<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>Shared State Cache</ulink>"
section in the Yocto Project Overview Manual.
</para>
</section>

14
documentation/ref-manual/ref-tasks.xml
View File

@@ -628,8 +628,8 @@
<para>
Running this task does not remove the
<link linkend='shared-state-cache'>sstate</link>) cache
files.
<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>sstate</ulink>
cache files.
Consequently, if no changes have been made and the recipe is
rebuilt after cleaning, output files are simply restored from the
sstate cache.
@@ -645,8 +645,9 @@
<para>
Removes all output files, shared state
(<link linkend='shared-state-cache'>sstate</link>) cache, and
downloaded source files for a target (i.e. the contents of
(<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>sstate</ulink>)
cache, and downloaded source files for a target (i.e. the contents
of
<link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>).
Essentially, the <filename>do_cleanall</filename> task is
identical to the
@@ -675,13 +676,14 @@
<para>
Removes all output files and shared state
(<link linkend='shared-state-cache'>sstate</link>)
(<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>sstate</ulink>)
cache for a target.
Essentially, the <filename>do_cleansstate</filename> task is
identical to the
<link linkend='ref-tasks-clean'><filename>do_clean</filename></link>
task with the added removal of shared state
(<link linkend='shared-state-cache'>sstate</link>) cache.
(<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>sstate</ulink>)
cache.
</para>
<para>

4
documentation/ref-manual/ref-variables.xml
View File

@@ -10654,11 +10654,11 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
<filename>PR</filename> to know when to rebuild a
recipe.
The build system uses the task
<ulink url='&YOCTO_DOCS_BB_URL;#checksums'>input checksums</ulink>
<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#overview-checksums'>input checksums</ulink>
along with the
<link linkend='structure-build-tmp-stamps'>stamp</link>
and
<link linkend='shared-state-cache'>shared state cache</link>
<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>shared state cache</ulink>
mechanisms.
</note>
The <filename>PR</filename> variable primarily becomes

603
documentation/ref-manual/technical-details.xml
View File

@@ -13,609 +13,6 @@
x32, Wayland support, and Licenses.
</para>
<section id="shared-state-cache">
<title>Shared State Cache</title>
<para>
By design, the OpenEmbedded build system builds everything from scratch unless
BitBake can determine that parts do not need to be rebuilt.
Fundamentally, building from scratch is attractive as it means all parts are
built fresh and there is no possibility of stale data causing problems.
When developers hit problems, they typically default back to building from scratch
so they know the state of things from the start.
</para>
<para>
Building an image from scratch is both an advantage and a disadvantage to the process.
As mentioned in the previous paragraph, building from scratch ensures that
everything is current and starts from a known state.
However, building from scratch also takes much longer as it generally means
rebuilding things that do not necessarily need to be rebuilt.
</para>
<para>
The Yocto Project implements shared state code that supports incremental builds.
The implementation of the shared state code answers the following questions that
were fundamental roadblocks within the OpenEmbedded incremental build support system:
<itemizedlist>
<listitem><para>What pieces of the system have changed and what pieces have
not changed?</para></listitem>
<listitem><para>How are changed pieces of software removed and replaced?</para></listitem>
<listitem><para>How are pre-built components that do not need to be rebuilt from scratch
used when they are available?</para></listitem>
</itemizedlist>
</para>
<para>
For the first question, the build system detects changes in the "inputs" to a given task by
creating a checksum (or signature) of the task's inputs.
If the checksum changes, the system assumes the inputs have changed and the task needs to be
rerun.
For the second question, the shared state (sstate) code tracks which tasks add which output
to the build process.
This means the output from a given task can be removed, upgraded or otherwise manipulated.
The third question is partly addressed by the solution for the second question
assuming the build system can fetch the sstate objects from remote locations and
install them if they are deemed to be valid.
</para>
<note>
The OpenEmbedded build system does not maintain
<link linkend='var-PR'><filename>PR</filename></link> information
as part of the shared state packages.
Consequently, considerations exist that affect maintaining shared
state feeds.
For information on how the OpenEmbedded build system
works with packages and can
track incrementing <filename>PR</filename> information, see the
"<ulink url='&YOCTO_DOCS_DEV_URL;#automatically-incrementing-a-binary-package-revision-number'>Automatically Incrementing a Binary Package Revision Number</ulink>"
section in the Yocto Project Development Tasks Manual.
</note>
<para>
The rest of this section goes into detail about the overall incremental build
architecture, the checksums (signatures), shared state, and some tips and tricks.
</para>
<section id='overall-architecture'>
<title>Overall Architecture</title>
<para>
When determining what parts of the system need to be built, BitBake
works on a per-task basis rather than a per-recipe basis.
You might wonder why using a per-task basis is preferred over a per-recipe basis.
To help explain, consider having the IPK packaging backend enabled and then switching to DEB.
In this case, the
<link linkend='ref-tasks-install'><filename>do_install</filename></link>
and
<link linkend='ref-tasks-package'><filename>do_package</filename></link>
task outputs are still valid.
However, with a per-recipe approach, the build would not include the
<filename>.deb</filename> files.
Consequently, you would have to invalidate the whole build and rerun it.
Rerunning everything is not the best solution.
Also, in this case, the core must be "taught" much about specific tasks.
This methodology does not scale well and does not allow users to easily add new tasks
in layers or as external recipes without touching the packaged-staging core.
</para>
</section>
<section id='checksums'>
<title>Checksums (Signatures)</title>
<para>
The shared state code uses a checksum, which is a unique signature of a task's
inputs, to determine if a task needs to be run again.
Because it is a change in a task's inputs that triggers a rerun, the process
needs to detect all the inputs to a given task.
For shell tasks, this turns out to be fairly easy because
the build process generates a "run" shell script for each task and
it is possible to create a checksum that gives you a good idea of when
the task's data changes.
</para>
<para>
To complicate the problem, there are things that should not be
included in the checksum.
First, there is the actual specific build path of a given task -
the <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>.
It does not matter if the work directory changes because it should
not affect the output for target packages.
Also, the build process has the objective of making native
or cross packages relocatable.
<note>
Both native and cross packages run on the build host.
However, cross packages generate output for the target
architecture.
</note>
The checksum therefore needs to exclude
<filename>WORKDIR</filename>.
The simplistic approach for excluding the work directory is to set
<filename>WORKDIR</filename> to some fixed value and create the
checksum for the "run" script.
</para>
<para>
Another problem results from the "run" scripts containing functions that
might or might not get called.
The incremental build solution contains code that figures out dependencies
between shell functions.
This code is used to prune the "run" scripts down to the minimum set,
thereby alleviating this problem and making the "run" scripts much more
readable as a bonus.
</para>
<para>
So far we have solutions for shell scripts.
What about Python tasks?
The same approach applies even though these tasks are more difficult.
The process needs to figure out what variables a Python function accesses
and what functions it calls.
Again, the incremental build solution contains code that first figures out
the variable and function dependencies, and then creates a checksum for the data
used as the input to the task.
</para>
<para>
Like the <filename>WORKDIR</filename> case, situations exist where dependencies
should be ignored.
For these cases, you can instruct the build process to ignore a dependency
by using a line like the following:
<literallayout class='monospaced'>
PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
</literallayout>
This example ensures that the
<link linkend='var-PACKAGE_ARCHS'><filename>PACKAGE_ARCHS</filename></link>
variable does not
depend on the value of
<link linkend='var-MACHINE'><filename>MACHINE</filename></link>,
even if it does reference it.
</para>
<para>
Equally, there are cases where we need to add dependencies BitBake is not able to find.
You can accomplish this by using a line like the following:
<literallayout class='monospaced'>
PACKAGE_ARCHS[vardeps] = "MACHINE"
</literallayout>
This example explicitly adds the <filename>MACHINE</filename> variable as a
dependency for <filename>PACKAGE_ARCHS</filename>.
</para>
<para>
Consider a case with in-line Python, for example, where BitBake is not
able to figure out dependencies.
When running in debug mode (i.e. using <filename>-DDD</filename>), BitBake
produces output when it discovers something for which it cannot figure out
dependencies.
The Yocto Project team has currently not managed to cover those dependencies
in detail and is aware of the need to fix this situation.
</para>
<para>
Thus far, this section has limited discussion to the direct inputs into a task.
Information based on direct inputs is referred to as the "basehash" in the
code.
However, there is still the question of a task's indirect inputs - the
things that were already built and present in the
<link linkend='build-directory'>Build Directory</link>.
The checksum (or signature) for a particular task needs to add the hashes
of all the tasks on which the particular task depends.
Choosing which dependencies to add is a policy decision.
However, the effect is to generate a master checksum that combines the basehash
and the hashes of the task's dependencies.
</para>
<para>
At the code level, there are a variety of ways both the basehash and the
dependent task hashes can be influenced.
Within the BitBake configuration file, we can give BitBake some extra information
to help it construct the basehash.
The following statement effectively results in a list of global variable
dependency excludes - variables never included in any checksum:
<literallayout class='monospaced'>
BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
</literallayout>
The previous example excludes
<link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>
since that variable is actually constructed as a path within
<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>, which is on
the whitelist.
</para>
<para>
The rules for deciding which hashes of dependent tasks to include through
dependency chains are more complex and are generally accomplished with a
Python function.
The code in <filename>meta/lib/oe/sstatesig.py</filename> shows two examples
of this and also illustrates how you can insert your own policy into the system
if so desired.
This file defines the two basic signature generators
<link linkend='oe-core'>OE-Core</link> uses: "OEBasic" and
"OEBasicHash".
By default, there is a dummy "noop" signature handler enabled in BitBake.
This means that behavior is unchanged from previous versions.
OE-Core uses the "OEBasicHash" signature handler by default
through this setting in the <filename>bitbake.conf</filename> file:
<literallayout class='monospaced'>
BB_SIGNATURE_HANDLER ?= "OEBasicHash"
</literallayout>
The "OEBasicHash" <filename>BB_SIGNATURE_HANDLER</filename> is the same as the
"OEBasic" version but adds the task hash to the stamp files.
This results in any
<link linkend='metadata'>Metadata</link>
change that changes the task hash, automatically
causing the task to be run again.
This removes the need to bump <link linkend='var-PR'><filename>PR</filename></link>
values, and changes to Metadata automatically ripple across the build.
</para>
<para>
It is also worth noting that the end result of these signature generators is to
make some dependency and hash information available to the build.
This information includes:
<itemizedlist>
<listitem><para><filename>BB_BASEHASH_task-</filename><replaceable>taskname</replaceable>:
The base hashes for each task in the recipe.
</para></listitem>
<listitem><para><filename>BB_BASEHASH_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
The base hashes for each dependent task.
</para></listitem>
<listitem><para><filename>BBHASHDEPS_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
The task dependencies for each task.
</para></listitem>
<listitem><para><filename>BB_TASKHASH</filename>:
The hash of the currently running task.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='shared-state'>
<title>Shared State</title>
<para>
Checksums and dependencies, as discussed in the previous section, solve half the
problem of supporting a shared state.
The other part of the problem is being able to use checksum information during the build
and being able to reuse or rebuild specific components.
</para>
<para>
The
<link linkend='ref-classes-sstate'><filename>sstate</filename></link>
class is a relatively generic implementation of how to "capture"
a snapshot of a given task.
The idea is that the build process does not care about the source of a task's output.
Output could be freshly built or it could be downloaded and unpacked from
somewhere - the build process does not need to worry about its origin.
</para>
<para>
There are two types of output, one is just about creating a directory
in <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>.
A good example is the output of either
<link linkend='ref-tasks-install'><filename>do_install</filename></link>
or
<link linkend='ref-tasks-package'><filename>do_package</filename></link>.
The other type of output occurs when a set of data is merged into a shared directory
tree such as the sysroot.
</para>
<para>
The Yocto Project team has tried to keep the details of the
implementation hidden in <filename>sstate</filename> class.
From a user's perspective, adding shared state wrapping to a task
is as simple as this
<link linkend='ref-tasks-deploy'><filename>do_deploy</filename></link>
example taken from the
<link linkend='ref-classes-deploy'><filename>deploy</filename></link>
class:
<literallayout class='monospaced'>
DEPLOYDIR = "${WORKDIR}/deploy-${PN}"
SSTATETASKS += "do_deploy"
do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
do_deploy[dirs] = "${DEPLOYDIR} ${B}"
</literallayout>
The following list explains the previous example:
<itemizedlist>
<listitem><para>
Adding "do_deploy" to <filename>SSTATETASKS</filename>
adds some required sstate-related processing, which is
implemented in the
<link linkend='ref-classes-sstate'><filename>sstate</filename></link>
class, to before and after the
<link linkend='ref-tasks-deploy'><filename>do_deploy</filename></link>
task.
</para></listitem>
<listitem><para>
The
<filename>do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"</filename>
declares that <filename>do_deploy</filename> places its
output in <filename>${DEPLOYDIR}</filename> when run
normally (i.e. when not using the sstate cache).
This output becomes the input to the shared state cache.
</para></listitem>
<listitem><para>
The
<filename>do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"</filename>
line causes the contents of the shared state cache to be
copied to <filename>${DEPLOY_DIR_IMAGE}</filename>.
<note>
If <filename>do_deploy</filename> is not already in
the shared state cache or if its input checksum
(signature) has changed from when the output was
cached, the task will be run to populate the shared
state cache, after which the contents of the shared
state cache is copied to
<filename>${DEPLOY_DIR_IMAGE}</filename>.
If <filename>do_deploy</filename> is in the shared
state cache and its signature indicates that the
cached output is still valid (i.e. if no
relevant task inputs have changed), then the contents
of the shared state cache will be copied directly to
<filename>${DEPLOY_DIR_IMAGE}</filename> by the
<filename>do_deploy_setscene</filename> task instead,
skipping the <filename>do_deploy</filename> task.
</note>
</para></listitem>
<listitem><para>
The following task definition is glue logic needed to make
the previous settings effective:
<literallayout class='monospaced'>
python do_deploy_setscene () {
sstate_setscene(d)
}
addtask do_deploy_setscene
</literallayout>
<filename>sstate_setscene()</filename> takes the flags
above as input and accelerates the
<filename>do_deploy</filename> task through the
shared state cache if possible.
If the task was accelerated,
<filename>sstate_setscene()</filename> returns True.
Otherwise, it returns False, and the normal
<filename>do_deploy</filename> task runs.
For more information, see the
"<ulink url='&YOCTO_DOCS_BB_URL;#setscene'>setscene</ulink>"
section in the BitBake User Manual.
</para></listitem>
<listitem><para>
The <filename>do_deploy[dirs] = "${DEPLOYDIR} ${B}"</filename>
line creates <filename>${DEPLOYDIR}</filename> and
<filename>${B}</filename> before the
<filename>do_deploy</filename> task runs, and also sets
the current working directory of
<filename>do_deploy</filename> to
<filename>${B}</filename>.
For more information, see the
"<ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'>Variable Flags</ulink>"
section in the BitBake User Manual.
<note>
In cases where
<filename>sstate-inputdirs</filename> and
<filename>sstate-outputdirs</filename> would be the
same, you can use
<filename>sstate-plaindirs</filename>.
For example, to preserve the
<filename>${PKGD}</filename> and
<filename>${PKGDEST}</filename> output from the
<link linkend='ref-tasks-package'><filename>do_package</filename></link>
task, use the following:
<literallayout class='monospaced'>
do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
</literallayout>
</note>
</para></listitem>
<listitem><para>
<filename>sstate-inputdirs</filename> and
<filename>sstate-outputdirs</filename> can also be used
with multiple directories.
For example, the following declares
<filename>PKGDESTWORK</filename> and
<filename>SHLIBWORK</filename> as shared state
input directories, which populates the shared state
cache, and <filename>PKGDATA_DIR</filename> and
<filename>SHLIBSDIR</filename> as the corresponding
shared state output directories:
<literallayout class='monospaced'>
do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
</literallayout>
</para></listitem>
<listitem><para>
These methods also include the ability to take a lockfile
when manipulating shared state directory structures,
for cases where file additions or removals are sensitive:
<literallayout class='monospaced'>
do_package[sstate-lockfile] = "${PACKAGELOCK}"
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<!--
<para>
In this example, we add some extra flags to the task, a name field ("deploy"), an
input directory where the task sends data, and the output
directory where the data from the task should eventually be copied.
We also add a <filename>_setscene</filename> variant of the task and add the task
name to the <filename>SSTATETASKS</filename> list.
</para>
<para>
If you have a directory whose contents you need to preserve, you can do this with
a line like the following:
<literallayout class='monospaced'>
do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
</literallayout>
This method, as well as the following example, also works for multiple directories.
<literallayout class='monospaced'>
do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
do_package[sstate-lockfile] = "${PACKAGELOCK}"
</literallayout>
These methods also include the ability to take a lockfile when manipulating
shared state directory structures since some cases are sensitive to file
additions or removals.
</para>
-->
<para>
Behind the scenes, the shared state code works by looking in
<link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link> and
<link linkend='var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></link>
for shared state files.
Here is an example:
<literallayout class='monospaced'>
SSTATE_MIRRORS ?= "\
file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \
file://.* file:///some/local/dir/sstate/PATH"
</literallayout>
<note>
The shared state directory (<filename>SSTATE_DIR</filename>) is
organized into two-character subdirectories, where the subdirectory
names are based on the first two characters of the hash.
If the shared state directory structure for a mirror has the
same structure as <filename>SSTATE_DIR</filename>, you must
specify "PATH" as part of the URI to enable the build system
to map to the appropriate subdirectory.
</note>
</para>
<para>
The shared state package validity can be detected just by looking at the
filename since the filename contains the task checksum (or signature) as
described earlier in this section.
If a valid shared state package is found, the build process downloads it
and uses it to accelerate the task.
</para>
<para>
The build processes use the <filename>*_setscene</filename> tasks
for the task acceleration phase.
BitBake goes through this phase before the main execution code and tries
to accelerate any tasks for which it can find shared state packages.
If a shared state package for a task is available, the shared state
package is used.
This means the task and any tasks on which it is dependent are not
executed.
</para>
<para>
As a real world example, the aim is when building an IPK-based image,
only the
<link linkend='ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></link>
tasks would have their
shared state packages fetched and extracted.
Since the sysroot is not used, it would never get extracted.
This is another reason why a task-based approach is preferred over a
recipe-based approach, which would have to install the output from every task.
</para>
</section>
<section id='tips-and-tricks'>
<title>Tips and Tricks</title>
<para>
The code in the build system that supports incremental builds is not
simple code.
This section presents some tips and tricks that help you work around
issues related to shared state code.
</para>
<section id='debugging'>
<title>Debugging</title>
<para>
Seeing what metadata went into creating the input signature
of a shared state (sstate) task can be a useful debugging aid.
This information is available in signature information
(<filename>siginfo</filename>) files in
<link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link>.
For information on how to view and interpret information in
<filename>siginfo</filename> files, see the
"<link linkend='usingpoky-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</link>"
section.
</para>
</section>
<section id='invalidating-shared-state'>
<title>Invalidating Shared State</title>
<para>
The OpenEmbedded build system uses checksums and shared state
cache to avoid unnecessarily rebuilding tasks.
Collectively, this scheme is known as "shared state code."
</para>
<para>
As with all schemes, this one has some drawbacks.
It is possible that you could make implicit changes to your
code that the checksum calculations do not take into
account.
These implicit changes affect a task's output but do not trigger
the shared state code into rebuilding a recipe.
Consider an example during which a tool changes its output.
Assume that the output of <filename>rpmdeps</filename> changes.
The result of the change should be that all the
<filename>package</filename> and
<filename>package_write_rpm</filename> shared state cache
items become invalid.
However, because the change to the output is
external to the code and therefore implicit,
the associated shared state cache items do not become
invalidated.
In this case, the build process uses the cached items rather
than running the task again.
Obviously, these types of implicit changes can cause problems.
</para>
<para>
To avoid these problems during the build, you need to
understand the effects of any changes you make.
Realize that changes you make directly to a function
are automatically factored into the checksum calculation.
Thus, these explicit changes invalidate the associated area of
shared state cache.
However, you need to be aware of any implicit changes that
are not obvious changes to the code and could affect the output
of a given task.
</para>
<para>
When you identify an implicit change, you can easily take steps
to invalidate the cache and force the tasks to run.
The steps you can take are as simple as changing a function's
comments in the source code.
For example, to invalidate package shared state files, change
the comment statements of
<link linkend='ref-tasks-package'><filename>do_package</filename></link>
or the comments of one of the functions it calls.
Even though the change is purely cosmetic, it causes the
checksum to be recalculated and forces the OpenEmbedded build
system to run the task again.
</para>
<note>
For an example of a commit that makes a cosmetic change to
invalidate shared state, see this
<ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54'>commit</ulink>.
</note>
</section>
</section>
</section>
<section id='automatically-added-runtime-dependencies'>
<title>Automatically Added Runtime Dependencies</title>

2
documentation/ref-manual/usingpoky.xml
View File

@@ -535,7 +535,7 @@
${BUILDDIR}/tmp/stamps/i586-poky-linux/db/6.0.30-r1.do_fetch.sigdata.7c048c18222b16ff0bcee2000ef648b1
</literallayout>
For tasks that are accelerated through the shared state
(<link linkend='shared-state-cache'>sstate</link>)
(<ulink url='&YOCTO_DOCS_OVERVIEW_URL;#shared-state-cache'>sstate</ulink>)
cache, an additional <filename>siginfo</filename> file is
written into
<link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link>