documentation/poky-ref-manual/usingpoky.xml: Removed comments
Removed some comments that were buried in the file that were notes for working on the sstate section. (From yocto-docs rev: bd03315031bbb1b682dcd2253f85fc184822a28e) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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<ulink url='http://git.yoctoproject.org/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54'>commit</ulink>.
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</note>
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</section>
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<!--
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<section id="considering-shared-state-cache">
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<title>Considering Shared State Cache</title>
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<para>
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What is shared state in general.
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Benefits?
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How we handle things
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(reference https://lists.yoctoproject.org/pipermail/yocto/2011-March/001157.htm),
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which is RP's dissertation on how YP solved it.
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We need to talk a bit about checksum generation for tasks and how the
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sstate code uses them to figure out what needs rebuilt and what can be re-loaded
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from the sstate cache.
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Need to tell about cases where an implicit change can mess things up and under
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normal situations the state in the sstate cache would be used but it shouldn't be.
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This is the scenario described by bug 1500 - typical case.
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Then we talk about how we can invalidate parts of the cache on a per-class basis
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if needed.
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there is a discussion at
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https://lists.yoctoproject.org/pipermail/yocto/2011-March/001157.htm
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that talks about sstate and how the YP team attacked and solved the problem.
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This is probably a good place to get information from to broach the whole
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sstate concept.
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YP, by default, builds from scratch.
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This is good but it means spending a lot of time rebuilding things that don't
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necessarily need rebuilding.
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The SSTATE_DIR variable points to the directory for the shared state cache that
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is used during a build.
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A task's inputs have a checksum or signature associated with them.
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If the checksum changes on an input as compared to a prior build, the task must be rerun.
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The shared state (sstate) code keeps track of what output is generated by which tasks.
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So if a task's inputs have not changed then the output associated with the task can
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be yanked from some place and re-used. No re-build required for that particular task.
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A "run" shell script is created for each task.
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You can create a checksum for the task based on the inputs to the task.
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When you have this checksum, the code will look at it and compare it to the previous
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checksum to see if the task's inputs have changed.
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If so, the task needs to be re-run.
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Python tasks have python functions that access variables.
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Python functions will call other python functions as well.
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The solution was to figure out the variable and function dependencies and create
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a checksum value for the data coming into the python task.
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Here is a conversation with Mark Hatle regarding bug 1500 (638 is related):
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(01:23:34 PM) scottrif: mark - you have a minute?
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(01:34:05 PM) Mark Hatle: sure..
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(01:34:11 PM) Mark Hatle: might be a bit slow to respond, but I'm here
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(01:34:45 PM) scottrif: Hi - I am looking at bug 1500 and trying to get a bit of better understanding. Here is the link to the bug - http://bugzilla.pokylinux.org/show_bug.cgi?id=1500
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(01:35:25 PM) scottrif: It seems that the key for the user here is to when to "Know" when to put some comments into a function to invalidate certain areas of sstate.
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(01:35:49 PM) Mark Hatle: what the issue is, if you make changes to something that is not normally calculated in the checksums for sstate, then you can get package mismatches..
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(01:35:50 PM) scottrif: This trick of "knowing"... does it need to be explained?
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(01:36:25 PM) Mark Hatle: The developer will have to know they made such a change.. Then to deal with this, they can use a patch like what is referenced to cause specific steps to be invalidated and various steps re-run..
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(01:37:01 PM) scottrif: so my question is will the developer know when they make a change like this?
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(01:37:04 PM) Mark Hatle: In this case, we change part of the back-end packaging mechanisms.. which changed internal dependency generation. The sstate code does not checksum the internal dependency generation, it assumes that is code that doesn't change behavior
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(01:37:24 PM) Mark Hatle: They should understand the ramifications of their changes — and thus know they need to do this.
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(01:37:46 PM) Mark Hatle: Examples of times you need to do this. Back end packaging changes occur — i.e. you change the format of dependency generation..
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(01:38:38 PM) scottrif: do you have any other examples?
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(01:38:39 PM) Mark Hatle: when you change a recipe itself, source code.. it is -not- necessary to do this
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(01:38:49 PM) Mark Hatle: RP might be better at examples of when to do it..
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(01:39:11 PM) scottrif: right - If I change a recipe then every thing dependent further down the line gets regenerated right?
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(01:39:17 PM) Mark Hatle: This should never be necessary when a recipe changes.. it will only be necessary when some classes or back-end (packaging frameworks) change..
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(01:39:21 PM) Mark Hatle: ya
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(01:39:33 PM) Mark Hatle: Another way to think of this is implicit dependencies..
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(01:40:01 PM) Mark Hatle: I change RPM.. If you build something that produces an RPM package.. the assumption is the RPM package won't change, even if the RPM binary changes..
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(01:40:10 PM) Mark Hatle: If the format of the package changes.. you would need to do this
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(01:40:53 PM) Mark Hatle: RP can probably give you an idea of the various implicit dependencies, and which ones this type of change is needed for
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(01:41:26 PM) scottrif: okay. I am struggling a bit with how to word it. what I will do is write something up and send it out to you and RP for a look
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(01:41:47 PM) Mark Hatle: ya, I understand.. it's an odd set of situations that can cause this — but we definitely need to document it
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(01:42:01 PM) scottrif: I just want the information to help the user understand the conditions when they will want to invalidate parts of the sstate
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(01:42:18 PM) scottrif: I will likely use the RPM example as the case to illustrate it
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(01:42:26 PM) scottrif: as it seems pretty straight forward
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(01:42:28 PM) Mark Hatle: yup. Key thing is it's only needed on implicit dependencies.. Normal case is back end packaging format changes..
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(01:42:31 PM) Mark Hatle: yup
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(01:42:47 PM) scottrif: ok - thanks Mark
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Here is what RP wants to address 1500:
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If its desired to change the checksum of a given subset of tasks, maybe
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due to a change which isn't directly visible in the code itself (e.g. a
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tool changed its output) its possible to do this by changing a function
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comments since the sstate checksums include the body of functions. To
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invalidate package sstate files for example, do_package or one of the
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functions it calls can be changed, even if its just a cosmetic change to
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the commends.
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http://git.yoctoproject.org/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54
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is an example of a commit which does this.
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-->
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</section>
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<section id='usingpoky-install'>
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<title>Installing and Using the Result</title>
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