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diff --git a/documentation/ref-manual/eclipse/html/poky-ref-manual/shared-state-cache.html b/documentation/ref-manual/eclipse/html/poky-ref-manual/shared-state-cache.html new file mode 100644 index 0000000000..8f2f5a5ed6 --- /dev/null +++ b/documentation/ref-manual/eclipse/html/poky-ref-manual/shared-state-cache.html @@ -0,0 +1,60 @@ +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>3.2. Shared State Cache</title> +<link rel="stylesheet" type="text/css" href="../book.css"> +<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> +<link rel="home" href="index.html" title="The Yocto Project Reference Manual"> +<link rel="up" href="technical-details.html" title="Chapter 3. Technical Details"> +<link rel="prev" href="usingpoky-components-configuration.html" title="3.1.4. Configuration"> +<link rel="next" href="overall-architecture.html" title="3.2.1. Overall Architecture"> +</head> +<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="section" title="3.2. Shared State Cache"> +<div class="titlepage"><div><div><h2 class="title" style="clear: both"> +<a name="shared-state-cache"></a>3.2. Shared State Cache</h2></div></div></div> +<p> + By design, the OpenEmbedded build system builds everything from scratch unless + BitBake can determine that parts don't 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. + </p> +<p> + 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 don't necessarily need rebuilt. + </p> +<p> + 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: + </p> +<div class="itemizedlist"><ul class="itemizedlist" type="disc"> +<li class="listitem">What pieces of the system have changed and what pieces have not changed?</li> +<li class="listitem">How are changed pieces of software removed and replaced?</li> +<li class="listitem">How are pre-built components that don't need to be rebuilt from scratch + used when they are available?</li> +</ul></div> +<p> + </p> +<p> + 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. + </p> +<p> + The rest of this section goes into detail about the overall incremental build + architecture, the checksums (signatures), shared state, and some tips and tricks. + </p> +</div></body> +</html> |