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Diffstat (limited to 'documentation/dev-manual')
-rw-r--r-- | documentation/dev-manual/dev-manual-common-tasks.xml | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml b/documentation/dev-manual/dev-manual-common-tasks.xml index 603ca1ff8e..f3f2a4b026 100644 --- a/documentation/dev-manual/dev-manual-common-tasks.xml +++ b/documentation/dev-manual/dev-manual-common-tasks.xml | |||
@@ -5475,6 +5475,79 @@ | |||
5475 | </section> | 5475 | </section> |
5476 | </section> | 5476 | </section> |
5477 | 5477 | ||
5478 | <section id='building-an-initramfs-image'> | ||
5479 | <title>Building an Initial RAM Filesystem (initramfs) Image</title> | ||
5480 | |||
5481 | <para> | ||
5482 | initramfs is the successor of Initial RAM Disk (initrd). | ||
5483 | It is a "copy in and out" (cpio) archive of the initial file system | ||
5484 | that gets loaded into memory during the Linux startup process. | ||
5485 | Because Linux uses the contents of the archive during | ||
5486 | initialization, the initramfs needs to contain all of the device | ||
5487 | drivers and tools needed to mount the final root filesystem. | ||
5488 | </para> | ||
5489 | |||
5490 | <para> | ||
5491 | To build an initramfs image and bundle it into the kernel, set the | ||
5492 | following variables: | ||
5493 | <literallayout class='monospaced'> | ||
5494 | INITRAMFS_IMAGE_BUNDLE = "1" | ||
5495 | INITRAMFS_IMAGE = "<replaceable>image_recipe_name</replaceable>" | ||
5496 | </literallayout> | ||
5497 | Setting the | ||
5498 | <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink> | ||
5499 | flag causes the initramfs created by the recipe | ||
5500 | and defined by | ||
5501 | <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE'><filename>INITRAMFS_IMAGE</filename></ulink> | ||
5502 | to be unpacked into the <filename>${B}/usr/</filename> directory. | ||
5503 | The unpacked initramfs is then passed to the kernel's | ||
5504 | <filename>Makefile</filename> using the | ||
5505 | <ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIG_INITRAMFS_SOURCE'><filename>CONFIG_INITRAMFS_SOURCE</filename></ulink> | ||
5506 | variable, allowing initramfs to be built in to the kernel | ||
5507 | normally. | ||
5508 | <note> | ||
5509 | The preferred method is to use the | ||
5510 | <filename>INITRAMFS_IMAGE</filename> variable rather than the | ||
5511 | <filename>INITRAMFS_TASK</filename> variable. | ||
5512 | Setting <filename>INITRAMFS_TASK</filename> is supported for | ||
5513 | backward compatibility. | ||
5514 | However, use of this variable has circular dependency | ||
5515 | problems. | ||
5516 | See the | ||
5517 | <ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink> | ||
5518 | variable for additional information on these dependency | ||
5519 | problems. | ||
5520 | </note> | ||
5521 | </para> | ||
5522 | |||
5523 | <para> | ||
5524 | The recipe that <filename>INITRAMFS_IMAGE</filename> | ||
5525 | points to must produce a <filename>.cpio.gz</filename>, | ||
5526 | <filename>.cpio.tar</filename>, <filename>.cpio.lz4</filename>, | ||
5527 | <filename>.cpio.lzma</filename>, or | ||
5528 | <filename>.cpio.xz</filename> file. | ||
5529 | You can ensure you produce one of these <filename>.cpio.*</filename> | ||
5530 | files by setting the | ||
5531 | <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink> | ||
5532 | variable in your configuration file to one or more of the above | ||
5533 | file types. | ||
5534 | <note> | ||
5535 | If you add items to the initramfs image by way of its recipe, | ||
5536 | you should use | ||
5537 | <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></ulink> | ||
5538 | rather than | ||
5539 | <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>. | ||
5540 | <filename>PACKAGE_INSTALL</filename> gives more direct control | ||
5541 | of what is added to the image as compared to the defaults you | ||
5542 | might not necessarily want that are set by the | ||
5543 | <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image'><filename>image</filename></ulink> | ||
5544 | or | ||
5545 | <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-core-image'><filename>core-image</filename></ulink> | ||
5546 | classes. | ||
5547 | </note> | ||
5548 | </para> | ||
5549 | </section> | ||
5550 | |||
5478 | <section id='configuring-the-kernel'> | 5551 | <section id='configuring-the-kernel'> |
5479 | <title>Configuring the Kernel</title> | 5552 | <title>Configuring the Kernel</title> |
5480 | 5553 | ||