diff options
-rw-r--r-- | documentation/ref-manual/terms.rst | 42 | ||||
-rw-r--r-- | documentation/ref-manual/variables.rst | 42 |
2 files changed, 42 insertions, 42 deletions
diff --git a/documentation/ref-manual/terms.rst b/documentation/ref-manual/terms.rst index 92cc723ff6..68313d0294 100644 --- a/documentation/ref-manual/terms.rst +++ b/documentation/ref-manual/terms.rst | |||
@@ -212,6 +212,48 @@ universal, the list includes them just in case: | |||
212 | of the supported image types that the Yocto Project provides, see the | 212 | of the supported image types that the Yocto Project provides, see the |
213 | ":ref:`ref-manual/images:Images`" chapter. | 213 | ":ref:`ref-manual/images:Images`" chapter. |
214 | 214 | ||
215 | :term:`Initramfs` | ||
216 | An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed | ||
217 | :wikipedia:`cpio <Cpio>` archive which is extracted | ||
218 | by the Linux kernel into RAM in a special :wikipedia:`tmpfs <Tmpfs>` | ||
219 | instance, used as the initial root filesystem. | ||
220 | |||
221 | This is a replacement for the legacy init RAM disk ("initrd") | ||
222 | technique, booting on an emulated block device in RAM, but being less | ||
223 | efficient because of the overhead of going through a filesystem and | ||
224 | having to duplicate accessed file contents in the file cache in RAM, | ||
225 | as for any block device. | ||
226 | |||
227 | .. note: | ||
228 | |||
229 | As far as bootloaders are concerned, :term:`Initramfs` and "initrd" | ||
230 | images are still copied to RAM in the same way. That's why most | ||
231 | most bootloaders refer to :term:`Initramfs` images as "initrd" | ||
232 | or "init RAM disk". | ||
233 | |||
234 | This kind of mechanism is typically used for two reasons: | ||
235 | |||
236 | - For booting the same kernel binary on multiple systems requiring | ||
237 | different device drivers. The :term:`Initramfs` image is then customized | ||
238 | for each type of system, to include the specific kernel modules | ||
239 | necessary to access the final root filesystem. This technique | ||
240 | is used on all GNU / Linux distributions for desktops and servers. | ||
241 | |||
242 | - For booting faster. As the root filesystem is extracted into RAM, | ||
243 | accessing the first user-space applications is very fast, compared | ||
244 | to having to initialize a block device, to access multiple blocks | ||
245 | from it, and to go through a filesystem having its own overhead. | ||
246 | For example, this allows to display a splashscreen very early, | ||
247 | and to later take care of mounting the final root filesystem and | ||
248 | loading less time-critical kernel drivers. | ||
249 | |||
250 | This cpio archive can either be loaded to RAM by the bootloader, | ||
251 | or be included in the kernel binary. | ||
252 | |||
253 | For information on creating and using an :term:`Initramfs`, see the | ||
254 | ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" | ||
255 | section in the Yocto Project Development Tasks Manual. | ||
256 | |||
215 | :term:`Layer` | 257 | :term:`Layer` |
216 | A collection of related recipes. Layers allow you to consolidate related | 258 | A collection of related recipes. Layers allow you to consolidate related |
217 | metadata to customize your build. Layers also isolate information used | 259 | metadata to customize your build. Layers also isolate information used |
diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst index faa7c036e5..39d279874d 100644 --- a/documentation/ref-manual/variables.rst +++ b/documentation/ref-manual/variables.rst | |||
@@ -3956,48 +3956,6 @@ system and gives an overview of their function and contents. | |||
3956 | even if the toolchain's binaries are strippable, there are other files | 3956 | even if the toolchain's binaries are strippable, there are other files |
3957 | needed for the build that are not strippable. | 3957 | needed for the build that are not strippable. |
3958 | 3958 | ||
3959 | :term:`Initramfs` | ||
3960 | An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed | ||
3961 | :wikipedia:`cpio <Cpio>` archive which is extracted | ||
3962 | by the Linux kernel into RAM in a special :wikipedia:`tmpfs <Tmpfs>` | ||
3963 | instance, used as the initial root filesystem. | ||
3964 | |||
3965 | This is a replacement for the legacy init RAM disk ("initrd") | ||
3966 | technique, booting on an emulated block device in RAM, but being less | ||
3967 | efficient because of the overhead of going through a filesystem and | ||
3968 | having to duplicate accessed file contents in the file cache in RAM, | ||
3969 | as for any block device. | ||
3970 | |||
3971 | .. note: | ||
3972 | |||
3973 | As far as bootloaders are concerned, :term:`Initramfs` and "initrd" | ||
3974 | images are still copied to RAM in the same way. That's why most | ||
3975 | most bootloaders refer to :term:`Initramfs` images as "initrd" | ||
3976 | or "init RAM disk". | ||
3977 | |||
3978 | This kind of mechanism is typically used for two reasons: | ||
3979 | |||
3980 | - For booting the same kernel binary on multiple systems requiring | ||
3981 | different device drivers. The :term:`Initramfs` image is then customized | ||
3982 | for each type of system, to include the specific kernel modules | ||
3983 | necessary to access the final root filesystem. This technique | ||
3984 | is used on all GNU / Linux distributions for desktops and servers. | ||
3985 | |||
3986 | - For booting faster. As the root filesystem is extracted into RAM, | ||
3987 | accessing the first user-space applications is very fast, compared | ||
3988 | to having to initialize a block device, to access multiple blocks | ||
3989 | from it, and to go through a filesystem having its own overhead. | ||
3990 | For example, this allows to display a splashscreen very early, | ||
3991 | and to later take care of mounting the final root filesystem and | ||
3992 | loading less time-critical kernel drivers. | ||
3993 | |||
3994 | This cpio archive can either be loaded to RAM by the bootloader, | ||
3995 | or be included in the kernel binary. | ||
3996 | |||
3997 | For information on creating and using an :term:`Initramfs`, see the | ||
3998 | ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" | ||
3999 | section in the Yocto Project Development Tasks Manual. | ||
4000 | |||
4001 | :term:`INITRAMFS_DEPLOY_DIR_IMAGE` | 3959 | :term:`INITRAMFS_DEPLOY_DIR_IMAGE` |
4002 | Indicates the deploy directory used by :ref:`ref-tasks-bundle_initramfs` | 3960 | Indicates the deploy directory used by :ref:`ref-tasks-bundle_initramfs` |
4003 | where the :term:`INITRAMFS_IMAGE` will be fetched from. This variable is | 3961 | where the :term:`INITRAMFS_IMAGE` will be fetched from. This variable is |