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The current mechanism for handling /lib/firmware was always a copy and sync from dom0 -> essential. This is problematic for the case of a read-only root file system or a top level volume which uses slow media backed with nonvolatile storage. The read-only rootfs support added the ability to mount the /opt/container volume early in the boot cycle which allows us to make the optimization that we can have just a single copy of the firmware in the dom0 container and avoid the complexity of syncing. This is in the new default. Should a particular use case warrant syncing the firmware to the /var/lib/cube/essential/lib/firmware directory all that is needed is to break the link. Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
88 lines
3.6 KiB
Plaintext
88 lines
3.6 KiB
Plaintext
Shared Firmware
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Since one of the goals for cube-essential is to keep a small
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footprint, the kernel firmware files pose a specific challenge. The
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/lib/firmware directory amounts to about half the total size of the
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cube-essential image. With such a large portion of the image being
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firmware, many updates to cube-essential could be triggered by the
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need to update firmware (yes the # of updates isn't proportional to
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the size ratio but it is also non-zero).
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With the above in mind it was determined that sharing firmware with
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dom0 we can perform firmware updates without ever having to update
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cube-essential. Firmware updates can be made in dom0 and the result
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will be shared with cube-essential.
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Filesystem changes
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-------------------------
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cube-essential
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---
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In cube-essential '/lib/firmware' is no longer populated with firmware
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blobs and associated files/directories. '/lib/firmware' becomes a link
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to '/var/lib/cube/essential/lib/firmware' ('/var/lib/cube/essential'
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being a directory which is visible to dom0 and keeping '/lib/firmware'
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part of the path to make it clear what it is). If you examine
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'/lib/firmware' on cube-essential you will see a typical firmware
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directory, beyond this being a link to another directory.
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NOTE: To accomplish the above you can examine the
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linux-firmware-cube-shared package (linux-firmware_git.bbappend)
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dom0
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---
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In dom0 you will find a '/lib/firmware' directory populated with
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firmware related files, per usual. You will also find that the
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dom0-ctl-core systemd service has a new 'ExecStartPre' called
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'firmware-sync'. This 'ExecStartPre' will call
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'/etc/dom0.d/firmware-sync' to allow the contents of dom0's
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'/lib/firmware' directory to be 'copied' to
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'/var/lib/cube/essential/lib/firmware', such that cube-essential will
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end up with a matching copy of the firmware in its '/lib/firmware'
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directory (link).
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NOTE: The 'copy' is a one direction sync from dom0 to cube-essential,
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additions/removals in dom0's '/lib/firmware' will be reflected in
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cube-essential's '/lib/firmware' after a sync, but not the other way
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around.
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NOTE ABOUT OPTIMIZATIONS:
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By default /var/lib/cube/essential/lib/firmware is a link to
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/opt/container/dom0/rootfs/lib/firmware. This is a short circuit
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which is put in place to allow for just a single copy of the firmware.
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If you replace the link with a directory a second copy of the firmware
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will be created.
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Syncing
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-------------------------
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Updating the cube-essential firmware now involves different steps than
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you would find in the traditional model. A typical update now might
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look like one of the following:
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1)
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a) replace dom0 (with the new image containing '/lib/firmware' updates)
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b) restart dom0 (the dom0-ctl-core will automatically sync firmware)
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* step b) is not needed if you are using the short circuit symlink
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c) reload cube-essential kernel modules affected by firmware updates
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2)
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a) update dom0 (with firmware related package updates)
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b) run '/etc/dom0.d/firmware-sync' to complete a sync
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* step b) is not needed if you are using the short circuit symlink
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c) reload cube-essential kernel modules affected by firmware updates
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3)
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a) update or replace dom0 (including firmware updates)
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b) run '/etc/dom0.d/firmware-sync' to complete a sync
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* step b) is not needed if you are using the short circuit symlink
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c) reboot the system
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NOTE that it may not always be possible to complete an update, which
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includes firmware updates, without having to perform a system
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reboot. This change doesn't change this but rather provides additional
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options to the system designer that can often avoid a system reboot in
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most cases.
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