* [Arista] Fix boot0 code for docker_inram
Enable docker_inram for all systems with 4GB or less of flash.
This is mandatory to allow these systems to store 2 SONiC images.
This change also fixes the missing docker_inram attribute when
installing a new image from SONiC.
Because the SWI image can ship with additional kernel parameters within
such as `sonic_fips=` this lead to a conflict.
To prevent the conflict, the extra kernel parameters from the SWI are
now stored in the file `kernel-cmdline-append` which isn't used anywhere.
* Add optional zram compression for docker_inram
Some devices running SONiC have a small storage device (2G and 4G mainly)
The SONiC image growth over time has made it impossible to install
2 images on a single device.
Some mitigations have been implemented in the past for some devices but
there is a need to do more.
One such mitigation is `docker_inram` which creates a `tmpfs` and
extracts `dockerfs.tar.gz` in it.
This all happens in the SONiC initramfs and by ensuring the installation
process does not extract `dockerfs.tar.gz` on the flash but keep the file as is.
This mitigation does a tradeoff by using more RAM to reduce the disk footprint.
It however creates new issues for devices with 4G of system memory since
the extracted `dockerfs.tar.gz` nears the 1.6G.
Considering debian upgrades (with dual base images) and the continuous
stream of features this is only going to get bigger.
This change introduces an alternative to the `tmpfs` by allowing a system
to extract the `dockerfs.tar.gz` inside a `zram` device thus bringing
compression in play at the detriment of performance.
Introduce 2 new optional kernel parameters to be consumed by SONiC initramfs.
- `docker_inram_size` which represent the max physical size of the
`zram` or `tmpfs` volume (defaults to DOCKER_RAMFS_SIZE)
- `docker_inram_algo` which is the method to use to extract the
`dockerfs.tar.gz` (defaults to `tmpfs`)
other values are considered to be compression algorithm for `zram`
(e.g `zstd`, `zlo-rle`, `lz4`)
Refactored the logic to mount the docker fs in the SONiC initramfs under
the `union-mount` script.
Moved the code into a function to make it cleaner and separated the
inram volume creation and docker extraction.
On Arista platform with a flash smaller or equal to 4GB set
`docker_inram_algo` to `zstd` which produces the best compression ratio
at the detriment of a slower write performance and a similar read
performance to other `zram` compression algorithms.
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