Possible working mode supported by nydus-snapshotter

[jiangliu]

Recently we are trying to enhance nydus-snapshotter with EROFS with tarfs mode, which can be used to:

• speed up OCIv1 image handling
• provide runtime data integrity for OCIv1 images
• support data integrity for confidential containers

With this new features and requirements, nydus-snapshotter need to support different working modes as below:

<style> </style>

Scenario	Kernel Device	Filesystem	Lazy Loading	Need Daemon	Shared Daemon
Lazy loading/data dedup for runC	fusedev	FUSE-RAFS	Yes	Yes	Optional
To be defined	fusedev	FUSE-RAFS	No	Yes	Optional
Lazy loading/data dedup for runC	fscache	EROFS on host	Yes	Yes	Must
Tarfs for runC/confidential containers	blockdev	EROFS on host/guest	No	No	N/A
Lazy loading for Kata/runD	nodev	EROFS in guest	Yes	No	N/A

Currently we useDaemonMode and FsDriver to control the working mode. We need to extend/refine the configuration file format to support new usage models. How about the new configuration format

[modes]
default = "fscache"
[modes.fusedev]
enabled = true
shared = true
nydusd_config = "/etc/nydus/nydusd-config.fusedev.json"
recover_policy = "restart"
threads_number = 4
[modes.fscache]
enabled = false
nydusd_config = "/etc/nydus/nydusd-config.fscache.json"
recover_policy = "restart"
threads_number = 4
[modes.blockdev]
enabled = true
nydusd_config = "/etc/nydus/nydusd-config.blockdev.json"
[modes.nulldev]
enabled = true
nydusd_config = "/etc/nydus/nydusd-config.nulldev.json"

DaemonMode and FsDriver will still be supported for backward compatibility and transition, and eventually will be deprecated in v1.0.

[changweige]

Are multiple shared nydusd daemons running simultaneously or only one nydusd is allowed for shared mode?