Hello, MD Autodetect allows for the assembly of raid-1 mirror filesystems in-kernel before userspace starts, without requiring the complexity and fragility of using an initrd and switch-root. It is still in widespread use and given that it has a wide use case in any system that wants fully resilient boot/root devices (which can be done even on EFI) is likely to remain essential. While the various high-profile general purpose Linux distributions such as Red Hat and Ubuntu may use initrd by default, there are innumerable scenarios, particularly in embedded space, where initrd is never used but RAID may be and hence auto-detect is used to assemble the actual root file system. Removing it would be a major regression in 'md' functionality. Yes, it requires CONFIG_MD and the appropriate RAID personality (typically CONFIG_MD_RAID1) to be set to 'y' in Kconfig. It doesn't (IIRC) get built if CONFIG_MD is set to M. Changing the default for CONFIG_MD should not have any impact on this so long as the ability to set CONFIG_MD=y does not get disabled (which would also be a regression). If auto-detect were to be considered for removal then IMO it needs to go through the full kernel feature deprecation/removal life cycle - i.e. first it gets marked as deprecated in KConfig, then after a decent time interval (years?) the default for the option is changed, and only after that has all happened without causing problems, the code gets considered for removal. Regards, Geoff. Geoff Back What if we're all just characters in someone's nightmares? On 07/03/2023 03:04, Xiao Ni wrote: > From the code of md-autodetect.c, it looks like it's used to create > the raid device > during boot. Now we use udev rules to assemble the raid. Do we still need it? > What's the usage of md-autodetect? > > And in Kconfig, it depends on md-raid as Y when building a kernel. If we change > the default to M, md-autodetect will not work anymore, right? > > Best Regards > Xiao >
