Re: Question on boot device information

[Pascal Hambourg]

Le 07/02/2020 à 11:52, Felipe Franciosi a écrit :
> I have a doubt around what information grub provides to initramfs
> regarding the boot device (Linux). IIUC, grub uses the system's
> firmware (or its own drivers?)

GRUB can use either the platform firmware or its own drivers to access 
devices.

> to load the kernel and initramfs, later
> jumping into the kernel entry point.
>
> At that point, what information does initiramfs has about where it was
> loaded from?

AFAIK, none. All the initramfs knows from GRUB is the kernel command line.

> In the simple case where both the kernel and the initramfs came from
> an NVMe drive (or a disk behind a PCI SCSI controller), is it possible
> for initramfs to find out that device's BDF?

You could pass the device to the kernel command line. But the mapping 
between GRUB device names (hd0, hd1...) and Linux device names 
(/dev/sda, /dev/nvme0...) is neither straightforward nor persistent, so 
that may not be very useful. You could use the "probe" function to 
retrieve a persistent identifier (UUID, label...) from the device, or 
simply an arbitrary value unique for each menu entry.