I saw the following discussion and had some questions: live resize of a NVMe drive
If the physical capacity of the nvme device changes (e.g., from 10GB to 20GB), how the operating system detect it without rebooting?
In the above link, re-scanning pci bus is solution.
When the re-scanning be executed, does the operating system ask the nvme device to update its meta-info (e.g., capacity, etc.) ?
How does OS interact with disk specifically? (How to read changed device parameters from the disk, not the old device parameters in memory?)
This is an AWS virtual-machine probably so the disk is actually a virtual-disk. You can't resize a physical disk like you upgrade its capacity physically (you'd need to change the disk).
With that said, this machine probably runs on top of a type 1 hypervisor. What I understand about these is that the virtual machines (VMs) run as processes on a different ring on top of a minimal operating-system (hypervisor). When the VMs execute privileged instructions, it will trigger a protection fault and the hypervisor can thus inspect who actually triggered the fault (was it the guest kernel or a user mode process within the guest kernel?). If it was the guest kernel than it can execute that instruction on behalf of the guest. Otherwise, it will probably do what a real kernel would do (trigger an exception). It can tell the difference because the guest kernel runs in a different ring than the ring 3 (user mode).
With that said, the NVME device isn't PCI it is NVME. The host controller of the NVME drive is PCI. To rescan the NVME drives, you will read/write to some registers that are memory mapped in RAM and ask the NVME PCI host controller what is the size of the different disks that are found. PCI is known to be hot pluggable (similarly to USB) in some cases but mostly not on consumer motherboards. I don't think you'll get any interrupt when a PCI device is hot plugged so you are left doing a rescan of the devices.
For NVME, it depends on the host controller if you'll get an interrupt when a disk is swapped/changes size. As to virtual-disks, it probably depends on a lot of different things. You could definitely be left doing a PCI rescan here. I guess it depends on the hypervisor, on the OS and on the host controller configurations.