Re: Query: SCSI Device node creation when UFS is loaded as a module

[asutoshd@codeaurora.org]

On 2019-10-24 02:50, Steffen Maier wrote:
> On 10/24/19 1:51 AM, asutoshd@codeaurora.org wrote:
>> Hi
>> I'm loading the ufs-qcom driver as a module but am not seeing the 
>> /dev/sda* device nodes.
>> Looks like it's not being created.
>> 
>> I find the sda nodes in other paths being enumerated though:
>> 
>> / # find /sys -name sda
>> /sys/kernel/debug/block/sda
>> /sys/class/block/sda
>> /sys/devices/platform/<...>/<xxx>.ufshc/host0/target0:0:0/0:0:0:0/block/sda
>> /sys/block/sda
>> 
>> All Luns are detected and I see sda is detected and prints for all the 
>> Luns as below -:
>> sd 0:0:0:0: [sda] .... ....-byte logical blocks:
>> 
>> ... so on ...
>> 
>> But if I link it statically instead of a module, it works fine. All 
>> device nodes are created.
>> 
>> I'm trying to figure out where/how in SCSI does it create these device 
>> nodes - /dev/sd<a/b/c/d> ?
> 
> That's from (systemd-)udevd user space based on uevents from the 
> kernel.
> 
>> I've looked into sd.c but I couldn't figure out the exact place yet.
> 
> Yeah, based on the SCSI device probe and add lun, the high level
> driver sd would emit udev events for block devices.

Thanks Steffen and Avri.

I understood that sd.c creates the devices based on scsi_device and 
establishes a relation between scsi_device (sdp) and scsi_disk (sdkp).
But I couldn't figure out why it creates the device fine when the 
ufs-qcom is linked statically, but is unable to create the devices when 
inserted as a module.

Does it follow a different method to create the device nodes when 
statically linked and needs (systemd-)udevd to handle the events during 
dynamic insertion?

Thanks
asd