On Wed, Apr 01, 2015 at 07:43:05AM -0400, Robert P. J. Day wrote:
i can trivially create misc character devices, and i know special device files for them will automatically show up under /dev, but what is the precise udev event/rule that comes into play for this?
if i start to monitor udevadm with:
$ udevadm monitor --kernel --udev --property
and insert my misc char module, i see:
KERNEL[5342.740294] add /module/mymisc (module) ACTION=add DEVPATH=/module/mymisc SEQNUM=3007 SUBSYSTEM=module
KERNEL[5342.740528] add /devices/virtual/misc/mymisc (misc) ACTION=add DEVNAME=/dev/mymisc DEVPATH=/devices/virtual/misc/mymisc MAJOR=10 MINOR=55 SEQNUM=3008 SUBSYSTEM=misc
UDEV [5342.741071] add /module/mymisc (module) ACTION=add DEVPATH=/module/mymisc SEQNUM=3007 SUBSYSTEM=module USEC_INITIALIZED=740419
UDEV [5342.741921] add /devices/virtual/misc/mymisc (misc) ACTION=add DEVNAME=/dev/mymisc DEVPATH=/devices/virtual/misc/mymisc MAJOR=10 MINOR=55 SEQNUM=3008 SUBSYSTEM=misc USEC_INITIALIZED=740750
so, yes, i can see the line "DEVNAME=/dev/mymisc", but is there something i can point at in the collection of udev rules that deals with that? or is that simply done internally?
Ok, I'll be nice here, udev doesn't create device nodes anymore, and hasn't for years, the kernel does that directly with devtmpfs. Yes, if you want to write your own version of udev, you can listen to the uevent messages, and pick out the right one to trigger off of to create a device node, but as the kernel does this all for you with devtmpfs, why would you want to? In fact, no one does this anymore, and people run systems without udev and have dynamic device nodes just fine. And have been doing so for years, udev isn't needed for device nodes anymore, if that's all you care about. Hint, you are correct, it's the DEVNAME event, but watch out here, you are seeing events twice, once from the kernel, the second from UDEV, which is exposing how udev works internally, but will quickly get confusing if you aren't careful. I'd recommend just filtering on the KERNEL events to keep things "sane" for now. good luck, greg k-h