udev rule, when RUN script is invoked?

[Alexander Ivanov]

On Thu, 22 Feb 2018 18:05 +0100, Greg KH <greg at kroah.com> wrote:
> On Thu, Feb 22, 2018 at 08:44:20AM -0800, Alexander Ivanov wrote:
> > Greg,
> > 
> > On Thu, 22 Feb 2018 08:56 +0100, Greg KH <greg at kroah.com> wrote:
> > > On Wed, Feb 21, 2018 at 03:36:44PM -0800, Alexander Ivanov wrote:
> > > > Hi All,
> > > > 
> > > > I have udev rule defined on a
> > > > 
> > > > DEVPATH="/dev/mydev0",..., ACTION="remove", ..., RUN+="/path/to/script"
> > > > 
> > > > When does /path/to/script is executed in respect to module's remove() and exit() ?
> > > 
> > > A module's lifecycle is different from a device's lifecycle, right?
> > > 
> > Sure. However, in this particular case, only one device for the module
> > can exist and user-land calls insmod/rmmod, Thus, on rmmod both
> > device's remove() and module's exit() are getting called.
> 
> What type of crazy "device" is this?  Have a pointer to the source code
> anywhere?
> 

Why crazy? :)
This is char device that is created by pcie driver. PCIe device has a channel to dump some debug information over to the host. This char device is an interface to that debug data. 
It's just a little addition to main pcie driver to help hw/fw development


> > > There is no remove() call for a module, only for a driver subsystem, so
> > > be careful as to what exactly you are referring to here.
> > > 
> > > Hopefully, all devices "owned" by the module should be removed from the
> > > kernel before the module is unloaded, so that should help you out here.
> > > 
> > > Also note that modules are never automatically unloaded, so that is
> > > never a normal operation in the system.
> > > 
> > > what exactly are you trying to do here with your udev script?
> > 
> > On action=="remove", I'd like to call device's close(), it was open()ed by action=="add"
> > It looks like device is removed before RUN gets a chance to execute..
> 
> Of course it is, because when the module is removed, you already removed
> the device, right?
> 
> > Basically, I need to start reading from device as soon as it appears
> > in the system, and stop it right before it get removed.
> 
> "right before" is hard if you don't tell your userspace program you are
> going to remove the module :)
> 
> Your program should be able to handle the device node being removed
> underneath it anyway, there's no need to have to "stop" the program, it
> can easily detect if the device goes away.
> 
Sure custom code can do it, no problem.
I though I could just use simple cat /dev/dbg0 > file, and then kill it .

anyway, thank you for explanation. 

--Alex

> So there's no real need for the udev rule here.
> 
> hope this helps,
> 
> greg k-h
> 
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-- 
  Alexander Ivanov
  amivanov at fastmail.com