driver close function not being call until munmap

dbrazeau · 06-30-2011, 11:53 AM

I'm writing a driver and a userspace test application. I have ran into some what of an issue. When I open a file, and do a mmap using that file descriptor then close the file descriptor, my driver's close function is not called until I do a munmap on the address received from the mmap.

Can someone explain to me why this is, and if there is a way to instantly get the close call to my driver (like it normally does when not doing a mmap) prior to performing the munmap?

raevin · 07-02-2011, 08:23 AM

Quote:

Originally Posted by dbrazeau

I'm writing a driver and a userspace test application. I have ran into some what of an issue. When I open a file, and do a mmap using that file descriptor then close the file descriptor, my driver's close function is not called until I do a munmap on the address received from the mmap.

Can someone explain to me why this is, and if there is a way to instantly get the close call to my driver (like it normally does when not doing a mmap) prior to performing the munmap?

I'm not familiar with driver programming, but is it possible to capture SIGs like you can in a userspace program? If so, you can try writing a handler for a specific SIG.

sundialsvcs · 07-03-2011, 11:57 AM

Think about it ... if you have mapped memory using a file-descriptor, then it does not make any sense at all to dismiss the driver until the memory has been unmapped. You've just pulled the rug out from underneath the ming vase.

Really, it surprises me that the attempt to close the file-descriptor did not throw an error ... did you check to see if it did?

dbrazeau · 07-06-2011, 11:07 AM

Quote:

Originally Posted by sundialsvcs

Think about it ... if you have mapped memory using a file-descriptor, then it does not make any sense at all to dismiss the driver until the memory has been unmapped. You've just pulled the rug out from underneath the ming vase.

Really, it surprises me that the attempt to close the file-descriptor did not throw an error ... did you check to see if it did?

I did check the return value of the close call and there is no error. I too am surprised that file descriptor close does not return an error, given the behavior.