John-Mark Gurney wrote: > Raaf wrote this message on Tue, Feb 07, 2006 at 01:42 +0100: >> John-Mark Gurney wrote: >>> Raaf wrote this message on Mon, Feb 06, 2006 at 22:54 +0100: >>>> Hi, i am working on a usb driver that allocates some memory when >>>> the device is opened using malloc. >>>> >>>> Now i want user processes to be able to access this memory using >>>> mmap and i want to free this memory when it is no longer needed. >>>> >>>> The problem is that there seems to be no way of knowing for my >>>> driver at what time the memory is no longer mapped in a process >>>> address space so that i can safely free this memory. >>> why not at close time? I would imagine that the device won't be closed >>> until all the mmap's that are backed by the device are unmapped.. it >>> shouldn't be hard to test... the mapping should hold a reference to >>> the device until it's munmapped.. >>> >> The problem is that it is perfectly legal to access the mapped memory >> after a close, consider following code: >> >> fd = open() >> mem = mmap() >> close(fd) >> process_data(mem) >> >> Unfortunately the mapping doesn't seem to hold a reference to the >> related fileobject, so the close in above code actually ends up >> in the close function of my driver but the mapping is still there. > > and you've tested that the mmap function still gets called after the > close function of your device driver is?
Yes, just tested it with some printf's in the driver. open mmap close mmap > If this is the case, we need > to fix FreeBSD.. the mmap should increase the ref count on the device, > and the close shouldn't initiate the close until the mapping goes away.. > That would be nice. > fd = open() # ref cnt = 1 > mem = mmap() # ref cnt++ > close(fd) # ref cnt-- > process_data(mem) # valid ref cnt > 0 > munmap(mem) # ref cnt-- and close sine ref cnt == 0 > _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
