John-Mark Gurney wrote:
Kamal R. Prasad wrote this message on Sun, Dec 05, 2004 at 00:38 +0530:
I wrote an mmap() interface for a USB device. But when I made a call to
it using mmap(), I saw that mmap interface is called 3-4 times. The
calls are being made from within mmap() i.e. sys/vm/vm_mmap.c. Can
someone tell me if there is something like a re-try going on for some
reason?
From userspace, I called it as
addr = mmap(NULL, 1024, PROT_READ, MAP_SHARED, fd, 0);
The version of OS is Freebsd 5.3(stable).
each mmap call will be called whenever the kernel needs to map that
specific page.. say you map 16k of your device... it won't map any
of the 16k until the first time it is accessed, then it will call the
mmap routine for each page as it is accessed... it is also possible that
memory for the mappings needs to be reclaimed, at which point those page
mappings will be reaped, and your mmap function will be called again when
they need to be accessed again..
Thanks. But then, the mmap'ed() address was yet to be used by the user
space and I don't see the need for multiple calls to my interface almost
as if in a while loop. Is there any return value from the mmap()
interface that could trigger another call? I am returning 0 after
setting the param to vtophys(kernel virtual address).
regards
-kamal
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