Hi,
I would like to use sparse on the OpenBSC[1] userspace application
and I'm searching for a hint on how to realize it or how to adopt the
sparse code to do the following.
In the code we have a struct called "struct gsm_subscriber" and it
is reference counted. We have various methods that query the
database (VLR) to find a subscriber and then we have subscr_put
and subscr_get to operate on the reference count.
One rule we have established in the code is that the "reference" is
never borrowed. This means code that is doing a subscr_get or a query
will need to do subscr_put on all exits paths. The only exception is
e.g. if work needs to be scheduled and the pointer is put into a talloc
allocated structure.
My first thought was that this almost works like locking in the kernel
but I was wrong. I have used the CHECKER macros from linux/compiler.h
and changed code to
struct gsm_subscriber *subscr_get(struct gsm_subscriber *subscr)
__acquires(subscr);
struct gsm_subscriber *subscr_put(struct gsm_subscriber *subscr)
__releases(subscr);
struct gsm_subscriber *subscr_find_by_tmsi(int tmsi)
__acquires(subscr);
and the code like
do_something()
{
subscr = subscr_find_by_tmsi(tmsi);
if (!subscr)
return;
if (some_condition) {
...
subscr_put(subscr);
}
...
return;
}
My assumption would be that sparse is looking at the flows and figures
out that one path exits without subscr_put being called. Is my assumption
wrong, would it be worth adding a check that goes through the flow and
counts ref's/unref's? Am I doing it completely wrong?
help and pointers to the code are very much appreciated.
z.
PS: I will update the wiki with some explanation when I get it to work.
[1] http://openbsc.gnumonks.org
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