On Sun, 25 Jun 2000, Andrew Morton wrote:
> > I'm less than happy about ->do_ioctl(), though - are you sure that it can
> > happen with refcount==0? AFAICS it does not touch the reference counter
> > and it means that we need to be extra cautious inside...
>
> Yes, these methods are called with refcount == 0. For example, the
> 'mii-diag' tool may be used to manipulate the device's MII when the
> interface is downed (via netdevice.do_ioctl())
And what happens if it blocks?
> netdevice.open() is a misnomer. The device is always "open". It should
> have been called 'start' or 'up'.
Let me get it straight: currently
a) we have a table of registered devices.
b) refcount on module is 1 iff interface is up.
c) methods may be called regardless the refcount value.
d) modules are loaded by dev_load() and nothing prevents them from
immediate removal.
e) normally, module can be unloaded if the interface is down. It
may destroy settings made by ->do_ioctl().
f) in some cases we do __dev_get_by_name(), in some dev_load().
Deliberate difference or inconsistence?
g) in several places we do dev_load() followed by blocking
operation and __dev_get_by_name(). Seems like we are asking for races
here, no?
IMO it means that refcounting for these beasts is bogus. I would rather
see dev_something(name) doing dev_load(), incrementing the reference
counter and returning the resulting struct net_device * along with
dev_somethingelse(dev) dropping that counter. That, and additional
increment/decrement upon up/down. Then we could be sure that whenever we
pick the structure by name it will stay around until we explicitly say
that we don't care and we would know that pointers to such structure
are stored only if the counter is positive (aside of the pointers in
device table, that is).
Comments?
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This archive was generated by hypermail 2b29 : Mon Jun 26 2000 - 21:00:06 EST