Ethernet Drivers: Question on ifp->if_ioctl invocation for SIOCADDMULTI and SIOCDELMULTI

[David Somayajulu]

Hi All,
When ifp->if_ioctl() is invoked for the ioctl cmd SIOCADDMULTI,



IN_MULTI_LOCK() is called in one of the functions in_joingroup()  in the caller stack.



>From netinet/in_var.h, line 357 :  #define IN_MULTI_LOCK()         mtx_lock(&in_multi_mtx)



>From netinet/in_mcast.c
1098 in_joingroup(struct ifnet *ifp, const struct in_addr *gina,
1099     /*const*/ struct in_mfilter *imf, struct in_multi **pinm)
1100 {
1101         int error;
1102
 1103         IN_MULTI_LOCK();
1104         error = in_joingroup_locked(ifp, gina, imf, pinm);
1105         IN_MULTI_UNLOCK();
1106

This is also the case for SIOCDELMULTI, where the function holding  "in_multi_mtx" lock is in_leavegroup()

This poses a problem in the driver in that the hardware dependent function performing it,  is not allowed to sleep() in case it needs to poll some state.

Question:

1.       If I want to implement any delays - for the above case - in the driver using DELAY(usec) macro, is there a maximum amount of time that the driver is allowed to complete this function? I am concerned that if it takes to too long I might run into a soft_lockup() situation.

2.       Is it o.k to defer the processing in a separate in a separate thread which can sleep() ?

Thanks
David S.



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