Ethernet Drivers: Question on ifp->if_ioctl invocation for
SIOCADDMULTI and SIOCDELMULTI
david.somayajulu at qlogic.com
Wed May 16 18:56:46 UTC 2012
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)
1098 in_joingroup(struct ifnet *ifp, const struct in_addr *gina,
1099 /*const*/ struct in_mfilter *imf, struct in_multi **pinm)
1101 int error;
1104 error = in_joingroup_locked(ifp, gina, imf, pinm);
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.
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() ?
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