On Tue, May 17, 2022 at 07:54:38PM +0200, Christophe JAILLET wrote: > Le 17/05/2022 à 14:16, Jason Gunthorpe a écrit : > > On Tue, May 17, 2022 at 09:33:28AM +0800, Haowen Bai wrote: > > > container_of() will never return NULL, so remove useless code. > > > > It is confusing here, but it can be null. > > Hi, > > out of curiosity, can you elaborate how it can be NULL? It is guarented/required that that container_of is a 0 offset. The normal usage of the ib_alloc_device macro: #define ib_alloc_device(drv_struct, member) \ container_of(_ib_alloc_device(sizeof(struct drv_struct) + \ BUILD_BUG_ON_ZERO(offsetof( \ struct drv_struct, member))), \ struct drv_struct, member) Enforces this property with a BUILD_BUG_ON So, if the input pointer to container_of is reliably NULL or ERR_PTR then the output pointer will be the same. The rvt code here open codes the call because it is a mid-layer and the sizeof() calculation above is not correct for it. Jason
