在 2022/5/18 上午2:03, Jason Gunthorpe 写道: > 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 Thank you for the explanation. : ) -- Haowen Bai
