From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH V8 libibverbs 1/7] Infrastructure to support verbs extensions Date: Tue, 30 Jul 2013 16:15:48 -0600 Message-ID: <20130730221548.GA14439@obsidianresearch.com> References: <1374741488-30895-1-git-send-email-yishaih@mellanox.com> <1374741488-30895-2-git-send-email-yishaih@mellanox.com> <20130725171408.GA17616@obsidianresearch.com> <51F268B1.9040003@dev.mellanox.co.il> <20130729233056.GB4439@obsidianresearch.com> <51F821A3.1010507@dev.mellanox.co.il> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <51F821A3.1010507-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Yishai Hadas Cc: Yishai Hadas , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, roland-BHEL68pLQRGGvPXPguhicg@public.gmane.org, ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, tzahio-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, Sean Hefty List-Id: linux-rdma@vger.kernel.org On Tue, Jul 30, 2013 at 11:27:15PM +0300, Yishai Hadas wrote: > Can accept it, however as it's a const pointer may need some casting later > which is not fully clean. Drop the const from the definition then. > Your suggestion for verbs_set_ctx_op can't not work as it calls internally > to verbs_get_ctx_op and will may fail as > at that step function pointer was not set and *(void **)((uint8_t *)vctx + > off) will be NULL. Yes, that is too bad in that case, but the old macro is still flawed: +#define verbs_set_ctx_op(vctx, op, ptr) ({ \ + if (vctx && (vctx->sz >= sizeof(*vctx) - offsetof(struct verbs_context, op))) \ + vctx->op = ptr; }) - Missing () on all vctx usages - Missing type enforcement on vctx Something like this: #define verbs_set_ctx_op(_vctx, op, ptr) ({ \ struct verbs_context *vctx = _vctx; \ if (vctx && (vctx->sz >= sizeof(*vctx) - offsetof(struct verbs_context, op))) \ vctx->op = ptr; }) > In addition changing to use const as part of returning from > __verbs_get_ctx_op causes some necessary casting to non const in some places > which > is not fully clean. (e.g. free((void *)context_ex); as part of > __ibv_close_device, verbs_ctx->has_comp_mask = VERBS_CONTEXT_XRCD | > VERBS_CONTEXT_SRQ | > VERBS_CONTEXT_QP; as part of mlx4_init_context) It is virtually impossible to do const-correctness fully and transparently in C, since the language has no feature to silently propogate the const. If you want to be 100% clean then provide a non-const version -- verbs_get_ctx_nc that takes non-const input. Functions that silently discard const are bad since it silently defeats static analysis around const. > I recommend staying with V8 suggestion for both macros, in case > you think there is any problem with missing () for the set operation > please point on and may handle. Using the inline to help the -Os case is definitely desirable, and the fix to the () at least. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html