On 09/05/2018 01:49 PM, Cong Wang wrote: > On Tue, Sep 4, 2018 at 8:25 PM Ying Xue <ying....@windriver.com> wrote: >> >> On 09/05/2018 05:54 AM, Cong Wang wrote: >>> __tipc_nl_compat_dumpit() uses a netlink_callback on stack, >>> so the only way to align it with other ->dumpit() call path >>> is calling tipc_dump_start() and tipc_dump_done() directly >>> inside it. Otherwise ->dumpit() would always get NULL from >>> cb->args[]. >>> >>> But tipc_dump_start() uses sock_net(cb->skb->sk) to retrieve >>> net pointer, the cb->skb here doesn't set skb->sk, the net pointer >>> is saved in msg->net instead, so introduce a helper function >>> __tipc_dump_start() to pass in msg->net. >>> >>> Ying pointed out cb->args[0...3] are already used by other >>> callbacks on this call path, so we can't use cb->args[0] any >>> more, use cb->args[4] instead. >> >> It's a common mechanism to save rhashtable iterator pointer in cb->args >> after tipc_dump_start() and tipc_dump_done() are introduced. Someday >> probably we will involve new dumpit function. In order to lower the risk >> that rhashtable iterator pointer saved is overwritten, it's better to >> use the last slot, ie, cb->args[5]. > > I don't understand, currently only cb->args[0..3] are used at most, > therefore cb->args[4] is pretty safe in current code base, there is > no reason to be so defensive to use cb->args[5]. >
Yes, at present cb->args[4] is safe. > If you really worry about future, you probably want to extend cb->args > from 6 to whatever larger, rather than just skipping cb->args[4]. > When we have to use the fifth slot of cb->args[] in the future, we need to skip sb->args[4], which is a bit wried. This is the reason why I suggested we could use the last one. > I don't see any reason to do so. As I said, the current version is safe. If you think it's unnecessary to change, it's okay to me. Acked-by: Ying Xue <ying....@windriver.com> > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ tipc-discussion mailing list tipc-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/tipc-discussion
