On Fri, Apr 11, 2025 at 12:56 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote: > > On Tue, Apr 08, 2025 at 08:49:54PM -0600, Caleb Sander Mateos wrote: > > The ublk driver calls blk_mq_tag_to_rq() in several places. > > blk_mq_tag_to_rq() tolerates an invalid tag for the tagset, checking it > > against the number of tags and returning NULL if it is out of bounds. > > But all the calls from the ublk driver have already verified the tag > > against the ublk queue's queue depth. In ublk_commit_completion(), > > ublk_handle_need_get_data(), and case UBLK_IO_COMMIT_AND_FETCH_REQ, the > > tag has already been checked in __ublk_ch_uring_cmd(). In > > ublk_abort_queue(), the loop bounds the tag by the queue depth. In > > __ublk_check_and_get_req(), the tag has already been checked in > > __ublk_ch_uring_cmd(), in the case of ublk_register_io_buf(), or in > > ublk_check_and_get_req(). > > > > So just index the tagset's rqs array directly in the ublk driver. > > Convert the tags to unsigned, as blk_mq_tag_to_rq() does. > > If blk_mq_tag_to_rq() turns out to be not efficient enough, we can kill it > in fast path by storing it in ublk_io and sharing space with 'struct io_uring_cmd *', > since the two's lifetime isn't overlapped basically. I agree it would be nice to just store a pointer from in struct ublk_io to its current struct request. I guess we would set it in ubq_complete_io_cmd() and clear it in ublk_commit_completion() (matching when UBLK_IO_FLAG_OWNED_BY_SRV is set), as well as in ublk_timeout() for UBLK_F_UNPRIVILEGED_DEV? I'm not sure it is possible to overlap the fields, though. When using UBLK_U_IO_NEED_GET_DATA, the cmd field is overwritten with the a pointer to the UBLK_U_IO_NEED_GET_DATA command, but the req would need to be recorded earlier upon completion of the UBLK_U_IO_(COMMIT_AND_)FETCH_REQ command. Would you be okay with 2 separate fields? Best, Caleb
