On 28/09/2023 21:19, Markus Armbruster wrote:
> We use errno after calling Libibverbs functions that are not
> documented to set errno (manual page does not mention errno), or where
> the documentation is unclear ("returns [...] the value of errno on
> failure"). While this could be read as "sets errno and returns it",
> a glance at the source code[*] kills that hope:
>
> static inline int ibv_post_send(struct ibv_qp *qp, struct ibv_send_wr
> *wr,
> struct ibv_send_wr **bad_wr)
> {
> return qp->context->ops.post_send(qp, wr, bad_wr);
> }
>
> The callback can be
>
> static int mana_post_send(struct ibv_qp *ibqp, struct ibv_send_wr *wr,
> struct ibv_send_wr **bad)
> {
> /* This version of driver supports RAW QP only.
> * Posting WR is done directly in the application.
> */
> return EOPNOTSUPP;
> }
>
> Neither of them touches errno.
>
> One of these errno uses is easy to fix, so do that now. Several more
> will go away later in the series; add temporary FIXME commments.
> Three will remain; add TODO comments. TODO, not FIXME, because the
> bug might be in Libibverbs documentation.
>
> [*] https://github.com/linux-rdma/rdma-core.git
> commit 55fa316b4b18f258d8ac1ceb4aa5a7a35b094dcf
>
> Signed-off-by: Markus Armbruster <arm...@redhat.com>
Reviewed-by: Li Zhijian <lizhij...@fujitsu.com>
> ---
> migration/rdma.c | 45 +++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 39 insertions(+), 6 deletions(-)
>
> diff --git a/migration/rdma.c b/migration/rdma.c
> index 28097ce604..bba8c99fa9 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -853,6 +853,12 @@ static int qemu_rdma_broken_ipv6_kernel(struct
> ibv_context *verbs, Error **errp)
>
> for (x = 0; x < num_devices; x++) {
> verbs = ibv_open_device(dev_list[x]);
> + /*
> + * ibv_open_device() is not documented to set errno. If
> + * it does, it's somebody else's doc bug. If it doesn't,
> + * the use of errno below is wrong.
> + * TODO Find out whether ibv_open_device() sets errno.
> + */
> if (!verbs) {
> if (errno == EPERM) {
> continue;
> @@ -1162,11 +1168,7 @@ static void qemu_rdma_advise_prefetch_mr(struct ibv_pd
> *pd, uint64_t addr,
> ret = ibv_advise_mr(pd, advice,
> IBV_ADVISE_MR_FLAG_FLUSH, &sg_list, 1);
> /* ignore the error */
> - if (ret) {
> - trace_qemu_rdma_advise_mr(name, len, addr, strerror(errno));
> - } else {
> - trace_qemu_rdma_advise_mr(name, len, addr, "successed");
> - }
> + trace_qemu_rdma_advise_mr(name, len, addr, strerror(ret));
> #endif
> }
>
> @@ -1183,7 +1185,12 @@ static int qemu_rdma_reg_whole_ram_blocks(RDMAContext
> *rdma)
> local->block[i].local_host_addr,
> local->block[i].length, access
> );
> -
> + /*
> + * ibv_reg_mr() is not documented to set errno. If it does,
> + * it's somebody else's doc bug. If it doesn't, the use of
> + * errno below is wrong.
> + * TODO Find out whether ibv_reg_mr() sets errno.
> + */
> if (!local->block[i].mr &&
> errno == ENOTSUP && rdma_support_odp(rdma->verbs)) {
> access |= IBV_ACCESS_ON_DEMAND;
> @@ -1291,6 +1298,12 @@ static int qemu_rdma_register_and_get_keys(RDMAContext
> *rdma,
> trace_qemu_rdma_register_and_get_keys(len, chunk_start);
>
> block->pmr[chunk] = ibv_reg_mr(rdma->pd, chunk_start, len, access);
> + /*
> + * ibv_reg_mr() is not documented to set errno. If it does,
> + * it's somebody else's doc bug. If it doesn't, the use of
> + * errno below is wrong.
> + * TODO Find out whether ibv_reg_mr() sets errno.
> + */
> if (!block->pmr[chunk] &&
> errno == ENOTSUP && rdma_support_odp(rdma->verbs)) {
> access |= IBV_ACCESS_ON_DEMAND;
> @@ -1408,6 +1421,11 @@ static int qemu_rdma_unregister_waiting(RDMAContext
> *rdma)
> block->remote_keys[chunk] = 0;
>
> if (ret != 0) {
> + /*
> + * FIXME perror() is problematic, bcause ibv_dereg_mr() is
> + * not documented to set errno. Will go away later in
> + * this series.
> + */
> perror("unregistration chunk failed");
> return -ret;
> }
> @@ -1658,6 +1676,11 @@ static int qemu_rdma_block_for_wrid(RDMAContext *rdma,
>
> ret = ibv_get_cq_event(ch, &cq, &cq_ctx);
> if (ret) {
> + /*
> + * FIXME perror() is problematic, because ibv_reg_mr() is
> + * not documented to set errno. Will go away later in
> + * this series.
> + */
> perror("ibv_get_cq_event");
> goto err_block_for_wrid;
> }
> @@ -2199,6 +2222,11 @@ retry:
> goto retry;
>
> } else if (ret > 0) {
> + /*
> + * FIXME perror() is problematic, because whether
> + * ibv_post_send() sets errno is unclear. Will go away later
> + * in this series.
> + */
> perror("rdma migration: post rdma write failed");
> return -ret;
> }
> @@ -2559,6 +2587,11 @@ static int qemu_rdma_connect(RDMAContext *rdma, bool
> return_path,
> ret = rdma_get_cm_event(rdma->channel, &cm_event);
> }
> if (ret) {
> + /*
> + * FIXME perror() is wrong, because
> + * qemu_get_cm_event_timeout() can fail without setting errno.
> + * Will go away later in this series.
> + */
> perror("rdma_get_cm_event after rdma_connect");
> ERROR(errp, "connecting to destination!");
> goto err_rdma_source_connect;
