the coding style against bool is more of a keenel thing. On Mon, Jul 20, 2026, 10:33 Maxime Leroy <[email protected]> wrote:
> On Fri, Jul 17, 2026 at 2:34 PM Stephen Hemminger > <[email protected]> wrote: > > > > Don't use int as a boolean. Use bool. Ideally find unused pad hole for it > > Agreed int-as-a-boolean is not great. But bool in a structure is > discouraged by coding_style.rst: > > "Uses of bool in structures are not preferred as is wastes space and > it's also not clear as to what type size the bool is." (Ref: LKML) > > and that very LKML reference is Linus recommending the opposite of > bool for struct members: > > "please don't use bool in structures at all. [...] Use bool mainly as a > return type from functions [...]. [...] just make sure the base type is > unsigned [...] you can specify the base type as you wish [...] for > packing." > > The current tap PMD follows that too: the existing flags (persist, > flow_init, flow_isolate) are all int, and stdbool.h is not even > included in the headers. > > So for v2 I'll use uint8_t for intr_mode and intr_mode_set: fixed > 1-byte size, unambiguous representation, and it fits the existing > padding so neither struct grows (pmd_internals stays 144 bytes, > rx_queue stays 80). That matches both the guide and the referenced > LKML guidance. > > I can also add a third patch at the end of the series converting the > existing int flags (persist, flow_init, flow_isolate) to uint8_t, to > make the driver consistent > > > > > On Fri, Jul 17, 2026, 11:59 AM Maxime Leroy <[email protected]> wrote: > >> > >> The tap Rx path is driven by a SIGIO trigger: pmd_rx_burst() returns > >> without reading the queue fd unless tap_trigger, bumped by the O_ASYNC > >> signal handler, has advanced. That avoids a readv() on every empty poll. > >> > >> In Rx interrupt mode the application blocks on the queue fd through > epoll > >> and polls only after a wakeup. The epoll wakeup and the trigger are > >> distinct signals, so the burst can return 0 right after a wakeup because > >> the trigger has not advanced, leaving the fd readable with no further > >> edge: traffic stalls. > >> > >> When the port is configured for Rx interrupts, drain the fd > >> unconditionally in the burst and do not arm the SIGIO trigger on the > data > >> queue fd. A data queue fd can be closed and recreated on a later setup, > >> so the mode must stay constant to keep every fd on the same SIGIO > policy: > >> it is fixed at configure time and a later change is rejected. Close and > >> reopen the port to switch modes. > >> > >> Fixes: 4870a8cdd968 ("net/tap: support Rx interrupt") > >> Cc: [email protected] > >> > >> Signed-off-by: Maxime Leroy <[email protected]> > >> --- > >> drivers/net/tap/rte_eth_tap.c | 18 +++++++++++++++++- > >> drivers/net/tap/rte_eth_tap.h | 2 ++ > >> 2 files changed, 19 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/net/tap/rte_eth_tap.c > b/drivers/net/tap/rte_eth_tap.c > >> index 99ede19e49..ea9ef76335 100644 > >> --- a/drivers/net/tap/rte_eth_tap.c > >> +++ b/drivers/net/tap/rte_eth_tap.c > >> @@ -254,6 +254,10 @@ tun_alloc(struct pmd_internals *pmd, int > is_keepalive, int persistent) > >> goto error; > >> } > >> > >> + /* interrupt mode wakes through epoll on the data queue fd, not > the SIGIO trigger */ > >> + if (pmd->intr_mode) > >> + return fd; > >> + > >> /* Find a free realtime signal */ > >> for (signo = SIGRTMIN + 1; signo < SIGRTMAX; signo++) { > >> struct sigaction sa; > >> @@ -477,7 +481,7 @@ pmd_rx_burst(void *queue, struct rte_mbuf **bufs, > uint16_t nb_pkts) > >> unsigned long num_rx_bytes = 0; > >> uint32_t trigger = tap_trigger; > >> > >> - if (trigger == rxq->trigger_seen) > >> + if (!rxq->intr_mode && trigger == rxq->trigger_seen) > >> return 0; > >> > >> process_private = rte_eth_devices[rxq->in_port].process_private; > >> @@ -937,6 +941,16 @@ tap_dev_configure(struct rte_eth_dev *dev) > >> struct pmd_internals *pmd = dev->data->dev_private; > >> int intr_mode = !!dev->data->dev_conf.intr_conf.rxq; > >> > >> + /* The queue fd is created once and its SIGIO trigger is armed > for poll > >> + * mode only; the interrupt mode cannot be toggled on an > existing port. > >> + */ > >> + if (pmd->intr_mode_set && pmd->intr_mode != intr_mode) { > >> + TAP_LOG(ERR, > >> + "%s: Rx interrupt mode is fixed after > configure, close and reopen the port to change it", > >> + dev->device->name); > >> + return -ENOTSUP; > >> + } > >> + > >> if (dev->data->nb_rx_queues != dev->data->nb_tx_queues) { > >> TAP_LOG(ERR, > >> "%s: number of rx queues %d must be equal to > number of tx queues %d", > >> @@ -947,6 +961,7 @@ tap_dev_configure(struct rte_eth_dev *dev) > >> } > >> > >> pmd->intr_mode = intr_mode; > >> + pmd->intr_mode_set = 1; > >> > >> TAP_LOG(INFO, "%s: %s: TX configured queues number: %u", > >> dev->device->name, pmd->name, dev->data->nb_tx_queues); > >> @@ -1620,6 +1635,7 @@ tap_rx_queue_setup(struct rte_eth_dev *dev, > >> rxq->queue_id = rx_queue_id; > >> rxq->max_rx_segs = max_rx_segs; > >> rxq->rxmode = &dev->data->dev_conf.rxmode; > >> + rxq->intr_mode = internals->intr_mode; > >> > >> dev->data->rx_queues[rx_queue_id] = rxq; > >> int fd = tap_setup_queue(dev, rx_queue_id, 1); > >> diff --git a/drivers/net/tap/rte_eth_tap.h > b/drivers/net/tap/rte_eth_tap.h > >> index 3180719c34..abe22aac9f 100644 > >> --- a/drivers/net/tap/rte_eth_tap.h > >> +++ b/drivers/net/tap/rte_eth_tap.h > >> @@ -50,6 +50,7 @@ struct rx_queue { > >> uint16_t queue_id; /* queue ID*/ > >> struct queue_stats stats; /* Stats for this RX queue */ > >> uint16_t max_rx_segs; /* max scatter segments per > packet */ > >> + uint16_t intr_mode; /* 1 when Rx queue interrupts > are used */ > >> struct rte_eth_rxmode *rxmode; /* RX features */ > >> struct rte_mbuf *pool; /* mbufs pool for this queue */ > >> struct tun_pi pi; /* packet info for iovecs */ > >> @@ -94,6 +95,7 @@ struct pmd_internals { > >> > >> struct rte_intr_handle *intr_handle; /* LSC interrupt > handle. */ > >> int intr_mode; /* Rx queue interrupt mode */ > >> + int intr_mode_set; /* intr_mode locked after > configure */ > >> int ka_fd; /* keep-alive file descriptor > */ > >> struct rte_mempool *gso_ctx_mp; /* Mempool for GSO packets > */ > >> }; > >> -- > >> 2.43.0 > >> > > > -- > ------------------------------- > Maxime Leroy > [email protected] >
