Re: [PATCH v2 5/5] flow: Introduce flow_epoll_set() to centralize epoll operations

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jan 08, 2026 at 03:01:19PM +0100, Laurent Vivier wrote:
> Currently, each flow type (TCP, TCP_SPLICE, PING, UDP) has its own
> code to add or modify file descriptors in epoll. This leads to
> duplicated boilerplate code across icmp.c, tcp.c, tcp_splice.c, and
> udp_flow.c, each setting up epoll_ref unions and calling epoll_ctl()
> with flow-type-specific details.
> 
> Introduce flow_epoll_set() in flow.c to handle epoll operations for
> all flow types in a unified way. The function takes an explicit epoll
> type parameter, allowing it to handle not only flow socket types but
> also the TCP timer (EPOLL_TYPE_TCP_TIMER).
> 
> This will be needed to migrate queue pair from an epollfd to another.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

I'm not totally convinced if folding in TCP timers with the socket fds
makes sense.  I think there's still room for improving consistency of
the epoll lifecycle (removing the in_epoll flag equivalent).  But both
of those can be looked at later.  So,

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  flow.c       | 33 ++++++++++++++++++++
>  flow.h       |  3 ++
>  icmp.c       | 11 +++----
>  tcp.c        | 64 ++++++++++++++++++++------------------
>  tcp_splice.c | 86 +++++++++++++++++++++++++---------------------------
>  udp_flow.c   | 12 +++-----
>  6 files changed, 119 insertions(+), 90 deletions(-)
> 
> diff --git a/flow.c b/flow.c
> index 4f53486586cd..73d24f9d3765 100644
> --- a/flow.c
> +++ b/flow.c
> @@ -20,6 +20,7 @@
>  #include "flow.h"
>  #include "flow_table.h"
>  #include "repair.h"
> +#include "epoll_ctl.h"
>  
>  const char *flow_state_str[] = {
>  	[FLOW_STATE_FREE]	= "FREE",
> @@ -390,6 +391,38 @@ void flow_epollid_clear(struct flow_common *f)
>  	f->epollid = EPOLLFD_ID_INVALID;
>  }
>  
> +/**
> + * flow_epoll_set() - Add or modify epoll registration for a flow socket
> + * @command:	epoll_ctl() command: EPOLL_CTL_ADD or EPOLL_CTL_MOD
> + * @type:	epoll type
> + * @f:		Flow to register socket for
> + * @events:	epoll events to watch for
> + * @fd:		File descriptor to register
> + * @sidei:	Side index of the flow
> + *
> + * Return: 0 on success, -1 on error (from epoll_ctl())
> + */
> +int flow_epoll_set(int command, enum epoll_type type,
> +		   const struct flow_common *f, uint32_t events, int fd,
> +		   unsigned int sidei)
> +{
> +	struct epoll_event ev;
> +	union epoll_ref ref;
> +
> +	ref.type = type;
> +	ref.fd = fd;
> +
> +	if (type == EPOLL_TYPE_TCP_TIMER)
> +		ref.flow = flow_idx(f);
> +	else
> +		ref.flowside = flow_sidx(f, sidei);
> +
> +	ev.events = events;
> +	ev.data.u64 = ref.u64;
> +
> +	return epoll_ctl(flow_epollfd(f), command, fd, &ev);
> +}
> +
>  /**
>   * flow_epollid_register() - Initialize the epoll id -> fd mapping
>   * @epollid:	epoll id to associate to
> diff --git a/flow.h b/flow.h
> index b43b0b1dd7f2..bd5c6d90322b 100644
> --- a/flow.h
> +++ b/flow.h
> @@ -265,6 +265,9 @@ bool flow_in_epoll(const struct flow_common *f);
>  int flow_epollfd(const struct flow_common *f);
>  void flow_epollid_set(struct flow_common *f, int epollid);
>  void flow_epollid_clear(struct flow_common *f);
> +int flow_epoll_set(int command, enum epoll_type type,
> +		   const struct flow_common *f, uint32_t events, int fd,
> +		   unsigned int sidei);
>  void flow_epollid_register(int epollid, int epollfd);
>  void flow_defer_handler(const struct ctx *c, const struct timespec *now);
>  int flow_migrate_source_early(struct ctx *c, const struct migrate_stage *stage,
> diff --git a/icmp.c b/icmp.c
> index 9564c4963f7b..b6bb36d80715 100644
> --- a/icmp.c
> +++ b/icmp.c
> @@ -177,7 +177,6 @@ static struct icmp_ping_flow *icmp_ping_new(const struct ctx *c,
>  	union flow *flow = flow_alloc();
>  	struct icmp_ping_flow *pingf;
>  	const struct flowside *tgt;
> -	union epoll_ref ref;
>  
>  	if (!flow)
>  		return NULL;
> @@ -211,13 +210,11 @@ static struct icmp_ping_flow *icmp_ping_new(const struct ctx *c,
>  		goto cancel;
>  
>  	flow_epollid_set(&pingf->f, EPOLLFD_ID_DEFAULT);
> -
> -	ref.type = EPOLL_TYPE_PING;
> -	ref.flowside = FLOW_SIDX(flow, TGTSIDE);
> -	ref.fd = pingf->sock;
> -
> -	if (epoll_add(flow_epollfd(&pingf->f), EPOLLIN, ref) < 0) {
> +	if (flow_epoll_set(EPOLL_CTL_ADD, EPOLL_TYPE_PING, &pingf->f,
> +			   EPOLLIN, pingf->sock,
> +			   TGTSIDE) < 0) {
>  		close(pingf->sock);
> +		flow_epollid_clear(&pingf->f);
>  		goto cancel;
>  	}
>  
> diff --git a/tcp.c b/tcp.c
> index 5141cdc7e839..d8cc11b377de 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -523,34 +523,44 @@ static uint32_t tcp_conn_epoll_events(uint8_t events, uint8_t conn_flags)
>  
>  /**
>   * tcp_epoll_ctl() - Add/modify/delete epoll state from connection events
> - * @c:		Execution context
>   * @conn:	Connection pointer
>   *
>   * Return: 0 on success, negative error code on failure (not on deletion)
>   */
> -static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
> +static int tcp_epoll_ctl(struct tcp_tap_conn *conn)
>  {
> -	int m = flow_in_epoll(&conn->f) ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
> -	union epoll_ref ref = { .type = EPOLL_TYPE_TCP, .fd = conn->sock,
> -		                .flowside = FLOW_SIDX(conn, !TAPSIDE(conn)), };
> -	struct epoll_event ev = { .data.u64 = ref.u64 };
> -	int epollfd = flow_in_epoll(&conn->f) ? flow_epollfd(&conn->f)
> -					      : c->epollfd;
> +	uint32_t events;
> +	int m;
>  
>  	if (conn->events == CLOSED) {
> -		if (flow_in_epoll(&conn->f))
> +		if (flow_in_epoll(&conn->f)) {
> +			int epollfd = flow_epollfd(&conn->f);
> +
>  			epoll_del(epollfd, conn->sock);
> -		if (conn->timer != -1)
> -			epoll_del(epollfd, conn->timer);
> +			if (conn->timer != -1)
> +				epoll_del(epollfd, conn->timer);
> +		}
> +
>  		return 0;
>  	}
>  
> -	ev.events = tcp_conn_epoll_events(conn->events, conn->flags);
> +	events = tcp_conn_epoll_events(conn->events, conn->flags);
>  
> -	if (epoll_ctl(epollfd, m, conn->sock, &ev))
> -		return -errno;
> +	if (flow_in_epoll(&conn->f)) {
> +		m = EPOLL_CTL_MOD;
> +	} else {
> +		flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
> +		m = EPOLL_CTL_ADD;
> +	}
> +
> +	if (flow_epoll_set(m, EPOLL_TYPE_TCP, &conn->f, events, conn->sock,
> +			   !TAPSIDE(conn)) < 0) {
> +		int ret = -errno;
>  
> -	flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
> +		if (m == EPOLL_CTL_ADD)
> +			flow_epollid_clear(&conn->f);
> +		return ret;
> +	}
>  
>  	return 0;
>  }
> @@ -569,11 +579,6 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
>  		return;
>  
>  	if (conn->timer == -1) {
> -		union epoll_ref ref = { .type = EPOLL_TYPE_TCP_TIMER,
> -					.flow = FLOW_IDX(conn) };
> -		struct epoll_event ev = { .data.u64 = ref.u64,
> -					  .events = EPOLLIN | EPOLLET };
> -		int epollfd = flow_epollfd(&conn->f);
>  		int fd;
>  
>  		fd = timerfd_create(CLOCK_MONOTONIC, 0);
> @@ -581,18 +586,17 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
>  			flow_dbg_perror(conn, "failed to get timer");
>  			if (fd > -1)
>  				close(fd);
> -			conn->timer = -1;
>  			return;
>  		}
> -		conn->timer = fd;
> -		ref.fd = conn->timer;
>  
> -		if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn->timer, &ev)) {
> +		if (flow_epoll_set(EPOLL_CTL_ADD, EPOLL_TYPE_TCP_TIMER,
> +				   &conn->f, EPOLLIN | EPOLLET, fd, 0) < 0) {
>  			flow_dbg_perror(conn, "failed to add timer");
> -			close(conn->timer);
> -			conn->timer = -1;
> +			close(fd);
>  			return;
>  		}
> +
> +		conn->timer = fd;
>  	}
>  
>  	if (conn->flags & ACK_TO_TAP_DUE) {
> @@ -669,7 +673,7 @@ void conn_flag_do(const struct ctx *c, struct tcp_tap_conn *conn,
>  	}
>  
>  	if (flag == STALLED || flag == ~STALLED)
> -		tcp_epoll_ctl(c, conn);
> +		tcp_epoll_ctl(conn);
>  
>  	if (flag == ACK_FROM_TAP_DUE || flag == ACK_TO_TAP_DUE		  ||
>  	    (flag == ~ACK_FROM_TAP_DUE && (conn->flags & ACK_TO_TAP_DUE)) ||
> @@ -726,7 +730,7 @@ void conn_event_do(const struct ctx *c, struct tcp_tap_conn *conn,
>  	} else {
>  		if (event == CLOSED)
>  			flow_hash_remove(c, TAP_SIDX(conn));
> -		tcp_epoll_ctl(c, conn);
> +		tcp_epoll_ctl(conn);
>  	}
>  
>  	if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED))
> @@ -1742,7 +1746,7 @@ static void tcp_conn_from_tap(const struct ctx *c, sa_family_t af,
>  		conn_event(c, conn, TAP_SYN_ACK_SENT);
>  	}
>  
> -	tcp_epoll_ctl(c, conn);
> +	tcp_epoll_ctl(conn);
>  
>  	if (c->mode == MODE_VU) { /* To rebind to same oport after migration */
>  		socklen_t sl = sizeof(sa);
> @@ -3984,7 +3988,7 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
>  	tcp_send_flag(c, conn, ACK);
>  	tcp_data_from_sock(c, conn);
>  
> -	if ((rc = tcp_epoll_ctl(c, conn))) {
> +	if ((rc = tcp_epoll_ctl(conn))) {
>  		flow_dbg(conn,
>  			 "Failed to subscribe to epoll for migrated socket: %s",
>  			 strerror_(-rc));
> diff --git a/tcp_splice.c b/tcp_splice.c
> index bf4ff466de07..26e9845c39ee 100644
> --- a/tcp_splice.c
> +++ b/tcp_splice.c
> @@ -135,37 +135,35 @@ static uint32_t tcp_splice_conn_epoll_events(uint16_t events, unsigned sidei)
>  
>  /**
>   * tcp_splice_epoll_ctl() - Add/modify/delete epoll state from connection events
> - * @c:		Execution context
>   * @conn:	Connection pointer
>   *
>   * Return: 0 on success, negative error code on failure (not on deletion)
>   */
> -static int tcp_splice_epoll_ctl(const struct ctx *c,
> -				struct tcp_splice_conn *conn)
> +static int tcp_splice_epoll_ctl(struct tcp_splice_conn *conn)
>  {
> -	int epollfd = flow_in_epoll(&conn->f) ? flow_epollfd(&conn->f)
> -					      : c->epollfd;
> -	int m = flow_in_epoll(&conn->f) ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
> -	const union epoll_ref ref[SIDES] = {
> -		{ .type = EPOLL_TYPE_TCP_SPLICE, .fd = conn->s[0],
> -		  .flowside = FLOW_SIDX(conn, 0) },
> -		{ .type = EPOLL_TYPE_TCP_SPLICE, .fd = conn->s[1],
> -		  .flowside = FLOW_SIDX(conn, 1) }
> -	};
> -	struct epoll_event ev[SIDES] = { { .data.u64 = ref[0].u64 },
> -					 { .data.u64 = ref[1].u64 } };
> -
> -	ev[0].events = tcp_splice_conn_epoll_events(conn->events, 0);
> -	ev[1].events = tcp_splice_conn_epoll_events(conn->events, 1);
> -
> -
> -	if (epoll_ctl(epollfd, m, conn->s[0], &ev[0]) ||
> -	    epoll_ctl(epollfd, m, conn->s[1], &ev[1])) {
> +	uint32_t events[2];
> +	int m;
> +
> +	if (flow_in_epoll(&conn->f)) {
> +		m = EPOLL_CTL_MOD;
> +	} else {
> +		flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
> +		m = EPOLL_CTL_ADD;
> +	}
> +
> +	events[0] = tcp_splice_conn_epoll_events(conn->events, 0);
> +	events[1] = tcp_splice_conn_epoll_events(conn->events, 1);
> +
> +	if (flow_epoll_set(m, EPOLL_TYPE_TCP_SPLICE, &conn->f, events[0],
> +			   conn->s[0], 0) ||
> +	    flow_epoll_set(m, EPOLL_TYPE_TCP_SPLICE, &conn->f, events[1],
> +			   conn->s[1], 1)) {
>  		int ret = -errno;
>  		flow_perror(conn, "ERROR on epoll_ctl()");
> +		if (m == EPOLL_CTL_ADD)
> +			flow_epollid_clear(&conn->f);
>  		return ret;
>  	}
> -	flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT);
>  
>  	return 0;
>  }
> @@ -205,7 +203,7 @@ static void conn_flag_do(struct tcp_splice_conn *conn,
>  	}
>  }
>  
> -#define conn_flag(c, conn, flag)					\
> +#define conn_flag(conn, flag)					\
>  	do {								\
>  		flow_trace(conn, "flag at %s:%i", __func__, __LINE__);	\
>  		conn_flag_do(conn, flag);				\
> @@ -213,12 +211,10 @@ static void conn_flag_do(struct tcp_splice_conn *conn,
>  
>  /**
>   * conn_event_do() - Set and log connection events, update epoll state
> - * @c:		Execution context
>   * @conn:	Connection pointer
>   * @event:	Connection event
>   */
> -static void conn_event_do(const struct ctx *c, struct tcp_splice_conn *conn,
> -			  unsigned long event)
> +static void conn_event_do(struct tcp_splice_conn *conn, unsigned long event)
>  {
>  	if (event & (event - 1)) {
>  		int flag_index = fls(~event);
> @@ -240,14 +236,14 @@ static void conn_event_do(const struct ctx *c, struct tcp_splice_conn *conn,
>  			flow_dbg(conn, "%s", tcp_splice_event_str[flag_index]);
>  	}
>  
> -	if (tcp_splice_epoll_ctl(c, conn))
> -		conn_flag(c, conn, CLOSING);
> +	if (tcp_splice_epoll_ctl(conn))
> +		conn_flag(conn, CLOSING);
>  }
>  
> -#define conn_event(c, conn, event)					\
> +#define conn_event(conn, event)					\
>  	do {								\
>  		flow_trace(conn, "event at %s:%i",__func__, __LINE__);	\
> -		conn_event_do(c, conn, event);				\
> +		conn_event_do(conn, event);				\
>  	} while (0)
>  
>  
> @@ -315,7 +311,7 @@ static int tcp_splice_connect_finish(const struct ctx *c,
>  			if (pipe2(conn->pipe[sidei], O_NONBLOCK | O_CLOEXEC)) {
>  				flow_perror(conn, "cannot create %d->%d pipe",
>  					    sidei, !sidei);
> -				conn_flag(c, conn, CLOSING);
> +				conn_flag(conn, CLOSING);
>  				return -EIO;
>  			}
>  
> @@ -329,7 +325,7 @@ static int tcp_splice_connect_finish(const struct ctx *c,
>  	}
>  
>  	if (!(conn->events & SPLICE_ESTABLISHED))
> -		conn_event(c, conn, SPLICE_ESTABLISHED);
> +		conn_event(conn, SPLICE_ESTABLISHED);
>  
>  	return 0;
>  }
> @@ -376,7 +372,7 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn)
>  
>  	pif_sockaddr(c, &sa, tgtpif, &tgt->eaddr, tgt->eport);
>  
> -	conn_event(c, conn, SPLICE_CONNECT);
> +	conn_event(conn, SPLICE_CONNECT);
>  
>  	if (connect(conn->s[1], &sa.sa, socklen_inany(&sa))) {
>  		if (errno != EINPROGRESS) {
> @@ -385,7 +381,7 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn)
>  			return -errno;
>  		}
>  	} else {
> -		conn_event(c, conn, SPLICE_ESTABLISHED);
> +		conn_event(conn, SPLICE_ESTABLISHED);
>  		return tcp_splice_connect_finish(c, conn);
>  	}
>  
> @@ -445,7 +441,7 @@ void tcp_splice_conn_from_sock(const struct ctx *c, union flow *flow, int s0)
>  		flow_trace(conn, "failed to set TCP_QUICKACK on %i", s0);
>  
>  	if (tcp_splice_connect(c, conn))
> -		conn_flag(c, conn, CLOSING);
> +		conn_flag(conn, CLOSING);
>  
>  	FLOW_ACTIVATE(conn);
>  }
> @@ -494,14 +490,14 @@ void tcp_splice_sock_handler(struct ctx *c, union epoll_ref ref,
>  
>  	if (events & EPOLLOUT) {
>  		fromsidei = !evsidei;
> -		conn_event(c, conn, ~OUT_WAIT(evsidei));
> +		conn_event(conn, ~OUT_WAIT(evsidei));
>  	} else {
>  		fromsidei = evsidei;
>  	}
>  
>  	if (events & EPOLLRDHUP)
>  		/* For side 0 this is fake, but implied */
> -		conn_event(c, conn, FIN_RCVD(evsidei));
> +		conn_event(conn, FIN_RCVD(evsidei));
>  
>  swap:
>  	eof = 0;
> @@ -536,7 +532,7 @@ retry:
>  				more = SPLICE_F_MORE;
>  
>  			if (conn->flags & lowat_set_flag)
> -				conn_flag(c, conn, lowat_act_flag);
> +				conn_flag(conn, lowat_act_flag);
>  		}
>  
>  		do
> @@ -568,8 +564,8 @@ retry:
>  						   "Setting SO_RCVLOWAT %i: %s",
>  						   lowat, strerror_(errno));
>  				} else {
> -					conn_flag(c, conn, lowat_set_flag);
> -					conn_flag(c, conn, lowat_act_flag);
> +					conn_flag(conn, lowat_set_flag);
> +					conn_flag(conn, lowat_act_flag);
>  				}
>  			}
>  
> @@ -583,7 +579,7 @@ retry:
>  			if (conn->read[fromsidei] == conn->written[fromsidei])
>  				break;
>  
> -			conn_event(c, conn, OUT_WAIT(!fromsidei));
> +			conn_event(conn, OUT_WAIT(!fromsidei));
>  			break;
>  		}
>  
> @@ -605,7 +601,7 @@ retry:
>  			if ((conn->events & FIN_RCVD(sidei)) &&
>  			    !(conn->events & FIN_SENT(!sidei))) {
>  				shutdown(conn->s[!sidei], SHUT_WR);
> -				conn_event(c, conn, FIN_SENT(!sidei));
> +				conn_event(conn, FIN_SENT(!sidei));
>  			}
>  		}
>  	}
> @@ -626,7 +622,7 @@ retry:
>  	return;
>  
>  close:
> -	conn_flag(c, conn, CLOSING);
> +	conn_flag(conn, CLOSING);
>  }
>  
>  /**
> @@ -762,10 +758,10 @@ void tcp_splice_timer(struct tcp_splice_conn *conn)
>  				flow_trace(conn, "can't set SO_RCVLOWAT on %d",
>  					   conn->s[sidei]);
>  			}
> -			conn_flag(c, conn, ~RCVLOWAT_SET(sidei));
> +			conn_flag(conn, ~RCVLOWAT_SET(sidei));
>  		}
>  	}
>  
>  	flow_foreach_sidei(sidei)
> -		conn_flag(c, conn, ~RCVLOWAT_ACT(sidei));
> +		conn_flag(conn, ~RCVLOWAT_ACT(sidei));
>  }
> diff --git a/udp_flow.c b/udp_flow.c
> index c4cf35c2c89d..b016a8095ec6 100644
> --- a/udp_flow.c
> +++ b/udp_flow.c
> @@ -74,7 +74,6 @@ static int udp_flow_sock(const struct ctx *c,
>  {
>  	const struct flowside *side = &uflow->f.side[sidei];
>  	uint8_t pif = uflow->f.pif[sidei];
> -	union epoll_ref ref;
>  	int rc;
>  	int s;
>  
> @@ -84,14 +83,11 @@ static int udp_flow_sock(const struct ctx *c,
>  		return s;
>  	}
>  
> -	ref.type = EPOLL_TYPE_UDP;
> -	ref.flowside = FLOW_SIDX(uflow, sidei);
> -	ref.fd = s;
> -
>  	flow_epollid_set(&uflow->f, EPOLLFD_ID_DEFAULT);
> -
> -	rc = epoll_add(flow_epollfd(&uflow->f), EPOLLIN, ref);
> -	if (rc < 0) {
> +	if (flow_epoll_set(EPOLL_CTL_ADD, EPOLL_TYPE_UDP, &uflow->f,
> +			   EPOLLIN, s, sidei) < 0) {
> +		rc = -errno;
> +		flow_epollid_clear(&uflow->f);
>  		close(s);
>  		return rc;
>  	}
> -- 
> 2.52.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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