askrene: make "child.c" to be the explicit child entry point.

The fork logic itself is pretty simple, so do that directly in
askrene.c, and then call into "run_child()" almost as soon as
we do the fork.

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

plugins/askrene/Makefile

@@ -1,10 +1,10 @@
 PLUGIN_ASKRENE_PARENT_SRC := \
 	plugins/askrene/askrene.c \
 	plugins/askrene/layer.c \
-	plugins/askrene/reserve.c \
+	plugins/askrene/reserve.c
 
 PLUGIN_ASKRENE_CHILD_SRC := \
-	plugins/askrene/child/entry.c \
+	plugins/askrene/child/child.c \
 	plugins/askrene/child/mcf.c \
 	plugins/askrene/child/dijkstra.c \
 	plugins/askrene/child/flow.c \

plugins/askrene/askrene.c

@@ -8,6 +8,7 @@
  */
 #include "config.h"
 #include <ccan/array_size/array_size.h>
+#include <ccan/noerr/noerr.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/str/str.h>
 #include <common/clock_time.h>
@@ -24,7 +25,8 @@
 #include <math.h>
 #include <plugins/askrene/askrene.h>
 #include <plugins/askrene/child/additional_costs.h>
-#include <plugins/askrene/child/entry.h>
+#include <plugins/askrene/child/child.h>
+#include <plugins/askrene/child/child_log.h>
 #include <plugins/askrene/layer.h>
 #include <plugins/askrene/reserve.h>
 #include <sys/wait.h>
@@ -517,12 +519,11 @@ static struct command_result *do_getroutes(struct command *cmd,
 	struct askrene *askrene = get_askrene(cmd->plugin);
 	const char *err;
 	struct timemono deadline;
-	int child_fd, log_fd;
+	int replyfds[2], logfds[2];
 	struct router_child *child;
 	const struct layer **layers;
 	s8 *biases;
 	fp16_t *capacities;
-	int ecode;
 
 	/* update the gossmap */
 	if (gossmap_refresh(askrene->gossmap)) {
@@ -594,30 +595,55 @@ static struct command_result *do_getroutes(struct command *cmd,
 	child->start = time_mono();
 	deadline = timemono_add(child->start,
 				time_from_sec(askrene->route_seconds));
-	child_fd = fork_router_child(askrene->gossmap,
-				     layers,
-				     biases,
-				     info->additional_costs,
-				     askrene->reserved,
-				     take(capacities),
-				     info->dev_algo == ALGO_SINGLE_PATH,
-				     deadline, srcnode, dstnode, info->amount,
-				     info->maxfee, info->finalcltv, info->maxdelay,
-				     info->maxparts, cmd->id, cmd->filter, &log_fd, &child->pid);
-	/* Save this, as remove_localmods won't preserve it. */
-	ecode = errno;
-	/* We don't need this any more. */
-	gossmap_remove_localmods(askrene->gossmap, localmods);
 
-	if (child_fd == -1) {
-		err = tal_fmt(tmpctx, "failed to fork: %s", strerror(ecode));
-		gossmap_remove_localmods(askrene->gossmap, localmods);
+	if (pipe(replyfds) != 0) {
+		err = tal_fmt(tmpctx, "failed to create pipes: %s", strerror(errno));
+		goto fail_broken;
+	}
+	if (pipe(logfds) != 0) {
+		err = tal_fmt(tmpctx, "failed to create pipes: %s", strerror(errno));
+		close_noerr(replyfds[0]);
+		close_noerr(replyfds[1]);
+		goto fail_broken;
+	}
+	child->pid = fork();
+	if (child->pid < 0) {
+		err = tal_fmt(tmpctx, "failed to fork: %s", strerror(errno));
+		close_noerr(replyfds[0]);
+		close_noerr(replyfds[1]);
+		close_noerr(logfds[0]);
+		close_noerr(logfds[1]);
 		goto fail_broken;
 	}
 
-	child->reply_conn = io_new_conn(child, child_fd,
+	if (child->pid == 0) {
+		/* We are the child.  Run the algo */
+		close(logfds[0]);
+		close(replyfds[0]);
+		set_child_log_fd(logfds[1]);
+
+		/* Does not return! */
+		run_child(askrene->gossmap,
+			  layers,
+			  biases,
+			  info->additional_costs,
+			  askrene->reserved,
+			  take(capacities),
+			  info->dev_algo == ALGO_SINGLE_PATH,
+			  deadline, srcnode, dstnode, info->amount,
+			  info->maxfee, info->finalcltv, info->maxdelay,
+			  info->maxparts, cmd->id, cmd->filter, replyfds[1]);
+		abort();
+	}
+
+	close(logfds[1]);
+	close(replyfds[1]);
+
+	/* We don't need this any more. */
+	gossmap_remove_localmods(askrene->gossmap, localmods);
+	child->reply_conn = io_new_conn(child, replyfds[0],
 					child_reply_init, child);
-	child->log_conn = io_new_conn(child, log_fd, child_log_init, child);
+	child->log_conn = io_new_conn(child, logfds[0], child_log_init, child);
 	child->cmd = cmd;
 
 	list_add_tail(&askrene->children, &child->list);

plugins/askrene/child/entry.c plugins/askrene/child/child.cplugins/askrene/child/entry.c renamed to plugins/askrene/child/child.c

@@ -1,18 +1,16 @@
 #include "config.h"
 #include <assert.h>
 #include <ccan/json_out/json_out.h>
-#include <ccan/noerr/noerr.h>
 #include <ccan/read_write_all/read_write_all.h>
 #include <ccan/tal/str/str.h>
 #include <common/json_stream.h>
 #include <common/route.h>
 #include <common/utils.h>
+#include <plugins/askrene/child/child.h>
 #include <plugins/askrene/child/child_log.h>
-#include <plugins/askrene/child/entry.h>
 #include <plugins/askrene/child/flow.h>
 #include <plugins/askrene/child/mcf.h>
 #include <plugins/askrene/child/route_query.h>
-#include <unistd.h>
 
 /* A single route. */
 struct route {
@@ -152,25 +150,22 @@ static struct route_query *new_route_query(const tal_t *ctx,
 	return rq;
 }
 
-/* Returns fd to child */
-int fork_router_child(const struct gossmap *gossmap,
-		      const struct layer **layers,
-		      const s8 *biases,
-		      const struct additional_cost_htable *additional_costs,
-		      struct reserve_htable *reserved,
-		      fp16_t *capacities TAKES,
-		      bool single_path,
-		      struct timemono deadline,
-		      const struct gossmap_node *srcnode,
-		      const struct gossmap_node *dstnode,
-		      struct amount_msat amount, struct amount_msat maxfee,
-		      u32 finalcltv, u32 maxdelay, size_t maxparts,
-		      const char *cmd_id,
-		      struct json_filter *cmd_filter,
-		      int *log_fd,
-		      int *child_pid)
+void run_child(const struct gossmap *gossmap,
+	       const struct layer **layers,
+	       const s8 *biases,
+	       const struct additional_cost_htable *additional_costs,
+	       struct reserve_htable *reserved,
+	       fp16_t *capacities TAKES,
+	       bool single_path,
+	       struct timemono deadline,
+	       const struct gossmap_node *srcnode,
+	       const struct gossmap_node *dstnode,
+	       struct amount_msat amount, struct amount_msat maxfee,
+	       u32 finalcltv, u32 maxdelay, size_t maxparts,
+	       const char *cmd_id,
+	       struct json_filter *cmd_filter,
+	       int replyfd)
 {
-	int replyfds[2], logfds[2];
 	double probability;
 	struct flow **flows;
 	struct route **routes;
@@ -179,35 +174,6 @@ int fork_router_child(const struct gossmap *gossmap,
 	size_t len;
 	struct route_query *rq;
 
-	if (pipe(replyfds) != 0)
-		goto parent_fail;
-	if (pipe(logfds) != 0) {
-		close_noerr(replyfds[0]);
-		close_noerr(replyfds[1]);
-		goto parent_fail;
-	}
-	*child_pid = fork();
-	if (*child_pid < 0) {
-		close_noerr(replyfds[0]);
-		close_noerr(replyfds[1]);
-		close_noerr(logfds[0]);
-		close_noerr(logfds[1]);
-		goto parent_fail;
-	}
-	if (*child_pid != 0) {
-		close(logfds[1]);
-		close(replyfds[1]);
-		*log_fd = logfds[0];
-		if (taken(capacities))
-			tal_free(capacities);
-		return replyfds[0];
-	}
-
-	/* We are the child.  Run the algo */
-	close(logfds[0]);
-	close(replyfds[0]);
-	set_child_log_fd(logfds[1]);
-
 	/* We exit below, so we don't bother freeing this */
 	rq = new_route_query(NULL, gossmap, cmd_id, layers,
 			     biases, additional_costs,
@@ -222,7 +188,7 @@ int fork_router_child(const struct gossmap *gossmap,
 				     maxparts, &flows, &probability);
 	}
 	if (err) {
-		write_all(replyfds[1], err, strlen(err));
+		write_all(replyfd, err, strlen(err));
 		/* Non-zero exit tells parent this is an error string. */
 		exit(1);
 	}
@@ -261,13 +227,8 @@ int fork_router_child(const struct gossmap *gossmap,
 	json_stream_close(js, NULL);
 
 	p = json_out_contents(js->jout, &len);
-	if (!write_all(replyfds[1], p, len))
+	if (!write_all(replyfd, p, len))
 		abort();
 	exit(0);
-
-parent_fail:
-	if (taken(capacities))
-		tal_free(capacities);
-	return -1;
 }
 

plugins/askrene/child/child.h

@@ -0,0 +1,35 @@
+#ifndef LIGHTNING_PLUGINS_ASKRENE_CHILD_CHILD_H
+#define LIGHTNING_PLUGINS_ASKRENE_CHILD_CHILD_H
+#include "config.h"
+#include <ccan/compiler/compiler.h>
+#include <ccan/short_types/short_types.h>
+#include <ccan/time/time.h>
+#include <common/amount.h>
+#include <common/fp16.h>
+#include <stdbool.h>
+
+struct additional_cost_htable;
+struct gossmap;
+struct json_filter;
+struct layer;
+struct reserve_htable;
+
+/* This is the child.  Do the thing. */
+void run_child(const struct gossmap *gossmap,
+	       const struct layer **layers,
+	       const s8 *biases,
+	       const struct additional_cost_htable *additional_costs,
+	       struct reserve_htable *reserved,
+	       fp16_t *capacities TAKES,
+	       bool single_path,
+	       struct timemono deadline,
+	       const struct gossmap_node *srcnode,
+	       const struct gossmap_node *dstnode,
+	       struct amount_msat amount, struct amount_msat maxfee,
+	       u32 finalcltv, u32 maxdelay, size_t maxparts,
+	       const char *cmd_id,
+	       struct json_filter *cmd_filter,
+	       int reply_fd) NORETURN;
+
+#endif /* LIGHTNING_PLUGINS_ASKRENE_CHILD_CHILD_H */
+