From d7895d5c9c02ac3b6eb652e309fa5dc45f5b680d Mon Sep 17 00:00:00 2001
From: Joachim Wiberg <troglobit@gmail.com>
Date: Mon, 16 Dec 2024 01:17:29 +0100
Subject: [PATCH] confd: handle dup calls to dagger_add_dep()

Some callbacks may run twice, e.g., lag_gen_ports().  Check if the link
already exists, and is the same, then we can exit silently.  However, in
case the link exists and does *not* point to the same target, we log an
error with current target for the post mortem.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
---
 src/confd/src/dagger.c | 28 +++++++++++++++++++++++++---
 src/confd/src/dagger.h |  2 +-
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/confd/src/dagger.c b/src/confd/src/dagger.c
index 9dfd3e28..a8aea6f5 100644
--- a/src/confd/src/dagger.c
+++ b/src/confd/src/dagger.c
@@ -87,10 +87,32 @@ FILE *dagger_fopen_net_exit(struct dagger *d, const char *node, enum netdag_exit
 	return dagger_fopen_current(d, "exit", node, order, script);
 }
 
-int dagger_add_dep(struct dagger *d, const char *depender, const char *dependee)
+int dagger_add_dep(const struct dagger *d, const char *depender, const char *dependee)
 {
-	return systemf("ln -s ../%s %s/%d/dag/%s", dependee,
-		       d->path, d->next, depender);
+	char link[strlen(d->path) + strlen(depender) + strlen(dependee) + 16];
+	char target[strlen(dependee) + 16];
+	char path[strlen(dependee) + 16];
+	ssize_t len;
+
+	/*
+	 * Some callbacks may run twice, double check symlink, if it
+	 * exists already and points to the same target, we're OK.
+	 */
+	snprintf(target, sizeof(target), "../%s", dependee);
+	snprintf(link, sizeof(link), "%s/%d/dag/%s/%s", d->path, d->next, depender, dependee);
+
+	len = readlink(link, path, sizeof(path));
+	if (len > 0) {
+		path[len] = 0;
+		if (strcmp(target, path)) {
+			ERROR("Dagger dependency already exists %s -> %s", target, path);
+			return errno = EEXIST;
+		}
+
+		return 0;	/* same, ignore */
+	}
+
+	return symlink(target, link);
 }
 
 int dagger_add_node(struct dagger *d, const char *node)
diff --git a/src/confd/src/dagger.h b/src/confd/src/dagger.h
index d98469b1..959aa8d6 100644
--- a/src/confd/src/dagger.h
+++ b/src/confd/src/dagger.h
@@ -21,7 +21,7 @@ FILE *dagger_fopen_next(struct dagger *d, const char *action, const char *node,
 FILE *dagger_fopen_current(struct dagger *d, const char *action, const char *node,
 			   unsigned char prio, const char *script);
 
-int dagger_add_dep(struct dagger *d, const char *depender, const char *dependee);
+int dagger_add_dep(const struct dagger *d, const char *depender, const char *dependee);
 int dagger_add_node(struct dagger *d, const char *node);
 int dagger_abandon(struct dagger *d);
 int dagger_evolve(struct dagger *d);