confd: add deterministic hostname management via /etc/hostname.d/

Resolve race condition between DHCP and configured hostname by introducing
priority-based hostname management using /etc/hostname.d/ directory pattern.

Priority order (highest wins):
  90-dhcp-<iface>  - DHCP assigned hostname
  50-configured    - YANG /system/hostname config
  10-default       - Bootstrap/factory default

The new /usr/libexec/infix/hostname helper reads all sources and applies the
highest priority hostname.  It exits early if hostname unchanged, preventing
unnecessary service restarts.

Fixes #1112

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

board/common/rootfs/usr/libexec/infix/hostname

@@ -0,0 +1,74 @@
+#!/bin/sh
+# Deterministically set system hostname from /etc/hostname.d/
+#
+# Highest numbered file wins (lexicographic sort, 90-dhcp > 50-configured > 10-default)
+#
+# Priority scheme:
+#   10-default       - Bootstrap/factory default (%h-%m format)
+#   50-configured    - From confd /system/hostname
+#   90-dhcp-<iface>  - From DHCP clietn on interface (highest priority)
+
+HOSTNAME_D="/etc/hostname.d"
+
+# Ensure directory exists
+mkdir -p "$HOSTNAME_D"
+
+# Find the highest priority file (reverse sort, take first)
+hostname_file=$(ls -1 "$HOSTNAME_D" 2>/dev/null | sort -r | head -1)
+
+if [ -z "$hostname_file" ]; then
+    logger -it confd "No hostname sources found in $HOSTNAME_D"
+    exit 1
+fi
+
+# Read hostname from the file (first line only, strip whitespace)
+new_hostname=$(cat "$HOSTNAME_D/$hostname_file" | head -1 | tr -d '\n\r\t ')
+if [ -z "$new_hostname" ]; then
+    logger -it confd "Empty hostname in $hostname_file"
+    exit 1
+fi
+
+if [ ${#new_hostname} -gt 64 ]; then
+    logger -it confd "Hostname too long (${#new_hostname} > 64) in $hostname_file"
+    exit 1
+fi
+
+# Check if hostname has actually changed
+current_hostname=$(hostname)
+if [ "$new_hostname" = "$current_hostname" ]; then
+    # No change needed, exit silently
+    exit 0
+fi
+
+# Set the hostname
+logger -it confd "Setting hostname to '$new_hostname' from $hostname_file"
+hostname "$new_hostname"
+
+# Update /etc/hostname (for persistence across reboots)
+echo "$new_hostname" > /etc/hostname
+
+# Update /etc/hosts (127.0.1.1 entry for proper name resolution)
+if grep -q "^127\.0\.1\.1" /etc/hosts; then
+    sed -i -E "s/^(127\.0\.1\.1\s+).*/\1$new_hostname/" /etc/hosts
+else
+    # Add entry if it doesn't exist
+    echo "127.0.1.1	$new_hostname" >> /etc/hosts
+fi
+
+# Notify services of hostname change, skip while in bootstrap
+initctl -nbq touch sysklogd
+if ! runlevel >/dev/null 2>&1; then
+    exit 0
+fi
+
+initctl -bq status lldpd && lldpcli configure system hostname "$new_hostname" 2>/dev/null
+initctl -bq status mdns  && avahi-set-host-name "$new_hostname" 2>/dev/null
+initctl -bq touch netbrowse 2>/dev/null
+
+# If called from dhcp script we need to reload to activate new name in syslogd
+# Otherwise we're called from confd, which does the reload when all is done.
+if [ -n "$1" ]; then
+    initctl -b reload
+fi
+
+exit 0

board/common/rootfs/usr/libexec/infix/init.d/05-hostname

@@ -0,0 +1,18 @@
+#!/bin/sh
+# Initialize default hostname for hostname.d pattern
+# This runs very early in boot to set up the default hostname entry
+
+HOSTNAME_D="/etc/hostname.d"
+
+# Ensure directory exists
+mkdir -p "$HOSTNAME_D"
+
+# If no default exists yet, create it from /etc/hostname (from squashfs)
+if [ ! -f "$HOSTNAME_D/10-default" ] && [ -f /etc/hostname ]; then
+    cp /etc/hostname "$HOSTNAME_D/10-default"
+fi
+
+# Apply hostname using the deterministic helper
+if [ -x /usr/libexec/infix/hostname ]; then
+    /usr/libexec/infix/hostname
+fi

board/common/rootfs/usr/share/udhcpc/default.script

@@ -108,6 +108,10 @@ case "$ACTION" in
 	# drop info from this interface
 	rm -f "$RESOLV_CONF"
 	rm -f "$NTPFILE"
+	if [ -f "/etc/hostname.d/90-dhcp-${interface}" ]; then
+	    rm -f "/etc/hostname.d/90-dhcp-${interface}"
+	    /usr/libexec/infix/hostname dhcp
+	fi
 	if [ -x /usr/sbin/avahi-autoipd ]; then
 	    /usr/sbin/avahi-autoipd -c $interface && /usr/sbin/avahi-autoipd -k $interface
 	fi
@@ -135,9 +139,10 @@ case "$ACTION" in
 
 	# set hostname if given
 	if [ -n "$hostname" ]; then
-	    log "setting new hostname: $hostname"
-	    hostname "$hostname"
-	    sed -i -E "s/^(127\.0\.1\.1\s+).*/\1$hostname/" /etc/hosts
+	    log "received DHCP hostname: $hostname"
+	    mkdir -p /etc/hostname.d
+	    echo "$hostname" > "/etc/hostname.d/90-dhcp-${interface}"
+	    /usr/libexec/infix/hostname dhcp
 	fi
 
 	# drop info from this interface

src/confd/src/ietf-system.c

@@ -206,11 +206,6 @@ done:
 	return rc;
 }
 
-static int sys_reload_services(void)
-{
-	return systemf("initctl -nbq touch sysklogd");
-}
-
 
 #define TIMEZONE_CONF "/etc/timezone"
 #define TIMEZONE_PREV TIMEZONE_CONF "-"
@@ -1558,11 +1553,10 @@ int hostnamefmt(struct confd *confd, const char *fmt, char *hostnm, size_t hostl
 
 static int change_hostname(sr_session_ctx_t *session, struct lyd_node *config, struct lyd_node *diff, sr_event_t event, struct confd *confd)
 {
-	const char *hostip = "127.0.1.1";
 	char  hostnm[65], domain[65];
-	char buf[256], *fmt;
-	FILE *nfp, *fp;
-	int err, fd;
+	int   rc = SR_ERR_OK;
+	char *fmt;
+	FILE *fp;
 
 	if (event != SR_EV_DONE || !lydx_get_xpathf(diff, XPATH_HOSTNAME_))
 		return SR_ERR_OK;
@@ -1572,82 +1566,36 @@ static int change_hostname(sr_session_ctx_t *session, struct lyd_node *config, s
 		fmt = strdup(nm);
 
 	if (hostnamefmt(confd, fmt, hostnm, sizeof(hostnm), domain, sizeof(domain))) {
-		err = SR_ERR_SYS;
-		goto err;
+		rc = SR_ERR_SYS;
+		goto failed;
 	}
 
-	err = sethostname(hostnm, strlen(hostnm));
-	if (err) {
-		ERROR("failed setting hostname");
-		err = SR_ERR_SYS;
-		goto err;
-	}
+	/* Use hostname.d for deterministic hostname management */
+	systemf("mkdir -p /etc/hostname.d");
 
+	fp = fopen("/etc/hostname.d/50-configured", "w");
+	if (!fp)
+		goto failed;
+
+	fprintf(fp, "%s\n", hostnm);
+	fclose(fp);
+
+	/* Handle domain name if present */
 	if (domain[0] && setdomainname(domain, strlen(domain))) {
 		ERROR("failed setting domain name");
 		/* Not cause for failing this function */
 	}
 
-	fp = fopen(_PATH_HOSTNAME, "w");
-	if (!fp) {
-		err = SR_ERR_INTERNAL;
-		goto err;
+	if (systemf("/usr/libexec/infix/hostname")) {
+	failed:
+		ERROR("failed setting hostname");
+		rc = SR_ERR_SYS;
 	}
 
-	fprintf(fp, "%s\n", hostnm);
-	fclose(fp);
-
-	nfp = fopen(_PATH_HOSTS "+", "w");
-	if (!nfp) {
-		err = SR_ERR_INTERNAL;
-		goto err;
-	}
-	fd = fileno(nfp);
-	if (fd == -1 || fchown(fd, 0, 0) || fchmod(fd, 0644)) {
-		fclose(nfp);
-		goto err;
-	}
-
-	fp = fopen(_PATH_HOSTS, "r");
-	if (!fp) {
-		err = SR_ERR_INTERNAL;
-		fclose(nfp);
-		goto err;
-	}
-
-	while (fgets(buf, sizeof(buf), fp)) {
-		if (!strncmp(buf, hostip, strlen(hostip))) {
-			if (domain[0])
-				snprintf(buf, sizeof(buf), "%s\t%s.%s %s\n", hostip, hostnm, domain, hostnm);
-			else
-				snprintf(buf, sizeof(buf), "%s\t%s\n", hostip, hostnm);
-		}
-		fputs(buf, nfp);
-	}
-
-	fclose(fp);
-	fclose(nfp);
-	if (rename(_PATH_HOSTS "+", _PATH_HOSTS))
-		ERRNO("Failed activating changes to "_PATH_HOSTS);
-
-	/* skip in bootstrap, lldpd and avahi have not started yet */
-	if (systemf("runlevel >/dev/null 2>&1"))
-		goto err;
-
-	/* Inform any running lldpd and avahi of the change ... */
-	systemf("initctl -bq status lldpd && lldpcli configure system hostname %s", hostnm);
-	systemf("initctl -bq status mdns  && avahi-set-host-name %s", hostnm);
-	systemf("initctl -bq touch netbrowse");
-err:
 	if (fmt)
 		free(fmt);
-
-	if (err) {
-		ERROR("Failed activating changes.");
-		return err;
-	}
-	if (sys_reload_services())
-		return SR_ERR_SYS;
+	if (rc)
+		return rc;
 
 	return SR_ERR_OK;
 }
@@ -1656,6 +1604,7 @@ err:
 int ietf_system_change(sr_session_ctx_t *session, struct lyd_node *config, struct lyd_node *diff, sr_event_t event, struct confd *confd)
 {
 	int rc = SR_ERR_OK;
+
 	if ((rc = change_auth(session, config, diff, event, confd)))
 		return rc;
 	if ((rc = change_ntp(session, config, diff, event, confd)))