From 9f233f555f80d1c416656c04ab81d19edc738f07 Mon Sep 17 00:00:00 2001
From: Daniel Golle <daniel@makrotopia.org>
Date: Fri, 13 Aug 2021 02:23:03 +0100
Subject: [PATCH] system: make rootfs type accessible through board call

Knowing the type of the root filesystem can be useful, e.g. for the
attended sysupgrade clients.
As the previously introduced 'initramfs' flag is covered the the new
'rootfs_type' being 'initramfs', remove the old flag which should have
any users yet.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 system.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 72 insertions(+), 3 deletions(-)

diff --git a/system.c b/system.c
index 83aea42..bd3f76c 100644
--- a/system.c
+++ b/system.c
@@ -44,6 +44,74 @@ enum vjson_state {
 	VJSON_SUCCESS,
 };
 
+static const char *system_rootfs_type(void) {
+	const char proc_mounts[] = "/proc/self/mounts";
+	static char fstype[16] = { 0 };
+	char *mountstr = NULL, *mp = "/", *pos, *tmp;
+	FILE *mounts;
+	ssize_t nread;
+	size_t len = 0;
+	bool found;
+
+	if (initramfs)
+		return "initramfs";
+
+	if (fstype[0])
+		return fstype;
+
+	mounts = fopen(proc_mounts, "r");
+	while ((nread = getline(&mountstr, &len, mounts)) != -1) {
+		found = false;
+
+		pos = strchr(mountstr, ' ');
+		if (!pos)
+			continue;
+
+		tmp = pos + 1;
+		pos = strchr(tmp, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		if (strcmp(tmp, mp))
+			continue;
+
+		tmp = pos + 1;
+		pos = strchr(tmp, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+
+		if (!strcmp(tmp, "overlay")) {
+			/*
+			 * there is no point in parsing overlay option string for
+			 * lowerdir, as that can point to "/" being a previous
+			 * overlay mount (after firstboot or sysuprade config
+			 * restore). Hence just assume the lowerdir is "/rom" and
+			 * restart searching for that instead.
+			 */
+			mp = "/rom";
+			fseek(mounts, 0, SEEK_SET);
+			continue;
+		}
+
+		found = true;
+		break;
+	}
+
+	if (found)
+		strncpy(fstype, tmp, sizeof(fstype));
+
+	free(mountstr);
+	fclose(mounts);
+
+	if (found)
+		return fstype;
+	else
+		return NULL;
+}
+
 static int system_board(struct ubus_context *ctx, struct ubus_object *obj,
                  struct ubus_request_data *req, const char *method,
                  struct blob_attr *msg)
@@ -51,14 +119,12 @@ static int system_board(struct ubus_context *ctx, struct ubus_object *obj,
 	void *c;
 	char line[256];
 	char *key, *val, *next;
+	const char *rootfs_type = system_rootfs_type();
 	struct utsname utsname;
 	FILE *f;
 
 	blob_buf_init(&b, 0);
 
-	if (initramfs)
-		blobmsg_add_u8(&b, "initramfs", 1);
-
 	if (uname(&utsname) >= 0)
 	{
 		blobmsg_add_string(&b, "kernel", utsname.release);
@@ -169,6 +235,9 @@ static int system_board(struct ubus_context *ctx, struct ubus_object *obj,
 		fclose(f);
 	}
 
+	if (rootfs_type)
+		blobmsg_add_string(&b, "rootfs_type", rootfs_type);
+
 	if ((f = fopen("/etc/openwrt_release", "r")) != NULL)
 	{
 		c = blobmsg_open_table(&b, "release");
-- 
2.30.2