I had trouble using an ext4 extroot overlay on my Zyxel NBG6817 running
18.06.2, so I took a closer look at the way libfstools and its block
tool setup the extroot overlay during PREINIT and found some things
broke extroot mounting on certain devices.
The issue and logs are documented in the following ticket:
https://bugs.openwrt.org/index.php?do=details&task_id=2231
What I found was that the main_extroot code would only look for
"rootfs_data" partitions on MTD storage (specifically only JFFS2 and
UBIFS partitions), before defaulting to calling mount_extroot with no
configuration path prefix.
mount_extroot would then try to load the fstab uci config at
/etc/config/fstab, which would fail as this isn't present on the normal
r/o squashfs eMMC partition.
With a /etc/config/fstab uci config be pre-placed on the squashfs,
mount_extroot would continue after loading it and successfully finding
an /overlay extroot entry, but fail during check_extroot when no MTD
partition or UBIFS volume can be found.
With the attached patch the behaviour of main_extroot and check_extroot
is expanded to allow detection of rootfs overlays on block devices such
as eMMC, without compromising the behavior for JFFS2 and UBIFS rootfs
discovery:
1. The default mount_extroot call now uses '/tmp/overlay' as a default
parameter should no MTD partition be detected. This results in
config_load attempting to load a uci fstab with this
prefix before defaulting to /etc/config/fstab.
2. UBIFS_EXTROOT now acts as a supplementary option instead of an
exclusionary one and will allow rootfs discovery on block devices even
when it fails to find UBIFS rootfs volumes.
(IMHO the best design decision as this option defaults to 'y' in the
fstools package configuration)
>From 9daabc73ed804fe969e0318dfe533794d6da73b6 Mon Sep 17 00:00:00 2001
From: Ken Miller <k...@miller.ec>
Date: Tue, 9 Apr 2019 01:03:26 +0200
Subject: [PATCH] block: make extroot mount preparation more robust
The extroot mount preparation code for r/w rootfs overlay discovery, and
determining the user-defined /etc/config/fstab location within, would only
discover overlays residing on JFFS2 or UBIFS MTD storage.
This led to attempts at loading the uci fstab configuration without the required
/tmp/overlay directory prefix on devices with a non-MTD r/w rootfs overlay, and
thus failure to find any custom fstab /overlay extroot entries on PREINIT.
(example: the default openwrt eMMC partition layout on the zyxel nbg6817)
Futher, with UBIFS_EXTROOT enabled (fstools package default), and no MTD rootfs
partitions present, check_extroot would not attempt rootfs discovery on block
devices, such as the ext4 mmcblk rootfs overlay on the nbg6817.
With this patch:
1) main_extroot now attempts to load uci fstab configuration from an already
mounted overlay, before defaulting to the prefix-less uci config dir when
no MTD rootfs partitions are detected.
2) check_extroot now also attempts to find rootfs partitions on block devices
when no MTD rootfs partitions are detected.
---
block.c | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)
diff --git a/block.c b/block.c
index 39212d2..3dfc4a5 100644
--- a/block.c
+++ b/block.c
@@ -1301,7 +1301,7 @@ static int find_block_ubi_RO(libubi_t libubi, char *name, char *part, int plen)
return err;
}
-#else
+#endif
static int find_root_dev(char *buf, int len)
{
@@ -1332,8 +1332,6 @@ static int find_root_dev(char *buf, int len)
return -1;
}
-#endif
-
static int test_fs_support(const char *name)
{
char line[128], *p;
@@ -1363,25 +1361,20 @@ static int check_extroot(char *path)
struct probe_info *pr = NULL;
char devpath[32];
-#ifdef UBIFS_EXTROOT
if (find_block_mtd("\"rootfs\"", devpath, sizeof(devpath))) {
int err = -1;
+#ifdef UBIFS_EXTROOT
libubi_t libubi;
libubi = libubi_open();
err = find_block_ubi_RO(libubi, "rootfs", devpath, sizeof(devpath));
libubi_close(libubi);
- if (err)
- return -1;
- }
-#else
- if (find_block_mtd("\"rootfs\"", devpath, sizeof(devpath))) {
- if (find_root_dev(devpath, sizeof(devpath))) {
+#endif
+ if (err && find_root_dev(devpath, sizeof(devpath))) {
ULOG_ERR("extroot: unable to determine root device\n");
return -1;
}
}
-#endif
list_for_each_entry(pr, &devices, list) {
if (!strcmp(pr->dev, devpath)) {
@@ -1585,7 +1578,7 @@ static int main_extroot(int argc, char **argv)
}
#endif
- return mount_extroot(NULL);
+ return mount_extroot("/tmp/overlay");
}
static int main_mount(int argc, char **argv)
--
2.21.0
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