meta-phosphor: phosphor-mmc-init: Fix commandline parsing for root

From Joel in [1]:

```
It expects a command line string to be in the form:

console=ttyS4,115200n8 rootwait root=PARTLABEL=rofs-a

If booting with root=PARTLABEL=rofs-a at the start of the command line
string (instead of the end), the parsing gets confused:

[    8.241229] /dev/disk/by-partlabel/root=PARTLABEL=rofs-a: Can't open blockdev
mount: mounting /dev/disk/by-partlabel/root=PARTLABEL=rofs-a on /mnt/rofs failed: No such file or directory

Similarly if the partition is not set, it gets confused:

[    1.919816] Run /init as init process
Starting version 251.8+
[    8.219396] /dev/disk/by-partlabel/rootwait: Can't open blockdev
mount: mounting /dev/disk/by-partlabel/rootwait on /mnt/rofs failed: No such file or directory

We should fix get_root so that it checks for the existance of
root=PARTLABEL, and matches on it. We could fall back on rofs-a if it
can't be found?
```

Based on Joel's example I tested the new implementation as follows:

```
$ declare -f old_get_root
old_get_root ()
{
    local root="$@";
    root="${root##* root=PARTLABEL=}";
    root="${root%% *}";
    [ "${root}" != "" ] && echo "${root}"
}
$ declare -f new_get_root
new_get_root ()
{
    local cmdline="$@";
    root=;
    for opt in $cmdline;
    do
        case $opt in
            root=PARTLABEL=*)
                root=${opt##root=PARTLABEL=}
            ;;
            *)

            ;;
        esac;
    done;
    [ -n "$root" ] && echo $root
}
```

Comparing the two under various commandline orderings:

```
$ echo $working_cmdline
console=ttyS4,115200n8 rootwait root=PARTLABEL=rofs-a
$ old_get_root $working_cmdline
rofs-a
$ new_get_root $working_cmdline
rofs-a
$
```

```
$ echo $broken_cmdline
root=PARTLABEL=rofs-a console=ttyS4,115200n8 rootwait
$ old_get_root $broken_cmdline
root=PARTLABEL=rofs-a
$ new_get_root $broken_cmdline
rofs-a
$
```

```
$ echo $maybe_cmdline
console=ttyS4,115200n8 root=PARTLABEL=rofs-a rootwait
$ old_get_root $maybe_cmdline
rofs-a
$ new_get_root $maybe_cmdline
rofs-a
$
```

```
$ echo $dev_cmdline
console=ttyS4,115200n8 root=/dev/sda1 rootwait
$ old_get_root $dev_cmdline
console=ttyS4,115200n8
$ new_get_root $dev_cmdline
$
```

In each case new_get_root() gives the expected output.

[1]: https://github.com/openbmc/openbmc/issues/3898

Fixes: 0998d1e4fc58 ("initramfs: Add init script for eMMC")
Change-Id: I68e95d74dd33c54d956d08ae3332ba7bdec9aeeb
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>

1 files changed, 13 insertions, 4 deletions

diff --git a/meta-phosphor/recipes-phosphor/initrdscripts/phosphor-mmc-init/mmc-init.sh b/meta-phosphor/recipes-phosphor/initrdscripts/phosphor-mmc-init/mmc-init.sh
index ad9748e651..316bffce8a 100644
--- a/meta-phosphor/recipes-phosphor/initrdscripts/phosphor-mmc-init/mmc-init.sh
+++ b/meta-phosphor/recipes-phosphor/initrdscripts/phosphor-mmc-init/mmc-init.sh
@@ -2,10 +2,19 @@
 
 # Get the value of the root env variable found in /proc/cmdline
 get_root() {
-    local root="$(cat /proc/cmdline)"
-    root="${root##* root=PARTLABEL=}"
-    root="${root%% *}"
-    [ "${root}" != "" ] && echo "${root}"
+    local cmdline="$(cat /proc/cmdline)"
+    root=
+    for opt in $cmdline
+    do
+        case $opt in
+            root=PARTLABEL=*)
+                root=${opt##root=PARTLABEL=}
+                ;;
+            *)
+                ;;
+        esac
+    done
+    [ -n "$root" ] && echo $root
 }
 
 fslist="proc sys dev run"