Re: [PATCH] expand-on-first-boot: wait for udev to create symlink

["Roberto A. Foglietta" <roberto.foglietta@gmail.com>]

On Thu, 8 Dec 2022 at 18:39, Henning Schild <henning.schild@siemens.com> wrote:
>
> Am Thu, 8 Dec 2022 17:55:42 +0100
> schrieb "T. Schaffner" <tobias.schaffner@siemens.com>:
>
> > From: Tobias Schaffner <tobias.schaffner@siemens.com>
> >
> > systemd-growfs depends on a symlink to the partition of the filesystem
> > that should be resized. This symlink is created by udev in
> > /dev/block/.
> >

reading that patch I had a flash-back about two patches I did recently
for another project

https://github.com/robang74/tinycore-editor/commit/d57271e3229551ddfbd3deba1363d2efe2914908
https://github.com/robang74/tinycore-editor/commit/4ff435bb8a73c7e956ea4f9303a36fe06a136e54

both altered this file

https://github.com/robang74/tinycore-editor/blob/main/tinycore/changes/rcS

the main problem and the final result was much the same: trigger udev
and wait for the dev link.

# Start Udev to populate /dev and handle hotplug events
/sbin/udevd --daemon 2>&1 >/dev/null
/sbin/udevadm trigger --action=add 2>&1 >/dev/null
/sbin/udevadm settle --timeout=5
echo -ne "\e[1;37m"
for i in $(seq 1 10); do
    if gettcdev; then
    break;
fi >/dev/null
echo -n .
sleep 1
done
echo -e "\e[0m"
/sbin/udevadm control --exit --timeout=5

in my case, the booting device is not meaningful because the rootfs is a file.

function gettcdev() {
    blkid --label $tclabel
}

So, the search for the USB stick device is done s by label

>
> > /dev/block/ as +# systemd-growfs depends on it
> > +while ! readlink /dev/block/* | grep -q "${LAST_PART_NAME}"; do
>
> I would make that much stricter to not be tricked by partial matches
>
> sda4 vs sda42

Irrelevant, if sda42 has been found then sda4 exists as well
considering the problem is not yet started.
However, for sake of precision and to avoid corner cases in which
sda42 is created before sda4 a dollar at the end of regex will solve
this issue.

+while ! readlink /dev/block/* | grep -qe "${LAST_PART_NAME}$"; do

>
> readlink -f /dev/block/* | grep -e -q "^${LAST_PART}$"
>
> > +    sleep 0.1
>
> I wonder if there is anything we could do here. Maybe "udevadm trigger"
> and depend on udev after all. Because the 5 is a nasty guess ...

This is the reason because I cited my patches. I hope they will help you.

Best regards, R-