setup-disk fails when installing over identical previous installation

Hello,

while instaling in "sys" mode, setup-disk fails to install on top of an identical previous installation in most cases, the behaviour produces this output:

[...]
WARNING: Erase the above disk(s) and continue? (y/n) [n] y
Partition #1 contains a ext4 signature.
Partition #2 contains a swap signature.
Partition #3 contains a ext4 signature.
Creating file systems...
The file /dev/sda1 does not exist and no size was specified.
The file /dev/sda3 does not exist and no size was specified.
mount: mounting /dev/sda3 on /mnt failed: No such file or directory

Sometimes either /dev/sda1 or /dev/sda3 are recognized, rarely both, meaning that this operation fails the overwhelming majority of times.

Solution

As I had previously seen funky behaviour with sfdisk when creating partitions on top of existing identical partitions, I remembered that the following consistently worked:

1. Create new disklabel
2. Create partitions (and optionally wipe signatures)

Doing both in one command as it is currently being done in line 848 of the script does not work reliably.

I suggest first running this to create the label:

echo "label: $DISKLABEL" | sfdisk --quiet $diskdev

Then modifying line 850 to look like this:

) sfdisk --quiet $diskdev

Even better would be this, to also wipe the previous signatures, otherwise you need to confirm overwriting the previous signatures again with the mkfs.$whatever commands:

) sfdisk --quiet -w always -W always $diskdev

Perhaps this is also needed in other places, I am not sure. I will submit a patch fixing this particular instance, please let me know if you have feedback!