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I'm trying to use xmlstarlet sel to list the disk partitions I need to create from an xml file (example : https://github.com/finley/SystemImager/blob/initrd-from-imageserver-and-dont-package-initrd/doc/examples/disk-layout-complex.xml)
Right now I'm doing the following:

local IFS=;
xmlstarlet sel -t -m "config/disk[@dev="${DISK_DEV}"]/part" -v "concat(@num,';',@size,';',@p_type,';',@id,';',@p_name,';',@flags,';',@lvm_group,';',@raid_dev)" -n ${DISKS_LAYOUT_FILE} | sed '/^s*$/d' |
while read P_NUM P_SIZE P_TYPE P_ID P_NAME P_FLAGS P_LVM_GROUP P_RAID_DEV
do # process partitions creation.

The problem is for variable size partition (use 100% ("*" in the file)). If one is listed before some other, there is no room left when it's time to process the last ones. Thus it is not possible to put a primary swap partition at the end of a diwk with a / of variable size.

Is there a clever way to use xmlstarlet sel to list partitions in the following order:

list all primary and extended partition in same order as written in the xml file until a partition with size "*" is seen;

keep this variable size partition in mind;

then list from the end in reverse order the other partitions;

and finally print the variable size partition;

Repeat operation with logical partitions if any.

For all partition, add a field stating if it was listed in order or reverse order so I can know if I have to create partition relative to beginning of free space or relating to end of free space. (variable partition would be tagged as normal order as they would be created starting at beginning of free space)

If more than one "*" sized partition is encountered in a loop; fail with error would be cool.

For the listed example (link above), this would list partitions to create in the following order (and without the header below):

LIST_FLAG P_NUM P_SIZE P_TYPE P_ID P_NAME P_FLAGS P_LVM_GROUP P_RAID_DEV
normal;1;500;primary;;;boot;;
normal;3;4096;primary;;;;;;
reverse;2;1024;primary;;;swap;;
normal;4;*;extended;;;;;;
normal;7;4096;logical;;;;;;
reverse;6;2048;logical;;;;;;
normal;5;*;logical;;;;;;

I'm processing this within a specially crafted initrd, so I only have access to most common utils like sed/grep/bash2/xmlstarlet/awk. no perl, no python, no language that needs libraries in general.

I'm pretty convinced that there is a solution that does most of the job if not all, but I'm far not enough skilled to even evaluate if it can be done this way. I think I can achieve that in pure bash, but this will be far less elegant.