feat: explicit symlink indicator

[lczyk]

a quick braindump / feature proposal. here is what we end up often doing in chisel-releases:

slices:
  bins:
    contents:
      /usr/sbin/ip6tables-nft-restore:  # Symlink to xtables-legacy-multi
      /usr/sbin/ip6tables-nft-save:  # Symlink to xtables-legacy-multi
      /usr/sbin/ip6tables-restore-translate:  # Symlink to xtables-legacy-multi
      ...

this is to make it easier to maintainers to unserstand which files ought to go together and how they relate to one another.

we could create the symlinks explicitly:

slices:
  bins:
    contents:
      /usr/sbin/ip6tables-nft-restore:
        symlink: xtables-legacy-multi
      /usr/sbin/ip6tables-nft-save:
        symlink: xtables-legacy-multi
      /usr/sbin/ip6tables-restore-translate:
        symlink: xtables-legacy-multi
      ...

but them we're not actually checking that that file really is a symlink. we're just making one. the problem is with release-to-release maintenance:

1. the underlying file e.g. /usr/sbin/ip6tables-nft-restore could be removed, and we would still be creating a symlink
2. the symlink target in the deb could change, and we would overwrite it
3. the file could change from symlink to binary and we would not catch it.

---

the very rough idea would be something like:

slices:
  bins:
    contents:
      /usr/sbin/ip6tables-nft-restore:
        expect-symlink: xtables-legacy-multi

which is a way of saying: "include this file. i expect it to be a symlink to $0. error otherwise"

i'm not strongly attached to the idea, but just thought i'd drop it here as a food-for-thought. :)

[upils]

@lczyk would you mind clarify the problem you are proposing to solve? From the issue I currently understand that what you propose would be harder to maintain without a clear advantage so I suppose I miss something.

Also, maybe I am wrong but I suspect in the first piece of YAML you wanted to show the links slice:

  links:
    contents:
      [...]
      /usr/sbin/ip6tables: {symlink: /usr/sbin/ip6tables-nft}
      /usr/sbin/ip6tables-restore: {symlink: /usr/sbin/ip6tables-nft-restore}
      /usr/sbin/ip6tables-save: {symlink: /usr/sbin/ip6tables-nft-save}
      /usr/sbin/iptables: {symlink: /usr/sbin/iptables-nft}
      /usr/sbin/iptables-restore: {symlink: /usr/sbin/iptables-nft-restore}
      /usr/sbin/iptables-save: {symlink: /usr/sbin/iptables-nft-save}

Is that right or am I missing something?

[lczyk]

I suspect in the first piece of YAML you wanted to show the links slice:

nope. i meant to write what i wrote.

these files are already symlinks in the deb. i'm proposing a way of validating that the symlinks in the deb are indeed what they claim to be.

this is a very low priority idea and maybe somewhat subtle tbh. let's just commit 1/2 hour to it in person next sprint 👍 :)