Discussion
`grub-probe` queries device info so GRUB can use upon booting your computer.
It starts with the normal OS-specific init, (mostly) zeroing out certain values, & parsing commandline flags. Then it considers setting $debug to "all", validates the `--device` flag, inits/finalizes various GRUB subsystems, determines which delimiter to use, invokes the core logic in one of 2 ways, possibly outputs a newline, & cleans up.
As for that core logic...
1/2?
`-t device` iterates over all devices & outputs them separated by the chosen delimiter skipping the rest of the core logic.
`-t disk` iterates over all devices retrieving its disk info if any & outputs it skipping the rest.
`-t drive` iterates over the gathered array of harddrives outputting each separated by the chosen delimiter skipping the rest.
`-t zero_check` iterates over those harddrives opening each to retrieve, iterate over, & read their sectors looking for non-zero values.
3/4?
`-t fs`, `-t fs_uuid`, or `-t fs_label` opens the 1st device probing it for filesystems, & outputs the appropriate property or result from the one of the filesystem's methods.
`-t hints_string` retrieves the BIOS disk & "ofpath" concatenates into something that looks like a command, guesses the BIOS drive & appends into the command, does so for the EFI or baremetal drives, does so for the BIOS disk compatability hint, & adds a newline or space.
4/5?
`-t compatibility_hint`, `-t bios_hints`, `-t ieee1275_hints`, `-t baremetal_hints`, `-t efi_hints`, or `-t arc_hints` given the host-disk ID prints the full disk name.
Otherwise `-t compatibility_hint` attempts to defer to one GRUB routine to get output falling back to another. With the rest of those doing something somewhat similar.
A recursive helper handles `-t abstraction` deferring to a few GRUB routines. `-t cryptodisk_uuid`'s recursive helper defers to `grub_util_cryptodisk_get_uuid`.
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The core logic fills in a default filepath & validates device names are given, branching depending on the commandline flags, iterates over the given devices to pull info on it & counting the number of devices, allocates an array & iterates again to populate that array, branches over that commandline flag some more, iterates over harddrives, & cleans up. For each harddrive it opens the device with logging, & branches over that commandline flag some more.
2/4?