Re: [PATCH] apply: Avoid ambiguous pointer provenance for CHERI/Arm's Morello

["René Scharfe" <l.s.r@web.de>]

Am 07.01.22 um 20:40 schrieb Junio C Hamano:
> René Scharfe <l.s.r@web.de> writes:
>
>>> I actually wonder if it results in code that is much easier to
>>> follow if we did:
>>>
>>>  * Introduce an "enum apply_symlink_treatment" that has
>>>    APPLY_SYMLINK_GOES_AWAY and APPLY_SYMLINK_IN_RESULT as its
>>>    possible values;
>>>
>>>  * Make register_symlink_changes() and check_symlink_changes()
>>>    work with "enum apply_symlink_treatment";
>>>
>>>  * (optional) stop using string_list() to store the symlink_changes;
>>>    use strintmap and use strintmap_set() and strintmap_get() to
>>>    access its entries, so that the ugly implementation detail
>>>    (i.e. "the container type we use only has a (void *) field to
>>>    store caller-supplied data, so we cast an integer and a pointer
>>>    back and forth") can be safely hidden.
>>>
>> Or strsets -- we only need two.
>
> True.
>
> When we check a path, we make a single look-up of two bit in a
> single hashtable but now we need two look-ups, but addition, removal
> and renaming of a symlink would be rare enough to matter either way.

Hmm, symlinks changes are rare, but this only affects the register phase
(which should be noticeably slow for the string_list based code with its
O(n*log(n)) lookup per registered symlink if there were a lot of them).
But the final lookups are done for each path _component_, of any file
type.

I suspect that two lookups in (sparsely populated) hash tables are still
fast enough.  (At least I couldn't measure any difference with git apply
and a patch between v2.33.0 and v2.34.0.)

René