[DTrace-devel] [PATCH v3] Add support for cleanpath() subroutine

[Eugene Loh]

On 1/24/24 16:04, Kris Van Hees wrote:

> On Thu, Dec 21, 2023 at 01:11:25PM -0500, eugene.loh at oracle.com wrote:
>> Replace all "//" with "/".
>> Replace all "/./" with "/".
>> Replace all "/foo/.." with "/".
>>
>> Notice that the results differ in some cases from what was
>> done in legacy DTrace:
> Some comments on this (after reviewing the documentation again):
>
>>      input string         current patch     legacy DTrace
>>
>>      "/."                 "/"               "/."
>>      "a/."                "a"               "a/."
>>      "./a"                "a"               "./a"
> These three seem correct to me in how the current patch handles it.
>
>>      "../.."              "../.."           "."
>>      "a/.."               "."               "a"
>>      "a/../.."            ".."              "a"
> A case could be made for all of them being "",

I do not see how "../.." and "" are equivalent.

> given that cleanpath() is
> supposed to remove redundant elements (. and ..)

".." by itself is not redundant, but the combination "/foo/.." can be 
collapsed.

> and no context is known
> for relative paths.  But I do agree that there is also a case to be made
> to not get rid of .. elements that would apply to the root of the relative
> path, becausae discarding them effectively causes information loss.
>
> Except for the case of "a/..".  That one should be "" because the .. should
> be considered redundant in view of having a present path element, and thus
> it is possible to back up one path element, which would yield "".  I do not
> see how the result of "." would be considered valid because that in itself
> is a redundant element (and thus should still be removed).

I guess I just don't know what standard or use case to consider. Anyhow, 
the documentation I saw speaks of removing "/./" without talking 
specifically about "." in isolation.  There are a lot of cases when 
someone would not consider "." and "" to be the same... e.g., "cd .", 
"pushd .", etc.  So "a/.." is the same as ".".  Are they also the same 
as ""?  It depends on the situation, and it's unclear to me where 
cleanpath() is used.  The documentation I saw (Oracle Linux DTrace 
Guide) didn't say anything was wrong with a bare ".".

>>      "a/../b"             "b"               "/b"
> I agree.
>
>> In the first set, legacy DTrace has unnecessary trailing "." or "/."
>> or unnecessary leading "./".  They would seem to be wrong.
>>
>> In the next cases, the legacy results are clearly wrong, not
>> handling ".." correctly.
>>
>> In the final case, a relative path is converted into an absolute
>> path, which is also clearly incorrect.