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From Oliver Deakin <oliver.dea...@googlemail.com>
Subject Re: [jira] Created: (HARMONY-6238) [classlib][luni] File path limit set to 1K chars for all file systems
Date Fri, 19 Jun 2009 09:15:00 GMT

Tim Ellison wrote:
> Regis wrote:
>   
>> Tim Ellison wrote:
>>     
>>> Oliver Deakin wrote:
>>>       
>>>> I've had a quick look around for the "right" way to do this, and it
>>>> seems there are 2 options:
>>>> 1) Determine the max path length from a system macro, probably PATH_MAX
>>>> in limits.h.
>>>> 2) Use the unix system call pathconf() to get the max path length.
>>>>
>>>> I think using a build time constant, as in 1, is preferable, however
>>>> this macro is not defined on all platforms. On zOS, for example, only
>>>> _POSIX_PATH_MAX is defined, and that is set to a paltry 256 (which is
>>>> not the real max path length - pathconf() tells me it is 1024).
>>>>
>>>> Perhaps to start with we can include /usr/include/linux/limits.h and use
>>>> PATH_MAX for linux platforms (I'm assuming that file exists for linux
>>>> distros in general here - perhaps someone can clarify this?) and on
>>>> non-linux platforms fall back to a default of 1024. We can add other
>>>> platforms in as we find the correct includes/macro definitions for them.
>>>>         
>>>> From the Harmony code I was looking at, the max path length is used to
>>>>         
>>> allocate char buffers so we can do path manipulations before passing
>>> through to OS calls.  We fail early if the path is greater than the
>>> expected max path length.
>>>
>>> Would could, as you say try to set the max path length based on the OS
>>> we are using, but even that is going to be a guess since who knows where
>>> the file path points (e.g. network drives etc.)?
>>>
>>> I wonder if we can be a bit lazier and set the Harmony max path length
>>> to a large number for the path manipulations, then let the OS call fail
>>> if the path is too long?
>>>       
>> agree
>>
>>     
>>> (caveat: I've not looked at all uses of the HyMaxPath const to see if
>>> that is a good idea or not)
>>>
>>> Regards,
>>> Tim
>>>
>>>       
>> I guess we have max path length because we used char array as buffer.
>> It's not efficient and a kind of waste memory if the buffer size was the
>> same as OS limit (on Windows it's 32,767 characters).
>>
>> So I wonder if we can set a threshold value, like 1024, if path length
>> is smaller than the value, we allocate char array as buffer, just like
>> we have done; otherwise dynamic malloc memory as buffer, and then let OS
>> tell us if the path is too long?
>>     
>
> Sounds good to me.
>
>   

And to me - I didn't realise it was being used to allocate a buffer. 
This sounds like a good solution to me.

Regards,
Oliver

> Tim
>
>
>   

-- 
Oliver Deakin
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