Re: max symlink = 5? ?bug? ?feature deficit?

[Linda Walsh <lkml@tlinx.org>]

Al Viro wrote:
> On Sun, Feb 12, 2006 at 02:54:33PM -0800, Linda Walsh wrote:
>   
>> Al Viro wrote:
>>     
>>> Care to RTFS? I mean, really - at least to the point of seeing what's
>>> involved in that recursion.
>>>  
>>>       
>> Hmmm...that's where I got the original parameter numbers, but
>> I see it's not so straightforward.  I tried a limit of
>> 40, but I quickly get an OS hang when trying to reference a
>> 13th link.  Twelve works at the limit, but would take more testing
>> to find out the bottleneck.
>>     
>
> Sigh...  12 works at the limit on your particular config, filesystems
> being used and syscall being issued (hint: amount of stuff on stack
> before we enter mutual recursion varies; so does the amount of stuff
> on stack we get from function that are not part of mutual recursion,
> but are called from the damn thing).
>   
---
    Yeah, I sorta figured that.  Is there any easier way to
remove the recursion?  I dunno about you, but I was always taught
that recursion, while elegant, was not always the most efficient in
terms of time and space requirements and one could get similar
functionality using iteration and a stack.

    The GNU libraries _seem_ to indicate a max of 20 links supported
there.  Googling around, I see I'm not the first person to be surprised
by the low limit.  I don't recall running into such a limit on any
other Unixes, though I'm sure they had some limit.

    It can be useful for creating a shadow file-system where only
root needs to point to a "target source", and the "symlink" overlay
lies over the top of any real, underlying file.

    Why can't things just be easy sometimes...:-/
Linda