Re: PING: fix ARG_MAX

[Eric Blake <ebb9 at byu dot net>]

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According to Corinna Vinschen on 9/12/2005 9:22 AM:
>>Even with your recent patches to make cygwin programs receive longer command
>>lines, whether or not they are not mounted cygexec, ARG_MAX should still reflect
>>the worst case limit so that programs (like xargs) that use ARG_MAX will work
>>reliably even when invoking non-cygwin programs that are really bound by the 32k
>>limit.
> 
> 
> I had a short talk with Chris and we both agree that it doesn't make
> overly sense to go down to the lowest limit just to accomodate
> non-Cygwin applications.  Users of those apps can easily use xargs -s
> so why penalize Cygwin apps?

Well, for now, xargs in findutils-4.2.25-2 is already hardcoded to 32k
max; attempting to use -s to get a larger value will fail, because of the
POSIX rules placed on xargs.  If, on the other hand, cygwin added
pathconf(_PC_ARG_MAX) as a legal extension to POSIX, then xargs could use
its preferred 128k default when calling cygwin apps, while using 32k for
windows apps without even requiring users to supply -s; not to mention the
fact that -s could then be used to obtain larger command lines than even
the default 128k for cygwin apps.  With that extension in place,
sysconf(_SC_ARG_MAX) at 32k is not much of a limit for applications that
know about cygwin's extension.

Also, the argument brought up on the findutils mailing list was that
beyond a certain size, the cost of processing each argument starts to
outweigh the benefits of forking fewer tasks, to the point that the
difference between a 32k ARG_MAX vs. a 1M ARG_MAX falls in the noise when
the same amount of data is divided by xargs to as few runs as possible, so
a 32k limit is not really penalizing cygwin apps.

But since I have not provided a patch for pathconf(_PC_ARG_MAX), and I do
not have copyright assignment, I will be understanding if 1.5.19 is
released with _SC_ARG_MAX still broken in the corner cases.  Just be aware
that xargs will remain at its hardcoded 32k limit unless it can find a way
to query cygwin whether a particular executable can be given a larger limit.

- --
Life is short - so eat dessert first!

Eric Blake             ebb9@byu.net
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