Knob to turn off _POSIX_NO_TRUNC

[Bruce Evans]

On Tue, 5 Apr 2011, Kostik Belousov wrote:

> On Tue, Apr 05, 2011 at 01:16:32PM -0400, John Baldwin wrote:
>> Personally, I find this a bit hackish. You could always "fix" the 3rd
>> party software by using LD_PRELOAD() to implement a wrapper around
>> open() that trimmed the name if open() fails with ENAMETOOLONG.

Or install it on one of the file systems that has {_PC_NO_TRUNC} = 0
(might need a chroot, and the following fix).

> Ok, I am taking the patch aside then. Please note that the change
> as is allowed any vfs syscall taking the path, to proceed. Also,
> the arbitrary path element, not only the last one, was handled.
> But this is only a question of amount of code in the preloaded
> library.

There is one thing that can be changed without incrementing the bug
count: make {_PC_NO_TRUNC} = 0 actually work.  Currently, this fails
for pathnames larger than NAME_MAX, since vfs doesn't know what
either {NAME_MAX} or {_PC_NO_TRUNC} are and always assumes the global
values.

Bruce