kern/161481: mount fails with ENAMETOOLONG with path shorter than 255 // 1023 characters

[Bruce Evans]

On Tue, 11 Oct 2011, Garrett Cooper wrote:

> The following reply was made to PR kern/161481; it has been noted by GNATS.
>
> From: Garrett Cooper <yanegomi at gmail.com>
> To: FreeBSD-gnats-submit at freebsd.org
> Cc: Garrett Cooper <yanegomi at gmail.com>
> Subject: Re: kern/161481: mount fails with ENAMETOOLONG with path shorter
> than 255 // 1023 characters
> Date: Tue, 11 Oct 2011 00:57:44 -0700 (PDT)
>
> I looked into this more closely after I submitted the bug and the problem
> is the arbitrarily short value attached to MNAMELEN:
>
> 122537   mckusick #define       MNAMELEN        88              /* size of
> on/from name bufs */
>
> The value has changed over the years (all the way back to the mid-90s)
> from 90 to 70 to 80 to 88, but each time the author doesn't clearly state
> why the change was required.

It's part of the statfs(2) ABI.  Perhaps other ABIs.  It can only be
reduced (as a hack to free space for other purposes), except when the
ABI is changed.  The ABI was last changed when struct statfs was
expanded to hold 64-bit numbers even on 32-bit arches.  Then the name
fields were restored to approximately their original sizes.

Bruce