svn commit: r279932 - head/sys/vm

[John Baldwin]

On Thursday, March 12, 2015 05:24:51 PM Ian Lepore wrote:
> On Thu, 2015-03-12 at 17:02 -0400, Ryan Stone wrote:
> > On Thu, Mar 12, 2015 at 2:06 PM, Ian Lepore <ian at freebsd.org> wrote:
> > 
> > >   Nullterminate strings returned via sysctl.
> > >
> > >   PR:           195668
> > >
> > 
> > To quote the manpage:
> > 
> > > The *sbuf* family of functions allows one to safely
> > > allocate, construct and release bounded null-terminated
> > > strings in kernel space.
> > 
> > IMO the sbuf API is broken if we have to explicitly null-terminate the
> > string ourselves.
> 
> If we want the nullterm to be counted in the length of data in the
> buffer (and thus get transmitted back across the syscall boundary) we
> need to put an explicit counted nullterm byte into the buffer.
> 
> I had started down the path of making that (counting the nullterm byte
> as part of the data in the buffer) a feature of sbuf that you could set
> with a flag, but then whoever added sbuf_new_for_sysctl() didn't
> propagate the flags field through the new function and I decided to not
> go off into the weeds making a new flavor of that takes flags.

One suggestion would be to consider using '\0' for a nul character instead of
a bare 0.  To me that communicates the intention more clearly to the reader.
(One of the things I did not like about C++ < C++11 was the use of 0 for
NULL.  I much prefer nullptr and NULL in C over bare 0's for pointers for
similar clarity reasons.)

-- 
John Baldwin