RE: [RFC PATCH] mempool: Fix some Coverity defects

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Monday, 9 June 2025 17.26
> 
> On Mon,  9 Jun 2025 14:42:26 +0000
> Morten Brørup <mb@smartsharesystems.com> wrote:
> 
> > @@ -141,8 +141,13 @@ rte_mem_page_size(void)
> >  {
> >  	static size_t page_size;
> >
> > -	if (!page_size)
> > +	if (page_size == 0) {
> > +		errno = 0; /* man sysconf(3) */
> >  		page_size = sysconf(_SC_PAGESIZE);
> > +		if ((ssize_t)page_size < 0)
> > +			rte_panic("sysconf(_SC_PAGESIZE) failed: %s",
> > +					errno == 0 ? "Indeterminate" :
> strerror(errno));
> > +	}
> 
> Why not make page_size a ssize_t or long?
> The return value of sysconf is long.

I guess it's a matter of preference...
This function returns size_t, i.e. an unsigned type. So I kept page_size (the cached return value) the same type, and put the type cast in the unlikely code path.
The alternative, changing page_size to a signed type (ssize_t or long), would require casting to an unsigned type in the return statement.

> Not sure if setting errno to zero is required, sysconf only touchs it if
> return value is negative.

The Linux man sysconf(3) page recommends setting errno to zero before calling sysconf(), so errno can be used to discriminate between actual errors and an indeterminate value when sysconf() returns -1.
Hence the "man sysconf(3)" comment.
BSD sysconf(3) behaves the same way, but the BSD man page is less explicit about setting errno to zero.