Re: Check return value of pclose() correctly

On 01.11.22 06:52, Tom Lane wrote:
> I think there are two issues here. POSIX says
>
> Upon successful return, pclose() shall return the termination status
> of the command language interpreter. Otherwise, pclose() shall return
> -1 and set errno to indicate the error.
>
> That is, first you need to make sure that pclose returned a valid
> child process status, and then you need to decode that status.
> It's not obvious to me that -1 is disjoint from the set of possible
> child statuses. Do we need to add some logic that clears and then
> checks errno?

This return convention is also used by system() and is widely used. So
I don't think we need to be concerned about this.

In practice, int is 4 bytes and WEXITSTATUS() and WTERMSIG() are one
byte each, so they are probably in the lower bytes, and wouldn't
accidentally make up a -1.

> Also, we have a number of places --- at least FreeDesc() and
> ClosePipeStream() --- that consider pclose()'s return value to be
> perfectly equivalent to that of close() etc, because they'll
> return either one without telling the caller which is which.
> It seems like we have to fix that if we want to issue sane
> error reports.

I think this works. FreeDesc() returns the pclose() exit status to
ClosePipeStream(), which returns it directly. No interpretation is done
within these functions.