errno strageness (in lpr)

[Paul.Emsley@chem.gla.ac.uk]

       Hi, 

       Following Marcus' message[1], I thought I'd have a look at lpr.


dh_testdir
pmake CFLAGS="-O2" CPPFLAGS="-D_BSD_SOURCE"
all ===> lpc
all ===> lpd
cc   -o lpd lpd.o printjob.o recvjob.o displayq.o rmjob.o
      startdaemon.o lpdchar.o common.o key.o modes.o getcap.o 
printjob.o: In function `printjob':
printjob.o(.text+0xfc): the use of `mktemp' is dangerous, better use
      `mkstemp'
lpd.o: In function `main':
lpd.o(.text+0x16a): undefined reference to `__errno_location'
lpd.o(.text+0x5d1): undefined reference to `__errno_location'
lpd.o(.text+0x6ba): undefined reference to `__errno_location'
lpd.o: In function `reapchild':
lpd.o(.text+0x7e3): undefined reference to `__errno_location'
lpd.o(.text+0x80a): undefined reference to `__errno_location'
printjob.o(.text+0x1d6): more undefined references to
      `__errno_location' follow
printjob.o: In function `sendmail':
printjob.o(.text+0x284b): undefined reference to `_IO_getc'
printjob.o: In function `opennet':
printjob.o(.text+0x339d): undefined reference to `__errno_location'
printjob.o: In function `opentty':
printjob.o(.text+0x34ad): undefined reference to `__errno_location'
collect2: ld returned 1 exit status
*** Error code 1

Stop.
*** Error code 1

Stop.
make: *** [build-stamp] Error 1

Here[2] Roland says '"errno" is a macro and cannot be used as a normal
variable or member name.'
      
So lets for example look at reapchild in lpd.c

static void
reapchild(signo)
        int signo;
{
        int status;
        int save_errno = errno;

        while (waitpid((pid_t)-1, &status, WNOHANG) > 0)
                ;
        errno = save_errno;
}

	Since it fails to compile I take it that this is an
      unacceptable usage of errno as a modifiable lvalue.  I intend to
      change the declaration of save_errno to "extern int save_errno"
      to fix this.  Correct?

      The problem of errno usage in main() I understand (even) less.

      e.g:

      if (errno == EWOULDBLOCK)  

      if (errno != EINTR)

      I would have thought that these usages were OK.  Apparently not.

      Help?
      
      Paul.


[1] http://lists.debian.org/debian-hurd-0106/msg00249.html
[2] http://lists.debian.org/debian-hurd-0102/msg00204.html