RFR: 8238161: use os::fopen in HS code where possible

[Baesken, Matthias]

> 
> On 3/02/2020 10:35 pm, Baesken, Matthias wrote:
> > Hi David, from what I understand it should behave in the same way it does
> when a file descriptor to a "normal" file is opened .
> > At least checking for  the FD_CLOEXEC   flag for such an fd  works as
> expected
> >
> >    /* check that O_CLOEXEC works */
> >    int fd = open64("/proc/cpuinfo", O_CLOEXEC, 0444);
> >    int flags;
> >
> >    flags = ::fcntl(fd, F_GETFD);
> >    if (flags != -1) {
> >      if ((flags & FD_CLOEXEC) != 0) {
> >        printf("setting O_CLOEXEC with open seems to work.\n");
> >      } else {
> >        printf("PROBLEM setting O_CLOEXEC with open !\n");
> >      }
> >    }
> >
> >
> >   ... outputs  :  "setting O_CLOEXEC with open seems to work."
> 
> I expect it to be applicable but does it actually do anything such that
> it is necessary to go and make these changes for /proc filesystem
> usages? This is probably harmless but it also seems somewhat unnecessary
> to do.
> 

Hi David ,  probably for  my small example  (or generally for /proc/cpuinfo)  it would not be necessary.
Regarding  other fds  dealing with /proc like

cgroupSubsystem_linux.cpp
66 cgroups = fopen("/proc/cgroups", "r");
121 cgroup = fopen("/proc/self/cgroup", "r");
170 mntinfo = fopen("/proc/self/mountinfo", "r");
224 mntinfo = fopen("/proc/self/mountinfo", "r");

 Maybe the cgroup/container folks could comment how important/unimportant it is to have the close-on-exec set on the fds  in this case?

Best regards, Matthias