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Re: [libvirt] PATCH: Allow specific FDs to be kept open in virExec()



On Fri, Aug 22, 2008 at 10:51:54AM +0200, Jim Meyering wrote:
> "Daniel P. Berrange" <berrange redhat com> wrote:
> > On Fri, Aug 22, 2008 at 09:22:06AM +0100, Richard W.M. Jones wrote:
> >> On Thu, Aug 21, 2008 at 02:58:30PM +0100, Daniel P. Berrange wrote:
> >> > +#define VIR_EXEC_FDSET_SIZE() (sysconf(_SC_OPEN_MAX)/8)
> >> > +#define VIR_EXEC_FDSET_CLEAR(set) memset((set), 0, VIR_EXEC_FDSET_SIZE())
> >> > +#define VIR_EXEC_FDSET_ON(set, fd) (set[(fd)/8] |= (1 << ((fd)%8)))
> >> > +#define VIR_EXEC_FDSET_OFF(set, fd) (set[(fd)/8] &= ~(1 << ((fd)%8)))
> >> > +#define VIR_EXEC_FDSET_ISON(set, fd) (set[(fd)/8] & (1 << ((fd)%8)))
> >>
> >> +1 although I'm interested to know why you didn't just use ordinary
> >> FD_SETs for this.
> >
> > For some reason I have it in my head that fd_set was limited to 32
> > but looking at the Linux source its clearly 1024, which is the sme
> > as my _SC_OPEN_MAX.   The manpage says its FD_SETSIZE, but doesn't
> > clarify whether FD_SETSIZE is guarenteed to be large enough to store
> > any FD upto _SC_OPEN_MAX.
> >
> > Jim, any thoughts on this ?  I'll happily switch to fd_set if we expect
> > it'll be suitable
> 
> AFAIK, FD_SET must work for any valid file descriptor.
> 
> The fd_set bit-manipulation function/macros like FD_SET, FD_CLR
> are specified in http://www.opengroup.org/susv3xsh/select.html

Ok, I'll redo this patch

Daniel
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