[Libguestfs] [libnbd PATCH] maint: Drop useless casts

[Eric Blake]

On Wed, May 24, 2023 at 08:18:32PM +0100, Richard W.M. Jones wrote:
> On Wed, May 24, 2023 at 10:00:03AM -0500, Eric Blake wrote:
> > diff --git a/copy/main.c b/copy/main.c
> > index 391c0c4f..9449440e 100644
> > --- a/copy/main.c
> > +++ b/copy/main.c
> > @@ -371,7 +371,7 @@ main (int argc, char *argv[])
> >  #else
> >      t = 1;
> >  #endif
> > -    threads = (unsigned)t;
> > +    threads = t;
> 
> This one doesn't give any warning about truncating from long (64 bits)
> to unsigned (32 bits)?

The compiler doesn't warn by default under -Wall.  There are other
knobs that can make it warn, but in this particular case,
sysconf(_SC_PROCESSORS_ONLN) is unlikely to overflow (if you have a
system with 4G cores, I'm jealous).  Still, I don't mind tweaking to
add an assert documenting our reasoning.

> 
> > diff --git a/fuse/nbdfuse.c b/fuse/nbdfuse.c
> > index 491f6db8..35d5ffac 100644
> > --- a/fuse/nbdfuse.c
> > +++ b/fuse/nbdfuse.c
> > @@ -415,7 +415,7 @@ main (int argc, char *argv[])
> >        handles_append (&nbd, h); /* reserved above, so can't fail */
> >      }
> >    }
> > -  connections = (unsigned)nbd.len;
> > +  connections = nbd.len;
> 
> Similarly this would be size_t -> unsigned, also a truncation on 64 bit.

Again, no compiler warning.  And in this one, no assertion needed:
nbd.len was just populated by a loop over the prior value of
connections, and thus won't overflow.

> 
> But if there are no warnings, then:
> 
> Reviewed-by: Richard W.M. Jones <rjones at redhat.com>
>

I decided to swap the order of these two patches (less churn); and
touched up this one with the above-mentioned assert.  Now committed
as 96fdc62a..17d0bc6a

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org