Re: [Libguestfs] [libnbd PATCH] maint: Drop useless casts
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(a)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