Re: [fsverity-utils PATCH 3/4] programs/utils: add full_pwrite() and preallocate_file()

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Jun 03, 2021 at 05:33:18PM -0700, Victor Hsieh wrote:
> > +
> > +bool full_pwrite(struct filedes *file, const void *buf, size_t count,
> > +                u64 offset)
> > +{
> > +       while (count) {
> > +               int n = raw_pwrite(file->fd, buf, min(count, INT_MAX), offset);
> > +
> > +               if (n < 0) {
> > +                       error_msg_errno("writing to '%s'", file->name);
> > +                       return false;
> > +               }
> > +               buf += n;
> I think this pointer arithmetic is not portable?  Consider changing
> the type of buf to "const char*".
> 

fsverity-utils is already using void pointer arithmetic elsewhere, for example
in full_read() and full_write().

I am allowing the use of some gcc/clang extensions which are widely used,
including in the Linux kernel (which fsverity-utils is generally trying to
follow the coding style of), and are annoying to do without.  Void pointer
arithmetic is one of these.

If we really needed to support someone compiling fsverity-utils with e.g.
Visual Studio, we could add -Wpedantic to the compiler flags and get rid of all
the gcc/clang extensions.  But I don't see a reason to do that now.

- Eric