svn commit: r358655 - head/sbin/mount_nfs

[Slawa Olhovchenkov]

On Thu, Mar 05, 2020 at 07:19:59PM +0100, Dimitry Andric wrote:

> On 5 Mar 2020, at 18:44, Gleb Smirnoff <glebius at FreeBSD.org> wrote:
> > 
> > On Thu, Mar 05, 2020 at 08:35:15PM +0300, Slawa Olhovchenkov wrote:
> > S> > > D> sbin/mount_nfs/mount_nfs.c:549:10: error: cast from 'char *' to 'struct
> > S> > > D> if_msghdr *' increases required alignment from 1 to 4
> > S> > > D> [-Werror,-Wcast-align]
> > S> > > D>                         ifm = (struct if_msghdr *)buf;
> > S> > > D>                               ^~~~~~~~~~~~~~~~~~~~~~~
> > S> > > D> 1 error generated.
> > S> > > D>
> > S> > > D> In practice I don't think the buffer can ever get misaligned, so can you
> > S> > > D> please add a NO_WCAST_ALIGN= to the Makefile?
> > S> > >
> > S> > > route(8) handles the same problem via intermediate (void *) cast. What is
> > S> > > preferred way to solve the problem? Change compiler flags file wide, or
> > S> > > just through (void *) cast?
> > S> >
> > S> > Copy to aligned buffer or got SIGBUS on some architectures?
> > S>
> > S> char buf[2048] __aligned(__alignof(struct if_msghdr));
> > S>
> > S> resolve this watning.
> > 
> > Thanks, Slawa! I think this is the most elegant solution.
> 
> Why don't just declare the buffer as:
> 
>   struct if_msghdr buf;
> 
> and then do:
> 
>   nread = read(s, &buf, sizeof buf);
> 
> ?  You are never reading more than one if_msghdr anyway, and then there
> is no need to cast anything.

My inspiration: route socket can return other messages (man 4 route)