Re: [PATCH 5/5] linux-user: Implement pivot_root

[Takashi Yamamoto]

On Wed, May 26, 2021 at 5:22 AM Laurent Vivier <laurent@vivier.eu> wrote:
>
> Le 24/05/2021 à 06:54, YAMAMOTO Takashi a écrit :
> > Used by runc.
> >
> > Signed-off-by: YAMAMOTO Takashi <yamamoto@midokura.com>
> > ---
> >  linux-user/syscall.c | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> >
> > diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> > index 2947e79dc0..e739921e86 100644
> > --- a/linux-user/syscall.c
> > +++ b/linux-user/syscall.c
> > @@ -35,6 +35,7 @@
> >  #include <sys/prctl.h>
> >  #include <sys/resource.h>
> >  #include <sys/swap.h>
> > +#include <sys/syscall.h>
>
> we don't need that include, see below
>
> >  #include <linux/capability.h>
> >  #include <sched.h>
> >  #include <sys/timex.h>
> > @@ -8254,6 +8255,11 @@ static int host_to_target_cpu_mask(const unsigned 
> > long *host_mask,
> >      return 0;
> >  }
> >
> > +static int pivot_root(const char *new_root, const char *put_old)
> > +{
> > +    return syscall(SYS_pivot_root, new_root, put_old);
> > +}
>
> Better to use:
>
> #if defined(TARGET_NR_pivot_root) && defined(__NR_pivot_root)
> _syscall2(int, pivot_root, const char *, new_root, const char *, put_old)
> #endif

ok. i haven't noticed the _syscall2 macro in this file. thank you.

>
> > +
> >  /* This is an internal helper for do_syscall so that it is easier
> >   * to have a single return point, so that actions, such as logging
> >   * of syscall results, can be performed.
> > @@ -13222,6 +13228,23 @@ static abi_long do_syscall1(void *cpu_env, int 
> > num, abi_long arg1,
> >          return ret;
> >  #endif
> >
> > +#if defined(TARGET_NR_pivot_root)
> > +    case TARGET_NR_pivot_root:
> > +        {
> > +            void *p2;
> > +            p = lock_user_string(arg1); /* new_root */
> > +            p2 = lock_user_string(arg2); /* put_old */
> > +            if (!p || !p2) {
> > +                ret = -TARGET_EFAULT;
> > +            } else {
> > +                ret = get_errno(pivot_root(p, p2));
> > +            }
> > +            unlock_user(p2, arg2, 0);
> > +            unlock_user(p, arg1, 0);
> > +        }
> > +        return ret;
> > +#endif
> > +
> >      default:
> >          qemu_log_mask(LOG_UNIMP, "Unsupported syscall: %d\n", num);
> >          return -TARGET_ENOSYS;
> >
>
> Thanks,
> Laurent
>