Re: [PATCH 2/5] Add fchmodat4(), a new syscall

[Palmer Dabbelt]

On Fri, 31 May 2019 12:51:00 PDT (-0700), Arnd Bergmann wrote:
> On Fri, May 31, 2019 at 9:23 PM Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:
> > man 3p says that fchmodat() takes a flags argument, but the Linux
> > syscall does not.  There doesn't appear to be a good userspace
> > workaround for this issue but the implementation in the kernel is pretty
> > straight-forward.  The specific use case where the missing flags came up
> > was WRT a fuse filesystem implemenation, but the functionality is pretty
> > generic so I'm assuming there would be other use cases.
> >
> > Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxx>
> > ---
> >  fs/open.c                | 21 +++++++++++++++++++--
> >  include/linux/syscalls.h |  5 +++++
> >  2 files changed, 24 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/open.c b/fs/open.c
> > index a00350018a47..cfad7684e8d3 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -568,11 +568,17 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
> >         return ksys_fchmod(fd, mode);
> >  }
> >
> > -int do_fchmodat(int dfd, const char __user *filename, umode_t mode)
> > +int do_fchmodat4(int dfd, const char __user *filename, umode_t mode, int flags)
> ...
> > +
> > +int do_fchmodat(int dfd, const char __user *filename, umode_t mode)
> > +{
> > +       return do_fchmodat4(dfd, filename, mode, 0);
> > +}
> > +
>
> There is only one external caller of do_fchmodat(), so just change that
> to pass the extra argument here, and keep a single do_fchmodat()
> function used by the sys_fchmod(), sys_fchmod4(), sys_chmod()
> and ksys_chmod().

OK, I'll roll that up into a v2.