Re: [PATCH 5/5] 9pfs: fix removing non-existent POSIX ACL xattr on macOS host

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

On Donnerstag, 21. April 2022 10:26:11 CEST Greg Kurz wrote:
> On Tue, 19 Apr 2022 13:43:30 +0200
> 
> Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> > When mapped POSIX ACL is used, we are ignoring errors when trying
> > to remove a POSIX ACL xattr that does not exist. On Linux hosts we
> > would get ENODATA in such cases, on macOS hosts however we get
> > ENOATTR instead, so ignore ENOATTR errors as well.
> > 
> > This patch fixes e.g. a command on Linux guest like:
> >   cp --preserve=mode old new
> > 
> > Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> > ---
> > 
> >  hw/9pfs/9p-posix-acl.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
> > index eadae270dd..2bf155f941 100644
> > --- a/hw/9pfs/9p-posix-acl.c
> > +++ b/hw/9pfs/9p-posix-acl.c
> > @@ -65,7 +65,13 @@ static int mp_pacl_removexattr(FsContext *ctx,
> > 
> >      int ret;
> >      
> >      ret = local_removexattr_nofollow(ctx, path, MAP_ACL_ACCESS);
> > 
> > -    if (ret == -1 && errno == ENODATA) {
> > +    if (ret == -1 &&
> > +          (errno == ENODATA
> > +#ifdef ENOATTR
> > +          || errno == ENOATTR
> > +#endif
> > +          )
> 
> We already have this in <qemu/xattr.h> which is included by
> 9p-posix-acl.c :
> 
> /*
>  * Modern distributions (e.g. Fedora 15), have no libattr.so, place attr.h
>  * in /usr/include/sys, and don't have ENOATTR.
>  */
> 
> 
> #ifdef CONFIG_LIBATTR
> #  include <attr/xattr.h>
> #else
> #  if !defined(ENOATTR)
> #    define ENOATTR ENODATA
> #  endif
> #  include <sys/xattr.h>
> #endif
> 
> I guess this patch could just s/ENODATA/ENOATTR/ to avoid the
> extra ifdefery.

Not viable, because macOS does have both ENODATA==96 and ENOATTR==93. On Linux 
the two macros were historically defined to the same numeric values, that's 
why it worked there.

Maybe I should define a separate macro like:

#if ...
# define P9_ENOATTR ENOATTR
#else
# define P9_ENOATTR ENODATA
#end

?

Actually good that you pointed me at this, because I just realized there is a 
2nd place in 9p-posix-acl.c which would require this as well. For some reason 
the 2nd place just did not trigger while I was testing it on macOS.

Best regards,
Christian Schoenebeck