compat: let architectures define __ARCH_WANT_COMPAT_SYS_GETDENTS64

For architecture dependent compat syscalls in common code an architecture
must define something like __ARCH_WANT_<WHATEVER> if it wants to use the
code.
This however is not true for compat_sys_getdents64 for which architectures
must define __ARCH_OMIT_COMPAT_SYS_GETDENTS64 if they do not want the code.

This leads to the situation where all architectures, except mips, get the
compat code but only x86_64, arm64 and the generic syscall architectures
actually use it.

So invert the logic, so that architectures actively must do something to
get the compat code.

This way a couple of architectures get rid of otherwise dead code.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>

arch/arm64/include/asm/unistd.h

@@ -14,6 +14,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #ifdef CONFIG_COMPAT
+#define __ARCH_WANT_COMPAT_SYS_GETDENTS64
 #define __ARCH_WANT_COMPAT_STAT64
 #define __ARCH_WANT_SYS_GETHOSTNAME
 #define __ARCH_WANT_SYS_PAUSE

arch/mips/include/asm/unistd.h

@@ -24,7 +24,6 @@
 
 #ifndef __ASSEMBLY__
 
-#define __ARCH_OMIT_COMPAT_SYS_GETDENTS64
 #define __ARCH_WANT_OLD_READDIR
 #define __ARCH_WANT_SYS_ALARM
 #define __ARCH_WANT_SYS_GETHOSTNAME

arch/x86/include/asm/unistd.h

@@ -23,6 +23,7 @@
 #  include <asm/unistd_64.h>
 #  include <asm/unistd_64_x32.h>
 #  define __ARCH_WANT_COMPAT_SYS_TIME
+#  define __ARCH_WANT_COMPAT_SYS_GETDENTS64
 
 # endif
 

fs/compat.c

@@ -981,7 +981,7 @@ asmlinkage long compat_sys_getdents(unsigned int fd,
 	return error;
 }
 
-#ifndef __ARCH_OMIT_COMPAT_SYS_GETDENTS64
+#ifdef __ARCH_WANT_COMPAT_SYS_GETDENTS64
 
 struct compat_getdents_callback64 {
 	struct dir_context ctx;
@@ -1066,7 +1066,7 @@ asmlinkage long compat_sys_getdents64(unsigned int fd,
 	fdput(f);
 	return error;
 }
-#endif /* ! __ARCH_OMIT_COMPAT_SYS_GETDENTS64 */
+#endif /* __ARCH_WANT_COMPAT_SYS_GETDENTS64 */
 
 /*
  * Exactly like fs/open.c:sys_open(), except that it doesn't set the

include/linux/compat.h

@@ -502,9 +502,11 @@ asmlinkage long compat_sys_old_readdir(unsigned int fd,
 asmlinkage long compat_sys_getdents(unsigned int fd,
 				    struct compat_linux_dirent __user *dirent,
 				    unsigned int count);
+#ifdef __ARCH_WANT_COMPAT_SYS_GETDENTS64
 asmlinkage long compat_sys_getdents64(unsigned int fd,
 				      struct linux_dirent64 __user *dirent,
 				      unsigned int count);
+#endif
 asmlinkage long compat_sys_vmsplice(int fd, const struct compat_iovec __user *,
 				    unsigned int nr_segs, unsigned int flags);
 asmlinkage long compat_sys_open(const char __user *filename, int flags,

include/uapi/asm-generic/unistd.h

@@ -191,6 +191,7 @@ __SYSCALL(__NR_quotactl, sys_quotactl)
 
 /* fs/readdir.c */
 #define __NR_getdents64 61
+#define __ARCH_WANT_COMPAT_SYS_GETDENTS64
 __SC_COMP(__NR_getdents64, sys_getdents64, compat_sys_getdents64)
 
 /* fs/read_write.c */