compat: fs: Generic compat_sys_sendfile implementation

This function is used by sparc, powerpc and arm64 for compat support.
The patch adds a generic implementation which calls do_sendfile()
directly and avoids set_fs().

The sparc architecture has wrappers for the sign extensions while
powerpc relies on the compiler to do the this. The patch adds wrappers
for powerpc to handle the u32->int type conversion.

compat_sys_sendfile64() can be replaced by a sys_sendfile() call since
compat_loff_t has the same size as off_t on a 64-bit system.

On powerpc, the patch also changes the 64-bit sendfile call from
sys_sendile64 to sys_sendfile.

Signed-off-by: Catalin Marinas <[email protected]>
Acked-by: David S. Miller <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>

fs/compat.c

@@ -1792,3 +1792,25 @@ compat_sys_open_by_handle_at(int mountdirfd,
 	return do_handle_open(mountdirfd, handle, flags);
 }
 #endif
+
+#ifdef __ARCH_WANT_COMPAT_SYS_SENDFILE
+asmlinkage long compat_sys_sendfile(int out_fd, int in_fd,
+				    compat_off_t __user *offset, compat_size_t count)
+{
+	loff_t pos;
+	off_t off;
+	ssize_t ret;
+
+	if (offset) {
+		if (unlikely(get_user(off, offset)))
+			return -EFAULT;
+		pos = off;
+		ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
+		if (unlikely(put_user(pos, offset)))
+			return -EFAULT;
+		return ret;
+	}
+
+	return do_sendfile(out_fd, in_fd, NULL, count, 0);
+}
+#endif /* __ARCH_WANT_COMPAT_SYS_SENDFILE */

fs/read_write.c

@@ -862,8 +862,8 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
 	return ret;
 }
 
-static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
-			   size_t count, loff_t max)
+ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos, size_t count,
+		    loff_t max)
 {
 	struct fd in, out;
 	struct inode *in_inode, *out_inode;

fs/read_write.h

@@ -12,3 +12,5 @@ ssize_t do_sync_readv_writev(struct file *filp, const struct iovec *iov,
 		unsigned long nr_segs, size_t len, loff_t *ppos, iov_fn_t fn);
 ssize_t do_loop_readv_writev(struct file *filp, struct iovec *iov,
 		unsigned long nr_segs, loff_t *ppos, io_fn_t fn);
+ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos, size_t count,
+		    loff_t max);