ceph: return the real size read when it hits EOF

Currently, if the sync read handler ends up reading more from the last
object in the file than the i_size indicates, then it'll end up
returning the wrong length. Ensure that we cap the returned length and
pos at the EOF.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -847,6 +847,7 @@ static ssize_t ceph_sync_read(struct kiocb *iocb, struct iov_iter *to,
 	ssize_t ret;
 	u64 off = iocb->ki_pos;
 	u64 len = iov_iter_count(to);
+	u64 i_size;
 
 	dout("sync_read on file %p %llu~%u %s\n", file, off, (unsigned)len,
 	     (file->f_flags & O_DIRECT) ? "O_DIRECT" : "");
@@ -870,7 +871,6 @@ static ssize_t ceph_sync_read(struct kiocb *iocb, struct iov_iter *to,
 		struct page **pages;
 		int num_pages;
 		size_t page_off;
-		u64 i_size;
 		bool more;
 		int idx;
 		size_t left;
@@ -953,11 +953,14 @@ static ssize_t ceph_sync_read(struct kiocb *iocb, struct iov_iter *to,
 	}
 
 	if (off > iocb->ki_pos) {
-		if (ret >= 0 &&
-		    iov_iter_count(to) > 0 && off >= i_size_read(inode))
+		if (off >= i_size) {
 			*retry_op = CHECK_EOF;
-		ret = off - iocb->ki_pos;
-		iocb->ki_pos = off;
+			ret = i_size - iocb->ki_pos;
+			iocb->ki_pos = i_size;
+		} else {
+			ret = off - iocb->ki_pos;
+			iocb->ki_pos = off;
+		}
 	}
 
 	dout("sync_read result %zd retry_op %d\n", ret, *retry_op);