libceph: separate CRC calculation from byte swapping

Calculate CRC in a separate step from rearranging the byte order
of the result, to improve clarity and readability.

Use offsetof() to determine the number of bytes to include in the
CRC calculation.

In read_partial_message(), switch which value gets byte-swapped,
since the just-computed CRC is already likely to be in a register.

Signed-off-by: Alex Elder <elder@dreamhost.com>
Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 204e229e66281d41babb2b3d1375d1ddb4fe339b..7ec6a228b6676ff9dd28922209f0a83551a64da3 100644 (file)
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -521,6 +521,7 @@ static void prepare_write_message_footer(struct ceph_connection *con)
 static void prepare_write_message(struct ceph_connection *con)
 {
        struct ceph_msg *m;
+       u32 crc;
 
        ceph_con_out_kvec_reset(con);
        con->out_kvec_is_msg = true;
@@ -569,17 +570,17 @@ static void prepare_write_message(struct ceph_connection *con)
                        m->middle->vec.iov_base);
 
        /* fill in crc (except data pages), footer */
-       con->out_msg->hdr.crc =
-               cpu_to_le32(crc32c(0, &m->hdr,
-                                     sizeof(m->hdr) - sizeof(m->hdr.crc)));
+       crc = crc32c(0, &m->hdr, offsetof(struct ceph_msg_header, crc));
+       con->out_msg->hdr.crc = cpu_to_le32(crc);
        con->out_msg->footer.flags = CEPH_MSG_FOOTER_COMPLETE;
-       con->out_msg->footer.front_crc =
-               cpu_to_le32(crc32c(0, m->front.iov_base, m->front.iov_len));
-       if (m->middle)
-               con->out_msg->footer.middle_crc =
-                       cpu_to_le32(crc32c(0, m->middle->vec.iov_base,
-                                          m->middle->vec.iov_len));
-       else
+
+       crc = crc32c(0, m->front.iov_base, m->front.iov_len);
+       con->out_msg->footer.front_crc = cpu_to_le32(crc);
+       if (m->middle) {
+               crc = crc32c(0, m->middle->vec.iov_base,
+                               m->middle->vec.iov_len);
+               con->out_msg->footer.middle_crc = cpu_to_le32(crc);
+       } else
                con->out_msg->footer.middle_crc = 0;
        con->out_msg->footer.data_crc = 0;
        dout("prepare_write_message front_crc %u data_crc %u\n",
@@ -875,12 +876,13 @@ static int write_partial_msg_pages(struct ceph_connection *con)
                            total_max_write);
 
                if (do_crc && !con->out_msg_pos.did_page_crc) {
+                       u32 crc;
                        void *base = kaddr + con->out_msg_pos.page_pos;
                        u32 tmpcrc = le32_to_cpu(con->out_msg->footer.data_crc);
 
                        BUG_ON(kaddr == NULL);
-                       con->out_msg->footer.data_crc =
-                               cpu_to_le32(crc32c(tmpcrc, base, len));
+                       crc = crc32c(tmpcrc, base, len);
+                       con->out_msg->footer.data_crc = cpu_to_le32(crc);
                        con->out_msg_pos.did_page_crc = true;
                }
                ret = kernel_sendpage(con->sock, page,
@@ -1650,8 +1652,9 @@ static int read_partial_message(struct ceph_connection *con)
                con->in_base_pos += ret;
                if (con->in_base_pos == sizeof(con->in_hdr)) {
                        u32 crc = crc32c(0, &con->in_hdr,
-                                sizeof(con->in_hdr) - sizeof(con->in_hdr.crc));
-                       if (crc != le32_to_cpu(con->in_hdr.crc)) {
+                                       offsetof(struct ceph_msg_header, crc));
+
+                       if (cpu_to_le32(crc) != con->in_hdr.crc) {
                                pr_err("read_partial_message bad hdr "
                                       " crc %u != expected %u\n",
                                       crc, con->in_hdr.crc);