libceph: isolate kmap() call in write_partial_msg_pages()

In write_partial_msg_pages(), every case now does an identical call
to kmap(page).  Instead, just call it once inside the CRC-computing
block where it's needed.  Move the definition of kaddr inside that
block, and make it a (char *) to ensure portable pointer arithmetic.

We still don't kunmap() it until after the sendpage() call, in case
that also ends up needing to use the mapping.

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

1 files changed, 2 insertions, 11 deletions

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 2bf9ab4429e6..f0993af2ae4d 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -835,7 +835,6 @@ static int write_partial_msg_pages(struct ceph_connection *con)
 
         while (data_len > con->out_msg_pos.data_pos) {
                 struct page *page = NULL;
-                void *kaddr = NULL;
                 int max_write = PAGE_SIZE;
                 int bio_offset = 0;
 
@@ -856,18 +855,12 @@ static int write_partial_msg_pages(struct ceph_connection *con)
 
                         page = list_first_entry(&msg->trail->head,
                                                 struct page, lru);
-                        if (do_datacrc)
-                                kaddr = kmap(page);
                         max_write = PAGE_SIZE;
                 } else if (msg->pages) {
                         page = msg->pages[con->out_msg_pos.page];
-                        if (do_datacrc)
-                                kaddr = kmap(page);
                 } else if (msg->pagelist) {
                         page = list_first_entry(&msg->pagelist->head,
                                                 struct page, lru);
-                        if (do_datacrc)
-                                kaddr = kmap(page);
 #ifdef CONFIG_BLOCK
                 } else if (msg->bio) {
                         struct bio_vec *bv;
@@ -875,14 +868,10 @@ static int write_partial_msg_pages(struct ceph_connection *con)
                         bv = bio_iovec_idx(msg->bio_iter, msg->bio_seg);
                         page = bv->bv_page;
                         bio_offset = bv->bv_offset;
-                        if (do_datacrc)
-                                kaddr = kmap(page);
                         max_write = bv->bv_len;
 #endif
                 } else {
                         page = zero_page;
-                        if (do_datacrc)
-                                kaddr = kmap(page);
                 }
                 len = min_t(int, max_write - con->out_msg_pos.page_pos,
                             total_max_write);
@@ -891,7 +880,9 @@ static int write_partial_msg_pages(struct ceph_connection *con)
                         void *base;
                         u32 crc;
                         u32 tmpcrc = le32_to_cpu(con->out_msg->footer.data_crc);
+                        char *kaddr;
 
+                        kaddr = kmap(page);
                         BUG_ON(kaddr == NULL);
                         base = kaddr + con->out_msg_pos.page_pos + bio_offset;
                         crc = crc32c(tmpcrc, base, len);