xfs: format log items write directly into the linear CIL buffer

Instead of setting up pointers to memory locations in iop_format which then
get copied into the CIL linear buffer after return move the copy into
the individual inode items.  This avoids the need to always have a memory
block in the exact same layout that gets written into the log around, and
allow the log items to be much more flexible in their in-memory layouts.

The only caveat is that we need to properly align the data for each
iovec so that don't have structures misaligned in subsequent iovecs.

Note that all log item format routines now need to be careful to modify
the copy of the item that was placed into the CIL after calls to
xlog_copy_iovec instead of the in-memory copy.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 37 insertions, 4 deletions

diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
index 384c6c469661..b0f4ef77fa70 100644
--- a/fs/xfs/xfs_log.h
+++ b/fs/xfs/xfs_log.h
@@ -31,18 +31,51 @@ struct xfs_log_vec {
 #define XFS_LOG_VEC_ORDERED     (-1)
 
 static inline void *
-xlog_copy_iovec(struct xfs_log_iovec **vecp, uint type, void *data, int len)
+xlog_prepare_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
+                uint type)
 {
         struct xfs_log_iovec *vec = *vecp;
 
+        if (vec) {
+                ASSERT(vec - lv->lv_iovecp < lv->lv_niovecs);
+                vec++;
+        } else {
+                vec = &lv->lv_iovecp[0];
+        }
+
         vec->i_type = type;
-        vec->i_addr = data;
-        vec->i_len = len;
+        vec->i_addr = lv->lv_buf + lv->lv_buf_len;
+
+        ASSERT(IS_ALIGNED((unsigned long)vec->i_addr, sizeof(uint64_t)));
 
-        *vecp = vec + 1;
+        *vecp = vec;
         return vec->i_addr;
 }
 
+static inline void
+xlog_finish_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec *vec, int len)
+{
+        /*
+         * We need to make sure the next buffer is naturally aligned for the
+         * biggest basic data type we put into it.  We already accounted for
+         * this when sizing the buffer.
+         */
+        lv->lv_buf_len += round_up(len, sizeof(uint64_t));
+        vec->i_len = len;
+}
+
+static inline void *
+xlog_copy_iovec(struct xfs_log_vec *lv, struct xfs_log_iovec **vecp,
+                uint type, void *data, int len)
+{
+        void *buf;
+
+        buf = xlog_prepare_iovec(lv, vecp, type);
+        memcpy(buf, data, len);
+        xlog_finish_iovec(lv, *vecp, len);
+        return buf;
+}
+
 /*
  * Structure used to pass callback function and the function's argument
  * to the log manager.