[PATCH RFC 04/20] libxc/xc_sr_save.c: add WRITE_TRIVIAL_RECORD_FN()

[Joshua Otto <jtotto@uwaterloo.ca>]

Writing the libxc save stream requires writing a few 'trivial' records,
consisting only of a header with a particular type.  As a readability
aid, it's nice to have obviously-named functions that write these sorts
of records into the stream - for example, the first such function was
write_end_record(), which reads much more pleasantly at its call-site
than write_generic_record(REC_TYPE_END) would.  However, it's tedious
and error-prone to copy-paste the generic body of such a function for
each new trivial record type.

Add a helper macro that takes a name base and a record type and declares
the corresponding trivial record write function.  Use this to re-define
the two existing trivial record functions, write_end_record() and
write_checkpoint_record().

No functional change.

Signed-off-by: Joshua Otto <jtotto@uwaterloo.ca>
---
 tools/libxc/xc_sr_save.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
index 61fc4a4..86f6903 100644
--- a/tools/libxc/xc_sr_save.c
+++ b/tools/libxc/xc_sr_save.c
@@ -47,24 +47,18 @@ static int write_headers(struct xc_sr_context *ctx, uint16_t guest_type)
 }
 
 /*
- * Writes an END record into the stream.
+ * Declares a helper function to write an empty record of a particular type.
  */
-static int write_end_record(struct xc_sr_context *ctx)
-{
-    struct xc_sr_record end = { REC_TYPE_END, 0, NULL };
-
-    return write_record(ctx, ctx->fd, &end);
-}
-
-/*
- * Writes a CHECKPOINT record into the stream.
- */
-static int write_checkpoint_record(struct xc_sr_context *ctx)
-{
-    struct xc_sr_record checkpoint = { REC_TYPE_CHECKPOINT, 0, NULL };
+#define WRITE_TRIVIAL_RECORD_FN(name, type)                         \
+    static int write_ ## name ## _record(struct xc_sr_context *ctx) \
+    {                                                               \
+        struct xc_sr_record name = { (type), 0, NULL };             \
+                                                                    \
+        return write_record(ctx, ctx->fd, &name);                   \
+    }
 
-    return write_record(ctx, ctx->fd, &checkpoint);
-}
+WRITE_TRIVIAL_RECORD_FN(end,                 REC_TYPE_END);
+WRITE_TRIVIAL_RECORD_FN(checkpoint,          REC_TYPE_CHECKPOINT);
 
 /*
  * Writes a batch of memory as a PAGE_DATA record into the stream.  The batch
-- 
2.7.4


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