[Mesa-dev] [PATCH 05/11] compiler/blob: Add a concept of a fixed-allocation blob

[Jason Ekstrand]

---
 src/compiler/blob.c | 24 +++++++++++++++++++++---
 src/compiler/blob.h | 23 ++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/src/compiler/blob.c b/src/compiler/blob.c
index 0b42871..59ad8a3 100644
--- a/src/compiler/blob.c
+++ b/src/compiler/blob.c
@@ -52,6 +52,11 @@ grow_to_fit(struct blob *blob, size_t additional)
    if (blob->size + additional <= blob->allocated)
       return true;
 
+   if (blob->fixed_allocation) {
+      blob->out_of_memory = true;
+      return false;
+   }
+
    if (blob->allocated == 0)
       to_allocate = BLOB_INITIAL_SIZE;
    else
@@ -86,7 +91,8 @@ align_blob(struct blob *blob, size_t alignment)
       if (!grow_to_fit(blob, new_size - blob->size))
          return false;
 
-      memset(blob->data + blob->size, 0, new_size - blob->size);
+      if (blob->data)
+         memset(blob->data + blob->size, 0, new_size - blob->size);
       blob->size = new_size;
    }
 
@@ -104,6 +110,16 @@ blob_init(struct blob *blob)
 {
    blob->data = NULL;
    blob->allocated = 0;
+   blob->fixed_allocation = false;
+   blob->size = 0;
+}
+
+void
+blob_init_fixed(struct blob *blob, void *data, size_t size)
+{
+   blob->data = data;
+   blob->allocated = size;
+   blob->fixed_allocation = true;
    blob->size = 0;
 }
 
@@ -119,7 +135,8 @@ blob_overwrite_bytes(struct blob *blob,
 
    VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
 
-   memcpy(blob->data + offset, bytes, to_write);
+   if (blob->data)
+      memcpy(blob->data + offset, bytes, to_write);
 
    return true;
 }
@@ -132,7 +149,8 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write)
 
    VG(VALGRIND_CHECK_MEM_IS_DEFINED(bytes, to_write));
 
-   memcpy(blob->data + blob->size, bytes, to_write);
+   if (blob->data)
+      memcpy(blob->data + blob->size, bytes, to_write);
    blob->size += to_write;
 
    return true;
diff --git a/src/compiler/blob.h b/src/compiler/blob.h
index fd13a16..1ef6d99 100644
--- a/src/compiler/blob.h
+++ b/src/compiler/blob.h
@@ -56,6 +56,12 @@ struct blob {
    /** The number of bytes that have actual data written to them. */
    size_t size;
 
+   /** True if \c data a fixed allocation that we cannot resize
+    *
+    * \see blob_init_fixed
+    */
+   bool fixed_allocation;
+
    /**
     * True if we've ever failed to realloc or if we go pas the end of a fixed
     * allocation blob.
@@ -85,12 +91,27 @@ void
 blob_init(struct blob *blob);
 
 /**
+ * Init a new, fixed-size blob.
+ *
+ * A fixed-size blob has a fixed block of data that will not be freed on
+ * blob_finish and will never be grown.  If we hit the end, we simply start
+ * returning false from the write functions.
+ *
+ * If a fixed-size blob has a NULL data pointer then the blob no data is
+ * written but it otherwise operates normally.  This can be used to determine
+ * the size that will be required to write a given data structure.
+ */
+void
+blob_init_fixed(struct blob *blob, void *data, size_t size);
+
+/**
  * Destroy a blob and free its memory.
  */
 static inline void
 blob_finish(struct blob *blob)
 {
-   free(blob->data);
+   if (!blob->fixed_allocation)
+      free(blob->data);
 }
 
 /**
-- 
2.5.0.400.gff86faf