Add support for dyamic buffers. These are allocated using

isc_dynbuffer_allocate() and freed with isc_dynbuffer_free(), and are
a linkable buffer type with a built-in data area.

lib/isc/buffer.c

@@ -22,9 +22,14 @@
 #include <isc/assertions.h>
 #include <isc/buffer.h>
 
+#define BUFFER_MAGIC			0x42756621U	/* Buf!. */
+#define DYNBUFFER_MAGIC			0x64427566U	/* dBuf. */
+
 #define VALID_BUFFER(b)			((b) != NULL && \
 					 (b)->magic == BUFFER_MAGIC)
-#define BUFFER_MAGIC			0x42756621U	/* Buf!. */
+
+#define VALID_DYNBUFFER(b)		((b) != NULL && \
+					 (b)->magic == DYNBUFFER_MAGIC)
 
 void
 isc_buffer_init(isc_buffer_t *b, void *base, unsigned int length,
@@ -349,3 +354,46 @@ isc_buffer_putuint32(isc_buffer_t *b, isc_uint32_t val)
 	cp[2] = (val & 0x0000ff00) >> 8;
 	cp[3] = (val & 0x000000ff);
 }
+
+isc_result_t
+isc_dynbuffer_allocate(isc_mem_t *mctx, isc_dynbuffer_t **dynbuffer,
+		       unsigned int length, unsigned int type)
+{
+	isc_dynbuffer_t *dbuf;
+
+	REQUIRE(dynbuffer != NULL);
+	REQUIRE(*dynbuffer == NULL);
+
+	dbuf = isc_mem_get(mctx, length + sizeof(isc_dynbuffer_t));
+	if (dbuf == NULL)
+		return (ISC_R_NOMEMORY);
+
+	dbuf->magic = DYNBUFFER_MAGIC;
+	ISC_LINK_INIT(dbuf, link);
+	isc_buffer_init(&dbuf->buffer,
+			((unsigned char *)dbuf) + sizeof(isc_dynbuffer_t),
+			length, type);
+
+	*dynbuffer = dbuf;
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+isc_dynbuffer_free(isc_mem_t *mctx, isc_dynbuffer_t **dynbuffer)
+{
+	unsigned int real_length;
+	isc_dynbuffer_t *dbuf;
+
+	REQUIRE(dynbuffer != NULL);
+	REQUIRE(VALID_DYNBUFFER(*dynbuffer));
+
+	dbuf = *dynbuffer;
+	*dynbuffer = NULL;	/* destroy external reference */
+
+	real_length = dbuf->buffer.length + sizeof(isc_dynbuffer_t);
+	isc_buffer_invalidate(&dbuf->buffer);
+	dbuf->magic = 0;
+
+	isc_mem_put(mctx, dbuf, real_length);
+}

lib/isc/include/isc/buffer.h

@@ -49,6 +49,24 @@
  * is empty.  If the current offset advances beyond the chosen offset, the
  * active region will also be empty.
  *
+ *  /----- used region -----\/-- available --\
+ *  +----------------------------------------+
+ *  | consumed  | remaining |                |
+ *  +----------------------------------------+
+ *  a           b     c     d                e
+ *
+ * a == base of buffer.
+ * b == current pointer.  Can be anywhere between a and d.
+ * c == active pointer.  Meaningful between b and d.
+ * d == used pointer.
+ * e == length of buffer.
+ *
+ * a-e == entire (length) of buffer.
+ * a-d == used region.
+ * a-b == consumed region.
+ * b-d == remaining region.
+ * b-c == optional active region.
+ *
  * The following invariants are maintained by all routines:
  *
  *	length > 0
@@ -60,6 +78,7 @@
  *	0 <= current <= used
  *
  *	0 <= active <= used
+ *	(although active < current implies empty active region)
  *
  * MP:
  *	Buffers have no synchronization.  Clients must ensure exclusive
@@ -69,7 +88,7 @@
  *	No anticipated impact.
  *
  * Resources:
- *	Memory: 2 pointers + 2 unsigned integers per buffer.
+ *	Memory: 1 pointer + 6 unsigned integers per buffer.
  *
  * Security:
  *	No anticipated impact.
@@ -83,6 +102,8 @@
  ***/
 
 #include <isc/lang.h>
+#include <isc/list.h>
+#include <isc/mem.h>
 #include <isc/region.h>
 #include <isc/int.h>
 
@@ -115,11 +136,57 @@ typedef struct isc_buffer {
 	unsigned int 	active;
 } isc_buffer_t;
 
+/*
+ * A handy thing to have, linkable buffers with built-in storage.  These
+ * are allocated and freed with the isc_dynbuffer_alloc() and _free()
+ * functions below.  These function should _ALWAYS_ be used to create these
+ * dynbuffers.  The link is initialized on allocation and is solely for the
+ * caller to use.
+ */
+typedef struct isc_dynbuffer isc_dynbuffer_t;
+struct isc_dynbuffer {
+	unsigned int			magic;
+	isc_buffer_t			buffer;
+	ISC_LINK(isc_dynbuffer_t)	link;
+};  /* variable sized */
 
 /***
  *** Functions
  ***/
 
+isc_result_t
+isc_dynbuffer_allocate(isc_mem_t *mctx, isc_dynbuffer_t **dynbuffer,
+		       unsigned int length, unsigned int type);
+/*
+ * Allocate a dynamic linkable buffer which has "length" bytes in the
+ * data region.
+ *
+ * Requires:
+ *	"mctx" is valid.
+ *
+ *	"dynbuffer" is non-NULL, and "*dynbuffer" is NULL.
+ *
+ * Returns:
+ *	ISC_R_SUCCESS		- success
+ *	ISC_R_NOMEMORY		- no memory available
+ */
+
+void
+isc_dynbuffer_free(isc_mem_t *mctx, isc_dynbuffer_t **dynbuffer);
+/*
+ * Release resources allocated for a dynamic buffer.
+ *
+ * Requires:
+ *	"dynbuffer" is not NULL.
+ *
+ *	"*dynbuffer" is a valid dynamic buffer.
+ *
+ *	"mctx" is valid.
+ *
+ * Ensures:
+ *	"*dynbuffer" will be NULL on return, and all memory associated with
+ *	the dynamic buffer is returned to memory context "mctx".
+ */
 
 void
 isc_buffer_init(isc_buffer_t *b, void *base, unsigned int length,