include/qemu: add documentation for memory callbacks

Some API documentation was missed, rectify that.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1497
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230315174331.2959-7-alex.bennee@linaro.org>

include/qemu/qemu-plugin.h

@@ -481,17 +481,56 @@ uint64_t qemu_plugin_hwaddr_phys_addr(const struct qemu_plugin_hwaddr *haddr);
  */
 const char *qemu_plugin_hwaddr_device_name(const struct qemu_plugin_hwaddr *h);
 
-typedef void
-(*qemu_plugin_vcpu_mem_cb_t)(unsigned int vcpu_index,
-                             qemu_plugin_meminfo_t info, uint64_t vaddr,
-                             void *userdata);
+/**
+ * typedef qemu_plugin_vcpu_mem_cb_t - memory callback function type
+ * @vcpu_index: the executing vCPU
+ * @info: an opaque handle for further queries about the memory
+ * @vaddr: the virtual address of the transaction
+ * @userdata: any user data attached to the callback
+ */
+typedef void (*qemu_plugin_vcpu_mem_cb_t) (unsigned int vcpu_index,
+                                           qemu_plugin_meminfo_t info,
+                                           uint64_t vaddr,
+                                           void *userdata);
 
+/**
+ * qemu_plugin_register_vcpu_mem_cb() - register memory access callback
+ * @insn: handle for instruction to instrument
+ * @cb: callback of type qemu_plugin_vcpu_mem_cb_t
+ * @flags: (currently unused) callback flags
+ * @rw: monitor reads, writes or both
+ * @userdata: opaque pointer for userdata
+ *
+ * This registers a full callback for every memory access generated by
+ * an instruction. If the instruction doesn't access memory no
+ * callback will be made.
+ *
+ * The callback reports the vCPU the access took place on, the virtual
+ * address of the access and a handle for further queries. The user
+ * can attach some userdata to the callback for additional purposes.
+ *
+ * Other execution threads will continue to execute during the
+ * callback so the plugin is responsible for ensuring it doesn't get
+ * confused by making appropriate use of locking if required.
+ */
 void qemu_plugin_register_vcpu_mem_cb(struct qemu_plugin_insn *insn,
                                       qemu_plugin_vcpu_mem_cb_t cb,
                                       enum qemu_plugin_cb_flags flags,
                                       enum qemu_plugin_mem_rw rw,
                                       void *userdata);
 
+/**
+ * qemu_plugin_register_vcpu_mem_inline() - register an inline op to any memory access
+ * @insn: handle for instruction to instrument
+ * @rw: apply to reads, writes or both
+ * @op: the op, of type qemu_plugin_op
+ * @ptr: pointer memory for the op
+ * @imm: immediate data for @op
+ *
+ * This registers a inline op every memory access generated by the
+ * instruction. This provides for a lightweight but not thread-safe
+ * way of counting the number of operations done.
+ */
 void qemu_plugin_register_vcpu_mem_inline(struct qemu_plugin_insn *insn,
                                           enum qemu_plugin_mem_rw rw,
                                           enum qemu_plugin_op op, void *ptr,