VbNvStorage cleanup and comments

firmware/include/vboot_nvstorage.h

Index: firmware/include/vboot_nvstorage.h
diff --git a/firmware/include/vboot_nvstorage.h b/firmware/include/vboot_nvstorage.h
index cd4f89dd6af8bc66b868a01d7b0e240af107fdeb..31bc539ed9be6d9e1ad43b3fde232a3516cff763 100644
--- a/firmware/include/vboot_nvstorage.h
+++ b/firmware/include/vboot_nvstorage.h
@@ -3,17 +3,17 @@
  * found in the LICENSE file.
  */
 
-/* Non-volatile storage routines.
+/* Non-volatile storage routines for verified boot.
  */
 
 #ifndef VBOOT_REFERENCE_NVSTORAGE_H_
 #define VBOOT_REFERENCE_NVSTORAGE_H_
 
-#define NV_BLOCK_SIZE 16  /* Size of NV storage block in bytes */
+#define VBNV_BLOCK_SIZE 16  /* Size of NV storage block in bytes */
 
 typedef struct VbNvContext {
   /* Raw NV data.  Caller must fill this before calling VbNvSetup(). */
-  uint8_t raw[NV_BLOCK_SIZE];
+  uint8_t raw[VBNV_BLOCK_SIZE];
   /* Flag indicating whether raw data has changed.  Set by VbNvTeardown() if
    * the raw data has changed and needs to be stored to the underlying
    * non-volatile data store. */
@@ -28,45 +28,109 @@ typedef struct VbNvContext {
 
 /* Parameter type for VbNvGet(), VbNvSet(). */
 typedef enum VbNvParam {
+  /* Parameter values have been reset to defaults (flag for firmware).
+   * 0=clear; 1=set. */
   VBNV_FIRMWARE_SETTINGS_RESET = 0,
+  /* Parameter values have been reset to defaults (flag for kernel).
+   * 0=clear; 1=set. */
   VBNV_KERNEL_SETTINGS_RESET,
+  /* Request debug reset on next S3->S0 transition.  0=clear; 1=set. */
   VBNV_DEBUG_RESET_MODE,
+  /* Number of times to try booting RW firmware slot B before slot A.
+   * Valid range: 0-15. */
   VBNV_TRY_B_COUNT,
+  /* Request recovery mode on next boot; see VBNB_RECOVERY_* below for
+   * currently defined reason codes.  8-bit value. */
   VBNV_RECOVERY_REQUEST,
+  /* Localization index for screen bitmaps displayed by firmware.
+   * 8-bit value. */
   VBNV_LOCALIZATION_INDEX,
+  /* Field reserved for kernel/user-mode use; 32-bit value. */
   VBNV_KERNEL_FIELD,
 } VbNvParam;
 
 
+/* Recovery reason codes for VBNV_RECOVERY_REQUEST */
+/* Recovery not requested. */
+#define VBNV_RECOVERY_NOT_REQUESTED   0x00
+/* Recovery requested from legacy utility.  (Prior to the NV storage
+ * spec, recovery mode was a single bitfield; this value is reserved
+ * so that scripts which wrote 1 to the recovery field are
+ * distinguishable from scripts whch use the recovery reasons listed
+ * here. */
+#define VBNV_RECOVERY_LEGACY          0x01
+/* User manually requested recovery via recovery button */
+#define VBNV_RECOVERY_RO_MANUAL       0x02
+/* RW firmware failed signature check (neither RW firmware slot was valid) */
+#define VBNV_RECOVERY_RO_INVALID_RW   0x03
+/* S3 resume failed */
+#define VBNV_RECOVERY_RO_S3_RESUME    0x04
+/* TPM error in read-only firmware */
+#define VBNV_RECOVERY_RO_TPM_ERROR    0x05
+/* Unspecified/unknown error in read-only firmware */
+#define VBNV_RECOVERY_RO_UNSPECIFIED  0x3F
+/* User manually requested recovery by pressing a key at developer
+ * warning screen */
+#define VBNV_RECOVERY_RW_DEV_SCREEN   0x41
+/* No OS kernel detected */
+#define VBNV_RECOVERY_RW_NO_OS        0x42
+/* OS kernel failed signature check */
+#define VBNV_RECOVERY_RW_INVALID_OS   0x43
+/* TPM error in rewritable firmware */
+#define VBNV_RECOVERY_RW_TPM_ERROR    0x44
+/* Unspecified/unknown error in rewritable firmware */
+#define VBNV_RECOVERY_RW_UNSPECIFIED  0x7F
+/* DM-verity error */
+#define VBNV_RECOVERY_KE_DM_VERITY    0x81
+/* Unspecified/unknown error in kernel */
+#define VBNV_RECOVERY_KE_UNSPECIFIED  0xBF
+/* Recovery mode test from user-mode */
+#define VBNV_RECOVERY_US_TEST         0xC1
+/* Unspecified/unknown error in user-mode */
+#define VBNV_RECOVERY_US_UNSPECIFIED  0xFF
+
+
 /* Initialize the NV storage library.  This must be called before any
- * other functions in this library. Returns 0 if success, non-zero if
+ * other functions in this library.  Returns 0 if success, non-zero if
  * error.
  *
- * If you have access to global variables, you may want to wrap this
- * in your own VbNvOpen() function which allocates a context, acquires
- * a lock to prevent race conditions accessing the underlying storage,
- * reads the raw data from underlying storage, and calls VbNvSetup().
- * We don't do that in here because there are no global variables in
- * UEFI BIOS during PEI phase. */
+ * Proper calling procedure:
+ *    1) Allocate a context struct.
+ *    2) If multi-threaded/multi-process, acquire a lock to prevent
+ *       other processes from modifying the underlying storage.
+ *    3) Read underlying storage and fill in context->raw.
+ *    4) Call VbNvSetup().
+ *
+ * If you have access to global variables, you may want to wrap all
+ * that in your own VbNvOpen() function.  We don't do that in here
+ * because there are no global variables in UEFI BIOS during the PEI
+ * phase (that's also why we have to pass around a context pointer). */
 int VbNvSetup(VbNvContext* context);
 
 /* Clean up and flush changes back to the raw data.  This must be
- * called after other functions in this library.  Caller must check
- * context.raw_changed after calling this function.  Returns 0 if
+ * called after other functions in this library.  Returns 0 if
  * success, non-zero if error.
  *
+ * Proper calling procedure:
+ *    1) Call VbNvExit().
+ *    2) If context.raw_changed, write data back to underlying storage.
+ *    3) Release any lock you acquired before calling VbNvSetup().
+ *    4) Free the context struct.
+ *
  * If you have access to global variables, you may want to wrap this
- * in your own VbNvClose() function which calls VbNvTeardown(), writes
- * the underlying storage if context.raw_changed, releases the lock
- * acquired in VbNvOpen, and frees the context. */
+ * in your own VbNvClose() function. */
 int VbNvTeardown(VbNvContext* context);
 
 /* Read a NV storage parameter into *dest.  Returns 0 if success,
- * non-zero if error. */
+ * non-zero if error.
+ *
+ * This may only be called between VbNvSetup() and VbNvTeardown(). */
 int VbNvGet(VbNvContext* context, VbNvParam param, uint32_t* dest);
 
 /* Set a NV storage param to a new value.  Returns 0 if success,
- * non-zero if error. */
+ * non-zero if error.
+ *
+ * This may only be called between VbNvSetup() and VbNvTeardown(). */
 int VbNvSet(VbNvContext* context, VbNvParam param, uint32_t value);