TDBStore: Keep copy of reserved data on both areas.

Change the "reserved data" logic so that every time we erase and area,
the content of reserved data is then immediately copied to newly erased
area. This keeps two copies of the data.
When data is requested, return only if checksum is matching.
When data is written, only allow if BOTH checksums are incorrect, meaning
that areas are either corrupted or erased.
Only exception is TDBStore::reset() which erases all keys and reserved data.

Removed all logic that tried to detect, if reserved are was erased or
corrupted. Rely entirely on checksum.

Add moduletest for reserved data.

Author: Seppo Takalo

features/storage/kvstore/tdbstore/TDBStore.cpp

@@ -848,33 +848,11 @@ int TDBStore::garbage_collection()
     int ret;
     size_t ind;
 
-    ret = check_erase_before_write(1 - _active_area, 0, _master_record_offset + _master_record_size);
+    ret = reset_area(1 - _active_area);
     if (ret) {
         return ret;
     }
 
-    ret = do_reserved_data_get(0, RESERVED_AREA_SIZE);
-
-    if (!ret) {
-        // Copy reserved data
-        to_offset = 0;
-        reserved_size = _master_record_offset;
-
-        while (reserved_size) {
-            chunk_size = std::min(work_buf_size, reserved_size);
-            ret = read_area(_active_area, to_offset, chunk_size, _work_buf);
-            if (ret) {
-                return ret;
-            }
-            ret = write_area(1 - _active_area, to_offset, chunk_size, _work_buf);
-            if (ret) {
-                return ret;
-            }
-            to_offset += chunk_size;
-            reserved_size -= chunk_size;
-        }
-    }
-
     to_offset = _master_record_offset + _master_record_size;
 
     // Initialize in case table is empty
@@ -1078,7 +1056,7 @@ int TDBStore::init()
         // Master record may be either corrupt or erased - either way erase it
         // (this will do nothing if already erased)
         if (ret == MBED_ERROR_INVALID_DATA_DETECTED) {
-            if (check_erase_before_write(area, _master_record_offset, _master_record_size, true)) {
+            if (reset_area(area)) {
                 MBED_ERROR(MBED_ERROR_READ_FAILED, "TDBSTORE: Unable to reset area at init");
             }
             area_state[area] = TDBSTORE_AREA_STATE_EMPTY;
@@ -1143,11 +1121,9 @@ int TDBStore::init()
         }
     }
 
-    reserved_ret = do_reserved_data_get(0, RESERVED_AREA_SIZE);
-
-    // If we either have a corrupt record somewhere, or the reserved area is corrupt,
-    // perform garbage collection to salvage all preceding records and/or clean reserved area.
-    if ((ret == MBED_ERROR_INVALID_DATA_DETECTED) || (reserved_ret == MBED_ERROR_INVALID_DATA_DETECTED)) {
+    // If we either have a corrupt record somewhere
+    // perform garbage collection to salvage all preceding records.
+    if ((ret == MBED_ERROR_INVALID_DATA_DETECTED)) {
         ret = garbage_collection();
         if (ret) {
             MBED_ERROR(ret, "TDBSTORE: Unable to perform GC at init");
@@ -1198,8 +1174,19 @@ int TDBStore::deinit()
 
 int TDBStore::reset_area(uint8_t area)
 {
+    uint8_t buf[RESERVED_AREA_SIZE + sizeof(reserved_trailer_t)];
+    int ret;
+    bool copy_reserved_data = do_reserved_data_get(buf, sizeof(buf), 0, buf + RESERVED_AREA_SIZE) == MBED_SUCCESS;
+
     // Erase reserved area and master record
-    return check_erase_before_write(area, 0, _master_record_offset + _master_record_size, true);
+    ret = check_erase_before_write(area, 0, _master_record_offset + _master_record_size, true);
+    if (ret) {
+        return ret;
+    }
+    if (copy_reserved_data) {
+        ret = write_area(area, 0, sizeof(buf), buf);
+    }
+    return ret;
 }
 
 int TDBStore::reset()
@@ -1215,7 +1202,7 @@ int TDBStore::reset()
 
     // Reset both areas
     for (area = 0; area < _num_areas; area++) {
-        ret = reset_area(area);
+        ret = check_erase_before_write(area, 0, _master_record_offset + _master_record_size, true);
         if (ret) {
             goto end;
         }
@@ -1362,116 +1349,97 @@ void TDBStore::update_all_iterators(bool added, uint32_t ram_table_ind)
 int TDBStore::reserved_data_set(const void *reserved_data, size_t reserved_data_buf_size)
 {
     reserved_trailer_t trailer;
-    int os_ret, ret = MBED_SUCCESS;
+    int ret;
 
     if (reserved_data_buf_size > RESERVED_AREA_SIZE) {
         return MBED_ERROR_INVALID_SIZE;
     }
 
     _mutex.lock();
 
-    ret = do_reserved_data_get(0, RESERVED_AREA_SIZE);
-    if ((ret == MBED_SUCCESS) || (ret == MBED_ERROR_INVALID_DATA_DETECTED)) {
+    ret = do_reserved_data_get(0, 0);
+    if (ret == MBED_SUCCESS) {
         ret = MBED_ERROR_WRITE_FAILED;
         goto end;
-    } else if (ret != MBED_ERROR_ITEM_NOT_FOUND) {
-        goto end;
-    }
-
-    ret = write_area(_active_area, 0, reserved_data_buf_size, reserved_data);
-    if (ret) {
-        goto end;
     }
 
     trailer.trailer_size = sizeof(trailer);
     trailer.data_size = reserved_data_buf_size;
     trailer.crc = calc_crc(initial_crc, reserved_data_buf_size, reserved_data);
 
-    ret = write_area(_active_area, RESERVED_AREA_SIZE, sizeof(trailer), &trailer);
-    if (ret) {
-        goto end;
-    }
-
-    os_ret = _buff_bd->sync();
-    if (os_ret) {
-        ret = MBED_ERROR_WRITE_FAILED;
-        goto end;
+    /*
+     * Write to both areas
+     * Both must success, as they are required to be erased when TDBStore initializes
+     * its area
+     */
+    for (int i = 0; i < _num_areas; ++i) {
+        ret = write_area(i, 0, reserved_data_buf_size, reserved_data);
+        if (ret) {
+            goto end;
+        }
+        ret = write_area(i, RESERVED_AREA_SIZE, sizeof(trailer), &trailer);
+        if (ret) {
+            goto end;
+        }
+        ret = _buff_bd->sync();
+        if (ret) {
+            goto end;
+        }
     }
-
+    ret = MBED_SUCCESS;
 end:
     _mutex.unlock();
     return ret;
 }
 
-int TDBStore::do_reserved_data_get(void *reserved_data, size_t reserved_data_buf_size, size_t *actual_data_size)
+int TDBStore::do_reserved_data_get(void *reserved_data, size_t reserved_data_buf_size, size_t *actual_data_size, void *copy_trailer)
 {
     reserved_trailer_t trailer;
-    uint8_t *buf;
+    uint8_t buf[RESERVED_AREA_SIZE];
     int ret;
-    bool erased = true;
-    size_t actual_size;
-    uint32_t crc = initial_crc;
-    uint32_t offset;
-    uint8_t blank = _buff_bd->get_erase_value();
-
-    ret = read_area(_active_area, RESERVED_AREA_SIZE, sizeof(trailer), &trailer);
-    if (ret) {
-        return ret;
-    }
+    uint32_t crc;
 
-    buf = reinterpret_cast <uint8_t *>(&trailer);
-    for (uint32_t i = 0; i < sizeof(trailer); i++) {
-        if (buf[i] != blank) {
-            erased = false;
-            break;
+    /*
+     * Try to keep reserved data identical on both areas, therefore
+     * we can return any of these data, if the checmsum is correct.
+     */
+    for (int i = 0; i < _num_areas; ++i) {
+        ret = read_area(i, RESERVED_AREA_SIZE, sizeof(trailer), &trailer);
+        if (ret) {
+            return ret;
         }
-    }
 
-    if (!erased) {
-        actual_size = trailer.data_size;
-        if (actual_data_size) {
-            *actual_data_size = actual_size;
+        // First validy check: is the trailer header size correct
+        if (trailer.trailer_size != sizeof(trailer)) {
+            continue;
         }
-        if (reserved_data_buf_size < actual_size) {
-            return MBED_ERROR_INVALID_SIZE;
+        // Second validy check: Is the data too big (corrupt header)
+        if (trailer.data_size > RESERVED_AREA_SIZE) {
+            continue;
         }
-    } else {
-        actual_size = std::min((size_t) RESERVED_AREA_SIZE, reserved_data_buf_size);
-    }
-
-    if (reserved_data) {
-        buf = reinterpret_cast <uint8_t *>(reserved_data);
-    } else {
-        buf = _work_buf;
-    }
-
-    offset = 0;
 
-    while (actual_size) {
-        uint32_t chunk = std::min(work_buf_size, (uint32_t) actual_size);
-        ret = read_area(_active_area, offset, chunk, buf + offset);
+        // Next, verify the checksum
+        ret = read_area(i, 0, trailer.data_size, buf);
         if (ret) {
             return ret;
         }
-        for (uint32_t i = 0; i < chunk; i++) {
-            if (buf[i] != blank) {
-                erased = false;
-                break;
+        crc = calc_crc(initial_crc, trailer.data_size, buf);
+        if (crc == trailer.crc) {
+            // Correct data, copy it and return to caller
+            if (reserved_data) {
+                memcpy(reserved_data, buf, trailer.data_size);
             }
+            if (actual_data_size) {
+                *actual_data_size = trailer.data_size;
+            }
+            if (copy_trailer) {
+                memcpy(copy_trailer, &trailer, sizeof(trailer));
+            }
+            return MBED_SUCCESS;
         }
-
-        crc = calc_crc(crc, chunk, buf + offset);
-        offset += chunk;
-        actual_size -= chunk;
     }
 
-    if (erased) {
-        return MBED_ERROR_ITEM_NOT_FOUND;
-    } else if (crc != trailer.crc) {
-        return MBED_ERROR_INVALID_DATA_DETECTED;
-    }
-
-    return MBED_SUCCESS;
+    return MBED_ERROR_ITEM_NOT_FOUND;
 }
 
 int TDBStore::reserved_data_get(void *reserved_data, size_t reserved_data_buf_size, size_t *actual_data_size)

features/storage/kvstore/tdbstore/TDBStore.h

@@ -23,6 +23,7 @@
 #include "features/storage/blockdevice/BlockDevice.h"
 #include "features/storage/blockdevice/BufferedBlockDevice.h"
 #include "PlatformMutex.h"
+#include "mbed_error.h"
 
 namespace mbed {
 
@@ -74,7 +75,7 @@ class TDBStore : public KVStore {
 
 
     /**
-     * @brief Reset TDBStore contents (clear all keys)
+     * @brief Reset TDBStore contents (clear all keys) and reserved data
      *
      * @returns MBED_SUCCESS                        Success.
      *          MBED_ERROR_NOT_READY                Not initialized.
@@ -338,6 +339,8 @@ class TDBStore : public KVStore {
 
     /**
      * @brief Reset an area (erase its start).
+     *        This erases master record, but preserves the
+     *        reserved area data.
      *
      * @param[in]  area                   Area.
      *
@@ -524,16 +527,22 @@ class TDBStore : public KVStore {
 
     /**
      * @brief Get data from reserved area - worker function.
+     *        This verifies that reserved data on both areas have
+     *        correct checksums. If given pointer is not NULL, also
+     *        write the reserved data to buffer. If checksums are not
+     *        valid, return error code, and don't write anything to any
+     *        pointers.
      *
-     * @param[in]  reserved_data        Reserved data buffer (0 to return nothing).
+     * @param[out] reserved_data        Reserved data buffer (NULL to return nothing).
      * @param[in]  reserved_data_buf_size
      *                                  Reserved data buffer size.
-     * @param[in]  actual_data_size     Return data size.
+     * @param[out] actual_data_size     If not NULL, return actual data size.
+     * @param[out] copy_trailer         If not NULL, copy the trailer content to given buffer.
      *
      * @returns 0 on success or a negative error code on failure
      */
     int do_reserved_data_get(void *reserved_data, size_t reserved_data_buf_size,
-                             size_t *actual_data_size = 0);
+                             size_t *actual_data_size = 0, void *copy_trailer = 0);
 
     /**
      * @brief Update all iterators after adding or deleting of keys.