commit 1f1ebb6d233ac5e07a9e0ad5bda1f10508beeff1
author David Rogers <davidrogers@google.com> Fri Jul 17 18:21:32 2020 -0700
committer CQ Bot Account <commit-bot@chromium.org> Tue Jul 21 00:30:33 2020 +0000
tree 77cbc72fd29fe6444f22e512bb0f1da96442ec95
parent 2d239e1ad910f3684fd4167e3543393b701a0310

pw_kvs: Add KVS method to get max size key-value

Add method to get the maximum size allowed for a key-value pair.

Change-Id: I09f83aeecdc2ea46ea7ae0d7891c89dc7c21eb13
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/14180
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: David Rogers <davidrogers@google.com>

pw_kvs/key_value_store_test.cc

diff --git a/pw_kvs/key_value_store_test.cc b/pw_kvs/key_value_store_test.cc
index f08f436..4479c56 100644
--- a/pw_kvs/key_value_store_test.cc
+++ b/pw_kvs/key_value_store_test.cc
@@ -430,8 +430,14 @@
                                                           default_format);
   ASSERT_OK(kvs.Init());
 
+  size_t max_key_value_size = kvs.max_key_value_size_bytes();
+  EXPECT_EQ(max_key_value_size,
+            KeyValueStore::max_key_value_size_bytes(
+                flash.partition.sector_size_bytes()));
+
   size_t max_value_size =
       flash.partition.sector_size_bytes() - sizeof(EntryHeader) - 1;
+  EXPECT_EQ(max_key_value_size, (max_value_size + 1));
 
   // Use the large_test_flash as a big chunk of data for the Put statement.
   ASSERT_GT(sizeof(large_test_flash), max_value_size + 2 * sizeof(EntryHeader));

pw_kvs/public/pw_kvs/internal/entry.h

diff --git a/pw_kvs/public/pw_kvs/internal/entry.h b/pw_kvs/public/pw_kvs/internal/entry.h
index 5305ab6..31b0acd 100644
--- a/pw_kvs/public/pw_kvs/internal/entry.h
+++ b/pw_kvs/public/pw_kvs/internal/entry.h
@@ -138,6 +138,10 @@
                    std::max(partition.alignment_bytes(), kMinAlignmentBytes));
   }
 
+  // Byte size of overhead (not-key, not-value) in an entry. Does not include
+  // any paddding used to get proper size alignment.
+  static constexpr size_t entry_overhead() { return sizeof(EntryHeader); }
+
   Address address() const { return address_; }
 
   void set_address(Address address) { address_ = address; }

pw_kvs/public/pw_kvs/key_value_store.h

diff --git a/pw_kvs/public/pw_kvs/key_value_store.h b/pw_kvs/public/pw_kvs/key_value_store.h
index 01b055d..6988d6f 100644
--- a/pw_kvs/public/pw_kvs/key_value_store.h
+++ b/pw_kvs/public/pw_kvs/key_value_store.h
@@ -303,6 +303,18 @@
 
   bool error_detected() const { return error_detected_; }
 
+  // Maximum number of bytes allowed for a key-value combination.
+  size_t max_key_value_size_bytes() const {
+    return max_key_value_size_bytes(partition_.sector_size_bytes());
+  }
+
+  // Maximum number of bytes allowed for a given sector size for a key-value
+  // combination.
+  static constexpr size_t max_key_value_size_bytes(
+      size_t partition_sector_size_bytes) {
+    return partition_sector_size_bytes - Entry::entry_overhead();
+  }
+
   // Check KVS for any error conditions. Primarily intended for test and
   // internal use.
   bool CheckForErrors();