Add stats for fuzzing

libraries/persistent_store/fuzz/Cargo.toml

@@ -11,6 +11,7 @@ cargo-fuzz = true
 [dependencies]
 libfuzzer-sys = "0.3"
 persistent_store = { path = "..", features = ["std"] }
+strum = { version = "0.19", features = ["derive"] }
 
 # Prevent this from interfering with workspaces
 [workspace]

libraries/persistent_store/fuzz/src/lib.rs

@@ -29,6 +29,9 @@
 #![allow(dead_code)]
 
 mod histogram;
+mod stats;
+
+pub use stats::{StatKey, Stats};
 
 /// Bit-level entropy source based on a byte slice shared reference.
 ///

libraries/persistent_store/fuzz/src/stats.rs

@@ -0,0 +1,187 @@
+// Copyright 2019-2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Helpers to compute and display fuzzing coverage statistics.
+//!
+//! This is not used during actual fuzzing, only when replaying a corpus to compute statistics.
+
+use crate::histogram::{bucket_from_width, Histogram};
+use crate::num_bits;
+use std::collections::HashMap;
+use strum::{Display, EnumIter, EnumString, IntoEnumIterator};
+
+/// Statistics for each fuzzing run.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, EnumIter, EnumString, Display)]
+pub enum StatKey {
+    /// The available entropy in bytes.
+    Entropy,
+
+    /// The size of a page in bytes.
+    PageSize,
+
+    /// The number of pages.
+    NumPages,
+
+    /// The maximum number times a page can be erased.
+    MaxPageErases,
+
+    /// The dirty length of the initial storage in bytes.
+    ///
+    /// This is the length of the prefix of the storage that is written using entropy before the
+    /// store is initialized. This permits to check the store against an invalid storage: it should
+    /// not crash but may misbehave.
+    DirtyLength,
+
+    /// The number of used erase cycles of the initial storage.
+    ///
+    /// This permits to check the store as if it already consumed lifetime. In particular it permits
+    /// to check the store when lifetime is almost out.
+    InitCycles,
+
+    /// The number of words written during fuzzing.
+    ///
+    /// This permits to get an idea of how much lifetime was exercised during fuzzing.
+    UsedLifetime,
+
+    /// Whether the store reached the end of the lifetime during fuzzing.
+    FinishedLifetime,
+
+    /// The number of times the store was fully compacted.
+    ///
+    /// The store is considered fully compacted when all pages have been compacted once. So each
+    /// page has been compacted at least that number of times.
+    NumCompactions,
+
+    /// The number of times the store was powered on.
+    PowerOnCount,
+
+    /// The number of times a transaction was applied.
+    TransactionCount,
+
+    /// The number of times a clear operation was applied.
+    ClearCount,
+
+    /// The number of times a prepare operation was applied.
+    PrepareCount,
+
+    /// The number of times an insert update was applied.
+    InsertCount,
+
+    /// The number of times a remove update was applied.
+    RemoveCount,
+
+    /// The number of times a store operation was interrupted.
+    InterruptionCount,
+}
+
+/// Statistics about multiple fuzzing runs.
+#[derive(Default)]
+pub struct Stats {
+    /// Maps each statistics to its histogram.
+    stats: HashMap<StatKey, Histogram>,
+}
+
+impl Stats {
+    /// Adds a measure for a statistics.
+    pub fn add(&mut self, key: StatKey, value: usize) {
+        self.stats.entry(key).or_default().add(value);
+    }
+
+    /// Merges another statistics into this one.
+    pub fn merge(&mut self, other: &Stats) {
+        for (&key, other) in &other.stats {
+            self.stats.entry(key).or_default().merge(other);
+        }
+    }
+
+    /// Returns the count of a bucket for a given key.
+    pub fn get_count(&self, key: StatKey, bucket: usize) -> Option<usize> {
+        self.stats.get(&key).and_then(|h| h.get(bucket))
+    }
+
+    /// Returns one past the highest non-empty bucket.
+    ///
+    /// In other words, all non-empty buckets of the histogram are smaller than the returned bucket.
+    fn bucket_lim(&self) -> usize {
+        self.stats
+            .values()
+            .map(|h| h.bucket_lim())
+            .max()
+            .unwrap_or(0)
+    }
+}
+
+impl std::fmt::Display for Stats {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        let mut matrix: Vec<Vec<String>> = Vec::new();
+
+        let mut header = Vec::new();
+        header.push(String::new());
+        let bits = num_bits(self.bucket_lim());
+        for width in 0..bits {
+            header.push(format!(" {}", bucket_from_width(width)));
+        }
+        header.push(" count".into());
+        matrix.push(header);
+
+        for key in StatKey::iter() {
+            let mut row = Vec::new();
+            row.push(format!("{}:", key));
+            for width in 0..bits {
+                row.push(match self.get_count(key, bucket_from_width(width)) {
+                    None => String::new(),
+                    Some(x) => format!(" {}", x),
+                });
+            }
+            let count = self.stats.get(&key).map_or(0, |h| h.count());
+            row.push(format!(" {}", count));
+            matrix.push(row);
+        }
+
+        write_matrix(f, matrix)
+    }
+}
+
+/// Prints a string aligned to the right for a given width.
+fn align(f: &mut std::fmt::Formatter, x: &str, n: usize) -> Result<(), std::fmt::Error> {
+    for _ in 0..n.saturating_sub(x.len()) {
+        write!(f, " ")?;
+    }
+    write!(f, "{}", x)
+}
+
+/// Prints a matrix with columns of minimal width to fit all elements.
+fn write_matrix(
+    f: &mut std::fmt::Formatter,
+    mut m: Vec<Vec<String>>,
+) -> Result<(), std::fmt::Error> {
+    if m.is_empty() {
+        return Ok(());
+    }
+    let num_cols = m.iter().map(|r| r.len()).max().unwrap();
+    let mut col_len = vec![0; num_cols];
+    for row in &mut m {
+        row.resize(num_cols, String::new());
+        for col in 0..num_cols {
+            col_len[col] = std::cmp::max(col_len[col], row[col].len());
+        }
+    }
+    for row in m {
+        for col in 0..num_cols {
+            align(f, &row[col], col_len[col])?;
+        }
+        writeln!(f)?;
+    }
+    Ok(())
+}