[cache_metadata_size (rust)] First code drop

src/bin/pdata_tools.rs

@@ -30,6 +30,8 @@ fn main_() -> Result<()> {
         cache_check::run(&new_args);
     } else if name_eq(name, "cache_dump") {
         cache_dump::run(&new_args);
+    } else if name_eq(name, "cache_metadata_size") {
+        cache_metadata_size::run(&new_args);
     } else if name_eq(name, "cache_repair") {
         cache_repair::run(&new_args);
     } else if name_eq(name, "cache_restore") {

src/cache/metadata_size.rs

@@ -0,0 +1,19 @@
+use anyhow::Result;
+
+pub struct CacheMetadataSizeOptions {
+    pub nr_blocks: u64,
+    pub max_hint_width: u32, // bytes
+}
+
+pub fn metadata_size(opts: &CacheMetadataSizeOptions) -> Result<u64> {
+    const SECTOR_SHIFT: u64 = 9; // 512 bytes per sector
+    const BYTES_PER_BLOCK_SHIFT: u64 = 4; // 16 bytes for key and value
+    const TRANSACTION_OVERHEAD: u64 = 8192; // in sectors; 4 MB
+    const HINT_OVERHEAD_PER_BLOCK: u64 = 8; // 8 bytes for the key
+
+    let mapping_size = (opts.nr_blocks << BYTES_PER_BLOCK_SHIFT) >> SECTOR_SHIFT;
+    let hint_size =
+        (opts.nr_blocks * (opts.max_hint_width as u64 + HINT_OVERHEAD_PER_BLOCK)) >> SECTOR_SHIFT;
+
+    Ok(TRANSACTION_OVERHEAD + mapping_size + hint_size)
+}

src/cache/mod.rs

@@ -3,6 +3,7 @@ pub mod dump;
 pub mod hint;
 pub mod ir;
 pub mod mapping;
+pub mod metadata_size;
 pub mod repair;
 pub mod restore;
 pub mod superblock;

src/commands/cache_metadata_size.rs

@@ -0,0 +1,88 @@
+extern crate clap;
+
+use clap::{value_t_or_exit, App, Arg, ArgGroup};
+use std::ffi::OsString;
+use std::process;
+
+use crate::cache::metadata_size::{metadata_size, CacheMetadataSizeOptions};
+use crate::math::div_up;
+
+//------------------------------------------
+
+fn parse_args<I, T>(args: I) -> CacheMetadataSizeOptions
+where
+    I: IntoIterator<Item = T>,
+    T: Into<OsString> + Clone,
+{
+    let parser = App::new("cache_metadata_size")
+        .version(crate::version::tools_version())
+        .about("Estimate the size of the metadata device needed for a given configuration.")
+        .usage("cache_metadata_size [OPTIONS] <--device-size <SECTORS> --block-size <SECTORS> | --nr-blocks <NUM>>")
+        // options
+        .arg(
+            Arg::with_name("BLOCK_SIZE")
+                .help("Specify the size of each cache block")
+                .long("block-size")
+                .requires("DEVICE_SIZE")
+                .value_name("SECTORS"),
+        )
+        .arg(
+            Arg::with_name("DEVICE_SIZE")
+                .help("Specify total size of the fast device used in the cache")
+                .long("device-size")
+                .requires("BLOCK_SIZE")
+                .value_name("SECTORS"),
+        )
+        .arg(
+            Arg::with_name("NR_BLOCKS")
+                .help("Specify the number of cache blocks")
+                .long("nr-blocks")
+                .value_name("NUM"),
+        )
+        .arg(
+            Arg::with_name("MAX_HINT_WIDTH")
+                .help("Specity the per-block hint width")
+                .long("max-hint-width")
+                .value_name("BYTES")
+                .default_value("4"),
+        )
+        .group(
+            ArgGroup::with_name("selection")
+            .args(&["DEVICE_SIZE", "NR_BLOCKS"])
+            .required(true)
+        );
+
+    let matches = parser.get_matches_from(args);
+
+    let nr_blocks = matches.value_of("NR_BLOCKS").map_or_else(
+        || {
+            let device_size = value_t_or_exit!(matches.value_of("DEVICE_SIZE"), u64);
+            let block_size = value_t_or_exit!(matches.value_of("BLOCK_SIZE"), u32);
+            div_up(device_size, block_size as u64)
+        },
+        |_| value_t_or_exit!(matches.value_of("NR_BLOCKS"), u64),
+    );
+
+    let max_hint_width = value_t_or_exit!(matches.value_of("MAX_HINT_WIDTH"), u32);
+
+    CacheMetadataSizeOptions {
+        nr_blocks,
+        max_hint_width,
+    }
+}
+
+pub fn run(args: &[std::ffi::OsString]) {
+    let opts = parse_args(args);
+
+    match metadata_size(&opts) {
+        Ok(size) => {
+            println!("{} sectors", size);
+        }
+        Err(reason) => {
+            eprintln!("{}", reason);
+            process::exit(1);
+        }
+    }
+}
+
+//------------------------------------------

src/commands/mod.rs

@@ -1,5 +1,6 @@
 pub mod cache_check;
 pub mod cache_dump;
+pub mod cache_metadata_size;
 pub mod cache_repair;
 pub mod cache_restore;
 pub mod era_check;