fix block devices getting reported as 0 size

flake.lock

@@ -17,16 +17,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1685043448,
+        "lastModified": 1686237827,
-        "narHash": "sha256-U3BwyDc2OzBcZ8tD09qXibyivgOtOQFTFCVgFyJ+6MM=",
+        "narHash": "sha256-fAZB+Zkcmc+qlauiFnIH9+2qgwM0NO/ru5pWEw3tDow=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "9886352ec9ab3945896ee8a4185e961fe29df209",
+        "rev": "81ed90058a851eb73be835c770e062c6938c8a9e",
         "type": "github"
       },
       "original": {
         "id": "nixpkgs",
-        "ref": "nixos-22.11",
+        "ref": "nixos-23.05",
         "type": "indirect"
       }
     },

flake.nix

@@ -1,41 +1,33 @@
 {
   inputs = {
     flake-utils.url = "github:numtide/flake-utils";
-    nixpkgs.url = "nixpkgs/nixos-22.11";
+    nixpkgs.url = "nixpkgs/nixos-23.05";
   };
 
-  outputs = { self, nixpkgs, flake-utils }: let
+  outputs = {
-      buildCube = pkgs: pkgs.rustPlatform.buildRustPackage rec {
+    self,
-        version = "0.1.0";
+    nixpkgs,
-        pname = "cube";
+    flake-utils,
-
+  }:
-        src = ./.;
+    flake-utils.lib.eachDefaultSystem (
-
-        cargoSha256 = "sha256-tHcIwMQrGIRC6W0/B476QT5nOUY/5KkzEeJKbg3sFUA=";
-
-        meta = with pkgs.lib; {
-          description = "A basic NBD block server with a single gimmick";
-          homepage = "https://github.com/icewind1991/cube";
-          license = licenses.mit;
-          platforms = platforms.linux;
-        };
-      };
-    in flake-utils.lib.eachDefaultSystem (
       system: let
-        pkgs = nixpkgs.legacyPackages."${system}";
+        pkgs = (import nixpkgs) {
-      in
+          inherit system;
-        rec {
+        };
-          # `nix build`
+      in rec {
-          packages.cube = buildCube pkgs;
+        # `nix build`
-          defaultPackage = packages.cube;
+        packages = rec {
-          defaultApp = packages.cube;
+          cube = pkgs.callPackage (import ./package.nix) {};
+          default = cube;
+        };
 
-          # `nix develop`
+        # `nix develop`
-          devShell = pkgs.mkShell {
+        devShells.default = pkgs.mkShell {
-            nativeBuildInputs = with pkgs; [ rustc cargo bacon cargo-edit cargo-outdated ];
+          nativeBuildInputs = with pkgs; [rustc cargo bacon cargo-edit cargo-outdated];
-          };
+        };
-        }
+      }
-    ) // {
+    )
+    // {
       nixosModule = {
         config,
         lib,
@@ -43,16 +35,18 @@
         ...
       }:
         with lib; let
-          cube = buildCube pkgs;
+          cube = pkgs.callPackage (import ./package.nix) {};
           cfg = config.services.cube;
           format = pkgs.formats.toml {};
-          configFile = format.generate "cube.toml" ({
+          configFile = format.generate "cube.toml" {
             inherit (cfg) listen;
-            exports = mapAttrs (_: export: {
+            exports =
-              inherit (export) path;
+              mapAttrs (_: export: {
-              read_only = export.readOnly;
+                inherit (export) path;
-            }) cfg.exports;
+                read_only = export.readOnly;
-          });
+              })
+              cfg.exports;
+          };
           pkg = self.defaultPackage.${pkgs.system};
         in {
           options.services.cube = {

package.nix

@@ -0,0 +1,23 @@
+{
+  rustPlatform,
+  lib,
+}: let
+  src = lib.sources.sourceByRegex (lib.cleanSource ./.) ["Cargo.*" "(src)(/.*)?"];
+in
+  rustPlatform.buildRustPackage rec {
+    version = "0.1.0";
+    pname = "cube";
+
+    inherit src;
+
+    cargoLock = {
+      lockFile = ./Cargo.lock;
+    };
+
+    meta = with lib; {
+      description = "A basic NBD block server with a single gimmick";
+      homepage = "https://github.com/icewind1991/cube";
+      license = licenses.mit;
+      platforms = platforms.linux;
+    };
+  }

src/config.rs

@@ -7,6 +7,7 @@ use std::fs::{read_to_string, File, OpenOptions};
 use std::net::ToSocketAddrs;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
+use tracing::{debug, info};
 
 #[derive(Debug, Deserialize)]
 pub struct Config {
@@ -103,6 +104,19 @@ impl ExportConfig {
             err: e,
             path: self.path.clone(),
         })?;
+        let size = match meta.len() {
+            0 => {
+                let path = self.path.canonicalize().map_err(|e| HandshakeError::Open {
+                    err: e,
+                    path: self.path.clone(),
+                })?;
+                if path != self.path {
+                    debug!(path = ?self.path, canonicalized = ?path, "path is configured in non canonicalized form");
+                }
+                get_block_size(&path).ok_or_else(|| HandshakeError::UnknownSize(path))?
+            }
+            size => size,
+        };
 
         let readonly = self.readonly || meta.permissions().readonly();
         let mut opt = OpenOptions::new();
@@ -116,9 +130,11 @@ impl ExportConfig {
             path: self.path.clone(),
         })?;
 
+        info!(readonly, size, "go export meta");
+
         Ok(Export {
             readonly,
-            size: meta.len(),
+            size,
             data: file,
             resizeable: false,
             rotational: false,
@@ -128,6 +144,18 @@ impl ExportConfig {
     }
 }
 
+#[tracing::instrument]
+fn get_block_size(path: &Path) -> Option<u64> {
+    let device = path.strip_prefix("/dev").ok()?;
+    let mut sys_path = PathBuf::from("/sys/class/block");
+    sys_path.push(device);
+    sys_path.push("size");
+    debug!(sysfs_path = ?sys_path, "getting block size");
+    let size_str = read_to_string(sys_path).ok()?;
+    debug!(block_count = size_str, "got size");
+    size_str.trim().parse().ok().map(|blocks: u64| blocks * 512)
+}
+
 #[derive(Debug, Clone, Deserialize)]
 #[serde(from = "HashMap<String, ExportConfig>")]
 pub struct Exports {

src/error.rs

@@ -53,6 +53,8 @@ pub enum HandshakeError {
     UnknownExport(String),
     #[error("Failed to open {path}")]
     Open { path: PathBuf, err: IoError },
+    #[error("Failed to determine size of source {0:?}")]
+    UnknownSize(PathBuf),
 }
 
 impl From<HandshakeError> for IoError {
@@ -62,6 +64,10 @@ impl From<HandshakeError> for IoError {
             HandshakeError::UnknownExport(export) => {
                 IoError::new(ErrorKind::InvalidData, format!("Unknown export: {export}"))
             }
+            HandshakeError::UnknownSize(path) => IoError::new(
+                ErrorKind::InvalidData,
+                format!("Failed to get size of: {path:?}"),
+            ),
         }
     }
 }