Derive the block size from the log block size (#662)

Derives the block size from the log block size.

Author: dkovba

Sources/ContainerizationEXT4/EXT4+Formatter.swift

@@ -25,7 +25,8 @@ extension EXT4 {
     /// The `EXT4.Formatter` class provides methods to format a block device with the ext4 filesystem.
     /// It allows customization of block size and maximum disk size.
     public class Formatter {
-        let blockSize: UInt32
+        private let logBlockSize: UInt32 = 2
+        var blockSize: UInt32 { 1024 << logBlockSize }
         private var size: UInt64
         private let groupDescriptorSize: UInt32 = 32
 
@@ -61,8 +62,6 @@ extension EXT4 {
         ///
         /// - Parameters:
         ///   - devicePath: The path to the block device where the ext4 filesystem will be created.
-        ///   - blockSize: The block size of the ext4 filesystem, specified in bytes. Common values are
-        ///                4096 (4KB) or 1024 (1KB). Default is 4096 (4KB)
         ///   - minDiskSize: The minimum disk size required for the formatted filesystem.
         ///
         /// - Note: This ext4 formatter is designed for creating block devices out of container images and does not support all the
@@ -71,7 +70,7 @@ extension EXT4 {
         ///
         /// - Important: Ensure that the destination block device is accessible and has sufficient permissions
         ///              for formatting. The formatting process will erase all existing data on the device.
-        public init(_ devicePath: FilePath, blockSize: UInt32 = 4096, minDiskSize: UInt64 = 256.kib()) throws {
+        public init(_ devicePath: FilePath, minDiskSize: UInt64 = 256.kib()) throws {
             /// The constructor performs the following steps:
             ///
             /// 1. Creates the first 10 inodes:
@@ -96,7 +95,6 @@ extension EXT4 {
                 throw Error.notFound(devicePath)
             }
             self.handle = fileHandle
-            self.blockSize = blockSize
             self.size = minDiskSize
             // make this a 0 byte file
             guard ftruncate(self.handle.fileDescriptor, 0) == 0 else {
@@ -850,8 +848,8 @@ extension EXT4 {
             let freeInodesCount = computedInodes.lo - totalInodes
             superblock.freeInodesCount = freeInodesCount
             superblock.firstDataBlock = 0
-            superblock.logBlockSize = 2
-            superblock.logClusterSize = 2
+            superblock.logBlockSize = logBlockSize
+            superblock.logClusterSize = logBlockSize
             superblock.blocksPerGroup = self.blocksPerGroup
             superblock.clustersPerGroup = self.blocksPerGroup
             superblock.inodesPerGroup = blockGroupSize.inodesPerGroup

Sources/ContainerizationEXT4/EXT4+Reader.swift

@@ -32,9 +32,7 @@ extension EXT4 {
 
         var hardlinks: [FilePath: InodeNumber] = [:]
         var tree: EXT4.FileTree = EXT4.FileTree(EXT4.RootInode, ".")
-        var blockSize: UInt64 {
-            UInt64(1024 * (1 << _superBlock.logBlockSize))
-        }
+        var blockSize: UInt64 { UInt64(_superBlock.blockSize) }
 
         private var groupDescriptorSize: UInt16 {
             if _superBlock.featureIncompat & EXT4.IncompatFeature.bit64.rawValue != 0 {
@@ -120,7 +118,7 @@ extension EXT4 {
         }
 
         private func readGroupDescriptor(_ number: UInt32) throws -> GroupDescriptor {
-            let bs = UInt64(1024 * (1 << _superBlock.logBlockSize))
+            let bs = self.blockSize
             let offset = bs + UInt64(number) * UInt64(self.groupDescriptorSize)
             try self.handle.seek(toOffset: offset)
             guard let data = try? self.handle.read(upToCount: MemoryLayout<EXT4.GroupDescriptor>.size) else {

Sources/ContainerizationEXT4/EXT4+Types.swift

@@ -28,6 +28,7 @@ extension EXT4 {
         public var firstDataBlock: UInt32 = 0
         public var logBlockSize: UInt32 = 0
         public var logClusterSize: UInt32 = 0
+        public var blockSize: UInt32 { 1024 << logBlockSize }
         public var blocksPerGroup: UInt32 = 0
         public var clustersPerGroup: UInt32 = 0
         public var inodesPerGroup: UInt32 = 0

Tests/ContainerizationEXT4Tests/TestEXT4Reader+IO.swift

@@ -37,14 +37,13 @@ struct EXT4PathIOTests {
     ///   }
     private func buildFS(
         minDiskSize: UInt64 = 4 * 1024 * 1024,  // 4 MiB is enough for these tests
-        blockSize: UInt32 = 4096,
         populate: (EXT4.Formatter) throws -> Void
     ) throws -> URL {
         let url = makeTempImageURL()
         let path = FilePath(url.path)
 
         // 1) Format image
-        let formatter = try EXT4.Formatter(path, blockSize: blockSize, minDiskSize: minDiskSize)
+        let formatter = try EXT4.Formatter(path, minDiskSize: minDiskSize)
 
         // 2) Populate contents
         try populate(formatter)