direct access for journal entries

src/lib.rs

@@ -4,7 +4,7 @@ extern crate alloc;
 
 use alloc::vec::Vec;
 use vapfs::{BlockDevice, Index};
-use crate::structs::{Inode, Superblock};
+use crate::structs::{Inode, JournalEntry, Superblock};
 
 pub mod btree;
 pub mod structs;
@@ -204,3 +204,28 @@ pub unsafe fn set_inode_allocation_status(index: Index, sb: &Superblock, bd: &mu
     let write_count = bd.write_blocks(&bitmap_buf);
     write_count == bitmap_length as usize
 }
+
+/// Reads a journal entry by index
+pub fn read_journal_entry(index: Index, sb: &Superblock, bd: &mut dyn BlockDevice) -> Option<JournalEntry> {
+    let mut buf: [u8; core::mem::size_of::<JournalEntry>()] = [0; core::mem::size_of::<JournalEntry>()];
+    bd.seek((sb.first_journal_block * sb.block_size as u64) + (index * core::mem::size_of::<JournalEntry>() as u64));
+    let read_count = bd.read_blocks(&mut buf);
+    if read_count < core::mem::size_of::<JournalEntry>() {
+        return None;
+    }
+    let mut entry = unsafe { core::ptr::read(buf.as_ptr() as *const JournalEntry) };
+    entry.convert_big_endian_to_native();
+    Some(entry)
+}
+
+/// Performs a direct write of a journal entry to the block device.
+/// # Safety
+/// unsafe because it assumes that the entry is correctly formatted and that everything has been performed correctly
+pub unsafe fn write_journal_entry(index: Index, sb: &Superblock, bd: &mut dyn BlockDevice, mut entry: JournalEntry) -> bool {
+    entry.convert_native_to_big_endian();
+    let mut buf: [u8; core::mem::size_of::<JournalEntry>()] = [0; core::mem::size_of::<JournalEntry>()];
+    core::ptr::write(buf.as_mut_ptr() as *mut JournalEntry, entry);
+    bd.seek((sb.first_journal_block * sb.block_size as u64) + (index * core::mem::size_of::<JournalEntry>() as u64));
+    let write_count = bd.write_blocks(&buf);
+    write_count == core::mem::size_of::<JournalEntry>()
+}

src/structs.rs

@@ -288,12 +288,55 @@ pub enum InodeFlags {
 /// # JournalEntry
 /// A Journal Entry
 #[repr(C)]
-pub struct JournalHeader {
+pub struct JournalEntry {
     pub flags: u32,
-    pub operation: JournalOperation,
+    /// JournalOperation
+    pub operation: u32,
     /// crc32 hash of the content with flags set to zero, used to verify journal was fully written without verifying the stage
     pub zeroed_content_crc32: u32,
-    pub content: JournalEntry,
+    pub content: JournalEntryContents,
+}
+
+impl JournalEntry {
+    /// in-place conversion from the storage representation (big endian) to the native representation
+    pub fn convert_big_endian_to_native(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::from_be(self.flags);
+            self.operation = u32::from_be(self.operation);
+            self.zeroed_content_crc32 = u32::from_be(self.zeroed_content_crc32);
+            match self.operation {
+                0 => { // SingleBlockWrite
+                    unsafe { self.content.block_write.convert_big_endian_to_native() };
+                }
+                1 => { // MultiblockWrite
+                    unsafe { self.content.multiblock_write.convert_big_endian_to_native() };
+                }
+
+                _ => {}
+            }
+        }
+    }
+
+    /// in-place conversion from the native representation to the storage representation (big endian)
+    pub fn convert_native_to_big_endian(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::to_be(self.flags);
+            self.operation = u32::to_be(self.operation);
+            self.zeroed_content_crc32 = u32::to_be(self.zeroed_content_crc32);
+            match self.operation {
+                0 => { // SingleBlockWrite
+                    unsafe { self.content.block_write.convert_native_to_big_endian() };
+                }
+                1 => { // MultiblockWrite
+                    unsafe { self.content.multiblock_write.convert_native_to_big_endian() };
+                }
+
+                _ => {}
+            }
+        }
+    }
 }
 
 /// # JournalOperation
@@ -326,8 +369,8 @@ pub enum JournalOperation {
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct JournalBlockWrite {
-    /// flags stating how far the write has progressed
-    pub flags: JBRFlags,
+    /// JBRFlags stating how far the write has progressed
+    pub flags: u32,
     /// are we writing to an inode instead of a data block?
     pub target_is_inode: bool,
     /// block number of target
@@ -338,6 +381,30 @@ pub struct JournalBlockWrite {
     pub source_block_crc32: u32,
 }
 
+impl JournalBlockWrite {
+    /// in-place conversion from the storage representation (big endian) to the native representation
+    pub fn convert_big_endian_to_native(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::from_be(self.flags);
+            self.target_block = u64::from_be(self.target_block);
+            self.source_block = u64::from_be(self.source_block);
+            self.source_block_crc32 = u32::from_be(self.source_block_crc32);
+        }
+    }
+
+    /// in-place conversion from the native representation to the storage representation (big endian)
+    pub fn convert_native_to_big_endian(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::to_be(self.flags);
+            self.target_block = u64::to_be(self.target_block);
+            self.source_block = u64::to_be(self.source_block);
+            self.source_block_crc32 = u32::to_be(self.source_block_crc32);
+        }
+    }
+}
+
 /// # JBRFlags
 /// Flags field of a JournalBlockWrite
 #[repr(u32)]
@@ -375,8 +442,8 @@ pub enum JBRFlags {
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct JournalMultiblockWrite {
-    /// flags stating how far the write has progressed
-    pub flags: JMWFlags,
+    /// JMWFlags stating how far the write has progressed
+    pub flags: u32,
     /// block number of first target block
     pub target_block: Index,
     /// number of target blocks
@@ -387,6 +454,32 @@ pub struct JournalMultiblockWrite {
     pub list_block_crc32: u32,
 }
 
+impl JournalMultiblockWrite {
+    /// in-place conversion from the storage representation (big endian) to the native representation
+    pub fn convert_big_endian_to_native(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::from_be(self.flags);
+            self.target_block = u64::from_be(self.target_block);
+            self.target_block_count = u64::from_be(self.target_block_count);
+            self.list_block = u64::from_be(self.list_block);
+            self.list_block_crc32 = u32::from_be(self.list_block_crc32);
+        }
+    }
+
+    /// in-place conversion from the native representation to the storage representation (big endian)
+    pub fn convert_native_to_big_endian(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            self.flags = u32::to_be(self.flags);
+            self.target_block = u64::to_be(self.target_block);
+            self.target_block_count = u64::to_be(self.target_block_count);
+            self.list_block = u64::to_be(self.list_block);
+            self.list_block_crc32 = u32::to_be(self.list_block_crc32);
+        }
+    }
+}
+
 /// # JMWFlags
 /// Flags field of a JournalMultiblockWrite
 #[repr(u32)]
@@ -417,10 +510,32 @@ pub struct ListBlock {
     pub direct_block_addresses: [Index; 12],
 }
 
-/// # JournalEntry
+impl ListBlock {
+    /// in-place conversion from the storage representation (big endian) to the native representation
+    pub fn convert_big_endian_to_native(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            for i in 0..12 {
+                self.direct_block_addresses[i] = u64::from_be(self.direct_block_addresses[i]);
+            }
+        }
+    }
+
+    /// in-place conversion from the native representation to the storage representation (big endian)
+    pub fn convert_native_to_big_endian(&mut self) {
+        #[cfg(target_endian = "little")]
+        {
+            for i in 0..12 {
+                self.direct_block_addresses[i] = u64::to_be(self.direct_block_addresses[i]);
+            }
+        }
+    }
+}
+
+/// # JournalEntryContents
 /// union of all possible journal entries
 #[repr(C)]
-pub union JournalEntry {
+pub union JournalEntryContents {
     pub block_write: JournalBlockWrite,
     pub multiblock_write: JournalMultiblockWrite,
 }