Kernel: Convert the DiskBackedFS write API to take "const u8*"

This way clients are not required to have instantiated ByteBuffers
and can choose whatever memory scheme works best for them.

Also converted some of the Ext2FS code to use stack buffers instead.

Kernel/FileSystem/DiskBackedFileSystem.cpp

@@ -81,15 +81,13 @@ DiskBackedFS::~DiskBackedFS()
 {
 }
 
-bool DiskBackedFS::write_block(unsigned index, const ByteBuffer& data)
+bool DiskBackedFS::write_block(unsigned index, const u8* data)
 {
 #ifdef DBFS_DEBUG
     kprintf("DiskBackedFileSystem::write_block %u, size=%u\n", index, data.size());
 #endif
-    ASSERT(data.size() == block_size());
-
     auto& entry = cache().get(index);
-    memcpy(entry.data, data.data(), data.size());
+    memcpy(entry.data, data, block_size());
     entry.is_dirty = true;
     entry.has_data = true;
 
@@ -97,13 +95,13 @@ bool DiskBackedFS::write_block(unsigned index, const ByteBuffer& data)
     return true;
 }
 
-bool DiskBackedFS::write_blocks(unsigned index, unsigned count, const ByteBuffer& data)
+bool DiskBackedFS::write_blocks(unsigned index, unsigned count, const u8* data)
 {
 #ifdef DBFS_DEBUG
     kprintf("DiskBackedFileSystem::write_blocks %u x%u\n", index, count);
 #endif
     for (unsigned i = 0; i < count; ++i)
-        write_block(index + i, data.slice(i * block_size(), block_size()));
+        write_block(index + i, data + i * block_size());
     return true;
 }
 

Kernel/FileSystem/DiskBackedFileSystem.h

@@ -22,8 +22,8 @@ protected:
     bool read_block(unsigned index, u8* buffer) const;
     bool read_blocks(unsigned index, unsigned count, u8* buffer) const;
 
-    bool write_block(unsigned index, const ByteBuffer&);
-    bool write_blocks(unsigned index, unsigned count, const ByteBuffer&);
+    bool write_block(unsigned index, const u8*);
+    bool write_blocks(unsigned index, unsigned count, const u8*);
 
 private:
     DiskCache& cache() const;

Kernel/FileSystem/Ext2FileSystem.cpp

@@ -10,6 +10,7 @@
 
 //#define EXT2_DEBUG
 
+static const size_t max_block_size = 4096;
 static const ssize_t max_inline_symlink_length = 60;
 
 static u8 to_ext2_file_type(mode_t mode)
@@ -121,8 +122,11 @@ bool Ext2FS::initialize()
     kprintf("ext2fs: desc size = %u\n", EXT2_DESC_SIZE(&super_block));
 #endif
 
+
     set_block_size(EXT2_BLOCK_SIZE(&super_block));
 
+    ASSERT(block_size() <= (int)max_block_size);
+
     m_block_group_count = ceil_div(super_block.s_blocks_count, super_block.s_blocks_per_group);
 
     if (m_block_group_count == 0) {
@@ -157,16 +161,16 @@ InodeIdentifier Ext2FS::root_inode() const
     return { fsid(), EXT2_ROOT_INO };
 }
 
-ByteBuffer Ext2FS::read_block_containing_inode(unsigned inode, unsigned& block_index, unsigned& offset) const
+bool Ext2FS::read_block_containing_inode(unsigned inode, unsigned& block_index, unsigned& offset, u8* buffer) const
 {
     LOCKER(m_lock);
     auto& super_block = this->super_block();
 
     if (inode != EXT2_ROOT_INO && inode < EXT2_FIRST_INO(&super_block))
-        return {};
+        return false;
 
     if (inode > super_block.s_inodes_count)
-        return {};
+        return false;
 
     auto& bgd = group_descriptor(group_index_from_inode(inode));
 
@@ -174,10 +178,7 @@ ByteBuffer Ext2FS::read_block_containing_inode(unsigned inode, unsigned& block_i
     block_index = bgd.bg_inode_table + (offset >> EXT2_BLOCK_SIZE_BITS(&super_block));
     offset &= block_size() - 1;
 
-    auto buffer = ByteBuffer::create_uninitialized(block_size());
-    if (!read_block(block_index, buffer.data()))
-        return {};
-    return buffer;
+    return read_block(block_index, buffer);
 }
 
 Ext2FS::BlockListShape Ext2FS::compute_block_list_shape(unsigned blocks)
@@ -290,7 +291,7 @@ bool Ext2FS::write_block_list_for_inode(InodeIndex inode_index, ext2_inode& e2in
             --remaining_blocks;
         }
         stream.fill_to_end(0);
-        bool success = write_block(e2inode.i_block[EXT2_IND_BLOCK], block_contents);
+        bool success = write_block(e2inode.i_block[EXT2_IND_BLOCK], block_contents.data());
         ASSERT(success);
     }
 
@@ -373,7 +374,7 @@ bool Ext2FS::write_block_list_for_inode(InodeIndex inode_index, ext2_inode& e2in
             }
 
             if (ind_block_dirty) {
-                bool success = write_block(indirect_block_index, ind_block_contents);
+                bool success = write_block(indirect_block_index, ind_block_contents.data());
                 ASSERT(success);
             }
         }
@@ -385,7 +386,7 @@ bool Ext2FS::write_block_list_for_inode(InodeIndex inode_index, ext2_inode& e2in
         }
 
         if (dind_block_dirty) {
-            bool success = write_block(e2inode.i_block[EXT2_DIND_BLOCK], dind_block_contents);
+            bool success = write_block(e2inode.i_block[EXT2_DIND_BLOCK], dind_block_contents.data());
             ASSERT(success);
         }
     }
@@ -509,7 +510,7 @@ void Ext2FS::flush_block_group_descriptor_table()
     LOCKER(m_lock);
     unsigned blocks_to_write = ceil_div(m_block_group_count * (unsigned)sizeof(ext2_group_desc), block_size());
     unsigned first_block_of_bgdt = block_size() == 1024 ? 2 : 1;
-    write_blocks(first_block_of_bgdt, blocks_to_write, m_cached_group_descriptor_table);
+    write_blocks(first_block_of_bgdt, blocks_to_write, m_cached_group_descriptor_table.data());
 }
 
 Ext2FSInode::Ext2FSInode(Ext2FS& fs, unsigned index)
@@ -585,15 +586,15 @@ RefPtr<Inode> Ext2FS::get_inode(InodeIdentifier inode) const
 
     unsigned block_index;
     unsigned offset;
-    auto block = read_block_containing_inode(inode.index(), block_index, offset);
-    if (!block)
+    u8 block[max_block_size];
+    if (!read_block_containing_inode(inode.index(), block_index, offset, block))
         return {};
 
     auto it = m_inode_cache.find(inode.index());
     if (it != m_inode_cache.end())
         return (*it).value;
     auto new_inode = adopt(*new Ext2FSInode(const_cast<Ext2FS&>(*this), inode.index()));
-    memcpy(&new_inode->m_raw_inode, reinterpret_cast<ext2_inode*>(block.offset_pointer(offset)), sizeof(ext2_inode));
+    memcpy(&new_inode->m_raw_inode, reinterpret_cast<ext2_inode*>(block + offset), sizeof(ext2_inode));
     m_inode_cache.set(inode.index(), new_inode);
     return new_inode;
 }
@@ -644,9 +645,7 @@ ssize_t Ext2FSInode::read_bytes(off_t offset, ssize_t count, u8* buffer, FileDes
     //kprintf("ok let's do it, read(%u, %u) -> blocks %u thru %u, oifb: %u\n", offset, count, first_block_logical_index, last_block_logical_index, offset_into_first_block);
 #endif
 
-    // Biggest block size should be 4096..
-    u8 block[4096];
-    ASSERT(block_size < (int)sizeof(block));
+    u8 block[max_block_size];
 
     for (int bi = first_block_logical_index; remaining_count && bi <= last_block_logical_index; ++bi) {
         bool success = fs().read_block(m_block_list[bi], block);
@@ -779,7 +778,7 @@ ssize_t Ext2FSInode::write_bytes(off_t offset, ssize_t count, const u8* data, Fi
 #ifdef EXT2_DEBUG
         dbgprintf("Ext2FSInode::write_bytes: writing block %u (offset_into_block: %u)\n", m_block_list[bi], offset_into_block);
 #endif
-        bool success = fs().write_block(m_block_list[bi], block);
+        bool success = fs().write_block(m_block_list[bi], block.data());
         if (!success) {
             kprintf("Ext2FSInode::write_bytes: write_block(%u) failed (lbi: %u)\n", m_block_list[bi], bi);
             ASSERT_NOT_REACHED();
@@ -985,10 +984,10 @@ bool Ext2FS::write_ext2_inode(unsigned inode, const ext2_inode& e2inode)
     LOCKER(m_lock);
     unsigned block_index;
     unsigned offset;
-    auto block = read_block_containing_inode(inode, block_index, offset);
-    if (!block)
+    u8 block[max_block_size];
+    if (!read_block_containing_inode(inode, block_index, offset, block))
         return false;
-    memcpy(reinterpret_cast<ext2_inode*>(block.offset_pointer(offset)), &e2inode, inode_size());
+    memcpy(reinterpret_cast<ext2_inode*>(block + offset), &e2inode, inode_size());
     bool success = write_block(block_index, block);
     ASSERT(success);
     return success;
@@ -1177,7 +1176,7 @@ bool Ext2FS::set_inode_allocation_state(InodeIndex inode_index, bool new_state)
     }
 
     bitmap.set(bit_index, new_state);
-    success = write_block(bgd.bg_inode_bitmap, block);
+    success = write_block(bgd.bg_inode_bitmap, block.data());
     ASSERT(success);
 
     // Update superblock
@@ -1241,7 +1240,7 @@ bool Ext2FS::set_block_allocation_state(BlockIndex block_index, bool new_state)
     }
 
     bitmap.set(bit_index, new_state);
-    success = write_block(bgd.bg_block_bitmap, block);
+    success = write_block(bgd.bg_block_bitmap, block.data());
     ASSERT(success);
 
     // Update superblock

Kernel/FileSystem/Ext2FileSystem.h

@@ -87,7 +87,7 @@ private:
     unsigned inode_size() const;
 
     bool write_ext2_inode(InodeIndex, const ext2_inode&);
-    ByteBuffer read_block_containing_inode(InodeIndex inode, BlockIndex& block_index, unsigned& offset) const;
+    bool read_block_containing_inode(InodeIndex inode, BlockIndex& block_index, unsigned& offset, u8* buffer) const;
 
     ByteBuffer read_super_block() const;
     bool write_super_block(const ext2_super_block&);