Kernel/FATFS: Cache the cluster list and don't cache the InodeMetadata

Caching the cluster list allows us to fill the two fields in the
InodeMetadata. While at it, don't cache the metadata as when we
have write support having to keep both InodeMetadata and FATEntry
correct is going to get very annoying.

Kernel/FileSystem/FATFS/FileSystem.cpp

@@ -354,6 +354,23 @@ u32 FATFS::cluster_number(KBuffer const& fat_sector, u32 entry_cluster_number, u
     return cluster;
 }
 
+u32 FATFS::end_of_chain_marker() const
+{
+    // Returns the end of chain entry for the given file system.
+    // Any FAT entry of this value or greater signifies the end
+    // of the chain has been reached for a given entry.
+    switch (m_fat_version) {
+    case FATVersion::FAT12:
+        return 0xFF8;
+    case FATVersion::FAT16:
+        return 0xFFF8;
+    case FATVersion::FAT32:
+        return 0x0FFFFFF8;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+}
+
 ErrorOr<u32> FATFS::fat_read(u32 cluster)
 {
     dbgln_if(FAT_DEBUG, "FATFS: Reading FAT entry for cluster {}", cluster);

Kernel/FileSystem/FATFS/FileSystem.h

@@ -91,6 +91,11 @@ private:
     // Reads the cluster number located at the offset within the table.
     u32 cluster_number(KBuffer const& fat_sector, u32 entry_cluster_number, u32 entry_offset) const;
 
+    // Returns cluster number value that indicates the end of the chain
+    // has been reached. Any cluster value >= this value indicates this
+    // is the last cluster.
+    u32 end_of_chain_marker() const;
+
     ErrorOr<u32> fat_read(u32 cluster);
     ErrorOr<void> fat_write(u32 cluster, u32 value);
 

Kernel/FileSystem/FATFS/Inode.cpp

@@ -14,7 +14,13 @@ namespace Kernel {
 ErrorOr<NonnullRefPtr<FATInode>> FATInode::create(FATFS& fs, FATEntry entry, FATEntryLocation inode_metadata_location, Vector<FATLongFileNameEntry> const& lfn_entries)
 {
     auto filename = TRY(compute_filename(entry, lfn_entries));
-    return adopt_nonnull_ref_or_enomem(new (nothrow) FATInode(fs, entry, inode_metadata_location, move(filename)));
+    u32 entry_first_cluster = entry.first_cluster_low;
+    if (fs.m_fat_version == FATVersion::FAT32)
+        entry_first_cluster |= (static_cast<u32>(entry.first_cluster_high) << 16);
+    auto inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) FATInode(fs, entry, inode_metadata_location, move(filename))));
+    MutexLocker locker(inode->m_inode_lock);
+    inode->m_cluster_list = TRY(inode->compute_cluster_list(fs, entry_first_cluster));
+    return inode;
 }
 
 FATInode::FATInode(FATFS& fs, FATEntry entry, FATEntryLocation inode_metadata_location, NonnullOwnPtr<KString> filename)
@@ -24,37 +30,20 @@ FATInode::FATInode(FATFS& fs, FATEntry entry, FATEntryLocation inode_metadata_lo
     , m_filename(move(filename))
 {
     dbgln_if(FAT_DEBUG, "FATFS: Creating inode {} with filename \"{}\"", index(), m_filename);
-
-    m_metadata = {
-        .inode = identifier(),
-        .size = m_entry.file_size,
-        .mode = static_cast<mode_t>((has_flag(m_entry.attributes, FATAttributes::Directory) ? S_IFDIR : S_IFREG) | 0777),
-        .uid = 0,
-        .gid = 0,
-        .link_count = 0,
-        .atime = time_from_packed_dos(m_entry.last_accessed_date, { 0 }),
-        .ctime = time_from_packed_dos(m_entry.creation_date, m_entry.creation_time),
-        .mtime = time_from_packed_dos(m_entry.modification_date, m_entry.modification_time),
-        .dtime = {},
-        .block_count = 0,
-        .block_size = 0,
-        .major_device = 0,
-        .minor_device = 0,
-    };
 }
 
-ErrorOr<Vector<u32>> FATInode::compute_cluster_list()
+ErrorOr<Vector<u32>> FATInode::compute_cluster_list(FATFS& fs, u32 first_cluster)
 {
     VERIFY(m_inode_lock.is_locked());
 
-    dbgln_if(FAT_DEBUG, "FATFS: computing cluster list for inode {}", index());
+    dbgln_if(FAT_DEBUG, "FATFS: computing block list starting with cluster {}", first_cluster);
 
-    u32 cluster = first_cluster();
+    u32 cluster = first_cluster;
 
     Vector<u32> cluster_list;
 
-    while (cluster < end_of_chain_marker()) {
-        dbgln_if(FAT_DEBUG, "FATFS: Appending cluster {} to inode {}'s cluster chain", cluster, index());
+    while (cluster < fs.end_of_chain_marker()) {
+        dbgln_if(FAT_DEBUG, "FATFS: Appending cluster {} to cluster chain starting with {}", cluster, first_cluster);
 
         TRY(cluster_list.try_append(cluster));
 
@@ -75,7 +64,7 @@ ErrorOr<Vector<u32>> FATInode::compute_cluster_list()
         }
 
         // Look up the next cluster to read, or read End of Chain marker from table.
-        cluster = TRY(fs().fat_read(cluster));
+        cluster = TRY(fs.fat_read(cluster));
     }
 
     return cluster_list;
@@ -89,9 +78,6 @@ ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> FATInode::get_block_list()
 
     Vector<BlockBasedFileSystem::BlockIndex> block_list;
 
-    if (m_cluster_list.is_empty())
-        m_cluster_list = TRY(compute_cluster_list());
-
     for (auto cluster : m_cluster_list) {
         auto span = fs().first_block_of_cluster(cluster);
         for (size_t i = 0; i < span.number_of_sectors; i++) {
@@ -103,23 +89,6 @@ ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> FATInode::get_block_list()
     return block_list;
 }
 
-u32 FATInode::end_of_chain_marker() const
-{
-    // Returns the end of chain entry for the given file system.
-    // Any FAT entry of this value or greater signifies the end
-    // of the chain has been reached for a given entry.
-    switch (fs().m_fat_version) {
-    case FATVersion::FAT12:
-        return 0xFF8;
-    case FATVersion::FAT16:
-        return 0xFFF8;
-    case FATVersion::FAT32:
-        return 0x0FFFFFF8;
-    default:
-        VERIFY_NOT_REACHED();
-    }
-}
-
 ErrorOr<NonnullOwnPtr<KBuffer>> FATInode::read_block_list()
 {
     VERIFY(m_inode_lock.is_locked());
@@ -275,7 +244,7 @@ ErrorOr<size_t> FATInode::read_bytes_locked(off_t offset, size_t size, UserOrKer
 {
     dbgln_if(FAT_DEBUG, "FATFS: Reading inode {}: size: {} offset: {}", identifier().index(), size, offset);
     VERIFY(offset >= 0);
-    if (offset >= m_metadata.size)
+    if (offset >= m_entry.file_size)
         return 0;
 
     // FIXME: Read only the needed blocks instead of the whole file
@@ -286,7 +255,7 @@ ErrorOr<size_t> FATInode::read_bytes_locked(off_t offset, size_t size, UserOrKer
     //   2. The file size.
     //   3. The number of blocks returned for reading.
     size_t read_size = min(
-        min(size, m_metadata.size - offset),
+        min(size, m_entry.file_size - offset),
         (m_cluster_list.size() * fs().m_device_block_size * fs().m_parameter_block->common_bpb()->sectors_per_cluster) - offset);
     TRY(buffer.write(blocks->data() + offset, read_size));
 
@@ -295,7 +264,23 @@ ErrorOr<size_t> FATInode::read_bytes_locked(off_t offset, size_t size, UserOrKer
 
 InodeMetadata FATInode::metadata() const
 {
-    return m_metadata;
+    return {
+        .inode = identifier(),
+        .size = m_entry.file_size,
+        // FIXME: Linux also removes the write permission if the file has the read only attribute set.
+        .mode = static_cast<mode_t>((has_flag(m_entry.attributes, FATAttributes::Directory) ? S_IFDIR : S_IFREG) | 0777),
+        .uid = 0,
+        .gid = 0,
+        .link_count = 0,
+        .atime = time_from_packed_dos(m_entry.last_accessed_date, { 0 }),
+        .ctime = time_from_packed_dos(m_entry.creation_date, m_entry.creation_time),
+        .mtime = time_from_packed_dos(m_entry.modification_date, m_entry.modification_time),
+        .dtime = {},
+        .block_count = m_cluster_list.size() * fs().m_parameter_block->common_bpb()->sectors_per_cluster,
+        .block_size = fs().m_device_block_size,
+        .major_device = 0,
+        .minor_device = 0,
+    };
 }
 
 ErrorOr<void> FATInode::traverse_as_directory(Function<ErrorOr<void>(FileSystem::DirectoryEntryView const&)> callback) const

Kernel/FileSystem/FATFS/Inode.h

@@ -35,11 +35,6 @@ public:
 private:
     FATInode(FATFS&, FATEntry, FATEntryLocation inode_metadata_location, NonnullOwnPtr<KString> filename);
 
-    // Returns cluster number value that indicates the end of the chain
-    // has been reached. Any cluster value >= this value indicates this
-    // is the last cluster.
-    u32 end_of_chain_marker() const;
-
     static constexpr u8 end_entry_byte = 0x00;
     static constexpr u8 unused_entry_byte = 0xE5;
 
@@ -52,7 +47,7 @@ private:
     static ErrorOr<NonnullOwnPtr<KString>> compute_filename(FATEntry&, Vector<FATLongFileNameEntry> const& = {});
     static StringView byte_terminated_string(StringView, u8);
 
-    ErrorOr<Vector<u32>> compute_cluster_list();
+    ErrorOr<Vector<u32>> compute_cluster_list(FATFS&, u32 first_cluster);
     ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> get_block_list();
     ErrorOr<NonnullOwnPtr<KBuffer>> read_block_list();
     ErrorOr<RefPtr<FATInode>> traverse(Function<ErrorOr<bool>(RefPtr<FATInode>)> callback);
@@ -81,7 +76,6 @@ private:
     FATEntry m_entry;
     FATEntryLocation m_inode_metadata_location;
     NonnullOwnPtr<KString> m_filename;
-    InodeMetadata m_metadata;
 };
 
 }