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Kernel/FileSystem: Mark ext2 inode block list non-const

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The block list required a bit of work, and now the only method being
declared const to bypass its const-iness is the read_bytes method that
calls a new method called compute_block_list_with_exclusive_locking that
takes care of proper locking before trying to update the block list data
of the ext2 inode.
This commit is contained in:
Liav A 2022-08-06 18:24:21 +03:00 • committed by Idan Horowitz
parent 843bd43c5b
commit 4f4717e351
2 changed files with 24 additions and 3 deletions
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21
Kernel/FileSystem/Ext2FileSystem.cpp
View file

@ -798,6 +798,19 @@ ErrorOr<NonnullLockRefPtr<Inode>> Ext2FS::get_inode(InodeIdentifier inode) const
return new_inode;
}
ErrorOr<void> Ext2FSInode::compute_block_list_with_exclusive_locking()
{
// Note: We verify that the inode mutex is being held locked. Because only the read_bytes_locked()
// method uses this method and the mutex can be locked in shared mode when reading the Inode if
// it is an ext2 regular file, but also in exclusive mode, when the Inode is an ext2 directory and being
// traversed, we use another exclusive lock to ensure we always mutate the block list safely.
VERIFY(m_inode_lock.is_locked());
MutexLocker block_list_locker(m_block_list_lock);
if (m_block_list.is_empty())
m_block_list = TRY(compute_block_list());
return {};
}
ErrorOr<size_t> Ext2FSInode::read_bytes(off_t offset, size_t count, UserOrKernelBuffer& buffer, OpenFileDescription* description) const
{
MutexLocker inode_locker(m_inode_lock);
@ -817,8 +830,12 @@ ErrorOr<size_t> Ext2FSInode::read_bytes(off_t offset, size_t count, UserOrKernel
return nread;
}
if (m_block_list.is_empty())
m_block_list = TRY(compute_block_list());
// Note: We bypass the const declaration of this method, but this is a strong
// requirement to be able to accomplish the read operation successfully.
// We call this special method becuase it locks a separate mutex to ensure we
// update the block list of the inode safely, as the m_inode_lock is locked in
// shared mode.
TRY(const_cast<Ext2FSInode&>(*this).compute_block_list_with_exclusive_locking());
if (m_block_list.is_empty()) {
dmesgln("Ext2FSInode[{}]::read_bytes(): Empty block list", identifier());

6
Kernel/FileSystem/Ext2FileSystem.h
View file

@ -61,6 +61,8 @@ private:
ErrorOr<void> grow_triply_indirect_block(BlockBasedFileSystem::BlockIndex, size_t, Span<BlockBasedFileSystem::BlockIndex>, Vector<BlockBasedFileSystem::BlockIndex>&, unsigned&);
ErrorOr<void> shrink_triply_indirect_block(BlockBasedFileSystem::BlockIndex, size_t, size_t, unsigned&);
ErrorOr<void> flush_block_list();
ErrorOr<void> compute_block_list_with_exclusive_locking();
ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> compute_block_list() const;
ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> compute_block_list_with_meta_blocks() const;
ErrorOr<Vector<BlockBasedFileSystem::BlockIndex>> compute_block_list_impl(bool include_block_list_blocks) const;
@ -70,9 +72,11 @@ private:
Ext2FS const& fs() const;
Ext2FSInode(Ext2FS&, InodeIndex);
mutable Vector<BlockBasedFileSystem::BlockIndex> m_block_list;
Vector<BlockBasedFileSystem::BlockIndex> m_block_list;
HashMap<NonnullOwnPtr<KString>, InodeIndex> m_lookup_cache;
ext2_inode m_raw_inode {};
Mutex m_block_list_lock { "BlockList"sv };
};
class Ext2FS final : public BlockBasedFileSystem {