From dcc5b7397f1bb9ee129aa38c9139bb85e15e84f9 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 26 Feb 2021 17:15:32 +0100
Subject: [PATCH] Kernel: Take FS lock in BlockBasedFS during seek/read/write
 operations

Since these filesystems operate on an underlying file descriptor
and rely on its offset for correctness, let's use the FS lock to
serialize these operations.

This also means that FS subclasses can rely on block-level read/write
operations being atomic.
---
 Kernel/FileSystem/BlockBasedFileSystem.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Kernel/FileSystem/BlockBasedFileSystem.cpp b/Kernel/FileSystem/BlockBasedFileSystem.cpp
index 84c8a29241..334cd40abd 100644
--- a/Kernel/FileSystem/BlockBasedFileSystem.cpp
+++ b/Kernel/FileSystem/BlockBasedFileSystem.cpp
@@ -136,6 +136,7 @@ BlockBasedFS::~BlockBasedFS()
 
 KResult BlockBasedFS::write_block(BlockIndex index, const UserOrKernelBuffer& data, size_t count, size_t offset, bool allow_cache)
 {
+    LOCKER(m_lock);
     VERIFY(m_logical_block_size);
     VERIFY(offset + count <= block_size());
     dbgln_if(BBFS_DEBUG, "BlockBasedFileSystem::write_block {}, size={}", index, count);
@@ -168,6 +169,7 @@ KResult BlockBasedFS::write_block(BlockIndex index, const UserOrKernelBuffer& da
 
 bool BlockBasedFS::raw_read(BlockIndex index, UserOrKernelBuffer& buffer)
 {
+    LOCKER(m_lock);
     u32 base_offset = index.value() * m_logical_block_size;
     file_description().seek(base_offset, SEEK_SET);
     auto nread = file_description().read(buffer, m_logical_block_size);
@@ -175,8 +177,10 @@ bool BlockBasedFS::raw_read(BlockIndex index, UserOrKernelBuffer& buffer)
     VERIFY(nread.value() == m_logical_block_size);
     return true;
 }
+
 bool BlockBasedFS::raw_write(BlockIndex index, const UserOrKernelBuffer& buffer)
 {
+    LOCKER(m_lock);
     size_t base_offset = index.value() * m_logical_block_size;
     file_description().seek(base_offset, SEEK_SET);
     auto nwritten = file_description().write(buffer, m_logical_block_size);
@@ -187,6 +191,7 @@ bool BlockBasedFS::raw_write(BlockIndex index, const UserOrKernelBuffer& buffer)
 
 bool BlockBasedFS::raw_read_blocks(BlockIndex index, size_t count, UserOrKernelBuffer& buffer)
 {
+    LOCKER(m_lock);
     auto current = buffer;
     for (unsigned block = index.value(); block < (index.value() + count); block++) {
         if (!raw_read(BlockIndex { block }, current))
@@ -195,8 +200,10 @@ bool BlockBasedFS::raw_read_blocks(BlockIndex index, size_t count, UserOrKernelB
     }
     return true;
 }
+
 bool BlockBasedFS::raw_write_blocks(BlockIndex index, size_t count, const UserOrKernelBuffer& buffer)
 {
+    LOCKER(m_lock);
     auto current = buffer;
     for (unsigned block = index.value(); block < (index.value() + count); block++) {
         if (!raw_write(block, current))
@@ -208,6 +215,7 @@ bool BlockBasedFS::raw_write_blocks(BlockIndex index, size_t count, const UserOr
 
 KResult BlockBasedFS::write_blocks(BlockIndex index, unsigned count, const UserOrKernelBuffer& data, bool allow_cache)
 {
+    LOCKER(m_lock);
     VERIFY(m_logical_block_size);
     dbgln_if(BBFS_DEBUG, "BlockBasedFileSystem::write_blocks {}, count={}", index, count);
     for (unsigned i = 0; i < count; ++i) {
@@ -220,6 +228,7 @@ KResult BlockBasedFS::write_blocks(BlockIndex index, unsigned count, const UserO
 
 KResult BlockBasedFS::read_block(BlockIndex index, UserOrKernelBuffer* buffer, size_t count, size_t offset, bool allow_cache) const
 {
+    LOCKER(m_lock);
     VERIFY(m_logical_block_size);
     VERIFY(offset + count <= block_size());
     dbgln_if(BBFS_DEBUG, "BlockBasedFileSystem::read_block {}", index);
@@ -253,6 +262,7 @@ KResult BlockBasedFS::read_block(BlockIndex index, UserOrKernelBuffer* buffer, s
 
 KResult BlockBasedFS::read_blocks(BlockIndex index, unsigned count, UserOrKernelBuffer& buffer, bool allow_cache) const
 {
+    LOCKER(m_lock);
     VERIFY(m_logical_block_size);
     if (!count)
         return EINVAL;