Kernel: Make it possible for KBufferBuilder creation to fail

This patch adds KBufferBuilder::try_create() and treats it like anything
else that can fail. And so, failure to allocate the initial internal
buffer of the builder will now propagate an ENOMEM to the caller. :^)

Kernel/Bus/USB/SysFSUSB.cpp

@@ -54,7 +54,7 @@ KResult SysFSUSBDeviceInformation::refresh_data(OpenFileDescription& description
     if (!cached_data) {
         cached_data = TRY(adopt_nonnull_own_or_enomem(new (nothrow) SysFSInodeData));
     }
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
     TRY(const_cast<SysFSUSBDeviceInformation&>(*this).try_generate(builder));
     auto& typed_cached_data = static_cast<SysFSInodeData&>(*cached_data);
     typed_cached_data.buffer = builder.build();

Kernel/Coredump.cpp

@@ -281,7 +281,7 @@ KResult Coredump::write()
     SpinlockLocker lock(m_process->address_space().get_lock());
     ScopedAddressSpaceSwitcher switcher(m_process);
 
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
     TRY(create_notes_segment_data(builder));
     TRY(write_elf_header());
     TRY(write_program_headers(builder.bytes().size()));

Kernel/FileSystem/Inode.cpp

@@ -47,7 +47,7 @@ void Inode::sync()
 
 KResultOr<NonnullOwnPtr<KBuffer>> Inode::read_entire(OpenFileDescription* description) const
 {
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
 
     u8 buffer[4096];
     off_t offset = 0;

Kernel/FileSystem/Plan9FileSystem.cpp

@@ -323,7 +323,7 @@ StringView Plan9FS::Message::Decoder::read_data()
 }
 
 Plan9FS::Message::Message(Plan9FS& fs, Type type)
-    : m_builder()
+    : m_builder(KBufferBuilder::try_create().release_value()) // FIXME: Don't assume KBufferBuilder allocation success.
     , m_tag(fs.allocate_tag())
     , m_type(type)
     , m_have_been_built(false)

Kernel/FileSystem/ProcFS.cpp

@@ -480,7 +480,7 @@ KResultOr<size_t> ProcFSProcessPropertyInode::read_bytes(off_t offset, size_t co
     VERIFY(buffer.user_or_kernel_ptr());
 
     if (!description) {
-        KBufferBuilder builder;
+        auto builder = TRY(KBufferBuilder::try_create());
         auto process = Process::from_pid(associated_pid());
         if (!process)
             return KResult(ESRCH);
@@ -579,7 +579,7 @@ KResult ProcFSProcessPropertyInode::refresh_data(OpenFileDescription& descriptio
         if (!cached_data)
             return ENOMEM;
     }
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
     TRY(try_to_acquire_data(*process, builder));
     return build_from_cached_data(builder, static_cast<ProcFSInodeData&>(*cached_data));
 }

Kernel/KBufferBuilder.cpp

@@ -46,8 +46,14 @@ OwnPtr<KBuffer> KBufferBuilder::build()
     return move(m_buffer);
 }
 
-KBufferBuilder::KBufferBuilder()
-    : m_buffer(KBuffer::try_create_with_size(4 * MiB, Memory::Region::Access::ReadWrite).release_value())
+KResultOr<KBufferBuilder> KBufferBuilder::try_create()
+{
+    auto buffer = TRY(KBuffer::try_create_with_size(4 * MiB, Memory::Region::Access::ReadWrite));
+    return KBufferBuilder { move(buffer) };
+}
+
+KBufferBuilder::KBufferBuilder(NonnullOwnPtr<KBuffer> buffer)
+    : m_buffer(move(buffer))
 {
 }
 

Kernel/KBufferBuilder.h

@@ -6,18 +6,22 @@
 
 #pragma once
 
-#include <AK/String.h>
+#include <AK/StringView.h>
 #include <Kernel/KBuffer.h>
 #include <stdarg.h>
 
 namespace Kernel {
 
 class KBufferBuilder {
+    AK_MAKE_NONCOPYABLE(KBufferBuilder);
+
 public:
     using OutputType = KBuffer;
 
-    KBufferBuilder();
+    static KResultOr<KBufferBuilder> try_create();
+
     KBufferBuilder(KBufferBuilder&&) = default;
+    KBufferBuilder& operator=(KBufferBuilder&&) = default;
     ~KBufferBuilder() = default;
 
     KResult append(const StringView&);
@@ -48,6 +52,8 @@ public:
     }
 
 private:
+    explicit KBufferBuilder(NonnullOwnPtr<KBuffer>);
+
     bool check_expand(size_t);
     u8* insertion_ptr()
     {

Kernel/Process.cpp

@@ -575,7 +575,12 @@ bool Process::dump_perfcore()
     }
 
     auto& description = *description_or_error.value();
-    KBufferBuilder builder;
+    auto builder_or_error = KBufferBuilder::try_create();
+    if (builder_or_error.is_error()) {
+        dbgln("Failed to generate perfcore for pid {}: Could not allocate KBufferBuilder.", pid());
+        return false;
+    }
+    auto builder = builder_or_error.release_value();
     if (!m_perf_event_buffer->to_json(builder)) {
         dbgln("Failed to generate perfcore for pid {}: Could not serialize performance events to JSON.", pid().value());
         return false;

Kernel/ProcessExposed.cpp

@@ -144,7 +144,7 @@ KResult ProcFSGlobalInformation::refresh_data(OpenFileDescription& description)
         if (!cached_data)
             return ENOMEM;
     }
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
     TRY(const_cast<ProcFSGlobalInformation&>(*this).try_generate(builder));
     auto& typed_cached_data = static_cast<ProcFSInodeData&>(*cached_data);
     typed_cached_data.buffer = builder.build();
@@ -157,7 +157,7 @@ KResultOr<size_t> ProcFSExposedLink::read_bytes(off_t offset, size_t count, User
 {
     VERIFY(offset == 0);
     MutexLocker locker(m_lock);
-    KBufferBuilder builder;
+    auto builder = TRY(KBufferBuilder::try_create());
     if (!const_cast<ProcFSExposedLink&>(*this).acquire_link(builder))
         return KResult(EFAULT);
     auto blob = builder.build();