Kernel: Use KBufferBuilder to build ProcFS files and backtraces

This is not perfect as it uses a lot of VM, but since the buffers are
supposed to be temporary it's not super terrible.

This could be improved by giving back the unused VM to the kernel's
RangeAllocator after finishing the buffer building.

Kernel/FileSystem/ProcFS.cpp

@@ -7,11 +7,11 @@
 #include <AK/JsonArray.h>
 #include <AK/JsonObject.h>
 #include <AK/JsonValue.h>
-#include <AK/StringBuilder.h>
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
+#include <Kernel/KBufferBuilder.h>
 #include <Kernel/KParams.h>
 #include <Kernel/Net/NetworkAdapter.h>
 #include <Kernel/Net/TCPSocket.h>
@@ -208,7 +208,7 @@ Optional<KBuffer> procfs$pid_fds(InodeIdentifier identifier)
         description_object.set("offset", description->offset());
         array.append(move(description_object));
     }
-    return array.to_string().to_byte_buffer();
+    return array.serialized<KBufferBuilder>();
 }
 
 Optional<KBuffer> procfs$pid_fd_entry(InodeIdentifier identifier)
@@ -241,35 +241,35 @@ Optional<KBuffer> procfs$pid_vm(InodeIdentifier identifier)
         region_object.set("name", region.name());
         array.append(move(region_object));
     }
-    return array.to_string().to_byte_buffer();
+    return array.serialized<KBufferBuilder>();
 }
 
 Optional<KBuffer> procfs$pci(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     PCI::enumerate_all([&builder](PCI::Address address, PCI::ID id) {
         builder.appendf("%b:%b.%b %w:%w\n", address.bus(), address.slot(), address.function(), id.vendor_id, id.device_id);
     });
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$uptime(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     builder.appendf("%u\n", (u32)(g_uptime / 1000));
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$cmdline(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     builder.appendf("%s\n", KParams::the().cmdline().characters());
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$netadapters(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     NetworkAdapter::for_each([&builder](auto& adapter) {
         builder.appendf("%s,%s,%s,%s\n",
             adapter.name().characters(),
@@ -277,7 +277,7 @@ Optional<KBuffer> procfs$netadapters(InodeIdentifier)
             adapter.mac_address().to_string().characters(),
             adapter.ipv4_address().to_string().characters());
     });
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$net_tcp(InodeIdentifier)
@@ -294,7 +294,7 @@ Optional<KBuffer> procfs$net_tcp(InodeIdentifier)
         obj.set("sequence_number", socket->sequence_number());
         json.append(obj);
     });
-    return json.to_string().to_byte_buffer();
+    return json.serialized<KBufferBuilder>();
 }
 
 Optional<KBuffer> procfs$pid_vmo(InodeIdentifier identifier)
@@ -303,7 +303,7 @@ Optional<KBuffer> procfs$pid_vmo(InodeIdentifier identifier)
     if (!handle)
         return {};
     auto& process = handle->process();
-    StringBuilder builder;
+    KBufferBuilder builder;
     builder.appendf("BEGIN       END         SIZE        NAME\n");
     for (auto& region : process.regions()) {
         builder.appendf("%x -- %x    %x    %s\n",
@@ -324,7 +324,7 @@ Optional<KBuffer> procfs$pid_vmo(InodeIdentifier identifier)
         }
         builder.appendf("\n");
     }
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$pid_stack(InodeIdentifier identifier)
@@ -333,7 +333,7 @@ Optional<KBuffer> procfs$pid_stack(InodeIdentifier identifier)
     if (!handle)
         return {};
     auto& process = handle->process();
-    return process.backtrace(*handle).to_byte_buffer();
+    return process.backtrace(*handle);
 }
 
 Optional<KBuffer> procfs$pid_regs(InodeIdentifier identifier)
@@ -342,7 +342,7 @@ Optional<KBuffer> procfs$pid_regs(InodeIdentifier identifier)
     if (!handle)
         return {};
     auto& process = handle->process();
-    StringBuilder builder;
+    KBufferBuilder builder;
     process.for_each_thread([&](Thread& thread) {
         builder.appendf("Thread %d:\n", thread.tid());
         auto& tss = thread.tss();
@@ -359,7 +359,7 @@ Optional<KBuffer> procfs$pid_regs(InodeIdentifier identifier)
         builder.appendf("pc:  %w:%x\n", tss.cs, tss.eip);
         return IterationDecision::Continue;
     });
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$pid_exe(InodeIdentifier identifier)
@@ -392,7 +392,7 @@ Optional<KBuffer> procfs$mm(InodeIdentifier)
 {
     // FIXME: Implement
     InterruptDisabler disabler;
-    StringBuilder builder;
+    KBufferBuilder builder;
     for (auto* vmo : MM.m_vmos) {
         builder.appendf("VMO: %p %s(%u): p:%4u\n",
             vmo,
@@ -403,22 +403,22 @@ Optional<KBuffer> procfs$mm(InodeIdentifier)
     builder.appendf("VMO count: %u\n", MM.m_vmos.size());
     builder.appendf("Free physical pages: %u\n", MM.user_physical_pages() - MM.user_physical_pages_used());
     builder.appendf("Free supervisor physical pages: %u\n", MM.super_physical_pages() - MM.super_physical_pages_used());
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$dmesg(InodeIdentifier)
 {
     InterruptDisabler disabler;
-    StringBuilder builder;
+    KBufferBuilder builder;
     for (char ch : Console::the().logbuffer())
         builder.append(ch);
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$mounts(InodeIdentifier)
 {
     // FIXME: This is obviously racy against the VFS mounts changing.
-    StringBuilder builder;
+    KBufferBuilder builder;
     VFS::the().for_each_mount([&builder](auto& mount) {
         auto& fs = mount.guest_fs();
         builder.appendf("%s @ ", fs.class_name());
@@ -431,7 +431,7 @@ Optional<KBuffer> procfs$mounts(InodeIdentifier)
         }
         builder.append('\n');
     });
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$df(InodeIdentifier)
@@ -449,12 +449,12 @@ Optional<KBuffer> procfs$df(InodeIdentifier)
         fs_object.set("mount_point", mount.absolute_path());
         json.append(fs_object);
     });
-    return json.to_string().to_byte_buffer();
+    return json.serialized<KBufferBuilder>();
 }
 
 Optional<KBuffer> procfs$cpuinfo(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     {
         CPUID cpuid(0);
         builder.appendf("cpuid:     ");
@@ -512,12 +512,12 @@ Optional<KBuffer> procfs$cpuinfo(InodeIdentifier)
         copy_brand_string_part_to_buffer(2);
         builder.appendf("brandstr:  \"%s\"\n", buffer);
     }
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$kmalloc(InodeIdentifier)
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     builder.appendf(
         "eternal:      %u\n"
         "allocated:    %u\n"
@@ -525,7 +525,7 @@ Optional<KBuffer> procfs$kmalloc(InodeIdentifier)
         kmalloc_sum_eternal,
         sum_alloc,
         sum_free);
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 Optional<KBuffer> procfs$memstat(InodeIdentifier)
@@ -541,7 +541,7 @@ Optional<KBuffer> procfs$memstat(InodeIdentifier)
     json.set("super_physical_available", MM.super_physical_pages());
     json.set("kmalloc_call_count", g_kmalloc_call_count);
     json.set("kfree_call_count", g_kfree_call_count);
-    return json.to_string().to_byte_buffer();
+    return json.serialized<KBufferBuilder>();;
 }
 
 Optional<KBuffer> procfs$all(InodeIdentifier)
@@ -577,18 +577,18 @@ Optional<KBuffer> procfs$all(InodeIdentifier)
     build_process(*Scheduler::colonel());
     for (auto* process : processes)
         build_process(*process);
-    return array.to_string().to_byte_buffer();
+    return array.serialized<KBufferBuilder>();
 }
 
 Optional<KBuffer> procfs$inodes(InodeIdentifier)
 {
     extern HashTable<Inode*>& all_inodes();
-    StringBuilder builder;
+    KBufferBuilder builder;
     for (auto it : all_inodes()) {
         RefPtr<Inode> inode = *it;
         builder.appendf("Inode{K%x} %02u:%08u (%u)\n", inode.ptr(), inode->fsid(), inode->index(), inode->ref_count());
     }
-    return builder.to_byte_buffer();
+    return builder.build();
 }
 
 struct SysVariableData final : public ProcFSInodeCustomData {

Kernel/Process.cpp

@@ -15,6 +15,7 @@
 #include <Kernel/FileSystem/SharedMemory.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 #include <Kernel/IO.h>
+#include <Kernel/KBufferBuilder.h>
 #include <Kernel/KSyms.h>
 #include <Kernel/Multiboot.h>
 #include <Kernel/Net/Socket.h>
@@ -2838,15 +2839,15 @@ int Process::sys$dbgputstr(const u8* characters, int length)
     return 0;
 }
 
-String Process::backtrace(ProcessInspectionHandle& handle) const
+KBuffer Process::backtrace(ProcessInspectionHandle& handle) const
 {
-    StringBuilder builder;
+    KBufferBuilder builder;
     for_each_thread([&](Thread& thread) {
         builder.appendf("Thread %d:\n", thread.tid());
         builder.append(thread.backtrace(handle));
         return IterationDecision::Continue;
     });
-    return builder.to_string();
+    return builder.build();
 }
 
 int Process::sys$set_process_icon(int icon_id)

Kernel/Process.h

@@ -18,6 +18,7 @@
 
 class ELFLoader;
 class FileDescription;
+class KBuffer;
 class PageDirectory;
 class Region;
 class VMObject;
@@ -57,7 +58,7 @@ public:
         Ring3 = 3,
     };
 
-    String backtrace(ProcessInspectionHandle&) const;
+    KBuffer backtrace(ProcessInspectionHandle&) const;
 
     bool is_dead() const { return m_dead; }