From 750dbe986de0b80772c1bd32627850b1105c0e60 Mon Sep 17 00:00:00 2001
From: Robin Burchell <robin+git@viroteck.net>
Date: Fri, 19 Jul 2019 09:04:12 +0200
Subject: [PATCH] Kernel: Avoid allocations for Select vectors by using inline
 capacity

Good tip by Andreas :)
---
 Kernel/Process.cpp   | 12 ++++++------
 Kernel/Scheduler.cpp |  2 +-
 Kernel/Thread.h      | 10 ++++++----
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index b2e2f7ebcc..07141a7ba3 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -1798,9 +1798,9 @@ int Process::sys$select(const Syscall::SC_select_params* params)
         select_has_timeout = true;
     }
 
-    Vector<int> rfds;
-    Vector<int> wfds;
-    Vector<int> efds;
+    Thread::SelectBlocker::FDVector rfds;
+    Thread::SelectBlocker::FDVector wfds;
+    Thread::SelectBlocker::FDVector efds;
 
     auto transfer_fds = [&](auto* fds, auto& vector) -> int {
         vector.clear_with_capacity();
@@ -1852,8 +1852,8 @@ int Process::sys$poll(pollfd* fds, int nfds, int timeout)
     if (!validate_read_typed(fds))
         return -EFAULT;
 
-    Vector<int> rfds;
-    Vector<int> wfds;
+    Thread::SelectBlocker::FDVector rfds;
+    Thread::SelectBlocker::FDVector wfds;
 
     for (int i = 0; i < nfds; ++i) {
         if (fds[i].events & POLLIN)
@@ -1882,7 +1882,7 @@ int Process::sys$poll(pollfd* fds, int nfds, int timeout)
 #endif
 
     if (has_timeout|| timeout < 0)
-        current->block(*new Thread::SelectBlocker(actual_timeout, has_timeout, rfds, wfds, Vector<int>()));
+        current->block(*new Thread::SelectBlocker(actual_timeout, has_timeout, rfds, wfds, Thread::SelectBlocker::FDVector()));
 
     int fds_with_revents = 0;
 
diff --git a/Kernel/Scheduler.cpp b/Kernel/Scheduler.cpp
index 070c40584e..60c0819f4d 100644
--- a/Kernel/Scheduler.cpp
+++ b/Kernel/Scheduler.cpp
@@ -143,7 +143,7 @@ bool Thread::SleepBlocker::should_unblock(Thread&, time_t, long)
     return m_wakeup_time <= g_uptime;
 }
 
-Thread::SelectBlocker::SelectBlocker(const timeval& tv, bool select_has_timeout, const Vector<int>& read_fds, const Vector<int>& write_fds, const Vector<int>& except_fds)
+Thread::SelectBlocker::SelectBlocker(const timeval& tv, bool select_has_timeout, const FDVector& read_fds, const FDVector& write_fds, const FDVector& except_fds)
     : m_select_timeout(tv)
     , m_select_has_timeout(select_has_timeout)
     , m_select_read_fds(read_fds)
diff --git a/Kernel/Thread.h b/Kernel/Thread.h
index b5e3998836..6144fb8db2 100644
--- a/Kernel/Thread.h
+++ b/Kernel/Thread.h
@@ -10,6 +10,7 @@
 #include <Kernel/KResult.h>
 #include <Kernel/UnixTypes.h>
 #include <Kernel/VM/Region.h>
+#include <LibC/fd_set.h>
 
 class Alarm;
 class FileDescription;
@@ -135,15 +136,16 @@ public:
 
     class SelectBlocker : public Blocker {
     public:
-        SelectBlocker(const timeval& tv, bool select_has_timeout, const Vector<int>& read_fds, const Vector<int>& write_fds, const Vector<int>& except_fds);
+        typedef Vector<int, FD_SETSIZE> FDVector;
+        SelectBlocker(const timeval& tv, bool select_has_timeout, const FDVector& read_fds, const FDVector& write_fds, const FDVector& except_fds);
         virtual bool should_unblock(Thread&, time_t, long) override;
 
     private:
         timeval m_select_timeout;
         bool m_select_has_timeout { false };
-        const Vector<int>& m_select_read_fds;
-        const Vector<int>& m_select_write_fds;
-        const Vector<int>& m_select_exceptional_fds;
+        const FDVector& m_select_read_fds;
+        const FDVector& m_select_write_fds;
+        const FDVector& m_select_exceptional_fds;
     };
 
     class WaitBlocker : public Blocker {