gol: Use memory-mapped IO

apps/gol.cpp

@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -24,6 +25,7 @@ static int g_fb_height;
 static int g_fd;
 
 static Cell* g_cells;
+static char* g_fb;
 
 static Result<void> fill_cells()
 {
@@ -47,27 +49,29 @@ static Cell& find_cell(int row, int column)
 
 static constexpr int BYTES_PER_PIXEL = 4;
 
-static char* g_buf;
-
 static void draw_cells()
 {
-    lseek(g_fd, 0, SEEK_SET);
-
     const int CELL_WIDTH = g_fb_width / g_num_columns;
     const int CELL_HEIGHT = g_fb_height / g_num_rows;
 
     for (int i = 0; i < g_num_rows; i++)
     {
-        memset(g_buf, 0, g_fb_width * BYTES_PER_PIXEL);
 
         for (int j = 0; j < g_num_columns; j++)
         {
-            auto& cell = find_cell(i, j);
-            if (cell.state) memset(g_buf + (j * CELL_WIDTH * BYTES_PER_PIXEL), 0xff, CELL_WIDTH * BYTES_PER_PIXEL);
-        }
+            char* buf = g_fb + (i * g_fb_width * CELL_HEIGHT * BYTES_PER_PIXEL);
 
-        for (int j = 0; j < CELL_HEIGHT; j++) { write(g_fd, g_buf, g_fb_width * BYTES_PER_PIXEL); }
+            auto& cell = find_cell(i, j);
+            u8 color = cell.state ? 0xff : 0x00;
+            for (int k = 0; k < CELL_HEIGHT; k++)
+            {
+                memset(buf + (j * CELL_WIDTH * BYTES_PER_PIXEL), color, CELL_WIDTH * BYTES_PER_PIXEL);
+                buf += g_fb_width * BYTES_PER_PIXEL;
+            }
+        }
     }
+
+    msync(g_fb, g_fb_height * g_fb_width * BYTES_PER_PIXEL, MS_SYNC);
 }
 
 static int find_neighbors(int row, int column)
@@ -137,7 +141,7 @@ Result<int> luna_main(int argc, char** argv)
     else
         srand((unsigned)time(NULL));
 
-    g_fd = open("/dev/fb0", O_WRONLY);
+    g_fd = open("/dev/fb0", O_RDWR);
     if (g_fd < 0)
     {
         perror("gol: cannot open framebuffer for writing");
@@ -149,7 +153,13 @@ Result<int> luna_main(int argc, char** argv)
 
     TRY(fill_cells());
 
-    g_buf = (char*)TRY(calloc_impl(g_fb_width, BYTES_PER_PIXEL));
+    g_fb =
+        (char*)mmap(nullptr, g_fb_height * g_fb_width * BYTES_PER_PIXEL, PROT_READ | PROT_WRITE, MAP_SHARED, g_fd, 0);
+    if (g_fb == MAP_FAILED)
+    {
+        perror("gol: cannot map framebuffer into memory");
+        return 1;
+    }
 
     draw_cells();
 
@@ -162,5 +172,8 @@ Result<int> luna_main(int argc, char** argv)
 
     usleep(delay_at_end * 1000);
 
+    munmap(g_fb, g_fb_height * g_fb_width * BYTES_PER_PIXEL);
+    free(g_cells);
+
     return 0;
 }

kernel/src/fs/devices/Device.h

@@ -10,6 +10,11 @@ class Device : public Shareable
 
     virtual Result<usize> write(const u8* buf, usize offset, usize length) = 0;
 
+    virtual Result<u64> query_shared_memory(off_t, usize)
+    {
+        return err(EACCES);
+    }
+
     virtual Result<u64> ioctl(int, void*)
     {
         return err(ENOTTY);
@@ -44,4 +49,7 @@ class Device : public Shareable
     virtual bool will_block_if_read() const = 0;
 
     virtual ~Device() = default;
+
+  protected:
+    Option<u64> m_shmid;
 };

kernel/src/fs/devices/FramebufferDevice.cpp

@@ -1,4 +1,6 @@
 #include "fs/devices/FramebufferDevice.h"
+#include "arch/MMU.h"
+#include "memory/SharedMemory.h"
 #include "video/Framebuffer.h"
 #include <bits/ioctl-defs.h>
 #include <luna/CString.h>
@@ -23,6 +25,32 @@ Result<usize> FramebufferDevice::write(const u8* buf, usize offset, usize length
     return length;
 }
 
+Result<u64> FramebufferDevice::query_shared_memory(off_t offset, usize count)
+{
+    if (offset + (count * ARCH_PAGE_SIZE) > Framebuffer::size()) return err(EINVAL);
+
+    if (!m_shmid.has_value())
+    {
+        u64 shmid = TRY(SharedMemory::create(Framebuffer::ptr() + offset, offset, count));
+        m_shmid = shmid;
+        auto* shm = g_shared_memory_map.try_get_ref(shmid);
+        shm->device = SharedPtr<Device> { this };
+        return shmid;
+    }
+
+    auto* shm = g_shared_memory_map.try_get_ref(*m_shmid);
+    if (shm->offset > offset)
+    {
+        TRY(shm->grow_backward(Framebuffer::ptr() + offset, (shm->offset - offset) / ARCH_PAGE_SIZE));
+    }
+    if (shm->frames.size() < count)
+    {
+        TRY(shm->grow_forward(Framebuffer::ptr() + offset + (shm->frames.size() * ARCH_PAGE_SIZE),
+                              count - shm->frames.size()));
+    }
+    return *m_shmid;
+}
+
 usize FramebufferDevice::size() const
 {
     return Framebuffer::size();

kernel/src/fs/devices/FramebufferDevice.h

@@ -11,6 +11,8 @@ class FramebufferDevice : public Device
 
     Result<usize> write(const u8*, usize, usize) override;
 
+    Result<u64> query_shared_memory(off_t offset, usize count) override;
+
     bool will_block_if_read() const override;
 
     bool is_block_device() const override

kernel/src/fs/tmpfs/Inode.cpp

@@ -138,6 +138,8 @@ namespace TmpFS
         {
             u64 shmid = TRY(SharedMemory::create(m_data_buffer.data() + offset, offset, count));
             m_shmid = shmid;
+            auto* shm = g_shared_memory_map.try_get_ref(shmid);
+            shm->inode = SharedPtr<VFS::Inode> { (VFS::Inode*)this };
             return shmid;
         }
 

kernel/src/fs/tmpfs/Inode.h

@@ -154,6 +154,11 @@ namespace TmpFS
             m_metadata.devid = id;
         }
 
+        Result<u64> query_shared_memory(off_t offset, usize count) override
+        {
+            return m_device->query_shared_memory(offset, count);
+        }
+
         VFS::FileSystem* fs() const override
         {
             return m_fs;

kernel/src/memory/AddressSpace.cpp

@@ -304,6 +304,10 @@ void VMRegion::sync_shared()
     if (used && (flags & MAP_SHARED) && (prot & PROT_WRITE))
     {
         SharedMemory* shmem = g_shared_memory_map.try_get_ref(shmid);
-        if (shmem) { shmem->inode->write((const u8*)start, offset, count * ARCH_PAGE_SIZE); }
+        if (shmem)
+        {
+            if (shmem->inode) shmem->inode->write((const u8*)start, offset, count * ARCH_PAGE_SIZE);
+            if (shmem->device) shmem->device->write((const u8*)start, offset, count * ARCH_PAGE_SIZE);
+        }
     }
 }

kernel/src/memory/SharedMemory.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "fs/VFS.h"
+#include "fs/devices/Device.h"
 #include <luna/HashMap.h>
 #include <luna/Vector.h>
 #include <sys/types.h>
@@ -10,6 +11,7 @@ struct SharedMemory
     off_t offset;
     int prot;
     SharedPtr<VFS::Inode> inode {};
+    SharedPtr<Device> device {};
     int refs { 0 };
 
     static Result<u64> create(u8* mem, off_t offset, usize count);

kernel/src/sys/mmap.cpp

@@ -46,7 +46,7 @@ Result<u64> sys_mmap(Registers*, SyscallArgs args)
         else
         {
             if ((params.prot & PROT_WRITE) && !(description->flags & O_WRONLY)) return err(EACCES);
-            shmid = TRY(description->inode->query_shared_memory(params.offset, params.len));
+            shmid = TRY(description->inode->query_shared_memory(params.offset, params.len / ARCH_PAGE_SIZE));
         }
         shmem = g_shared_memory_map.try_get_ref(shmid);
         shmem->refs++;
@@ -72,10 +72,10 @@ Result<u64> sys_mmap(Registers*, SyscallArgs args)
     if (params.prot == PROT_NONE) mmu_flags = MMU::NoExecute;
 
 #ifdef MMAP_DEBUG
-    kdbgln("mmap: mapping memory at %#lx, size=%zu", address, len);
+    kdbgln("mmap: mapping memory at %#lx, size=%zu", address, params.len);
 #endif
 
-    if (shmem) { TRY(shmem->map(address, mmu_flags, params.offset, get_blocks_from_size(params.len, ARCH_PAGE_SIZE))); }
+    if (shmem) { TRY(shmem->map(address, mmu_flags, params.offset, params.len / ARCH_PAGE_SIZE)); }
     else
     {
         TRY(MemoryManager::alloc_at_zeroed(address, get_blocks_from_size(params.len, ARCH_PAGE_SIZE), mmu_flags));