kernel: Let devices use shared memory

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/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);