libc+init+shmem-test: Add POSIX shared memory objects

apps/init.cpp

@@ -292,6 +292,15 @@ static void mount_tmpfs()
     if (chmod("/tmp", 01777) < 0) exit(255);
 }
 
+static void mount_shmfs()
+{
+    if (mkdir("/dev/shm", 0755) < 0) exit(255);
+
+    if (mount("/dev/shm", "tmpfs", "tmpfs") < 0) exit(255);
+
+    if (chmod("/dev/shm", 01777) < 0) exit(255);
+}
+
 int main()
 {
     if (getpid() != 1)
@@ -307,6 +316,7 @@ int main()
     stderr = fopen("/dev/console", "w");
 
     mount_tmpfs();
+    mount_shmfs();
 
     umask(022);
 

apps/shmem-test.cpp

@@ -1,3 +1,4 @@
+#include <fcntl.h>
 #include <stdio.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
@@ -5,15 +6,27 @@
 
 int main()
 {
-    void* address = mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+    int fd = shm_open("/shared", O_CREAT | O_RDWR, 0666);
+    if (fd < 0)
+    {
+        perror("shm_open");
+        return 1;
+    }
+
+    ftruncate(fd, PAGE_SIZE);
+
+    void* address = mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
     if (address == MAP_FAILED)
     {
         perror("mmap");
         return 1;
     }
 
-    int* ptr = (int*)address;
-    *ptr = 16;
+    char* ptr = (char*)address;
+
+    printf("the value is %c\n", *ptr);
+
+    *ptr = 'a';
 
     pid_t child = fork();
     if (child < 0)
@@ -23,13 +36,13 @@ int main()
     }
     if (child == 0)
     {
-        *ptr = 32;
+        *ptr = 'e';
         _exit(0);
     }
 
     waitpid(child, NULL, 0);
 
-    printf("the value is %d\n", *ptr);
+    printf("the value is %c\n", *ptr);
 
     return 0;
 }

kernel/src/fs/devices/FramebufferDevice.cpp

@@ -39,6 +39,11 @@ Result<u64> FramebufferDevice::query_shared_memory(off_t offset, usize count)
     }
 
     auto* shm = g_shared_memory_map.try_get_ref(*m_shmid);
+    if (!shm)
+    {
+        m_shmid = {};
+        return query_shared_memory(offset, count);
+    }
     if (shm->offset > offset)
     {
         TRY(shm->grow_backward(Framebuffer::ptr() + offset, (shm->offset - offset) / ARCH_PAGE_SIZE));

kernel/src/fs/tmpfs/Inode.cpp

@@ -144,6 +144,12 @@ namespace TmpFS
         }
 
         auto* shm = g_shared_memory_map.try_get_ref(*m_shmid);
+        if (!shm)
+        {
+            m_shmid = {};
+            return query_shared_memory(offset, count);
+        }
+
         if (shm->offset > offset)
         {
             TRY(shm->grow_backward(m_data_buffer.data() + offset, (shm->offset - offset) / ARCH_PAGE_SIZE));

kernel/src/memory/SharedMemory.cpp

@@ -107,12 +107,16 @@ Result<void> SharedMemory::map(u64 virt, int flags, off_t _offset, usize count)
 
 void SharedMemory::free()
 {
-    if (inode && (prot & PROT_WRITE))
+    if ((inode || device) && (prot & PROT_WRITE))
     {
         for (u64 i = 0; i < frames.size(); i++)
         {
+            if (inode)
                 inode->write((u8*)MMU::translate_physical_address(frames[i]), offset + (i * ARCH_PAGE_SIZE),
                              ARCH_PAGE_SIZE);
+            if (device)
+                device->write((u8*)MMU::translate_physical_address(frames[i]), offset + (i * ARCH_PAGE_SIZE),
+                              ARCH_PAGE_SIZE);
         }
     }
 

kernel/src/memory/SharedMemory.h

@@ -14,6 +14,9 @@ struct SharedMemory
     SharedPtr<Device> device {};
     int refs { 0 };
 
+    SharedMemory() = default;
+    SharedMemory(SharedMemory&&) = default;
+
     static Result<u64> create(u8* mem, off_t offset, usize count);
 
     Result<void> grow_forward(u8* mem, usize count);
@@ -22,6 +25,8 @@ struct SharedMemory
     Result<void> map(u64 virt, int flags, off_t offset, usize count);
 
     void free();
+
+    ~SharedMemory() = default;
 };
 
 extern HashMap<u64, SharedMemory> g_shared_memory_map;

kernel/src/sys/mmap.cpp

@@ -50,6 +50,7 @@ Result<u64> sys_mmap(Registers*, SyscallArgs args)
         }
         shmem = g_shared_memory_map.try_get_ref(shmid);
         shmem->refs++;
+        shmem->prot |= params.prot;
     }
 
     u64 address;

libc/include/sys/mman.h

@@ -28,6 +28,12 @@ extern "C"
     /* Write modified shared memory back to its associated file. */
     int msync(void* addr, size_t len, int flags);
 
+    /* Create a new POSIX shared memory object. */
+    int shm_open(const char* name, int oflag, mode_t mode);
+
+    /* Delete a POSIX shared memory object from the file system. */
+    int shm_unlink(const char* name);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/sys/mman.cpp

@@ -1,6 +1,8 @@
 #include <bits/errno-return.h>
 #include <bits/mmap.h>
+#include <fcntl.h>
 #include <luna/Heap.h>
+#include <stdio.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <unistd.h>
@@ -25,4 +27,18 @@ extern "C"
         long rc = syscall(SYS_msync, addr, len);
         __errno_return(rc, int);
     }
+
+    int shm_open(const char* name, int oflag, mode_t mode)
+    {
+        char buf[BUFSIZ];
+        snprintf(buf, sizeof(buf), "/dev/shm%s", name);
+        return open(buf, oflag | O_CLOEXEC, mode);
+    }
+
+    int shm_unlink(const char* name)
+    {
+        char buf[BUFSIZ];
+        snprintf(buf, sizeof(buf), "/dev/shm%s", name);
+        return unlink(buf);
+    }
 }

libluna/include/luna/SharedPtr.h

@@ -23,7 +23,7 @@ struct Shareable
         return m_ref_count == 0;
     }
 
-    Atomic<int> m_ref_count { 1 };
+    Atomic<int> m_ref_count { 0 };
 };
 
 template <typename T> class SharedPtr
@@ -36,6 +36,7 @@ template <typename T> class SharedPtr
 
     SharedPtr(T* ptr) : m_ptr(ptr)
     {
+        if (m_ptr) shareable()->ref();
     }
 
     SharedPtr(const SharedPtr<T>& other) : m_ptr(other.m_ptr)
@@ -50,7 +51,6 @@ template <typename T> class SharedPtr
 
     template <typename Tp> operator SharedPtr<Tp>()
     {
-        if (m_ptr) shareable()->ref();
         return { (Tp*)m_ptr };
     }