Kernel: More work towards POSIX SHM, also add ftruncate().

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/26a06f3fcd6

Kernel/FileSystem/FileDescriptor.cpp

@@ -11,6 +11,7 @@
 #include <Kernel/Process.h>
 #include <Kernel/Devices/BlockDevice.h>
 #include <Kernel/VM/MemoryManager.h>
+#include <Kernel/SharedMemory.h>
 
 Retained<FileDescriptor> FileDescriptor::create(RetainPtr<Inode>&& inode)
 {
@@ -357,6 +358,11 @@ const char* to_string(SocketRole role)
     }
 }
 
+bool FileDescriptor::is_file() const
+{
+    return !is_tty() && !is_fifo() && !is_device() && !is_socket() && !is_shared_memory();
+}
+
 KResultOr<String> FileDescriptor::absolute_path()
 {
     Stopwatch sw("absolute_path");
@@ -439,3 +445,12 @@ const CharacterDevice* FileDescriptor::character_device() const
 {
     return is_character_device() ? static_cast<const CharacterDevice*>(device()) : nullptr;
 }
+
+KResult FileDescriptor::truncate(off_t length)
+{
+    if (is_file()) {
+        return m_inode->truncate(length);
+    }
+    ASSERT(is_shared_memory());
+    return shared_memory()->truncate(length);
+}

Kernel/FileSystem/FileDescriptor.h

@@ -15,6 +15,7 @@ class MasterPTY;
 class Process;
 class Region;
 class CharacterDevice;
+class SharedMemory;
 
 class FileDescriptor : public Retainable<FileDescriptor> {
 public:
@@ -85,6 +86,11 @@ public:
     bool is_fifo() const { return m_fifo; }
     FIFO::Direction fifo_direction() { return m_fifo_direction; }
 
+    bool is_file() const;
+    bool is_shared_memory() const { return m_shared_memory; }
+    SharedMemory* shared_memory() { return m_shared_memory.ptr(); }
+    const SharedMemory* shared_memory() const { return m_shared_memory.ptr(); }
+
     ByteBuffer& generator_cache() { return m_generator_cache; }
 
     void set_original_inode(Badge<VFS>, Retained<Inode>&& inode) { m_inode = move(inode); }
@@ -92,6 +98,8 @@ public:
     SocketRole socket_role() const { return m_socket_role; }
     void set_socket_role(SocketRole);
 
+    KResult truncate(off_t);
+
 private:
     friend class VFS;
     FileDescriptor(RetainPtr<Socket>&&, SocketRole);
@@ -115,6 +123,8 @@ private:
     RetainPtr<FIFO> m_fifo;
     FIFO::Direction m_fifo_direction { FIFO::Neither };
 
+    RetainPtr<SharedMemory> m_shared_memory;
+
     bool m_closed { false };
 };
 

Kernel/Makefile

@@ -31,6 +31,7 @@ KERNEL_OBJS = \
        ELF/ELFImage.o \
        ELF/ELFLoader.o \
        KSyms.o \
+       SharedMemory.o \
        FileSystem/DevPtsFS.o \
        Devices/BXVGADevice.o \
        PCI.o \

Kernel/Process.cpp

@@ -2468,3 +2468,14 @@ int Process::sys$shm_unlink(const char* name)
         return -EFAULT;
     return -ENOTIMPL;
 }
+
+int Process::sys$ftruncate(int fd, off_t length)
+{
+    auto* descriptor = file_descriptor(fd);
+    if (!descriptor)
+        return -EBADF;
+    // FIXME: Check that fd is writable, otherwise EINVAL.
+    if (!descriptor->is_file() && !descriptor->is_shared_memory())
+        return -EINVAL;
+    return descriptor->truncate(length);
+}

Kernel/Process.h

@@ -101,6 +101,7 @@ public:
     int sys$donate(int tid);
     int sys$shm_open(const char* name, int flags, mode_t);
     int sys$shm_unlink(const char* name);
+    int sys$ftruncate(int fd, off_t);
     pid_t sys$setsid();
     pid_t sys$getsid(pid_t);
     int sys$setpgid(pid_t pid, pid_t pgid);

Kernel/SharedMemory.cpp

@@ -0,0 +1,27 @@
+#include <Kernel/SharedMemory.h>
+#include <Kernel/VM/VMObject.h>
+
+SharedMemory::SharedMemory()
+{
+}
+
+SharedMemory::~SharedMemory()
+{
+}
+
+KResult SharedMemory::truncate(int length)
+{
+    if (!length) {
+        m_vmo = nullptr;
+        return KSuccess;
+    }
+
+    if (!m_vmo) {
+        m_vmo = VMObject::create_anonymous(length);
+        return KSuccess;
+    }
+
+    // FIXME: Support truncation.
+    ASSERT_NOT_REACHED();
+    return KResult(-ENOTIMPL);
+}

Kernel/SharedMemory.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <AK/Retainable.h>
+#include <AK/RetainPtr.h>
+#include <Kernel/KResult.h>
+
+class VMObject;
+
+class SharedMemory : public Retainable<SharedMemory> {
+public:
+    static Retained<SharedMemory> create();
+    ~SharedMemory();
+
+    KResult truncate(int);
+
+private:
+    SharedMemory();
+
+    int m_uid { 0 };
+    int m_gid { 0 };
+    RetainPtr<VMObject> m_vmo;
+};

Kernel/Syscall.cpp

@@ -247,6 +247,8 @@ static dword handle(RegisterDump& regs, dword function, dword arg1, dword arg2,
         return current->process().sys$shm_open((const char*)arg1, (int)arg2, (mode_t)arg3);
     case Syscall::SC_shm_close:
         return current->process().sys$shm_unlink((const char*)arg1);
+    case Syscall::SC_ftruncate:
+        return current->process().sys$ftruncate((int)arg1, (off_t)arg2);
     default:
         kprintf("<%u> int0x82: Unknown function %u requested {%x, %x, %x}\n", current->process().pid(), function, arg1, arg2, arg3);
         break;

Kernel/Syscall.h

@@ -98,6 +98,7 @@
     __ENUMERATE_SYSCALL(rename) \
     __ENUMERATE_SYSCALL(shm_open) \
     __ENUMERATE_SYSCALL(shm_close) \
+    __ENUMERATE_SYSCALL(ftruncate) \
 
 
 namespace Syscall {

LibC/unistd.cpp

@@ -442,7 +442,8 @@ int create_thread(int(*entry)(void*), void* argument)
 
 int ftruncate(int fd, off_t length)
 {
-    ASSERT_NOT_REACHED();
+    int rc = syscall(SC_ftruncate, fd, length);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
 int gettid()