Add a /proc/PID/fds text files that lists all the fds open in a process.

Kernel/ProcFileSystem.cpp

@@ -27,6 +27,22 @@ ProcFileSystem::~ProcFileSystem()
 {
 }
 
+ByteBuffer procfs$pid_fds(const Process& process)
+{
+    char* buffer;
+    auto stringImpl = StringImpl::createUninitialized(process.number_of_open_file_descriptors() * 80, buffer);
+    memset(buffer, 0, stringImpl->length());
+    char* ptr = buffer;
+    for (size_t i = 0; i < process.max_open_file_descriptors(); ++i) {
+        auto* handle = process.file_descriptor(i);
+        if (!handle)
+            continue;
+        ptr += ksprintf(ptr, "% 3u %s\n", i, handle->absolute_path().characters());
+    }
+    *ptr = '\0';
+    return ByteBuffer::copy((byte*)buffer, ptr - buffer);
+}
+
 ByteBuffer procfs$pid_vm(const Process& process)
 {
     InterruptDisabler disabler;
@@ -109,6 +125,7 @@ void ProcFileSystem::addProcess(Process& process)
     m_pid2inode.set(process.pid(), dir.index());
     addFile(createGeneratedFile("vm", [&process] { return procfs$pid_vm(process); }), dir.index());
     addFile(createGeneratedFile("stack", [&process] { return procfs$pid_stack(process); }), dir.index());
+    addFile(createGeneratedFile("fds", [&process] { return procfs$pid_fds(process); }), dir.index());
     if (process.executableInode().isValid())
         addFile(createGeneratedFile("exe", [&process] { return procfs$pid_exe(process); }, 00120777), dir.index());
 }

Kernel/Process.cpp

@@ -867,8 +867,9 @@ int Process::sys$close(int fd)
     auto* handle = fileHandleIfExists(fd);
     if (!handle)
         return -EBADF;
-    // FIXME: Implement.
+    int rc = handle->close();
-    return 0;
+    m_file_descriptors[fd] = nullptr;
+    return rc;
 }
 
 int Process::sys$lstat(const char* path, Unix::stat* statbuf)
@@ -966,9 +967,13 @@ int Process::sys$open(const char* path, int options)
     if (options & O_DIRECTORY && !handle->isDirectory())
         return -ENOTDIR; // FIXME: This should be handled by VFS::open.
 
-    int fd = m_file_descriptors.size();
+    int fd = 0;
+    for (; fd < m_max_open_file_descriptors; ++fd) {
+        if (!m_file_descriptors[fd])
+            break;
+    }
     handle->setFD(fd);
-    m_file_descriptors.append(move(handle));
+    m_file_descriptors[fd] = move(handle);
     return fd;
 }
 

Kernel/Process.h

@@ -136,6 +136,9 @@ public:
     InodeIdentifier executableInode() const { return m_executable ? m_executable->inode : InodeIdentifier(); }
 
     size_t number_of_open_file_descriptors() const;
+    size_t max_open_file_descriptors() const { return m_max_open_file_descriptors; }
+    FileHandle* file_descriptor(size_t i) { return m_file_descriptors[i].ptr(); }
+    const FileHandle* file_descriptor(size_t i) const { return m_file_descriptors[i].ptr(); }
 
 private:
     friend class MemoryManager;

VirtualFileSystem/FileHandle.cpp

@@ -175,3 +175,15 @@ const TTY* FileHandle::tty() const
         return static_cast<const TTY*>(device);
     return nullptr;
 }
+
+int FileHandle::close()
+{
+    return 0;
+}
+
+String FileHandle::absolute_path() const
+{
+    if (isTTY())
+        return tty()->ttyName();
+    return VirtualFileSystem::the().absolutePath(m_vnode->inode);
+}

VirtualFileSystem/FileHandle.h

@@ -11,6 +11,8 @@ public:
     explicit FileHandle(RetainPtr<VirtualFileSystem::Node>&&);
     ~FileHandle();
 
+    int close();
+
     Unix::off_t seek(Unix::off_t, int whence);
     Unix::ssize_t read(byte*, Unix::size_t);
     Unix::ssize_t write(const byte* data, Unix::size_t);
@@ -22,7 +24,7 @@ public:
 
     ByteBuffer readEntireFile();
 
-    String absolutePath() const;
+    String absolute_path() const;
 
     bool isDirectory() const;