Implement sys$chdir() and teach sh+ls to cd around and browse different dirs.

Kernel/Syscall.cpp

@@ -110,6 +110,8 @@ DWORD handle(DWORD function, DWORD arg1, DWORD arg2, DWORD arg3)
         return 0;
     case Syscall::GetArguments:
         return current->sys$get_arguments((int*)arg1, (char***)arg2);
+    case Syscall::PosixChdir:
+        return current->sys$chdir((const char*)arg1);
     default:
         kprintf("int0x80: Unknown function %x requested {%x, %x, %x}\n", function, arg1, arg2, arg3);
         break;

Kernel/Syscall.h

@@ -32,6 +32,7 @@ enum Function {
     PosixGettimeofday = 0x2000,
     PosixGethostname = 0x2001,
     GetArguments = 0x2002,
+    PosixChdir = 0x2003,
 };
 
 void initialize();

Kernel/Task.cpp

@@ -205,7 +205,14 @@ Task* Task::createUserTask(const String& path, uid_t uid, gid_t gid, pid_t paren
         return nullptr;
     }
 
-    auto handle = VirtualFileSystem::the().open(path);
+    RetainPtr<VirtualFileSystem::Node> cwd;
+    {
+        InterruptDisabler disabler;
+        if (auto* parentTask = Task::fromPID(parentPID))
+            cwd = parentTask->m_cwd.copyRef();
+    }
+
+    auto handle = VirtualFileSystem::the().open(path, cwd.ptr());
     if (!handle) {
         error = -ENOENT; // FIXME: Get a more detailed error from VFS.
         return nullptr;
@@ -327,9 +334,9 @@ Task::Task(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel ring)
 
     auto* parentTask = Task::fromPID(parentPID);
     if (parentTask)
-        m_cwd = parentTask->m_cwd;
+        m_cwd = parentTask->m_cwd.copyRef();
     else
-        m_cwd = "/";
+        m_cwd = nullptr;
 
     m_nextRegion = LinearAddress(0x600000);
 
@@ -712,22 +719,29 @@ int Task::sys$close(int fd)
 
 int Task::sys$lstat(const char* path, void* statbuf)
 {
-    auto handle = VirtualFileSystem::the().open(move(path));
+    auto handle = VirtualFileSystem::the().open(move(path), m_cwd.ptr());
     if (!handle)
         return -1;
     handle->stat((Unix::stat*)statbuf);
     return 0;
 }
 
+int Task::sys$chdir(const char* path)
+{
+    auto handle = VirtualFileSystem::the().open(path, m_cwd.ptr());
+    if (!handle)
+        return -ENOENT; // FIXME: More detailed error.
+    if (!handle->isDirectory())
+        return -ENOTDIR;
+    m_cwd = handle->vnode();
+    kprintf("m_cwd <- %p (%u)\n", m_cwd.ptr(), handle->vnode()->inode.index());
+    return 0;
+}
+
 int Task::sys$getcwd(char* buffer, size_t size)
 {
-    if (size < m_cwd.length() + 1) {
-        // FIXME: return -ERANGE;
-        return -1;
-    }
-    memcpy(buffer, m_cwd.characters(), m_cwd.length());
-    buffer[m_cwd.length()] = '\0';
-    return 0;
+    // FIXME: Implement!
+    return -ENOTIMPL;
 }
 
 int Task::sys$open(const char* path, size_t pathLength)
@@ -744,7 +758,7 @@ int Task::sys$open(const char* path, size_t pathLength)
 
 FileHandle* Task::openFile(String&& path)
 {
-    auto handle = VirtualFileSystem::the().open(move(path));
+    auto handle = VirtualFileSystem::the().open(move(path), m_cwd.ptr());
     if (!handle) {
 #ifdef DEBUG_IO
         kprintf("vfs::open() failed\n");

Kernel/Task.h

@@ -6,6 +6,7 @@
 #include "TSS.h"
 #include <AK/Vector.h>
 #include "i386.h"
+#include <VirtualFileSystem/VirtualFileSystem.h>
 
 //#define TASK_SANITY_CHECKS
 
@@ -98,6 +99,7 @@ public:
     int sys$munmap(void*, size_t size);
     int sys$get_dir_entries(int fd, void*, size_t);
     int sys$getcwd(char*, size_t);
+    int sys$chdir(const char*);
     int sys$sleep(unsigned seconds);
     int sys$gettimeofday(timeval*);
     int sys$gethostname(char* name, size_t length);
@@ -150,7 +152,7 @@ private:
     pid_t m_waitee { -1 };
     int m_fdBlockedOnRead { -1 };
 
-    String m_cwd;
+    RetainPtr<VirtualFileSystem::Node> m_cwd;
 
     struct Region {
         Region(LinearAddress, size_t, RetainPtr<Zone>&&, String&&);

Kernel/errno.h

@@ -37,3 +37,5 @@
 #define ENAMETOOLONG 36 // Name too long
 
 #define EOVERFLOW 75    // Value too large for defined data type
+
+#define ENOTIMPL 999    // Not implemented