Kernel, libc: Add a getdents() system call

This is meant to be a low-level interface to implement dirent.h on top of.

kernel/include/fs/VFS.h

@@ -19,6 +19,7 @@ namespace VFS
     typedef Node* (*node_finddir)(Node*, const char*);
     typedef int (*node_mkdir)(Node*, const char*);
     typedef int (*node_block)(Node*);
+    typedef Node* (*node_readdir)(Node*, long);
 
     struct Node
     {
@@ -29,6 +30,7 @@ namespace VFS
         int flags;
         node_read read_func;
         node_finddir find_func;
+        node_readdir readdir_func;
         node_mkdir mkdir_func;
         node_write write_func;
         node_block block_func;
@@ -55,4 +57,6 @@ namespace VFS
     void unmount(Node* mountpoint);
 
     Node* root();
+
+    Node* readdir(Node* dir, long offset);
 }

kernel/include/sys/Syscall.h

@@ -24,9 +24,11 @@
 #define SYS_access 19
 #define SYS_fstat 20
 #define SYS_pstat 21
+#define SYS_getdents 22
 
 struct stat;
 struct pstat;
+struct luna_dirent;
 
 namespace Syscall
 {
@@ -55,3 +57,4 @@ void sys_waitpid(Context* context, long pid, int* wstatus, int options);
 void sys_access(Context* context, const char* path, int amode);
 void sys_fstat(Context* context, int fd, struct stat* buf);
 void sys_pstat(Context* context, long pid, struct pstat* buf);
+void sys_getdents(Context* context, int fd, struct luna_dirent* buf, size_t count);

kernel/src/fs/FileDescriptor.cpp

@@ -39,7 +39,7 @@ ssize_t Descriptor::write(size_t size, const char* buffer)
 
 int Descriptor::seek(long offset)
 {
-    if (m_node->type != VFS_DEVICE && (uint64_t)offset > m_node->length)
+    if (m_node->type == VFS_FILE && (uint64_t)offset > m_node->length)
         return -EINVAL; // FIXME: Support seeking beyond the current file's length.
     m_offset = (uint64_t)offset;
     return 0;

kernel/src/fs/VFS.cpp

@@ -202,3 +202,10 @@ void VFS::unmount(Node* mountpoint)
     if (!(mountpoint->flags & VFS_MOUNTPOINT)) return;
     mountpoint->flags &= ~VFS_MOUNTPOINT;
 }
+
+VFS::Node* VFS::readdir(VFS::Node* dir, long offset)
+{
+    if (!dir) return 0;
+    if (!dir->readdir_func) return 0;
+    return dir->readdir_func(dir, offset);
+}

kernel/src/init/InitRD.cpp

@@ -186,6 +186,15 @@ VFS::Node* initrd_scan_dir(VFS::Node* node, const char* filename)
     return 0;
 }
 
+VFS::Node* initrd_read_dir(VFS::Node* node, long offset)
+{
+    if (!node) return 0;
+    if (node->inode >= total_dirs) return 0;
+    InitRD::Directory dir = dirs[node->inode];
+    if (offset >= dir.entries) return 0;
+    return dir.files[offset];
+}
+
 int initrd_mkdir(VFS::Node* node, const char* name) // FIXME: Return proper error numbers.
 {
     if (total_dirs >= 32)
@@ -222,6 +231,7 @@ int initrd_mkdir(VFS::Node* node, const char* name) // FIXME: Return proper erro
     dir.entries = 0;
     dirs[total_dirs++] = dir; // FIXME: Right now this isn't of worry, but there is a possibility for a TOCTOU bug here.
                               // Should use a spinlock or something.
+    node->length++;
     parent.files[parent.entries++] = &new_node;
     return 0;
 }
@@ -270,10 +280,13 @@ static bool initrd_register_dir(InitRD::Directory& dir, uint64_t inode)
                 node.length = 0;
                 node.type = VFS_DIRECTORY;
                 node.mkdir_func = initrd_mkdir;
+                node.readdir_func = initrd_read_dir;
+                node.length = 0;
                 strncpy(node.name, buffer, sizeof(node.name));
                 strncpy(dir.name, buffer, sizeof(dir.name));
 
                 parent.files[parent.entries++] = &node;
+                current_node->length++;
 
                 kfree(buffer);
                 return true;
@@ -332,6 +345,7 @@ static bool initrd_register_file(InitRD::File& f, uint64_t inode)
                 strncpy(f.name, buffer, sizeof(f.name));
 
                 parent.files[parent.entries++] = &node;
+                current_node->length++;
                 kfree(buffer);
                 return true;
             }
@@ -375,6 +389,7 @@ static void initrd_initialize_root()
     strncpy(root.name, "initrd", sizeof(root.name));
     initrd_root.find_func = initrd_scan_dir;
     initrd_root.mkdir_func = initrd_mkdir;
+    initrd_root.readdir_func = initrd_read_dir;
 }
 
 void InitRD::init()

kernel/src/sys/Syscall.cpp

@@ -33,6 +33,9 @@ void Syscall::entry(Context* context)
     case SYS_access: sys_access(context, (const char*)context->rdi, (int)context->rsi); break;
     case SYS_fstat: sys_fstat(context, (int)context->rdi, (struct stat*)context->rsi); break;
     case SYS_pstat: sys_pstat(context, (long)context->rdi, (struct pstat*)context->rsi); break;
+    case SYS_getdents:
+        sys_getdents(context, (int)context->rdi, (struct luna_dirent*)context->rsi, (size_t)context->rdx);
+        break;
     default: context->rax = -ENOSYS; break;
     }
     VMM::exit_syscall_context();

kernel/src/sys/dirent.cpp

@@ -0,0 +1,61 @@
+#define MODULE "dir"
+
+#include "luna/dirent.h"
+#include "fs/VFS.h"
+#include "interrupts/Context.h"
+#include "std/errno.h"
+#include "std/string.h"
+#include "sys/UserMemory.h"
+#include "thread/Scheduler.h"
+
+void sys_getdents(Context* context, int fd, struct luna_dirent* buf, size_t count)
+{
+    if (fd < 0 || fd > TASK_MAX_FDS)
+    {
+        context->rax = -EBADF;
+        return;
+    }
+    Task* current_task = Scheduler::current_task();
+    if (!current_task->files[fd].is_open())
+    {
+        context->rax = -EBADF;
+        return;
+    }
+    Descriptor& dir = current_task->files[fd];
+    VFS::Node* node = dir.node();
+    if (node->type != VFS_DIRECTORY)
+    {
+        context->rax = -ENOTDIR;
+        return;
+    }
+    size_t nread = 0;
+    while (count)
+    {
+        VFS::Node* entry = VFS::readdir(node, dir.offset());
+        if (!entry)
+        {
+            context->rax = nread;
+            return;
+        }
+
+        auto* kdirent = obtain_user_ref(buf);
+        if (!kdirent)
+        {
+            context->rax = -EFAULT;
+            return;
+        }
+
+        kdirent->total = node->length;
+        kdirent->offset = dir.offset();
+        kdirent->inode = entry->inode;
+        strlcpy(kdirent->name, entry->name, sizeof(kdirent->name));
+
+        release_user_ref(kdirent);
+
+        dir.seek(dir.offset() + 1);
+        buf++;
+        nread++;
+        count--;
+    }
+    context->rax = nread;
+}

libs/libc/include/luna/dirent.h

@@ -0,0 +1,26 @@
+#ifndef _LUNA_DIRENT_H
+#define _LUNA_DIRENT_H
+
+#include <sys/types.h>
+
+struct luna_dirent
+{
+    ino_t inode;
+    char name[64];
+    size_t total;
+    off_t offset;
+};
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Retrieve directory entries from the kernel. This is the raw interface, use readdir() instead. */
+    ssize_t getdents(int fd, struct luna_dirent* buf, size_t count);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

libs/libc/include/sys/syscall.h

@@ -23,5 +23,6 @@
 #define SYS_access 19
 #define SYS_fstat 20
 #define SYS_pstat 21
+#define SYS_getdents 22
 
 #endif

libs/libc/src/luna/dirent.cpp

@@ -0,0 +1,11 @@
+#include <luna/dirent.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+extern "C"
+{
+    ssize_t getdents(int fd, struct luna_dirent* buf, size_t count)
+    {
+        return syscall(SYS_getdents, fd, buf, count);
+    }
+}

libs/libc/src/syscall.cpp

@@ -31,6 +31,7 @@ extern "C" long syscall(long number, ...)
         result = __luna_syscall2(number, arg0, arg1);
         break;
     }
+    case SYS_getdents:
     case SYS_fcntl:
     case SYS_seek:
     case SYS_write: