Add file and directory creation, `mkdir`

build.sh

@@ -22,3 +22,4 @@ mcopy -i build/os.img@@"$((partition_offset * sector_size))" build/echo ::bin/ec
 mcopy -i build/os.img@@"$((partition_offset * sector_size))" build/ls ::bin/ls
 mcopy -i build/os.img@@"$((partition_offset * sector_size))" build/cat ::bin/cat
 mcopy -i build/os.img@@"$((partition_offset * sector_size))" build/cp ::bin/cp
+mcopy -i build/os.img@@"$((partition_offset * sector_size))" build/mkdir ::bin/mkdir

meson.build

@@ -349,3 +349,42 @@ custom_target(
   command: ['objcopy', '-O', 'binary', '@INPUT@', '@OUTPUT@'],
   build_by_default: true,
 )
+
+mkdir_start = custom_target(
+  'mkdir_start',
+  input:  'src/user/start.asm',
+  output: 'mkdir_start.o',
+  command: [nasm, '-f', 'elf64', '-o', '@OUTPUT@', '@INPUT@'],
+)
+
+mkdir_syscall = custom_target(
+  'mkdir_syscall',
+  input:  'src/user/syscall.asm',
+  output: 'mkdir_syscall.o',
+  command: [nasm, '-f', 'elf64', '-o', '@OUTPUT@', '@INPUT@'],
+)
+
+mkdir_elf = executable(
+  'mkdir.elf',
+  sources: [mkdir_start, mkdir_syscall, lib_sources, 'src/user/app/mkdir/mkdir.c'],
+  c_args: [
+    '-ffreestanding',
+    '-nostdlib',
+    '-fno-stack-protector',
+    '-mcmodel=large',
+    '-DVERSION="' + meson.project_version() + '"',
+  ],
+  link_args: [
+    '-T', meson.project_source_root() / 'src/user/linker.ld',
+    '-nostdlib',
+  ],
+  link_depends: 'src/user/linker.ld',
+)
+
+custom_target(
+  'mkdir',
+  input:  mkdir_elf,
+  output: 'mkdir',
+  command: ['objcopy', '-O', 'binary', '@INPUT@', '@OUTPUT@'],
+  build_by_default: true,
+)

src/kernel/fat16.c

@@ -5,6 +5,7 @@
 #include "src/kernel/stream.h"
 #include "src/lib/memory.h"
 #include "src/lib/string.h"
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 
 #define SECTOR_SIZE 512
@@ -179,35 +180,34 @@ static void flush_fat() {
   ata_write_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors, (uint8_t)bpb.sectors_per_fat, fat);
 }
 
-static fat16_dir_entry_t *read_directory(uint16_t dir_cluster) {
+static uint16_t read_directory(uint16_t dir_cluster, fat16_dir_entry_t **entries) {
-  fat16_dir_entry_t *entries;
-
   if (!dir_cluster) {
     uint8_t sectors = (uint8_t)((sizeof(fat16_dir_entry_t) * bpb.root_entry_count + SECTOR_SIZE - 1) / SECTOR_SIZE);
-    entries = memory_allocate(sectors * SECTOR_SIZE + sizeof(fat16_dir_entry_t)); // One extra as null terminator.
+    *entries = memory_allocate(sectors * SECTOR_SIZE);
-    ata_read_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors + bpb.fats_count * bpb.sectors_per_fat, sectors, entries);
+    ata_read_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors + bpb.fats_count * bpb.sectors_per_fat, sectors, *entries);
+    return bpb.root_entry_count;
   } else {
     ensure_fat();
 
     uint16_t next_cluster = dir_cluster;
-    uint32_t cluster_count = 0;
+    uint16_t cluster_count = 0;
     while (next_cluster < 0xFFF8) {
       cluster_count++;
       next_cluster = fat[next_cluster];
     }
-    entries =
+    *entries = memory_allocate(cluster_count * bpb.sectors_per_cluster * SECTOR_SIZE);
-        memory_allocate(cluster_count * bpb.sectors_per_cluster * SECTOR_SIZE + sizeof(fat16_dir_entry_t)); // One extra as null terminator.
 
-    uint8_t *chunk = (uint8_t *)entries;
+    uint8_t *chunk = (uint8_t *)*entries;
     next_cluster = dir_cluster;
     while (next_cluster < 0xFFF8) {
       ata_read_sectors(data_start + bpb.sectors_per_cluster * (next_cluster - 2), bpb.sectors_per_cluster, chunk);
       chunk += bpb.sectors_per_cluster * SECTOR_SIZE;
       next_cluster = fat[next_cluster];
     }
+    return cluster_count * bpb.sectors_per_cluster * SECTOR_SIZE / sizeof(fat16_dir_entry_t);
   }
 
-  return entries;
+  return (uint64_t)-1;
 }
 
 static fs_node_t *open_entry(uint16_t dir_cluster, const fat16_dir_entry_t *entries, uint16_t index) {
@@ -233,37 +233,47 @@ static fs_node_t *open_entry(uint16_t dir_cluster, const fat16_dir_entry_t *entr
   return (fs_node_t *)result;
 }
 
-static void write_directory(uint16_t dir_cluster, const fat16_dir_entry_t *entries) {
+static void write_directory(uint16_t dir_cluster, const fat16_dir_entry_t *entries, uint16_t count) {
+  ASSERT((count * sizeof(fat16_dir_entry_t)) % (bpb.sectors_per_cluster * SECTOR_SIZE) == 0,
+         "write_directory: entries must be aligned to clusters");
+
   if (!dir_cluster) {
     ata_write_sectors(FIRST_PARTITION_SECTOR + bpb.reserved_sectors + bpb.fats_count * bpb.sectors_per_fat,
                       (uint8_t)((sizeof(fat16_dir_entry_t) * bpb.root_entry_count + SECTOR_SIZE - 1) / SECTOR_SIZE), entries);
   } else {
     ensure_fat();
 
-    // Assuming no entries were added or removed.
     uint8_t *chunk = (uint8_t *)entries;
     uint16_t next_cluster = dir_cluster;
-    while (next_cluster < 0xFFF8) {
+    while (count) {
       ata_write_sectors(data_start + bpb.sectors_per_cluster * (next_cluster - 2), bpb.sectors_per_cluster, chunk);
       chunk += bpb.sectors_per_cluster * SECTOR_SIZE;
+      count -= bpb.sectors_per_cluster * SECTOR_SIZE / sizeof(fat16_dir_entry_t);
+      if (count && fat[next_cluster] >= 0xFFF8) {
+        fat[next_cluster] = allocate_cluster();
+      }
       next_cluster = fat[next_cluster];
     }
+    flush_fat();
   }
 }
 
-fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name) {
+fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name, uint64_t flags) {
   if (directory->type != FAT16 || !directory->is_dir) {
     return NUL;
   }
 
+  uint16_t dir_cluster = ((fat16_node_t *)directory)->inode->first_cluster;
+
   char name_8_3[12];
   to_8_3(name, name_8_3);
 
-  fat16_dir_entry_t *entries = read_directory(((fat16_node_t *)directory)->inode->first_cluster);
+  fat16_dir_entry_t *entries;
+  uint16_t entries_count = read_directory(dir_cluster, &entries);
 
   fat16_dir_entry_t *entry = entries;
   uint16_t index = 0;
-  while (entry->name[0]) {
+  while (index < entries_count && entry->name[0]) {
     if ((uint8_t)entry->name[0] != 0xE5 && (uint8_t)entry->attributes != 0x0F && bytes_equal(name_8_3, (char *)entry, 11)) {
       break;
     }
@@ -271,20 +281,82 @@ fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name) {
     index++;
   }
 
-  fs_node_t *result = open_entry(((fat16_node_t *)directory)->inode->first_cluster, entries, index);
+  fs_node_t *result = open_entry(dir_cluster, entries, index);
+
+  if (result && (flags & OPEN_EXCLUSIVE)) {
+    memory_free(entries);
+    return NUL;
+  }
+
+  if (!result && (flags & OPEN_CREATE)) {
+    index = 0;
+    while (index < entries_count && entries[index].name[0]) {
+      index++;
+    }
+    if (index >= entries_count) {
+      if (!dir_cluster) {
+        memory_free(entries);
+        return NUL;
+      } else {
+        uint16_t new_entries_count = entries_count + bpb.sectors_per_cluster * SECTOR_SIZE / sizeof(fat16_dir_entry_t);
+        fat16_dir_entry_t *new_entries = memory_allocate(new_entries_count * sizeof(fat16_dir_entry_t));
+        memory_copy(entries, entries_count * sizeof(fat16_dir_entry_t), new_entries);
+        memory_free(entries);
+        entries_count = new_entries_count;
+        entries = new_entries;
+      }
+    }
+
+    memory_copy(name_8_3, 11, &entries[index]);
+
+    if (flags & OPEN_DIRECTORY && !(flags & OPEN_FILE)) {
+      entries[index].attributes = ATTRIBUTE_SUBDIRECTORY;
+      entries[index].first_cluster = allocate_cluster();
+      fat16_dir_entry_t *inner_entries = memory_allocate(bpb.sectors_per_cluster * SECTOR_SIZE);
+      memory_copy(".          ", 11, inner_entries[0].name);
+      inner_entries[0].attributes = ATTRIBUTE_SUBDIRECTORY;
+      inner_entries[0].first_cluster = entries[index].first_cluster;
+      memory_copy("..         ", 11, inner_entries[1].name);
+      inner_entries[1].attributes = ATTRIBUTE_SUBDIRECTORY;
+      inner_entries[1].first_cluster = dir_cluster;
+      write_directory(entries[index].first_cluster, inner_entries, bpb.sectors_per_cluster * SECTOR_SIZE / sizeof(fat16_dir_entry_t));
+      memory_free(inner_entries);
+    }
+
+    write_directory(dir_cluster, entries, entries_count);
+
+    result = open_entry(dir_cluster, entries, index);
+  }
+
   memory_free(entries);
+
+  if (!result) {
+    return NUL;
+  }
+
+  if (result->is_dir && !(flags & OPEN_DIRECTORY)) {
+    return NUL;
+  }
+
+  if (!result->is_dir && !(flags & OPEN_FILE)) {
+    return NUL;
+  }
+
   return result;
 }
 
-fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index) {
+fs_node_t *fat16_open_at(const fs_node_t *directory, uint16_t index, uint64_t flags) {
   if (directory->type != FAT16 || !directory->is_dir) {
     return NUL;
   }
 
-  fat16_dir_entry_t *entries = read_directory(((fat16_node_t *)directory)->inode->first_cluster);
+  uint16_t dir_cluster = ((fat16_node_t *)directory)->inode->first_cluster;
+
+  fat16_dir_entry_t *entries;
+  uint16_t entries_count = read_directory(dir_cluster, &entries);
 
   uint16_t ei = 0, vi = 0;
-  while (entries[ei].name[0]) {
+  while (ei < entries_count && entries[ei].name[0]) {
     if ((uint8_t)entries[ei].name[0] != 0xE5 && (uint8_t)entries[ei].attributes != 0x0F) {
       if (vi == index) {
         break;
@@ -295,7 +367,25 @@ fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index) {
   }
 
   fs_node_t *result = open_entry(((fat16_node_t *)directory)->inode->first_cluster, entries, ei);
+
   memory_free(entries);
+
+  if (result && (flags & OPEN_EXCLUSIVE)) {
+    return NUL;
+  }
+
+  if (!result) {
+    return NUL;
+  }
+
+  if (result->is_dir && !(flags & OPEN_DIRECTORY)) {
+    return NUL;
+  }
+
+  if (!result->is_dir && !(flags & OPEN_FILE)) {
+    return NUL;
+  }
+
   return result;
 }
 
@@ -432,10 +522,11 @@ uint64_t fat16_write(fs_node_t *file, uint32_t offset, const void *from, uint32_
   if (offset + written > fat_file->inode->size) {
     fat_file->inode->size = offset + written;
 
-    fat16_dir_entry_t *entries = read_directory(fat_file->inode->dir_cluster);
+    fat16_dir_entry_t *entries;
+    uint16_t entries_count = read_directory(fat_file->inode->dir_cluster, &entries);
     entries[fat_file->inode->dir_index].first_cluster = fat_file->inode->first_cluster;
     entries[fat_file->inode->dir_index].size = fat_file->inode->size;
-    write_directory(fat_file->inode->dir_cluster, entries);
+    write_directory(fat_file->inode->dir_cluster, entries, entries_count);
     memory_free(entries);
   }
 
@@ -482,10 +573,11 @@ uint64_t fat16_truncate(fs_node_t *file, uint32_t size) {
     flush_fat();
 
     fat_file->inode->size = size;
-    fat16_dir_entry_t *entries = read_directory(fat_file->inode->dir_cluster);
+    fat16_dir_entry_t *entries;
+    uint16_t entries_count = read_directory(fat_file->inode->dir_cluster, &entries);
     entries[fat_file->inode->dir_index].first_cluster = fat_file->inode->first_cluster;
     entries[fat_file->inode->dir_index].size = fat_file->inode->size;
-    write_directory(fat_file->inode->dir_cluster, entries);
+    write_directory(fat_file->inode->dir_cluster, entries, entries_count);
     memory_free(entries);
 
     return size;
@@ -535,7 +627,7 @@ static void file_stream_close(stream_t *self) {
 typedef struct {
   stream_t stream;
   fs_node_t *node;
-  uint32_t index;
+  uint16_t index;
 } fat16_directory_stream_t;
 
 static uint64_t directory_stream_write(__attribute__((unused)) stream_t *self, __attribute__((unused)) const char *from,
@@ -545,7 +637,7 @@ static uint64_t directory_stream_write(__attribute__((unused)) stream_t *self, _
 
 static uint64_t directory_stream_read(stream_t *self, uint64_t max, char *to) {
   fat16_directory_stream_t *fds = (fat16_directory_stream_t *)self;
-  fs_node_t *node = fat16_open_at(fds->node, fds->index++);
+  fs_node_t *node = fat16_open_at(fds->node, fds->index++, OPEN_FILE | OPEN_DIRECTORY);
   if (!node) {
     return 0;
   }

src/kernel/fat16.h

@@ -7,9 +7,9 @@
 
 fs_node_t *fat16_mount();
 
-fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name);
+fs_node_t *fat16_open_by(const fs_node_t *directory, const char *name, uint64_t flags);
 
-fs_node_t *fat16_open_at(const fs_node_t *directory, uint64_t index);
+fs_node_t *fat16_open_at(const fs_node_t *directory, uint16_t index, uint64_t flags);
 
 fs_node_t *fat16_open_again(const fs_node_t *source);
 

src/kernel/fs.c

@@ -5,12 +5,12 @@ fs_node_t *fs_mount() {
   return fat16_mount();
 }
 
-fs_node_t *fs_open_by(const fs_node_t *directory, const char *name) {
+fs_node_t *fs_open_by(const fs_node_t *directory, const char *name, uint64_t flags) {
-  return fat16_open_by(directory, name);
+  return fat16_open_by(directory, name, flags);
 }
 
-fs_node_t *fs_open_at(const fs_node_t *directory, uint64_t index) {
+fs_node_t *fs_open_at(const fs_node_t *directory, uint16_t index, uint64_t flags) {
-  return fat16_open_at(directory, index);
+  return fat16_open_at(directory, index, flags);
 }
 
 fs_node_t *fs_open_again(const fs_node_t *source) {

src/kernel/fs.h

@@ -1,7 +1,6 @@
 #pragma once
 
 #include "src/kernel/stream.h"
-#include <stdint.h>
 
 #define FILENAME_SIZE_LIMIT 255
 
@@ -14,9 +13,9 @@ typedef struct fs_node {
 
 fs_node_t *fs_mount();
 
-fs_node_t *fs_open_by(const fs_node_t *directory, const char *name);
+fs_node_t *fs_open_by(const fs_node_t *directory, const char *name, uint64_t flags);
 
-fs_node_t *fs_open_at(const fs_node_t *directory, uint64_t index);
+fs_node_t *fs_open_at(const fs_node_t *directory, uint16_t index, uint64_t flags);
 
 fs_node_t *fs_open_again(const fs_node_t *source);
 

src/kernel/kernel.c

@@ -14,6 +14,7 @@
 #include "src/kernel/vga.h"
 #include "src/lib/layout.h"
 #include "src/lib/memory.h"
+#include "src/lib/syscall.h"
 
 __attribute__((interrupt)) void isr_divide_by_zero(__attribute__((unused)) struct interrupt_frame *frame) {
   vga_set_string(VGA_HEIGHT - 1, 0, "EXCEPTION: divide by zero", 0x4F);
@@ -65,8 +66,8 @@ void kernel_main() {
   current_process = kernel;
   tss.rsp0 = (uint64_t)kernel->kernel_stack;
 
-  fs_node_t *terminal_node = path_open_file(kernel->root, kernel->cwd, "bin/terminal");
+  fs_node_t *terminal_node = path_open_node(kernel->root, kernel->cwd, "bin/terminal", OPEN_FILE);
-  fs_node_t *shell_node = path_open_file(kernel->root, kernel->cwd, "bin/shell");
+  fs_node_t *shell_node = path_open_node(kernel->root, kernel->cwd, "bin/shell", OPEN_FILE);
 
   ASSERT(terminal_node, "kernel: terminal not found");
   ASSERT(shell_node, "kernel: shell not found");

src/kernel/path.c

@@ -3,9 +3,10 @@
 #include "src/kernel/stream.h"
 #include "src/lib/memory.h"
 #include "src/lib/string.h"
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 
-path_t *path_open(const fs_node_t *root, const path_t *source, const char *path) {
+path_t *path_open(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags) {
   uint64_t length = string_length(path);
   char *path_own = memory_allocate(length + 1);
   memory_copy(path, length + 1, path_own);
@@ -29,7 +30,9 @@ path_t *path_open(const fs_node_t *root, const path_t *source, const char *path)
       }
     } else {
       const fs_node_t *prev = result->depth ? result->stack[result->depth - 1] : root;
-      fs_node_t *next = prev->is_dir ? fs_open_by(prev, path_components[i]) : NUL;
+      fs_node_t *next = prev->is_dir ? fs_open_by(prev, path_components[i],
+                                                  i < path_length - 1 ? (flags & ~(uint64_t)OPEN_EXCLUSIVE) | OPEN_DIRECTORY : flags)
+                                     : NUL;
       if (!next || result->depth >= PATH_DEPTH) {
         path_close(result);
         memory_free(path_own);
@@ -45,8 +48,8 @@ path_t *path_open(const fs_node_t *root, const path_t *source, const char *path)
   return result;
 }
 
-fs_node_t *path_open_node(const fs_node_t *root, const path_t *source, const char *path) {
+fs_node_t *path_open_node(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags) {
-  path_t *p = path_open(root, source, path);
+  path_t *p = path_open(root, source, path, flags);
   if (!p) {
     return NUL;
   }
@@ -55,40 +58,8 @@ fs_node_t *path_open_node(const fs_node_t *root, const path_t *source, const cha
   return n;
 }
 
-fs_node_t *path_open_file(const fs_node_t *root, const path_t *source, const char *path) {
+stream_t *path_open_stream(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags) {
-  path_t *p = path_open(root, source, path);
+  path_t *p = path_open(root, source, path, flags);
-  if (!p) {
-    return NUL;
-  }
-  if (!p->depth || p->stack[p->depth - 1]->is_dir) {
-    path_close(p);
-    return NUL;
-  }
-  fs_node_t *n = fs_open_again(p->stack[p->depth - 1]);
-  path_close(p);
-  return n;
-}
-
-fs_node_t *path_open_directory(const fs_node_t *root, const path_t *source, const char *path) {
-  path_t *p = path_open(root, source, path);
-  if (!p) {
-    return NUL;
-  }
-  if (!p->depth) {
-    path_close(p);
-    return fs_open_again(root);
-  }
-  if (!p->stack[p->depth - 1]->is_dir) {
-    path_close(p);
-    return NUL;
-  }
-  fs_node_t *n = fs_open_again(p->stack[p->depth - 1]);
-  path_close(p);
-  return n;
-}
-
-stream_t *path_open_stream(const fs_node_t *root, const path_t *source, const char *path) {
-  path_t *p = path_open(root, source, path);
   if (!p) {
     return NUL;
   }

src/kernel/path.h

@@ -10,14 +10,10 @@ typedef struct {
   uint8_t depth;
 } path_t;
 
-path_t *path_open(const fs_node_t *root, const path_t *source, const char *path);
+path_t *path_open(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags);
 
-fs_node_t *path_open_node(const fs_node_t *root, const path_t *source, const char *path);
+fs_node_t *path_open_node(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags);
 
-fs_node_t *path_open_file(const fs_node_t *root, const path_t *source, const char *path);
+stream_t *path_open_stream(const fs_node_t *root, const path_t *source, const char *path, uint64_t flags);
-
-fs_node_t *path_open_directory(const fs_node_t *root, const path_t *source, const char *path);
-
-stream_t *path_open_stream(const fs_node_t *root, const path_t *source, const char *path);
 
 void path_close(path_t *path);

src/kernel/syscall.c

@@ -7,6 +7,7 @@
 #include "src/lib/layout.h"
 #include "src/lib/memory.h"
 #include "src/lib/string.h"
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 
 #define MSR_EFER 0xC0000080
@@ -79,22 +80,17 @@ static uint64_t getcwd(uint64_t max, char *to) {
 }
 
 static uint64_t chdir(const char *path) {
-  path_t *cwd = path_open(current_process->root, current_process->cwd, path);
+  path_t *cwd = path_open(current_process->root, current_process->cwd, path, OPEN_DIRECTORY);
   if (!cwd) {
     return (uint64_t)-1;
   }
-  if (!cwd->depth || !cwd->stack[cwd->depth - 1]->is_dir) {
-    path_close(cwd);
-    return (uint64_t)-1;
-  }
-
   path_close((path_t *)current_process->cwd);
   current_process->cwd = cwd;
   return current_process->cwd->depth;
 }
 
 static uint64_t spawn(const char *path, uint64_t argc, const char **argv) {
-  fs_node_t *node = path_open_file(current_process->root, current_process->cwd, path);
+  fs_node_t *node = path_open_node(current_process->root, current_process->cwd, path, OPEN_FILE);
   if (!node) {
     return EXIT_CODE_NOT_FOUND;
   }
@@ -161,11 +157,11 @@ static exit_code_t wait(uint64_t pid) {
   return code;
 }
 
-static uint64_t open(const char *path) {
+static uint64_t open(const char *path, uint64_t flags) {
   if (current_process->free_fd >= MAX_FDS) {
     return (uint64_t)-1;
   }
-  stream_t *stream = path_open_stream(current_process->root, current_process->cwd, path);
+  stream_t *stream = path_open_stream(current_process->root, current_process->cwd, path, flags);
   if (!stream) {
     return (uint64_t)-1;
   }
@@ -218,7 +214,7 @@ uint64_t syscall_dispatch(uint64_t func, uint64_t arg1, uint64_t arg2, uint64_t
   case SYSCALL_WAIT:
     return wait(arg1);
   case SYSCALL_OPEN:
-    return open((const char *)arg1);
+    return open((const char *)arg1, arg2);
   case SYSCALL_CLOSE:
     return close(arg1);
   case SYSCALL_TRUNCATE:

src/kernel/syscall.h

@@ -2,17 +2,6 @@
 
 #include <stdint.h>
 
-#define SYSCALL_READ 0
-#define SYSCALL_WRITE 1
-#define SYSCALL_GETCWD 2
-#define SYSCALL_CHDIR 3
-#define SYSCALL_SPAWN 4
-#define SYSCALL_WAIT 5
-#define SYSCALL_OPEN 6
-#define SYSCALL_CLOSE 7
-#define SYSCALL_TRUNCATE 8
-#define SYSCALL_EXIT 60
-
 void syscall_init();
 
 uint64_t syscall_dispatch(uint64_t func, uint64_t arg1, uint64_t arg2, uint64_t arg3, uint64_t arg4);

src/kernel/vga.c

@@ -172,8 +172,10 @@ stream_t *vga_init() {
 void vga_set_string(uint8_t row, uint8_t col, const char *str, uint8_t c) {
   ASSERT(row < VGA_HEIGHT && col < VGA_WIDTH, "vga_set_string: invalid coordinates")
   color = (uint16_t)((uint16_t)c << 8);
+  uint16_t prev_offset = offset;
   offset = row * VGA_WIDTH + col;
   while (*str) {
     on_char_received(*str++);
   }
+  offset = prev_offset;
 }

src/lib/syscall.h

@@ -0,0 +1,15 @@
+#define SYSCALL_READ 0
+#define SYSCALL_WRITE 1
+#define SYSCALL_GETCWD 2
+#define SYSCALL_CHDIR 3
+#define SYSCALL_SPAWN 4
+#define SYSCALL_WAIT 5
+#define SYSCALL_OPEN 6
+#define SYSCALL_CLOSE 7
+#define SYSCALL_TRUNCATE 8
+#define SYSCALL_EXIT 60
+
+#define OPEN_CREATE 0b0001
+#define OPEN_EXCLUSIVE 0b0010
+#define OPEN_FILE 0b0100
+#define OPEN_DIRECTORY 0b1000

src/user/app/cat/cat.c

@@ -1,3 +1,4 @@
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 #include "src/user/syscall.h"
 
@@ -7,7 +8,7 @@
 #define PRINT_D(s) write(1, s, string_length(s));
 
 exit_code_t cat(const char *path) {
-  uint64_t fd = open(path);
+  uint64_t fd = open(path, OPEN_FILE);
 
   if (fd == (uint64_t)-1) {
     PRINT_S("cat: path does not exist\n");

src/user/app/cp/cp.c

@@ -1,3 +1,4 @@
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 #include "src/user/syscall.h"
 
@@ -12,15 +13,15 @@ exit_code_t main(uint64_t argc, const char **argv) {
     return EXIT_CODE_GENERAL_FAILURE;
   }
 
-  uint64_t source = open(argv[1]);
+  uint64_t source = open(argv[1], OPEN_FILE);
   if (source == (uint64_t)-1) {
     PRINT_S("cp: source does not exist\n");
     return EXIT_CODE_GENERAL_FAILURE;
   }
 
-  uint64_t target = open(argv[2]);
+  uint64_t target = open(argv[2], OPEN_FILE | OPEN_CREATE);
   if (target == (uint64_t)-1) {
-    PRINT_S("cp: target does not exist\n");
+    PRINT_S("cp: target path does not exist\n");
     close(source);
     return EXIT_CODE_GENERAL_FAILURE;
   }

src/user/app/ls/ls.c

@@ -1,4 +1,5 @@
 #include "src/lib/string.h"
+#include "src/lib/syscall.h"
 #include "src/lib/util.h"
 #include "src/user/syscall.h"
 
@@ -6,7 +7,7 @@
 #define PRINT_D(s) write(1, s, string_length(s));
 
 exit_code_t ls(const char *path) {
-  uint64_t fd = open(path);
+  uint64_t fd = open(path, OPEN_DIRECTORY);
 
   if (fd == (uint64_t)-1) {
     PRINT_S("ls: path does not exist\n");

src/user/app/mkdir/mkdir.c

@@ -0,0 +1,28 @@
+#include "src/lib/syscall.h"
+#include "src/lib/util.h"
+#include "src/user/syscall.h"
+#include <stdint.h>
+
+#define BLOCK_SIZE 65536
+
+#define PRINT_S(s) write(1, s, sizeof(s) - 1);
+#define PRINT_D(s) write(1, s, string_length(s));
+
+exit_code_t main(uint64_t argc, const char **argv) {
+  if (argc < 2) {
+    PRINT_S("mkdir: requires target(s)\n");
+    return EXIT_CODE_GENERAL_FAILURE;
+  }
+
+  for (uint64_t i = 1; i < argc; i++) {
+    uint64_t fd = open(argv[i], OPEN_DIRECTORY | OPEN_CREATE | OPEN_EXCLUSIVE);
+    if (fd == (uint64_t)-1) {
+      PRINT_S("mkdir: could not create directory\n");
+      return EXIT_CODE_GENERAL_FAILURE;
+    } else {
+      close(fd);
+    }
+  }
+
+  return EXIT_CODE_OK;
+}

src/user/syscall.h

@@ -1,7 +1,6 @@
 #pragma once
 
 #include "src/lib/util.h"
-#include <stdint.h>
 
 uint64_t read(int64_t fd, uint64_t max, void *to);
 
@@ -15,7 +14,7 @@ uint64_t spawn(const char *path, uint64_t argc, const char **argv);
 
 exit_code_t waitpid(uint64_t pid);
 
-uint64_t open(const char *path);
+uint64_t open(const char *path, uint64_t flags);
 
 uint64_t close(uint64_t fd);