kernel+libc: Add O_* flags and parse them in open()

O_RDONLY, O_WRONLY, O_RDWR, O_TRUNC, O_CREAT and O_EXCL are fully implemented.

O_APPEND is partially implemented.

Other flags are not here yet.

apps/app.c

@@ -14,7 +14,7 @@ int main()
     atexit(bye);
     printf("Welcome to %s from userspace (pid %d)!\n", "Luna", getpid());
 
-    int fd = open("/etc/motd", 0);
+    int fd = open("/etc/motd", O_RDONLY);
     if (fd < 0)
     {
         perror("open");

kernel/src/fs/VFS.h

@@ -26,6 +26,8 @@ namespace VFS
 
         virtual Result<usize> write(const u8* buf, usize offset, usize length) = 0;
 
+        virtual Result<void> truncate(usize size) = 0;
+
         // Generic methods
         virtual FileSystem& fs() const = 0;
 

kernel/src/fs/tmpfs/FileSystem.cpp

@@ -118,4 +118,15 @@ namespace TmpFS
 
         return length;
     }
+
+    Result<void> FileInode::truncate(usize size)
+    {
+        usize old_size = m_data_buffer.size();
+
+        TRY(m_data_buffer.try_resize(size));
+
+        if (size > old_size) memset(m_data_buffer.data() + old_size, 0, size - old_size);
+
+        return {};
+    }
 }

kernel/src/fs/tmpfs/FileSystem.h

@@ -63,6 +63,8 @@ namespace TmpFS
 
         Result<usize> write(const u8*, usize, usize) override;
 
+        Result<void> truncate(usize size) override;
+
         virtual ~FileInode() = default;
 
       private:
@@ -103,6 +105,11 @@ namespace TmpFS
             return err(EISDIR);
         }
 
+        Result<void> truncate(usize) override
+        {
+            return err(EISDIR);
+        }
+
         VFS::FileSystem& fs() const override
         {
             return *m_fs;

kernel/src/sys/file.cpp

@@ -15,17 +15,15 @@ Result<u64> sys_read(Registers*, SyscallArgs args)
 
     if (!MemoryManager::validate_user_write(buf, size)) return err(EFAULT);
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    auto& descriptor = *TRY(current->resolve_fd(fd));
 
-    if (!descriptor.has_value()) return err(EBADF);
+    if (!descriptor.is_readable()) return err(EBADF);
 
-    usize nread = TRY(descriptor->inode->read(buf, descriptor->offset, size));
+    usize nread = TRY(descriptor.inode->read(buf, descriptor.offset, size));
 
-    descriptor->offset += nread;
+    descriptor.offset += nread;
 
     return nread;
 }
@@ -38,17 +36,17 @@ Result<u64> sys_write(Registers*, SyscallArgs args)
 
     if (!MemoryManager::validate_user_read(buf, size)) return err(EFAULT);
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    auto& descriptor = *TRY(current->resolve_fd(fd));
 
-    if (!descriptor.has_value()) return err(EBADF);
+    if (!descriptor.is_writable()) return err(EBADF);
 
-    usize nwritten = TRY(descriptor->inode->write(buf, descriptor->offset, size));
+    if (descriptor.should_append()) todo();
 
-    descriptor->offset += nwritten;
+    usize nwritten = TRY(descriptor.inode->write(buf, descriptor.offset, size));
+
+    descriptor.offset += nwritten;
 
     return nwritten;
 }
@@ -59,27 +57,23 @@ Result<u64> sys_lseek(Registers*, SyscallArgs args)
     off_t offset = (long)args[1];
     int whence = (int)args[2];
 
-    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
-
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
-
-    if (!descriptor.has_value()) return err(EBADF);
+    auto& descriptor = *TRY(current->resolve_fd(fd));
 
     off_t new_offset;
 
     switch (whence)
     {
     case SEEK_SET: new_offset = offset; break;
-    case SEEK_CUR: new_offset = TRY(safe_add((long)descriptor->offset, offset)); break;
+    case SEEK_CUR: new_offset = TRY(safe_add((long)descriptor.offset, offset)); break;
     case SEEK_END: todo();
     default: return err(EINVAL);
     }
 
     if (new_offset < 0) return err(EINVAL);
 
-    descriptor->offset = (usize)new_offset;
+    descriptor.offset = (usize)new_offset;
 
     return (u64)new_offset;
 }

kernel/src/sys/open.cpp

@@ -3,6 +3,10 @@
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
+#include <bits/open-flags.h>
+
+// These flags are needed after open(), the rest only affect open().
+constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND;
 
 Result<u64> sys_open(Registers*, SyscallArgs args)
 {
@@ -16,11 +20,28 @@ Result<u64> sys_open(Registers*, SyscallArgs args)
 
     kinfoln("open: trying to open file %s, flags %d", path, flags);
 
-    auto inode = TRY(VFS::resolve_path(path));
+    SharedPtr<VFS::Inode> inode;
+
+    // Caller did not pass either O_RDONLY, O_WRONLY or O_RDWR
+    if ((flags & O_RDWR) == 0) { return err(EINVAL); }
+
+    auto maybe_inode = VFS::resolve_path(path);
+    if (maybe_inode.has_error())
+    {
+        if (maybe_inode.error() == ENOENT && (flags & O_CREAT)) inode = TRY(VFS::create_file(path));
+        else
+            return maybe_inode.release_error();
+    }
+    else if (flags & O_EXCL)
+        return err(EEXIST);
+    else
+        inode = maybe_inode.release_value();
+
+    if ((flags & O_WRONLY) && (flags & O_TRUNC)) inode->truncate(0);
 
     int fd = TRY(current->allocate_fd(0));
 
-    current->fd_table->fds[fd] = FileDescriptor { inode, 0, flags };
+    current->fd_table[fd] = FileDescriptor { inode, 0, flags & FLAGS_TO_KEEP };
 
     kinfoln("open: allocated file descriptor %d for inode %zu", fd, inode->inode_number());
 
@@ -34,7 +55,7 @@ Result<u64> sys_close(Registers*, SyscallArgs args)
 
     Thread* current = Scheduler::current();
 
-    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+    Option<FileDescriptor>& descriptor = current->fd_table[fd];
 
     if (!descriptor.has_value()) return err(EBADF);
 

kernel/src/thread/Scheduler.cpp

@@ -151,8 +151,6 @@ namespace Scheduler
         guard.deactivate();
         directory_guard.deactivate();
 
-        thread->fd_table = FileDescriptorTable {};
-
         kinfoln("Created userspace thread: id %lu with ip %#.16lx and sp %#.16lx (ksp %#lx)", thread->id, thread->ip(),
                 thread->sp(), thread->kernel_stack.top());
 

kernel/src/thread/Thread.cpp

@@ -1,4 +1,5 @@
 #include "thread/Thread.h"
+#include <bits/open-flags.h>
 #include <luna/Alloc.h>
 #include <luna/Atomic.h>
 
@@ -27,8 +28,34 @@ Result<int> Thread::allocate_fd(int min)
     {
         // FIXME: Possible race condition if multiple threads share a FileDescriptorTable? Let's not worry about it for
         // now, we're still a long way away from reaching that point.
-        if (!fd_table->fds[i].has_value()) { return i; }
+        if (!fd_table[i].has_value()) { return i; }
     }
 
     return err(EMFILE);
 }
+
+Result<FileDescriptor*> Thread::resolve_fd(int fd)
+{
+    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
+
+    Option<FileDescriptor>& maybe_descriptor = fd_table[fd];
+
+    if (!maybe_descriptor.has_value()) return err(EBADF);
+
+    return maybe_descriptor.value_ptr();
+}
+
+bool FileDescriptor::should_append()
+{
+    return flags & O_APPEND;
+}
+
+bool FileDescriptor::is_readable()
+{
+    return flags & O_RDONLY;
+}
+
+bool FileDescriptor::is_writable()
+{
+    return flags & O_WRONLY;
+}

kernel/src/thread/Thread.h

@@ -27,15 +27,14 @@ struct FileDescriptor
     SharedPtr<VFS::Inode> inode;
     usize offset { 0 };
     int flags { 0 };
+
+    bool should_append();
+    bool is_writable();
+    bool is_readable();
 };
 
 static constexpr int FD_MAX = 64;
 
-struct FileDescriptorTable
-{
-    Option<FileDescriptor> fds[FD_MAX] = {};
-};
-
 struct Thread : public LinkedListNode<Thread>
 {
     Registers regs;
@@ -53,9 +52,10 @@ struct Thread : public LinkedListNode<Thread>
     Stack kernel_stack;
 
     OwnedPtr<UserVM> vm_allocator;
-    Option<FileDescriptorTable> fd_table;
+    Option<FileDescriptor> fd_table[FD_MAX] = {};
 
     Result<int> allocate_fd(int min);
+    Result<FileDescriptor*> resolve_fd(int fd);
 
     FPData fp_data;
 

libc/include/bits/open-flags.h

@@ -0,0 +1,14 @@
+/* bits/open-flags.h: O_* constants for open(). */
+
+#ifndef _BITS_OPEN_FLAGS_H
+#define _BITS_OPEN_FLAGS_H
+
+#define O_RDONLY 1
+#define O_WRONLY 2
+#define O_RDWR 3
+#define O_APPEND 4
+#define O_CREAT 8
+#define O_EXCL 16
+#define O_TRUNC 32
+
+#endif

libc/include/fcntl.h

@@ -3,6 +3,8 @@
 #ifndef _FCNTL_H
 #define _FCNTL_H
 
+#include <bits/open-flags.h>
+
 #ifdef __cplusplus
 extern "C"
 {

libc/src/stdio.cpp

@@ -21,7 +21,7 @@ extern "C"
     FILE* fopen(const char* path, const char*)
     {
         // FIXME: Parse the mode string.
-        int fd = open(path, 0);
+        int fd = open(path, O_RDWR);
         if (fd < 0) return nullptr;
 
         FILE* f = (FILE*)malloc(sizeof(FILE));

libluna/include/luna/Option.h

@@ -116,6 +116,18 @@ template <typename T> class Option
         return &m_storage.fetch_reference();
     }
 
+    T& operator*()
+    {
+        expect(has_value(), "Option::operator* called on an empty Option");
+        return m_storage.fetch_reference();
+    }
+
+    T* value_ptr(SourceLocation caller = SourceLocation::current())
+    {
+        expect_at(has_value(), caller, "Option::value_ptr called on an empty Option");
+        return &m_storage.fetch_reference();
+    }
+
     ~Option()
     {
         if (has_value()) m_storage.destroy();