Luna/kernel/src/sys/file.cpp

#include "Log.h"
#include "fs/VFS.h"
#include "memory/MemoryManager.h"
#include "sys/Syscall.h"
#include "thread/Scheduler.h"
#include <bits/seek.h>
#include <luna/SafeArithmetic.h>
#include <sys/types.h>

Result<u64> sys_read(Registers*, SyscallArgs args)
{
    int fd = (int)args[0];
    u8* buf = (u8*)args[1];
    usize size = (usize)args[2];

    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];

    if (!descriptor.has_value()) return err(EBADF);

    usize nread = TRY(descriptor->inode->read(buf, descriptor->offset, size));

    descriptor->offset += nread;

    return nread;
}

Result<u64> sys_write(Registers*, SyscallArgs args)
{
    int fd = (int)args[0];
    const u8* buf = (const u8*)args[1];
    usize size = (usize)args[2];

    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];

    if (!descriptor.has_value()) return err(EBADF);

    usize nwritten = TRY(descriptor->inode->write(buf, descriptor->offset, size));

    descriptor->offset += nwritten;

    return nwritten;
}

Result<u64> sys_lseek(Registers*, SyscallArgs args)
{
    int fd = (int)args[0];
    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);

    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_END: todo();
    default: return err(EINVAL);
    }

    if (new_offset < 0) return err(EINVAL);

    descriptor->offset = (usize)new_offset;

    return (u64)new_offset;
}