Luna/kernel/src/sys/open.cpp

#include "Log.h"
#include "fs/VFS.h"
#include "memory/MemoryManager.h"
#include "sys/Syscall.h"
#include "thread/Scheduler.h"
#include <bits/modes.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 | O_NONBLOCK | O_CLOEXEC;

Result<u64> sys_open(Registers*, SyscallArgs args)
{
    auto path = TRY(MemoryManager::strdup_from_user(args[0]));
    int flags = (int)args[1];
    mode_t mode = (mode_t)args[2];

    Thread* current = Scheduler::current();

    kinfoln("open: trying to open file %s, flags %d", path.chars(), flags);

    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.chars());
    if (maybe_inode.has_error())
    {
        if (maybe_inode.error() == ENOENT && (flags & O_CREAT))
        {
            inode = TRY(VFS::create_file(path.chars()));
            inode->chmod(mode);
        }
        else
            return maybe_inode.release_error();
    }
    else if (flags & O_EXCL)
        return err(EEXIST);
    else
    {
        inode = maybe_inode.release_value();
        if ((flags & O_RDONLY) && (inode->mode() & S_IRUSR) == 0) return err(EACCES);
        if ((flags & O_WRONLY) && (inode->mode() & S_IWUSR) == 0) return err(EACCES);
    }

    if ((flags & O_WRONLY) && (flags & O_TRUNC)) inode->truncate(0);

    int fd = TRY(current->allocate_fd(0));

    current->fd_table[fd] = FileDescriptor { inode, 0, flags & FLAGS_TO_KEEP };

    kinfoln("open: allocated file descriptor %d for inode %zu", fd, inode->inode_number());

    return (u64)fd;
}

Result<u64> sys_close(Registers*, SyscallArgs args)
{
    int fd = (int)args[0];
    if (fd < 0 || fd >= FD_MAX) return err(EBADF);

    Thread* current = Scheduler::current();

    Option<FileDescriptor>& descriptor = current->fd_table[fd];

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

    kinfoln("close: closing file descriptor %d (was referencing inode %zu)", fd, descriptor->inode->inode_number());

    descriptor = {};

    return 0;
}