Kernel+LibC+LibCore: Implement mknodat(2)

Author: https://github.com/implicitfield
Commit: https://github.com/SerenityOS/serenity/commit/4574a8c334
Pull-request: https://github.com/SerenityOS/serenity/pull/23099
Reviewed-by: https://github.com/timschumi ✅

Kernel/API/Syscall.h

@@ -417,6 +417,7 @@ struct SC_mknod_params {
     StringArgument path;
     u16 mode;
     dev_t dev;
+    int dirfd;
 };
 
 struct SC_symlink_params {

Kernel/Syscalls/mknod.cpp

@@ -20,7 +20,7 @@ ErrorOr<FlatPtr> Process::sys$mknod(Userspace<Syscall::SC_mknod_params const*> u
     if (!credentials->is_superuser() && !is_regular_file(params.mode) && !is_fifo(params.mode) && !is_socket(params.mode))
         return EPERM;
     auto path = TRY(get_syscall_path_argument(params.path));
-    TRY(VirtualFileSystem::the().mknod(credentials, path->view(), params.mode & ~umask(), params.dev, current_directory()));
+    TRY(VirtualFileSystem::the().mknod(credentials, path->view(), params.mode & ~umask(), params.dev, TRY(custody_for_dirfd(params.dirfd))));
     return 0;
 }
 

Userland/Libraries/LibC/unistd.cpp

@@ -828,12 +828,18 @@ int faccessat(int dirfd, char const* pathname, int mode, int flags)
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/mknod.html
 int mknod(char const* pathname, mode_t mode, dev_t dev)
+{
+    return mknodat(AT_FDCWD, pathname, mode, dev);
+}
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/mknodat.html
+int mknodat(int dirfd, char const* pathname, mode_t mode, dev_t dev)
 {
     if (!pathname) {
         errno = EFAULT;
         return -1;
     }
-    Syscall::SC_mknod_params params { { pathname, strlen(pathname) }, mode, dev };
+    Syscall::SC_mknod_params params { { pathname, strlen(pathname) }, mode, dev, dirfd };
     int rc = syscall(SC_mknod, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Userland/Libraries/LibC/unistd.h

@@ -108,6 +108,7 @@ int access(char const* pathname, int mode);
 int faccessat(int dirfd, char const* pathname, int mode, int flags);
 int isatty(int fd);
 int mknod(char const* pathname, mode_t, dev_t);
+int mknodat(int dirfd, char const* pathname, mode_t, dev_t);
 long fpathconf(int fd, int name);
 long pathconf(char const* path, int name);
 char* getlogin(void);

Userland/Libraries/LibCore/System.cpp

@@ -1622,7 +1622,7 @@ ErrorOr<void> mknod(StringView pathname, mode_t mode, dev_t dev)
         return Error::from_syscall("mknod"sv, -EFAULT);
 
 #ifdef AK_OS_SERENITY
-    Syscall::SC_mknod_params params { { pathname.characters_without_null_termination(), pathname.length() }, mode, dev };
+    Syscall::SC_mknod_params params { { pathname.characters_without_null_termination(), pathname.length() }, mode, dev, AT_FDCWD };
     int rc = syscall(SC_mknod, &params);
     HANDLE_SYSCALL_RETURN_VALUE("mknod", rc, {});
 #else