DFA (Dependent Failure Analysis)

Persistency DFA		status: valid security: NO safety: ASIL_B
tags: persistency version: 1 realizes: wp__feature_dfa
doc__persistency_dfa		Generic Document

The DFA applies the dependent failure initiators of gd_guidl__dfa_failure_initiators to the static view of Persistency KVS Feature Arc... (doc__persistency_kvs_architecture).

Dependent Failure Initiators

Shared resources

The dependent failure initiators related to shared resources are not applicable for the features. The shared resources will be considered in the platform DFA.

Communication between the two elements

Receiving function is affected by information that is false, lost, sent multiple times, or in the wrong order etc. from the sender.

Table 19 DFA communication between elements

ID	Violation cause communication between elements	Applicability	Rationale
CO_01_01	Information passed via argument through a function call, or via writing/reading a variable being global to the two software functions (data flow)	no	Only function arguments and return values within the calling thread; no shared globals. Corruption: see CO_01_02.
CO_01_02	Data or message corruption / repetition / loss / delay / masquerading or incorrect addressing of information	yes	Corruption of persisted data (feat_saf_dfa__persistency__data_corruption)
CO_01_03	Insertion / sequence of information	no	Data and hash files are written and read as a whole; see CO_01_02.
CO_01_04	Corruption of information, inconsistent data	yes	Covered by Corruption of persisted data (feat_saf_dfa__persistency__data_corruption).
CO_01_05	Asymmetric information sent from a sender to multiple receivers, so that not all defined receivers have the same information	no	No communication with multiple receivers.
CO_01_06	Information from a sender received by only a subset of the receivers	no	Same as CO_01_05.
CO_01_07	Blocking access to a communication channel	no	No communication channel used; blocking of the caller: see UI_01_06.

Shared information inputs

Same information input used by multiple functions.

Table 20 DFA shared information inputs

ID	Violation cause shared information inputs	Applicability	Rationale
SI_01_02	Configuration data	no	Each instance uses its own data, hash and default value files (instance ID). Shared instances: see SI_01_03.
SI_01_03	Constants, or variables, being global to the two software functions	yes	Shared KVS instance within ... (feat_saf_dfa__persistency__shared_instance)
SI_01_04	Basic software passes data (read from hardware register and converted into logical information) to two applications software functions	no	No hardware registers are read; file access via the OS.
SI_01_05	Data / function parameter arguments / messages delivered by software function to more than one other function	no	Values are returned to the calling function only.

Unintended impact

Unintended impacts to function due to various failures.

Table 21 DFA unintended impact

ID	Violation cause unintended impact	Applicability	Rationale
UI_01_01	Memory miss-allocation and leaks	no	Allocation: see UI_01_11. Leaks are addressed by Rust ownership, C++ RAII and component verification.
UI_01_02	Read/Write access to memory allocated to another software element	no	Only own instance memory and caller memory is accessed. Access by others is prevented by OS process isolation (platform DFA).
UI_01_03	Stack/Buffer under-/overflow	no	Rust bounds checking, C++ standard containers. Overflows by others: platform DFA.
UI_01_04	Deadlocks	no	One mutex per instance (Rust additionally one for the instance pool in the builder); never more than one lock is held at a time. Rust waits for the lock; C++ does not wait and returns MutexLockFailed.
UI_01_05	Livelocks	no	Same as UI_01_04; no retry loops.
UI_01_06	Blocking of execution	yes	Persistency execution blocking (feat_saf_dfa__persistency__execution_blocking)
UI_01_07	Incorrect allocation of execution time	no	No own execution context; see UI_01_06.
UI_01_08	Incorrect execution flow	no	Execution flow defined by the dynamic views; corruption: see UI_01_02.
UI_01_09	Incorrect synchronization between software elements	yes	Access to a KVS instance fr... (feat_saf_dfa__persistency__multi_process)
UI_01_10	CPU time depletion	no	No own execution context; see UI_01_06.
UI_01_11	Memory depletion	yes	Memory depletion by the kvs (feat_saf_dfa__persistency__memory_depletion)
UI_01_12	Other HW unavailability	no	Storage medium only, via file system; unavailability is reported and handled by aou_req__persistency__error_handling.

DFA

Persistency execution blocking		status: valid
failure_effect: Blocking of execution, persistency is not available. failure_id: UI_01_06 safety_relevant: yes sufficient: yes version: 2 mitigated_by: aou_req__persistency__error_handling violates: feat_arc_sta__persistency__static
Persistency runs in the calling context; blocking (by the application or OS scheduling) leads to no or a too late response, handled by Persistency Error handling (aou_req__persistency__error_handling).
feat_saf_dfa__persistency__execution_blocking		Feature DFA (Dependent Failure Analysis)

Corruption of persisted data		status: valid
failure_effect: Data exchanged with the file system is corrupted, lost or inconsistent. failure_id: CO_01_02 safety_relevant: yes sufficient: yes version: 1 mitigated_by: aou_req__persistency__error_handling, feat_req__persistency__access_control, feat_req__persistency__integrity_check, feat_req__persistency__reset_resistant violates: feat_arc_sta__persistency__static
Causes: storage medium, interrupted write, other software writing the files. Detected by the hash check (feat_req__persistency__integrity_check), writes are reset resistant (feat_req__persistency__reset_resistant), access by others is prevented by feat_req__persistency__access_control. Reported errors: Persistency Error handling (aou_req__persistency__error_handling).
feat_saf_dfa__persistency__data_corruption		Feature DFA (Dependent Failure Analysis)

Shared KVS instance within a process		status: valid
failure_effect: Two software elements of a process use the same KVS instance and modify each other's data. failure_id: SI_01_03 safety_relevant: yes sufficient: yes version: 1 mitigated_by: aou_req__persistency__instance_separation violates: feat_arc_sta__persistency__static
Within a process, the same instance ID gives access to the same data. Mitigated by Separate KVS Instances per ... (aou_req__persistency__instance_separation).
feat_saf_dfa__persistency__shared_instance		Feature DFA (Dependent Failure Analysis)

Access to a KVS instance from multiple processes		status: valid
failure_effect: Unsynchronized access of two processes makes the persisted data inconsistent. failure_id: UI_01_09 safety_relevant: yes sufficient: yes version: 1 mitigated_by: feat_req__persistency__multiple_app violates: feat_arc_sta__persistency__static
Synchronization covers threads of one process only. Access from multiple processes is prevented by feat_req__persistency__multiple_app. Note: Not yet implemented (only in-process mutexes; component level).
feat_saf_dfa__persistency__multi_process		Feature DFA (Dependent Failure Analysis)

Memory depletion by the kvs		status: valid
failure_effect: Runtime allocation of the kvs depletes the heap shared with other software elements. failure_id: UI_01_11 safety_relevant: yes sufficient: yes version: 1 mitigated_by: feat_req__persistency__cfg, feat_req__persistency__dynamic_memory_alloc violates: feat_arc_sta__persistency__static
Refined in Memory depletion by the kvs (comp_saf_dfa__kvs__memory_depletion).
feat_saf_dfa__persistency__memory_depletion		Feature DFA (Dependent Failure Analysis)

Deadlock by completion callback		status: valid
failure_effect: The application and the persistency block each other, persistency and the calling application are not available. failure_id: UI_01_04 safety_relevant: yes sufficient: yes version: 1 mitigated_by: feat_req__persistency__concurrency violates: feat_arc_sta__persistency__static
Note: The implementations still allocate at runtime (component level).
feat_saf_dfa__persistency__callback_deadlock		Feature DFA (Dependent Failure Analysis)