Fix #1703, update docs for CFE_FS_BackgroundFileDumpRequest

Update notes to better clarify that the meta object must persist
for the duration of the dump operation, which occurs in another task,
so it must not be on the stack.

Also update documentation for background even callbacks to better
clarify arguments and expectations of the implementation.

modules/core_api/fsw/inc/cfe_fs.h

@@ -291,8 +291,8 @@ CFE_Status_t CFE_FS_ExtractFilenameFromPath(const char *OriginalPath, char *File
 **        Puts the previously-initialized metadata into the pending request queue
 **
 ** \par Assumptions, External Events, and Notes:
-**        Metadata structure should be stored in a static memory area (not on heap) as it
-**        must persist and be accessible by the file writer task throughout the asynchronous
+**        Metadata structure should be stored in a persistent memory area (not on stack) as
+**        it must remain accessible by the file writer task throughout the asynchronous
 **        job operation.
 **
 ** \param[inout] Meta        The background file write persistent state object

modules/core_api/fsw/inc/cfe_fs_api_typedefs.h

@@ -84,6 +84,18 @@ typedef enum
  * Data Getter routine provided by requester
  *
  * Outputs a data block.  Should return true if the file is complete (last record/EOF), otherwise return false.
+ *
+ * \param[inout] Meta       Pointer to the metadata object
+ * \param[in]    RecordNum  Incrementing record number counter
+ * \param[out]   Buffer     Pointer to buffer data block, should be set by implementation
+ * \param[out]   BufSize    Pointer to buffer data size, should be set by implementation
+ *
+ * \returns End of file status
+ * \retval  true if at last data record, and output file should be closed
+ * \retval  false if not at last record, more data records to write
+ *
+ * \note The implementation of this function must always set the "Buffer" and "BufSize" outputs.  If
+ *       no data is avaliable, they may be set to NULL and 0, respectively.
  */
 typedef bool (*CFE_FS_FileWriteGetData_t)(void *Meta, uint32 RecordNum, void **Buffer, size_t *BufSize);
 
@@ -92,6 +104,14 @@ typedef bool (*CFE_FS_FileWriteGetData_t)(void *Meta, uint32 RecordNum, void **B
  *
  * Invoked from certain points in the file write process.  Implementation may invoke CFE_EVS_SendEvent() appropriately
  * to inform of progress.
+ *
+ * \param[inout] Meta       Pointer to the metadata object
+ * \param[in]    Event      Generalized type of event to report (not actual event ID)
+ * \param[in]    Status     Generalized status code (may be from OSAL or CFE)
+ * \param[in]    RecordNum  Record number counter at which event occurred
+ * \param[in]    BlockSize  Size of record being processed when event occured (if applicable)
+ * \param[in]    Position   File position/size when event occurred
+ *
  */
 typedef void (*CFE_FS_FileWriteOnEvent_t)(void *Meta, CFE_FS_FileWriteEvent_t Event, int32 Status, uint32 RecordNum,
                                           size_t BlockSize, size_t Position);