IBM General Parallel File System for AIX: Data Management API Guide

Enhancements to data structures

Following is a description of GPFS enhancements to data structures defined in the XDSM standard. For complete C declarations of all DMAPI data structures that are used in the GPFS implementation of DMAPI, see Appendix A, "DMAPI data types and structures in GPFS".

• All file offsets and sizes in DMAPI data structures are 64 bits long.
• Names (or paths) that are passed in event messages are character strings, terminated by a null character. The length of the name buffer, as specified in the dm_vardata_t structure, includes the null character.
• The dm_region_t structure has a new 4-byte field, rg_opaque. The DMAPI implementation does not interpret rg_opaque. The DM application can use this field to store additional information within the managed region.
• The dt_change field in the dm_stat structure is not implemented in the i-node. The value will change each time it is returned by the dm_get_fileattr function.
• The dt_dtime field in the dm_stat structure is overloaded on the dt_ctime field.
• The dm_eventmsg structure has a new 4-byte field, ev_nodeid. It uniquely identifies the node which generated the event. The id is the SDR node number (attribute node_number in the SDR).
• The ne_mode field in the dm_namesp_event structure has an additional flag, DM_LOCAL_MOUNT. For the events preunmount and unmount when this flag is set, the unmount operation is local to the session node. (See "Mount and unmount").
• The me_mode field in the dm_mount_event structure has two additional flags; DM_LOCAL_MOUNT, and DM_REMOTE_MOUNT. (See "Mount and unmount").
• There are two "quick access" single-bit opaque DM attributes for each file, stored directly in the i-node. (See "Data Management attributes")
• The data type dm_eventset_t is implemented as a bit map, containing one bit for each event that is defined in DMAPI. The bit is set if, and only if, the event is present.

  Variables of type dm_eventset_t should be manipulated only via special macros. The XDSM standard provides a basic set of such macros. GPFS provides a number of additional macros. The names of all such macros begin with the prefix DMEV_.

  Following is the list of additional macros that are provided by the GPFS implementation of DMAPI:

  DMEV_ALL(eset)

  Add all events to eset

  DMEV_ISZERO(eset)

  Check if eset is empty

  DMEV_ISALL(eset)

  Check if eset contains all events

  DMEV_ADD(eset1, eset2)

  Add to eset2 all events in eset1

  DMEV_REM(eset1, eset2)

  Remove from eset2 all events in eset1

  DMEV_RES(eset1, eset2)

  Restrict eset2 by eset1

  DMEV_ISEQ(eset1, eset2)

  Check if eset1 and eset2 are equal

  DMEV_ISDISJ(eset1, eset2)

  Check if eset1 and eset2 are disjoint

  DMEV_ISSUB(eset2)

  Check if eset1 is a subset of eset2

  DMEV_NORM(eset)

  Normalize the internal format of eset, clearing all unused bits.

• GPFS provides a set of macros for comparison of token ids (value of type dm_token_t).

  DM_TOKEN_EQ (x,y)

  Check if x and y are the same

  DM_TOKEN_NE (x,y)

  Check if x and y are different

  DM_TOKEN_LT (x,y)

  Check if x is less than y

  DM_TOKEN_GT (x,y)

  Check if x is greater than y

  DM_TOKEN_LE (x,y)

  Check if x is less than or equal to y

  DM_TOKEN_GE (x,y)

  Check if x is greater than or equal to y