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OpenVMS I/O User's Reference Manual

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1.5 ACP--QIO Attributes Statistics Block

Figure 1-8 shows the format of the attributes statistics block.Table 1-10 lists the contents of this block.

Figure 1-8 ACP--QIO Attributes Statistics Block

Table 1-10 Contents of the Statistics Block
Field Subfields Meaning
SBK$L_STLBN   Contains the starting LBN of the file if the file is contiguous. If the file is not contiguous, this field contains a value of 0. The LBN appears as an inverted longword (the high- and low-order 16 bits are transposed for PDP-11 compatibility). The following subfields are defined:
  SBK$W_STLBNH Starting LBN (high-order 16 bits)
  SBK$W_STLBNL Starting LBN (low-order 16 bits)
SBK$L_FILESIZE   Contains the size of the file in blocks. The file size appears as an inverted longword (the high- and low-order 16 bits are transposed for PDP-11 compatibility). The following subfields are defined:
  SBK$W_FILESIZH File size (high-order 16 bits)
  SBK$W_FILESIZL File size (low-order 16 bits)
SBK$B_ACNT 1   Access count (low byte). Field is for PDP-11 compatibility.
SBK$B_LCNT 1   Lock count (low byte). Field is for PDP-11 compatibility.
SBK$L_FCB   System pool address of the file's file control block.
SBK$W_ACNT 1   Access count (number of channels with file open currently).
SBK$W_LCNT 1   Lock count (the number of access operations that have locked the file against writers).
SBK$W_WCNT 1   Writer count (the number of channels that currently have the file open for write).
SBK$W_TCNT 1   Truncate lock count (the number of access operations that have locked the file against truncation).
SBK$L_READS   Number of read operations executed for the file on this channel.
SBK$L_WRITES   Number of write operations executed for the file on this channel.
1Accesses from processes on the local node in a cluster arecounted.

1.6 Major Functions

The following sections describe the operation of the major ACP functions. Each section describes the required and optional parameters for a particular function, as well as the sequence in which the function is performed. For clarity, when a major function invokes a subfunction, the input parameters used by the subfunction are omitted.

1.6.1 Create File

Create file is a virtual I/O function that creates a directory entry ora file on a disk device, or a file on a magnetic tape device.

The following is the function code:

  • IO$_CREATE

The following are the function modifiers:

  • IO$M_CREATE---Creates a file.
  • IO$M_ACCESS---Opens the file on your channel.
  • IO$M_DELETE---Marks the file for deletion (applicable only to disk devices).

1.6.1.1 Input Parameters

The following are the device- or function-dependent arguments forIO$_CREATE:

  • P1---The address of the file information block (FIB) descriptor.
  • P2---The address of the file name string descriptor (optional).
  • P3---The address of the word that is to receive the length of the resultant file name string (optional).
  • P4---The address of a descriptor for a buffer that is to receive the resultant file name string (optional).
  • P5---The address of a list of attribute descriptors (optional).

Table 1-11 lists fields in the FIB that are applicable to theIO$_CREATE operation.

Table 1-11 IO$_CREATE and the FIB
Field Subfields Meaning
FIB$L_ACCTL   Specifies field values that control access to the file. The following bits are applicable to the IO$_CREATE function:
  FIB$V_REWIND Set to rewind magnetic tape before creating the file. Any data currently on the tape is overwritten.
  FIB$V_CURPOS Set to create magnetic tape file at the current tape position. (Note: a magnetic tape file is created at the end of the volume set if neither FIB$V_REWIND nor FIB$V_CURPOS is set.) If the tape is not positioned at the end of a file, FIB$V_CURPOS creates a file at the next file position. Any data currently on the tape past the current file position is overwritten.
  FIB$V_WRITETHRU Specifies that the file header is to be written back to the disk. If not specified and the file is opened, writing of the file header can be deferred to some later time.
FIB$W_CNTRLFUNC   Specifies the following value, which allows you to control actions subsequent to EOT detection on a magnetic tape file.
FIB$W_FID   Contains the file ID of the file created or entered.
FIB$W_DID   Contains the file identifier of the directory file.
FIB$W_NMCTL   Controls the processing of the file name in a directory operation. The following bits are applicable to the IO$_CREATE function:
  FIB$V_NEWVER Set to create a file of the same name with the next higher version number. Only for disk devices.
  FIB$V_SUPERSEDE Set to supersede an existing file of the same name, type, and version. Only for disk devices.
  FIB$V_LOWVER Set on return if a lower numbered version of the file exists. Only for disk devices.
  FIB$V_HIGHVER Set on return if a higher numbered version of the file exists. Only for disk devices.
FIB$W_VERLIMIT   Specifies the version limit for the directory entry created. Used only for disk devices and only when the first version of a new file is created. If 0, the directory default is used. If a directory operation was performed, FIB$W_VERLIMIT always contains the actual version limit of the file.
FIB$L_ACL_STATUS   Status of the requested ACL attribute operation, if any. The ACL attributes are included in Table 1-7. If no ACL attributes are given, SS$_NORMAL is returned here.

1.6.1.2 Disk ACP Operation

If the modifier IO$M_CREATE is specified, a file is created. The fileID of the file created is returned in FIB$W_FID. If the modifierIO$M_DELETE is specified, the file is marked for deletion.

If a nonzero directory ID is specified in FIB$W_DID, a directory entryis created. The file name specified by parameter P2 is entered in thedirectory, together with the file ID in FIB$W_FID. ( Section 1.3.1.1describes the format for the file name string.) Wildcards are notpermitted. Negative version numbers are treated as equivalent to a 0version number. If a result string buffer and length are specified byP3 and P4, the actual file name entered, and its length, are returned.

The version number of the file receives the following treatment:

  • If the version number in the specified file name is 0 or negative, the directory entry created gets a version number one greater than the highest previously existing version of that file (or version 1 if the file did not previously exist).
  • If the version number in the specified file name is a nonzero number and FIB$V_NEWVER is set, the directory entry created gets a version number one greater than the highest previously existing version of that file, or the specified version number, whichever is greater.
  • If the version number in the specified file name is a nonzero number and the directory already contains a file of the same name, type, and version, the previously existing file is set aside for deletion if FIB$V_SUPERSEDE is specified. If FIB$V_SUPERSEDE is not specified, the create operation fails with a SS$_DUPFILNAM status.
  • If, after creating the new directory entry, the number of versions of the file exceeds the version limit, the lowest numbered version is set aside for deletion.
  • If the file did not previously exist, the new directory entry is given a version limit as follows: the version limit is taken from FIB$W_VERLIMIT if it is a nonzero number; if it is 0, the version limit is taken from the default version limit of the directory file; if the default version limit of the directory file is 0, the version limit is set to 32,767 (the highest possible number).

The file name string entered in the directory is returned using the P3and P4 result string parameters, if present. The file name string isalso written into the header. If no directory operation was requested(FIB$W_DID is 0), the file name string specified by P2, if any, iswritten into the file header.

If an attribute list is specified by P5, a write attributes subfunctionis performed (see Section 1.3.5).

If the modifier IO$M_ACCESS is specified, the file is opened (seeSection 1.3.2).

If the extend enable bit FIB$V_EXTEND is specified in the FIB, anextend subfunction is performed (see Section 1.3.3).

Finally, if a file was set aside for deletion (IO$M_DELETE isspecified), that file is deleted. If the file is deleted because theFIB$V_SUPERSEDE bit was set, the alternate success status SS$_SUPERSEDEis returned in the I/O status block. If the file is deleted because theversion limit was exceeded, the alternate success status SS$_FILEPURGEDis returned.

If an error occurs in the operation of an IO$_CREATE function, allactions performed to that point are reversed (the file is neithercreated nor changed), and the error status is returned to the user inthe I/O status block.

1.6.1.3 Directory Entry Creation

Creating a new version of a file eliminates default access to thepreviously highest version of the file. For example, creatingRESUME.TXT;4 masks RESUME.TXT;3 so the DCL command TYPE RESUME.TXTyields the contents of version 4, not version 3. To protect thecontents of the earlier version of a file, the creator of a file musthave write access to the previous version of a file of the same name.

1.6.1.4 Magnetic Tape ACP Operation

No operation is performed unless the IO$M_CREATE modifier is specified.The magnetic tape is positioned as specified by FIB$V_REWIND andFIB$V_CURPOS, and the file is created. The name specified by the P2parameter is written into the file header label.

If P5 specifies an attribute list, a write attributes subfunction isperformed (see Section 1.3.5).

If the modifier IO$M_ACCESS is specified, the file is opened (seeSection 1.3.2).

1.6.2 Access File

This virtual I/O function searches a directory on a disk device or amagnetic tape for a specified file and accesses that file if found.

The following is the function code:

  • IO$_ACCESS

The following are the function modifiers:

  • IO$M_CREATE---Creates a file.
  • IO$M_ACCESS---Opens the file on your channel.

1.6.2.1 Input Parameters

The following are the device- or function-dependent arguments forIO$_ACCESS:

  • P1---The address of the file information block (FIB) descriptor.
  • P2---The address of the file name string descriptor (optional).
  • P3---The address of the word that is to receive the length of the resultant file name string (optional).
  • P4---The address of a descriptor for a buffer that is to receive the resultant file name string (optional).
  • P5---The address of a list of attribute descriptors (optional).

Table 1-12 lists FIB fields that are applicable to the IO$_ACCESSoperation.

Table 1-12 IO$_ACCESS and the File Information Block
Field Subfields Meaning
FIB$W_CNTRLFUNC   Specifies the value that allows the user to control actions subsequent to EOT detection on a magnetic tape file.
FIB$W_VERLIMIT   Receives the version limit for the file. Applicable only if FIB$W_DID is a nonzero number (if a directory lookup is done). Used only for disk devices.
FIB$L_ACL_STATUS   Status of the requested ACL attribute operation, if any. The ACL attributes are included in Table 1-7. If no ACL attributes are given, SS$_NORMAL is returned here. (For Files-11 C/D, this field is always set to SS$_NORMAL.)
FIB$L_STATUS   Alternate access status. The following bits are supported:
  FIB$V_ALT_REQ Set to indicate whether the alternate access bit is required for the current operation. If not set, the alternate access bit is optional.
  FIB$V_ALT_GRANTED If FIB$V_ALT_REQ = 0 and the alternate access check succeeded, the FIB bit returned from the file system is set.
FIB$L_ALT_ACCESS   A 32-bit mask that represents an access mask to check against file protection; for example, to open a file for read and to check whether it can be deleted. The mask has the same configuration as the standard protection mask.

1.6.2.2 Operation

If a nonzero directory file ID is specified in FIB$W_DID, a lookupsubfunction is performed (see Section 1.3.1.) The version limit of thefile found is returned in FIB$W_VERLIMIT.

If the directory search fails with a "file not found"condition and the IO$M_CREATE function modifier is specified, thefunction is reexecuted as a CREATE. In that case, the argumentinterpretations for IO$_CREATE, rather than those for IO$_ACCESS, apply.

If IO$M_ACCESS is specified, an access subfunction is performed to openthe file (see Section 1.3.2).

If P5 specifies an attribute list, a read attributes subfunction isperformed (see Section 1.3.5).

1.6.3 Deaccess File

Deaccess file is a virtual I/O function that deaccesses a file and, ifspecified, writes final attributes in the file header.

The following is the function code:

  • IO$_DEACCESS

IO$_DEACCESS takes no function modifiers.

1.6.3.1 Input Parameters

The following are the device- or function-dependent arguments forIO$_DEACCESS:

  • P1---The address of the file information block (FIB) descriptor.
  • P5---The address of a list of attribute descriptors (optional).

The following FIB field is applicable to a IO$_DEACCESS function:

Field Meaning
FIB$W_FID File ID of the file being deaccessed. This field can contain a value of 0. If it does not, it must match the file identifier of the accessed file.
FIB$L_ACL_STATUS Status of the requested ACL attribute operation, if any. The ACL attributes are included in Table 1-7. If no ACL attributes are given, SS$_NORMAL is returned here. (For Files-11 C/D, this field is always set to SS$_NORMAL.)

1.6.3.2 Operation

For disk files, if P5 specifies an attribute control list and thefile was accessed for a write operation, a write attributes subfunctionis performed (see Section 1.3.5). If the file was opened for write, noattributes were specified, and FIB$V_DLOCK was set when the file wasaccessed, the deaccess lock bit is set in the file header, inhibitingfurther access to that file.

For disk files, if the truncate enable bit FIB$V_TRUNC is specified inthe FIB, a truncate subfunction is performed (see Section 1.3.4).

Finally, the file is closed. Trailer labels are written for a magnetictape file that was opened for write.

1.6.4 Modify File

Modify file is a virtual I/O function that modifies the file attributesor allocation of a disk file. The IO$_MODIFY function is not applicableto magnetic tape; that is, the function returns success, but no actionis performed.

The following is the function code:

  • IO$_MODIFY

The following is the function modifier:

  • IO$M_MOVEFILE

1.6.4.1 Input Parameters

The following are the device- or function-dependent arguments forIO$_MODIFY:

  • P1---The address of the file information block (FIB) descriptor.
  • P2---The address of the file name string descriptor (optional). If specified, the directory is searched for the name.
  • P3---The address of the word that is to receive the length of the resultant file name string (optional).
  • P4---The address of a descriptor for a buffer that is to receive the resultant file name string (optional).
  • P5---The address of a list of attribute descriptors (optional).

The following FIB fields are applicable to the IO$_MODIFY function:

Field Subfields Meaning
FIB$L_ACCTL   Specifies field values that control access to the file. The following bit is applicable to the IO$_MODIFY function:
  FIB$V_WRITETHRU Specifies that the file header is to be written back to the disk. If not specified and the file is currently open, writing of the file header can be deferred to some later time.
FIB$W_VERLIMIT   If a nonzero number, specifies the version limit for the file.
FIB$L_ACL_STATUS   Status of the requested ACL attribute operation, if any. The ACL attributes are included in Table 1-7. If no ACL attributes are given, SS$_NORMAL is returned here.

1.6.4.2 Operation

If a nonzero directory ID is specified in FIB$W_DID, a lookupsubfunction is executed (see Section 1.3.1). If a nonzero version limitis specified in FIB$W_VERLIMIT and the directory entry found is thelatest version of that file, the version limit is set to the valuespecified.

If P5 specifies an attribute list, a write attributes subfunction isperformed (see Section 1.3.5).

The file can be either extended or truncated. If FIB$V_EXTEND isspecified in the FIB, an extend subfunction is performed (seeSection 1.3.3). If FIB$V_TRUNC is specified in the FIB, a truncatesubfunction is performed (see Section 1.3.4). Extend and truncateoperations cannot be performed at the same time.

1.6.5 Delete File

Delete file is a virtual I/O function that removes a directory entry orfile header from a disk volume.

The following is the function code:

  • IO$_DELETE

The following is the function modifier:

  • IO$M_DELETE---Deletes the file (or marks it for deletion).

The following are the device- or function-dependent arguments forIO$_DELETE:

  • P1---The address of the file information block (FIB) descriptor.
  • P2---The address of the file name string descriptor (optional).
  • P3---The address of the word that is to receive the length of the resultant file name string (optional).
  • P4---The address of a descriptor for a buffer that is to receive the resultant file name string (optional).

The following FIB fields are applicable to the IO$_DELETE function:

Field Subfields Meaning
FIB$L_ACCTL   Specifies field values that control access to the file. The following bit is applicable to the IO$_DELETE function.
  FIB$V_WRITETHRU Specifies that the file header is to be written back to the disk. If not specified and the file is currently open, writing of the file header can be deferred to some later time.
FIB$W_FID   Specifies the file identification to be deleted.

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