vn_readdir — Read directory entries

Function

The vn_readdir operation reads entries from the directory that is represented by the input Token_structure, and returns as many entries as will fit in the caller's buffer.

Environment on entry and exit

See Environment for PFS operations.

Input parameter format

vn_readdir  (Token_structure,
             OSI_structure,
             Audit_structure,
             User_IO_structure,
             Return_value,
             Return_code,
             Reason_code)

Parameters

Token_structure

Supplied parameter

Type:: TOKSTR
Length:: Specified by TOKSTR.ts_hdr.cblen.

The Token_structure represents the file (vnode) that is being operated on. It contains the PFS's initialization token, mount token, and the file token. Refer to LFS/PFS control block structure for a discussion of this structure, and to the TOKSTR typedef in BPXYPFSI in Interface structures for C language servers and clients for its mapping.

OSI_structure

Supplied and returned parameter

Type:: OSI
Length:: Specified by OSI.osi_hdr.cblen.

The OSI_structure contains information that is used by the OSI operations that may be called by the PFS. See OSI services for more information.

It also contains MVS-specific information that needs to be passed to the PFS, including SMF accounting fields, a work area, a recovery area, and an optional pointer to an output ATTR structure. For more information about the OSI structure, see The OSI structure.

This area is mapped by the OSI typedef in BPXYPFSI in Interface structures for C language servers and clients.

Audit_structure

Supplied parameter

Type:: CRED
Length:: Specified by CRED.cred_hdr.cblen.

The Audit_structure contains information that is used by the security product for access checks and auditing. It is passed to most SAF routines that are invoked by the PFS.

Refer to Security responsibilities and considerations for a discussion of security processing, and to the CRED typedef in BPXYPFSI in Interface structures for C language servers and clients for the mapping of this structure.

User_IO_structure

Supplied and returned parameter

Type:: UIO
Length:: Specified by UIO.u_hdr.cblen.

An area containing the parameters for the I/O that is to be performed. This area is mapped by the UIO typedef in the BPXYVFSI header file (see Interface structures for C language servers and clients). See "Specific processing notes" for details on how the fields in this structure are processed.

Return_value

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readdir operation returns the results of the operation, as one of the following return codes:

Return_value: Meaning
-1: The operation was not successful. The Return_code and Reason_Code values must be completed by the PFS when Return_value is -1.
0: The operation was successful, and there are no more directory entries to be read. No entries are returned.
0 or greater: The operation was successful; the value represents the number of directory entries that are returned.

Return_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readdir operation stores the return code. The vn_readdir operation returns Return_code only if Return_value is -1. For a complete list of supported return code values, see z/OS UNIX System Services Messages and Codes.

The vn_readdir operation must support at least the following error values:

Return_code	Explanation
EACCES	The caller does not have search permission for the directory.
EFAULT	A buffer address that was specified is not in addressable storage.
EINVAL	There was a parameter error, such as an input buffer that is too small for any entries.

Reason_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readdir operation stores the reason code. The vn_readdir operation returns Reason_code only if Return_value is -1. Reason_code further qualifies the Return_code value. These reason codes are documented by the PFS product.

Implementation notes

Overview of vn_readdir processing

Reading directories provides an overview of readdir operation.

Specific processing notes

The token structure that is passed on input represents the directory that is to be read.

The following UIO fields are provided by the LFS:

UIO.u_hdr.cbid: Contains UIO_ID (from the BPXYVFSI header file)
UIO.u_hdr.cblen: Specifies the length of the user_IO_structure
UIO.u_buffaddr: Specifies the address of the caller's buffer
UIO.u_alet: Specifies the ALET of the caller's buffer
UIO.u_offseth: Specifies the high-order word of the cursor
UIO.u_offset: Specifies the low-order word of the cursor
UIO.u_count: Specifies the maximum number of bytes that can be written to the caller's buffer
UIO.u_asid: Specifies the ASID of the caller
UIO.u_key: Specifies the storage key of the caller's buffer
UIO.u_rdindex: Specifies the readdir index field

The following UIO fields must be set by the PFS:
- UIO.u_offseth
- UIO.u_offset
The PFS is expected to write directory entries into the caller's buffer. These directory entries are mapped by the DIRENT and DIREXT typedefs in the BPXYVFSI header file (see Interface structures for C language servers and clients).
For more information about the semantics of this operation for a POSIX-conforming PFS, see the description of readdir (BPX1RDD, BPX4RDD) in z/OS UNIX System Services Programming: Assembler Callable Services Reference.

Serialization provided by the LFS

The vn_readdir operation is invoked with a shared latch held on the vnode of the directory.

Security calls to be made by the PFS

The PFS is expected to invoke SAF's Check Access callable service to verify that the user has read permission to the directory.

For a discussion of vn_link processing in a multilevel security environment, see PFS support for multilevel security.

Related services

vn_open — Open a file