vn_readlink — Read a symbolic link

Function

The vn_readlink operation reads the symbolic link file that is represented by Token_structure, and returns the contents in the buffer that is described by User_IO_structure.

Environment on entry and exit

See Environment for PFS operations.

Input parameter format

vn_readlink (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 details on 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 that contains 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).

Return_value

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readlink service returns the results of the operation, as one of the following:

Return_value: Meaning
-1: The operation was not successful. The Return_code and Reason_Code values must be filled in by the PFS when Return_value is -1.
0 or greater: The operation was successful and represents the number of bytes that were transferred.

Return_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readlink service stores the return code. The vn_readlink service 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_readlink service should support at least the following error value:

Return_code	Explanation
EFAULT	The buffer address that was specified in the input user_IO_structure is not in addressable storage.

Reason_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_readlink service stores the reason code. The vn_readlink service 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.

Implementation notes

Overview of vn_readlink processing

Reading from and writing to files provides an overview of file read and write processing.

The vn_readlink operation reads a symbolic link file. A symbolic link file contains the pathname or external name that was specified when the symbolic link was created.

Specific processing notes

The token structure that is passed on input represents the symbolic link 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_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
If the buffer that is supplied to vn_readlink is too small to contain the contents of the symbolic link, the value should be truncated to the length of the buffer (UIO.u_count).
There is no difference in vn_readlink processing for symbolic and external links.
Refer to the readlink() function in the POSIX .1a standard (IEEE Std 1003.1a), draft 7, for more information about the semantics of this operation for a POSIX-conforming PFS.

Serialization provided by the LFS

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

Security calls to be made by the PFS

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

Related services

vn_symlink — Create a symbolic link