Function

The vn_open operation opens a file.

Environment on entry and exit

See Environment for PFS operations.

Parameters

Token_structure

Supplied parameter

Type:

TOKSTR

Length:

Specified by TOKSTR.ts_hdr.cblen.

The Token_structure represents the file (vnode) 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 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 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.

Open_flags

Supplied parameter

Type:

Bit

Length:

Fullword

A fullword containing the binary flags that describe how the file is to be opened. These flags are defined by fcntl.h.

Return_value

Returned parameter

Type:

Integer

Length:

Fullword

A fullword where the vn_open operation 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

The operation was successful.

Return_code

Returned parameter

Type:

Integer

Length:

Fullword

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

The vn_open operation should support at least the following error values:

Return_code	Explanation
EACCES	The caller does not have permission for the requested (read or write) access.
ENOENT	The file does not exist.
EROFS	An attempt was made to open a file for write in a read-only file system.

Reason_code

Returned parameter

Type:

Integer

Length:

Fullword

A fullword where the vn_open operation stores the reason code. The vn_open 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.

Implementation notes

Overview of vn_open processing

See Opening and closing files and first references to files for a discussion of open processing.

For more information about the semantics of this operation for a POSIX-conforming PFS, refer to the open() function in the POSIX .1 standard (IEEE Std 1003.1-1990).

Specific processing notes

• The O_RDONLY and O_WRONLY bits in the Open_flags control whether the SAF Check Access callable service is called for a read, write, or read and write access check.
• When the O_EXEC flag is ON in the Open_flags, the SAF Check Access call must be made with a check for execute permission rather than read or write permission. This bit is a z/OS UNIX extension that is defined in Interface structures for C language servers and clients.
• When the O_TRUNC flag is ON in the Open_flags the PFS must truncate the file to zero length.
• The LFS implements the semantics of the O_CREAT and O_EXCL flags.
• The Open_flags will be remembered by the LFS and passed to the PFS on all read/write type operations that are related to this open. The O_APPEND and O_NONBLOCK flags, for instance, are processed by the PFS during those read/write operations from the flags passed to it at that time. The O_SYNC flag is transferred by the LFS to the UIO.u_sync flag for all read/write type operations so that this function can be processed by the PFS the same way for both POSIX and NFS users.

Serialization provided by the LFS

The vn_open operation is invoked with an exclusive latch held on the vnode of the file. Shared read support for the file being opened may be modified in the OSI by the PFS upon returning from the vn_open operation.

Security calls to be made by the PFS

The PFS is expected to invoke SAF's Check Access callable service to check that the user has permission for the requested (read, write, or execute) access.

Related services

• vn_close — Close a file or socket