vn_srx — Send or receive CSM buffers

Function

The vn_srx operation sends or receives data using CSM (Communications Storage Manager) buffers.

Environment on entry and exit

Input parameter format

vn_srx      (Token_structure,
             OSI_structure,
             Audit_structure,
             Open_flags,
             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 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.

Open_flags

Supplied parameter

Type:: Structure
Length:: Fullword

A fullword that contains the bits that are associated with the socket. The defined values for this field are mapped by fcntl.h.

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). See "Specific processing notes" for information about how the fields in this structure are processed.

Return_value

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_srx operation returns the results of the operation, as one of the following values:

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. The value represents the number of bytes that were transferred.

Return_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_srx operation stores the return code. The vn_srx 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_srx operation should support at least the following error values:

Return_code	Explanation
EFAULT	A buffer address that was specified is not in addressable storage.
EINVAL	An incorrect parameter was specified.
EWOULDBLOCK	A socket that has been defined as nonblocking cannot complete its operation without blocking.

Reason_code

Returned parameter

Type:: Integer
Length:: Fullword

A fullword in which the vn_srx operation stores the reason code. The vn_srx 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_srx processing

The Communications Storage Manager (CSM) provides a facility that allows programs to avoid data moves on a communications session by transferring buffer ownership instead of copying the buffer contents. See z/OS Communications Server: CSM Guide for more information about CSM.

The controlling parameters of the vn_srx operation are passed in a msghdrx structure, which is pointed to from the UIO. Included in the msghdrx is a pointer to an array of structures, each of which points to a data buffer that is obtained from CSM. For more information about the msghdrx structure and the semantics of this operation, see srx_np (BPX1SRX, BPX4SRX) — Send or receive CSM buffers on a socket in z/OS UNIX System Services Programming: Assembler Callable Services Reference.

The vn_srx call can be used on either connected or unconnected sockets.

Specific processing notes

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 a primary address space copy of the caller's msghdrx structure

UIO.u_buffalet

Specifies the ALET, 0, of the msghdrx structure

UIO.u_count

Specifies the length of the msghdrx structure that is being passed

UIO.u_asid

Specifies the ASID of the caller

UIO.u_rw

Specifies whether the request is a read (0) or a write (1)

UIO.u_key

Specifies the storage key of the caller
The msghdrx structure is defined in bpxysrxh.h.
The user's msghdrx is copied into the kernel by the LFS, and this copy is passed to the PFS. This kernel msghdrx, with any changes that are made by the PFS, is copied back to the user after the operation.
The use of Msghdrx_length=0 in BPX1SRX to determine support for this operation is handled by the LFS, and not passed down to the PFS.

Serialization provided by the LFS

The vn_srx operation is invoked with an exclusive latch held on the vnode.

Security calls to be made by the PFS

None.