VxWorks系统库函数详解与系统调用

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VxWorks系统函数是WindRiver Systems公司为他们的实时操作系统VxWorks设计的一系列库函数和系统调用。这些函数和调用是VxWorks核心功能的重要组成部分，旨在提供高效、稳定的嵌入式系统开发环境。VxWorks Reference Manual 5.4 Edition 1是一个详细的文档，它包含了关于这些功能的全面指南和API参考。在VxWorks中，系统函数扮演着底层硬件抽象的角色，使得上层软件开发者能够与硬件进行交互，而无需深入了解底层硬件的具体细节。这些函数包括但不限于进程管理（如创建、同步和通信）、内存操作（如内存分配和释放）、文件系统操作（读写文件、目录操作等）、网络通信（TCP/IP协议栈支持）、以及设备驱动接口等。它们是模块化设计，允许用户根据项目需求选择性地使用，提高了代码的可维护性和可扩展性。系统调用则是VxWorks中实现操作系统功能的基本机制，它们通过硬件中断或特定指令从用户态切换到内核态，执行由操作系统预定义的任务。这些调用通常涉及对硬件资源的控制，例如进程调度、中断处理、时钟管理等，它们确保了系统的稳定性和性能。 VxWorks库函数和系统调用的特点包括： 1. **低级接口**：这些函数直接操作硬件，提供了对硬件访问的原始能力。 2. **安全性**：由于执行权限在内核态，系统调用可以避免数据损坏或安全漏洞，保证系统的可靠性。 3. **效率**：由于VxWorks设计为实时操作系统，这些函数通常具有高效的执行速度，对时间敏感的应用至关重要。 4. **易用性**：虽然底层，但经过精心设计的API使得开发者能以相对较高的抽象层次进行编程，降低了复杂性。在使用VxWorks系统函数和调用时，开发者需要熟悉其使用方法、参数含义以及可能引发的异常情况。同时，理解VxWorks的内存管理和中断模型也是关键，因为这些函数往往与这两个核心概念密切相关。VxWorks Reference Manual提供了详尽的示例和错误代码，有助于理解和解决在实际开发中遇到的问题。 VxWorks系统函数和系统调用是VxWorks平台开发嵌入式系统的核心技术，对于任何从事VxWorks开发的工程师来说，深入理解和熟练掌握它们是必不可少的。

VxWorks Reference Manual, 5.4

aioPxLib

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return (ERROR);

/* enable SCSI interupts */

sysIntEnablePIC (SCSI_INT_LVL);

}

return (OK);

}

SEE ALSO scsiLib, scsi2Lib, cacheLib, AIC-7880 Design In Handbook, AIC-7880 Data Book, Adaptec

Hardware Interface Module (HIM) Specification, VxWorks Programmer’s Guide: I/O System

aioPxLib

NAME aioPxLib – asynchronous I/O (AIO) library (POSIX)

ROUTINES aioPxLibInit() – initialize the asynchronous I/O (AIO) library

aio_read() – initiate an asynchronous read (POSIX)

aio_write() – initiate an asynchronous write (POSIX)

lio_listio() – initiate a list of asynchronous I/O requests (POSIX)

aio_suspend() – wait for asynchronous I/O request(s) (POSIX)

aio_fsync() – asynchronous file synchronization (POSIX)

aio_error() – retrieve error status of asynchronous I/O operation (POSIX)

aio_return() – retrieve return status of asynchronous I/O operation (POSIX)

DESCRIPTION This library implements asynchronous I/O (AIO) according to the definition given by the

POSIX standard 1003.1b (formerly 1003.4, Draft 14). AIO provides the ability to overlap

application processing and I/O operations initiated by the application. With AIO, a task

can perform I/O simultaneously to a single file multiple times or to multiple files.

After an AIO operation has been initiated, the AIO proceeds in logical parallel with the

processing done by the application. The effect of issuing an asynchronous I/O request is

as if a separate thread of execution were performing the requested I/O.

AIO LIBRARY The AIO library is initialized by calling aioPxLibInit(), which should be called once

(typically at system start-up) after the I/O system has already been initialized.

AIO COMMANDS The file to be accessed asynchronously is opened via the standard open call. Open returns

a file descriptor which is used in subsequent AIO calls.

The caller initiates asynchronous I/O via one of the following routines:

aio_read()

initiates an asynchronous read

1. Libraries

aioPxLib

1 - 5

aio_write()

initiates an asynchronous write

lio_listio()

initiates a list of asynchronous I/O requests

Each of these routines has a return value and error value associated with it; however,

these values indicate only whether the AIO request was successfully submitted (queued),

not the ultimate success or failure of the AIO operation itself.

There are separate return and error values associated with the success or failure of the

AIO operation itself. The error status can be retrieved using aio_error(); however, until

the AIO operation completes, the error status will be

EINPROGRESS. After the AIO

operation completes, the return status can be retrieved with aio_return().

The aio_cancel()call cancels a previously submitted AIO request. The aio_suspend()call

waits for an AIO operation to complete.

Finally, the aioShow() call (not a standard POSIX function) displays outstanding AIO

requests.

AIO CONTROL BLOCK

Each of the calls described above takes an AIO control block (aiocb) as an argument. The

calling routine must allocate space for the aiocb, and this space must remain available for

the duration of the AIO operation. (Thus the aiocb must not be created on the task’s stack

unless the calling routine will not return until after the AIO operation is complete and

aio_return() has been called.) Each aiocb describes a single AIO operation. Therefore,

simultaneous asynchronous I/O operations using the same aiocb are not valid and

produce undefined results.

The aiocb structure and the data buffers referenced by it are used by the system to

perform the AIO request. Therefore, once the aiocb has been submitted to the system, the

application must not modify the aiocb structure until after a subsequent call to

aio_return(). The aio_return() call retrieves the previously submitted AIO data

structures from the system. After the aio_return() call, the calling application can modify

the aiocb, free the memory it occupies, or reuse it for another AIO call.

As a result, if space for the aiocb is allocated off the stack the task should not be deleted

(or complete running) until the aiocb has been retrieved from the system via an

aio_return().

The aiocb is defined in aio.h. It has the following elements:

struct

{

int aio_fildes;

off_t aio_offset;

volatile void * aio_buf;

size_t aio_nbytes;

int aio_reqprio;

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