lio_listio - list directed I/O (REALTIME)
#include <aio.h> int lio_listio(int mode, struct aiocb * const list, int nent, struct sigevent *sig);
The lio_listio() function allows the calling process to initiate a list of I/O requests with a single function call.
The mode argument takes one of the values LIO_WAIT or LIO_NOWAIT declared in <aio.h> and determines whether the function returns when the I/O operations have been completed, or as soon as the operations have been queued. If the mode argument is LIO_WAIT, the function waits until all I/O is complete and the sig argument is ignored.
If the mode argument is LIO_NOWAIT, the function returns immediately, and asynchronous notification occurs, according to the sig argument, when all the I/O operations complete. If sig is NULL, then no asynchronous notification occurs. If sig is not NULL, asynchronous notification occurs as specified in
Signal Generation and Deliverywhen all the requests in list have completed.
The I/O requests enumerated by list are submitted in an unspecified order.
The list argument is an array of pointers to aiocb structures. The array contains nent elements. The array may contain NULL elements, which are ignored.
The aio_lio_opcode field of each aiocb structure specifies the operation to be performed. The supported operations are LIO_READ, LIO_WRITE and LIO_NOP; these symbols are defined in <aio.h>. The LIO_NOP operation causes the list entry to be ignored. If the aio_lio_opcode element is equal to LIO_READ, then an I/O operation is submitted as if by a call to aio_read() with the aiocbp equal to the address of the aiocb structure. If the aio_lio_opcode element is equal to LIO_WRITE, then an I/O operation is submitted as if by a call to aio_write() with the aiocbp equal to the address of the aiocb structure.
The aio_fildes member specifies the file descriptor on which the operation is to be performed.
The aio_buf member specifies the address of the buffer to or from which the data is to be transferred.
The aio_nbytes member specifies the number of bytes of data to be transferred.
The members of the aiocb structure further describe the I/O operation to be performed, in a manner identical to that of the corresponding aiocb structure when used by the aio_read() and aio_write() functions.
The nent argument specifies how many elements are members of the list, that is, the length of the array.
The behaviour of this function is altered according to the definitions of synchronised I/O data integrity completion and synchronised I/O file integrity completion. if synchronised I/O is enabled on the file associated with aio_fildes.
For regular files, no data transfer will occur past the offset maximum established in the open file description associated with aiocbp->aio_fildes.
If the mode argument has the value LIO_NOWAIT, the lio_listio() function returns the value zero if the I/O operations are successfully queued; otherwise, the function returns the value -1 and sets errno to indicate the error.
If the mode argument has the value LIO_WAIT, the lio_listio() function returns the value zero when all the indicated I/O has completed successfully. Otherwise, lio_listio() returns a value of -1 and sets errno to indicate the error.
In either case, the return value only indicates the success or failure of the lio_listio() call itself, not the status of the individual I/O requests. In some cases one or more of the I/O requests contained in the list may fail. Failure of an individual request does not prevent completion of any other individual request. To determine the outcome of each I/O request, the application examines the error status associated with each aiocb control block. The error statuses so returned are identical to those returned as the result of an aio_read() or aio_write() function.
The lio_listio() function will fail if:
- The resources necessary to queue all the I/O requests were not available. The application may check the error status for each aiocb to determine the individual request(s) that failed.
- The number of entries indicated by nent would cause the systemwide limit AIO_MAX to be exceeded.
- The mode argument is not a proper value, or the value of nent was greater than AIO_LISTIO_MAX.
- A signal was delivered while waiting for all I/O requests to complete during a LIO_WAIT operation. Note that, since each I/O operation invoked by lio_listio() may possibly provoke a signal when it completes, this error return may be caused by the completion of one (or more) of the very I/O operations being awaited. Outstanding I/O requests are not canceled, and the application examines each list element to determine whether the request was initiated, canceled, or completed.
- One or more of the individual I/O operations failed. The application may check the error status for each aiocb structure to determine the individual request(s) that failed.
- The lio_listio() function is not supported by this implementation.
In addition to the errors returned by the lio_listio() function, if the lio_listio() function succeeds or fails with errors of [EAGAIN], [EINTR], or [EIO], then some of the I/O specified by the list may have been initiated. If the lio_listio() function fails with an error code other than [EAGAIN], [EINTR], or [EIO], no operations from the list have been initiated. The I/O operation indicated by each list element can encounter errors specific to the individual read or write function being performed. In this event, the error status for each aiocb control block contains the associated error code. The error codes that can be set are the same as would be set by a read() or write() function, with the following additional error codes possible:
- The requested I/O operation was not queued due to resource limitations.
- The requested I/O was canceled before the I/O completed due to an explicit aio_cancel() request.
- The aiocbp->aio_lio_opcode is LIO_WRITE, the file is a regular file, aiocbp->aio_nbytes is greater than 0, and the aiocbp->aio_offset is greater than or equal to the offset maximum in the open file description associated with aiocbp->aio_fildes.
- The requested I/O is in progress.
- The aiocbp->aio_lio_opcode is LIO_READ, the file is a regular file, aiocbp->aio_nbytes is greater than 0, and the aiocbp->aio_offset is before the end-of-file and is greater than or equal to the offset maximum in the open file description associated with aiocbp->aio_fildes.
aio_read(), aio_write(), aio_error(), aio_return(), aio_cancel(), read(), lseek(), close(), _exit(), exec, fork().
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)