aio_read - asynchronous read from a file (REALTIME)
The aio_read() function shall read aiocbp->aio_nbytes from the file associated with aiocbp->aio_fildes into the buffer pointed to by aiocbp->aio_buf. The function call shall return when the read request has been initiated or queued to the file or device (even when the data cannot be delivered immediately).
[PIO]
If prioritized I/O is supported for this file, then the asynchronous operation shall be submitted at a priority equal to a base scheduling priority minus aiocbp->aio_reqprio. If Thread Execution Scheduling is not supported, then the base scheduling priority is that of the calling process;
[PIO TPS]
The aiocbp value may be used as an argument to aio_error() and aio_return() in order to determine the error status and return status, respectively, of the asynchronous operation while it is proceeding. If an error condition is encountered during queuing, the function call shall return without having initiated or queued the request. The requested operation takes place at the absolute position in the file as given by aio_offset, as if lseek() were called immediately prior to the operation with an offset equal to aio_offset and a whence equal to SEEK_SET. After a successful call to enqueue an asynchronous I/O operation, the value of the file offset for the file is unspecified.
The aiocbp->aio_lio_opcode field shall be ignored by aio_read().
The aiocbp argument points to an aiocb structure. If the buffer pointed to by aiocbp->aio_buf or the control block pointed to by aiocbp becomes an illegal address prior to asynchronous I/O completion, then the behavior is undefined.
Simultaneous asynchronous operations using the same aiocbp produce undefined results.
[SIO]
For any system action that changes the process memory space while an asynchronous I/O is outstanding to the address range being changed, the result of that action is undefined.
For regular files, no data transfer shall occur past the offset maximum established in the open file description associated with aiocbp->aio_fildes.
The aio_read() function shall return the value zero if the I/O operation is successfully queued; otherwise, the function shall return the value -1 and set errno to indicate the error.
The aio_read() function shall fail if:
- [EAGAIN]
- The requested asynchronous I/O operation was not queued due to system resource limitations.
Each of the following conditions may be detected synchronously at the time of the call to aio_read(), or asynchronously. If any of the conditions below are detected synchronously, the aio_read() function shall return -1 and set errno to the corresponding value. If any of the conditions below are detected asynchronously, the return status of the asynchronous operation is set to -1, and the error status of the asynchronous operation is set to the corresponding value.
- [EBADF]
- The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.
- [EINVAL]
- The file offset value implied by aiocbp->aio_offset would be invalid, [PIO]
In the case that the aio_read() successfully queues the I/O operation but the operation is subsequently canceled or encounters an error, the return status of the asynchronous operation is one of the values normally returned by the read() function call. In addition, the error status of the asynchronous operation is set to one of the error statuses normally set by the read() function call, or one of the following values:
- [EBADF]
- The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.
- [ECANCELED]
- The requested I/O was canceled before the I/O completed due to an explicit aio_cancel() request.
- [EINVAL]
- The file offset value implied by aiocbp->aio_offset would be invalid.
The following condition may be detected synchronously or asynchronously:
- [EOVERFLOW]
- The file is a regular file, aiobcp->aio_nbytes is greater than 0, and the starting offset in aiobcp->aio_offset is before the end-of-file and is at or beyond the offset maximum in the open file description associated with aiocbp->aio_fildes.
None.
The aio_read() function is part of the Asynchronous Input and Output option and need not be available on all implementations.
None.
None.
aio_cancel(), aio_error(), lio_listio(), aio_return(), aio_write(), close(), exec(), exit(), fork(), lseek(), read(), the Base Definitions volume of IEEE Std 1003.1-2001, <aio.h>
First released in Issue 5. Included for alignment with the POSIX Realtime Extension.
Large File Summit extensions are added.
The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Asynchronous Input and Output option.
The APPLICATION USAGE section is added.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
In the DESCRIPTION, text is added to indicate setting of the offset maximum in the open file description. This change is to support large files.
In the ERRORS section, the [EOVERFLOW] condition is added. This change is to support large files.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/12 is applied, rewording the DESCRIPTION when prioritized I/O is supported to account for threads, and removing the words ``to the calling process'' in the RETURN VALUE section.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/13 is applied, updating the [EINVAL] error, so that detection of an [EINVAL] error for an invalid value of aiocbp->aio_reqprio is only required if the Prioritized Input and Output option is supported.