AIO_READ(3C)AIO_READ(3C)NAMEaio_read - asynchronous read from a file
int aio_read(struct aiocb *aiocbp);
The aio_read() function allows the calling process to read
aiocbp->aio_nbytes from the file associated with aiocbp->aio_fildes
into the buffer pointed to by aiocbp->aio_buf. The function call
returns when the read request has been initiated or queued to the file
or device (even when the data cannot be delivered immediately). If
_POSIX_PRIORITIZED_IO is defined and prioritized I/O is supported for
this file, then the asynchronous operation is submitted at a priority
equal to the scheduling priority of the process minus
aiocbp->aio_reqprio. The aiocbp value may be used as an argument to
aio_error(3C) and aio_return(3C) 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 returns 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(2) 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 unspeci‐
The aiocbp->aio_sigevent structure defines what asynchronous notifica‐
tion is to occur when the asynchronous operation completes, as speci‐
fied in signal.h(3HEAD).
The aiocbp->aio_lio_opcode field is 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
If _POSIX_SYNCHRONIZED_IO is defined and synchronized I/O is enabled on
the file associated with aiocbp->aio_fildes, the behavior of this func‐
tion is according to the definitions of synchronized I/O data integrity
completion and synchronized I/O file integrity completion.
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 will occur past the offset maximum
established in the open file description associated with
The aio_read() function returns 0 to the calling process if the I/O
operation is successfully queued; otherwise, the function returns −1
and sets errno to indicate the error.
The aio_read() function will fail if:
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 condi‐
tions below are detected synchronously, the aio_read() function returns
-1 and sets errno to the corresponding value. If any of the conditions
below are detected asynchronously, the return status of the asynchro‐
nous operation is set to −1, and the error status of the asynchronous
operation will be set to the corresponding value.
The aiocbp->aio_fildes argument is not a valid file descrip‐
tor open for reading.
The file offset value implied by aiocbp->aio_offset would be
invalid, aiocbp->aio_reqprio is not a valid value, or
aiocbp->aio_nbytes is an invalid value.
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 nor‐
mally returned by the read(2) function call. In addition, the error
status of the asynchronous operation will be set to one of the error
statuses normally set by the read() function call, or one of the fol‐
The aiocbp->aio_fildes argument is not a valid file
descriptor open for reading.
The requested I/O was canceled before the I/O completed
due to an explicit aio_cancel(3C) request.
The file offset value implied by aiocbp->aio_offset would
The following condition may be detected synchronously or asyn‐
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 max‐
imum in the open file description associated with
For portability, the application should set aiocb->aio_reqprio to 0.
The aio_read() function has a transitional interface for 64-bit file
offsets. See lf64(5).
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Committed │
│MT-Level │ MT-Safe │
│Standard │ See standards(5). │
SEE ALSOclose(2), exec(2), exit(2), fork(2), lseek(2), read(2), write(2),
aio_cancel(3C), aio_return(3C), aio.h(3HEAD), lio_listio(3C), sig‐
info.h(3HEAD), signal.h(3HEAD), attributes(5), lf64(5), standards(5)
Feb 5, 2008 AIO_READ(3C)