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aio_read(3c)
Standard C Library Functions aio_read(3C)
NAME
aio_read - asynchronous read from a file
SYNOPSIS
#include <aio.h>
int aio_read(struct aiocb *aiocbp);
DESCRIPTION
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‐
fied.
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).
If SIGEV_MEM sigevent type is specified, the error and return values
are updated in the aiocb_t structure when I/O is completed. Applica‐
tions can get the error value using aio_error(3C) and the return value
using aio_return(3C). For SIGEV_MEM sigevent type requests,
aio_error(3C) and aio_return(3C) simply return the error and return
values from the structure, no system calls are involved. While the I/O
is in progress an EINPROGRESS error is returned. I/O completion can be
detected by monitoring the error value returned by aio_error(3C).
I/O completion notifications of SIGEV_MEM sigevent type requests cannot
be collected using aio_waitn(3C) or aio_suspend(3C) calls.
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
undefined results.
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
aiocbp->aio_fildes.
RETURN VALUES
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.
ERRORS
The aio_read() function will 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 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.
EBADF The aiocbp->aio_fildes argument is not a valid file descrip‐
tor open for reading.
EINVAL 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‐
lowing 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(3C) request.
EINVAL The file offset value implied by aiocbp->aio_offset would
be invalid.
The following condition may be detected synchronously or asyn‐
chronously:
EOVERFLOW The file is a regular file, aiocbp->aio_nbytes is greater
than 0 and the starting offset in aiocbp->aio_offset is
before the end-of-file and is at or beyond the offset max‐
imum in the open file description associated with
aiocbp->aio_fildes.
USAGE
For portability, the application should set aiocbp->aio_reqprio to 0.
The aio_read() function has a transitional interface for 64-bit file
offsets. See lf64(7).
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe _ Stan‐
dardSee standards(7).
SEE ALSO
close(2), exec(2), exit(2), fork(2), lseek(2), read(2), write(2),
aio_cancel(3C), aio_return(3C), lio_listio(3C), aio.h(3HEAD), sig‐
info.h(3HEAD), signal.h(3HEAD), attributes(7), lf64(7), standards(7)
Oracle Solaris 11.4 17 Aug 2018 aio_read(3C)