aio_read(3) Library Functions Manual aio_read(3)
NAME
aio_read - asynchronous read
LIBRARY
Real-time library (librt, -lrt)
SYNOPSIS
#include <aio.h>
int aio_read(struct aiocb *aiocbp);
DESCRIPTION
The aio_read() function queues the I/O request described by the buffer
pointed to by aiocbp. This function is the asynchronous analog of
read(2). The arguments of the call
read(fd, buf, count)
correspond (in order) to the fields aio_fildes, aio_buf, and aio_nbytes
of the structure pointed to by aiocbp. (See aio(7) for a description
of the aiocb structure.)
The data is read starting at the absolute position aiocbp->aio_offset,
regardless of the file offset. After the call, the value of the file
offset is unspecified.
The "asynchronous" means that this call returns as soon as the request
has been enqueued; the read may or may not have completed when the call
returns. One tests for completion using aio_error(3). The return sta-
tus of a completed I/O operation can be obtained by aio_return(3).
Asynchronous notification of I/O completion can be obtained by setting
aiocbp->aio_sigevent appropriately; see sigevent(7) for details.
If _POSIX_PRIORITIZED_IO is defined, and this file supports it, then
the asynchronous operation is submitted at a priority equal to that of
the calling process minus aiocbp->aio_reqprio.
The field aiocbp->aio_lio_opcode is ignored.
No data is read from a regular file beyond its maximum offset.
RETURN VALUE
On success, 0 is returned. On error, the request is not enqueued, -1
is returned, and errno is set to indicate the error. If an error is
detected only later, it will be reported via aio_return(3) (returns
status -1) and aio_error(3) (error status—whatever one would have got-
ten in errno, such as EBADF).
ERRORS
EAGAIN Out of resources.
EBADF aio_fildes is not a valid file descriptor open for reading.
EINVAL One or more of aio_offset, aio_reqprio, or aio_nbytes are in-
valid.
ENOSYS aio_read() is not implemented.
EOVERFLOW
The file is a regular file, we start reading before end-of-file
and want at least one byte, but the starting position is past
the maximum offset for this file.
VERSIONS
The aio_read() function is available since glibc 2.1.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│aio_read() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2001, POSIX.1-2008.
NOTES
It is a good idea to zero out the control block before use. The con-
trol block must not be changed while the read operation is in progress.
The buffer area being read into must not be accessed during the opera-
tion or undefined results may occur. The memory areas involved must
remain valid.
Simultaneous I/O operations specifying the same aiocb structure produce
undefined results.
EXAMPLES
See aio(7).
SEE ALSO
aio_cancel(3), aio_error(3), aio_fsync(3), aio_return(3), aio_sus-
pend(3), aio_write(3), lio_listio(3), aio(7)
Linux man-pages 6.03 2023-02-05 aio_read(3)
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