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Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
This function initiates an asynchronous read operation. It immediately returns after the operation was enqueued or when an error was encountered.
The first aiocbp->aio_nbytes bytes of the file for which
aiocbp->aio_fildes is a descriptor are written to the buffer
starting at aiocbp->aio_buf. Reading starts at the absolute
position aiocbp->aio_offset in the file.
If prioritized I/O is supported by the platform the
aiocbp->aio_reqprio value is used to adjust the priority before
the request is actually enqueued.
The calling process is notified about the termination of the read
request according to the aiocbp->aio_sigevent value.
When aio_read returns, the return value is zero if no error
occurred that can be found before the process is enqueued. If such an
early error is found, the function returns -1 and sets
errno to one of the following values:
EAGAINThe request was not enqueued due to (temporarily) exceeded resource limitations.
ENOSYSThe aio_read function is not implemented.
EBADFThe aiocbp->aio_fildes descriptor is not valid. This condition
need not be recognized before enqueueing the request and so this error
might also be signaled asynchronously.
EINVALThe aiocbp->aio_offset or aiocbp->aio_reqpiro value is
invalid. This condition need not be recognized before enqueueing the
request and so this error might also be signaled asynchronously.
If aio_read returns zero, the current status of the request
can be queried using aio_error and aio_return functions.
As long as the value returned by aio_error is EINPROGRESS
the operation has not yet completed. If aio_error returns zero,
the operation successfully terminated, otherwise the value is to be
interpreted as an error code. If the function terminated, the result of
the operation can be obtained using a call to aio_return. The
returned value is the same as an equivalent call to read would
have returned. Possible error codes returned by aio_error are:
EBADFThe aiocbp->aio_fildes descriptor is not valid.
ECANCELEDThe operation was canceled before the operation was finished (see Cancellation of AIO Operations)
EINVALThe aiocbp->aio_offset value is invalid.
When the sources are compiled with _FILE_OFFSET_BITS == 64 this
function is in fact aio_read64 since the LFS interface transparently
replaces the normal implementation.
Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
This function is similar to the aio_read function. The only
difference is that on 32 bit machines, the file descriptor should
be opened in the large file mode. Internally, aio_read64 uses
functionality equivalent to lseek64 (see Setting the File Position of a Descriptor) to position the file descriptor correctly for the reading,
as opposed to the lseek functionality used in aio_read.
When the sources are compiled with _FILE_OFFSET_BITS == 64, this
function is available under the name aio_read and so transparently
replaces the interface for small files on 32 bit machines.
To write data asynchronously to a file, there exists an equivalent pair of functions with a very similar interface.
Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
This function initiates an asynchronous write operation. The function call immediately returns after the operation was enqueued or if before this happens an error was encountered.
The first aiocbp->aio_nbytes bytes from the buffer starting at
aiocbp->aio_buf are written to the file for which
aiocbp->aio_fildes is a descriptor, starting at the absolute
position aiocbp->aio_offset in the file.
If prioritized I/O is supported by the platform, the
aiocbp->aio_reqprio value is used to adjust the priority before
the request is actually enqueued.
The calling process is notified about the termination of the read
request according to the aiocbp->aio_sigevent value.
When aio_write returns, the return value is zero if no error
occurred that can be found before the process is enqueued. If such an
early error is found the function returns -1 and sets
errno to one of the following values.
EAGAINThe request was not enqueued due to (temporarily) exceeded resource limitations.
ENOSYSThe aio_write function is not implemented.
EBADFThe aiocbp->aio_fildes descriptor is not valid. This condition
may not be recognized before enqueueing the request, and so this error
might also be signaled asynchronously.
EINVALThe aiocbp->aio_offset or aiocbp->aio_reqprio value is
invalid. This condition may not be recognized before enqueueing the
request and so this error might also be signaled asynchronously.
In the case aio_write returns zero, the current status of the
request can be queried using the aio_error and aio_return
functions. As long as the value returned by aio_error is
EINPROGRESS the operation has not yet completed. If
aio_error returns zero, the operation successfully terminated,
otherwise the value is to be interpreted as an error code. If the
function terminated, the result of the operation can be obtained using a call
to aio_return. The returned value is the same as an equivalent
call to read would have returned. Possible error codes returned
by aio_error are:
EBADFThe aiocbp->aio_fildes descriptor is not valid.
ECANCELEDThe operation was canceled before the operation was finished. (see Cancellation of AIO Operations)
EINVALThe aiocbp->aio_offset value is invalid.
When the sources are compiled with _FILE_OFFSET_BITS == 64, this
function is in fact aio_write64 since the LFS interface transparently
replaces the normal implementation.
Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
This function is similar to the aio_write function. The only
difference is that on 32 bit machines the file descriptor should
be opened in the large file mode. Internally aio_write64 uses
functionality equivalent to lseek64 (see Setting the File Position of a Descriptor) to position the file descriptor correctly for the writing,
as opposed to the lseek functionality used in aio_write.
When the sources are compiled with _FILE_OFFSET_BITS == 64, this
function is available under the name aio_write and so transparently
replaces the interface for small files on 32 bit machines.
Besides these functions with the more or less traditional interface,
POSIX.1b also defines a function which can initiate more than one
operation at a time, and which can handle freely mixed read and write
operations. It is therefore similar to a combination of readv and
writev.
Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
The lio_listio function can be used to enqueue an arbitrary
number of read and write requests at one time. The requests can all be
meant for the same file, all for different files or every solution in
between.
lio_listio gets the nent requests from the array pointed to
by list. The operation to be performed is determined by the
aio_lio_opcode member in each element of list. If this
field is LIO_READ a read operation is enqueued, similar to a call
of aio_read for this element of the array (except that the way
the termination is signalled is different, as we will see below). If
the aio_lio_opcode member is LIO_WRITE a write operation
is enqueued. Otherwise the aio_lio_opcode must be LIO_NOP
in which case this element of list is simply ignored. This
“operation” is useful in situations where one has a fixed array of
struct aiocb elements from which only a few need to be handled at
a time. Another situation is where the lio_listio call was
canceled before all requests are processed (see Cancellation of AIO Operations) and the remaining requests have to be reissued.
The other members of each element of the array pointed to by
list must have values suitable for the operation as described in
the documentation for aio_read and aio_write above.
The mode argument determines how lio_listio behaves after
having enqueued all the requests. If mode is LIO_WAIT it
waits until all requests terminated. Otherwise mode must be
LIO_NOWAIT and in this case the function returns immediately after
having enqueued all the requests. In this case the caller gets a
notification of the termination of all requests according to the
sig parameter. If sig is NULL no notification is
sent. Otherwise a signal is sent or a thread is started, just as
described in the description for aio_read or aio_write.
If mode is LIO_WAIT, the return value of lio_listio
is 0 when all requests completed successfully. Otherwise the
function returns -1 and errno is set accordingly. To find
out which request or requests failed one has to use the aio_error
function on all the elements of the array list.
In case mode is LIO_NOWAIT, the function returns 0 if
all requests were enqueued correctly. The current state of the requests
can be found using aio_error and aio_return as described
above. If lio_listio returns -1 in this mode, the
global variable errno is set accordingly. If a request did not
yet terminate, a call to aio_error returns EINPROGRESS. If
the value is different, the request is finished and the error value (or
0) is returned and the result of the operation can be retrieved
using aio_return.
Possible values for errno are:
EAGAINThe resources necessary to queue all the requests are not available at the moment. The error status for each element of list must be checked to determine which request failed.
Another reason could be that the system wide limit of AIO requests is exceeded. This cannot be the case for the implementation on GNU systems since no arbitrary limits exist.
EINVALThe mode parameter is invalid or nent is larger than
AIO_LISTIO_MAX.
EIOOne or more of the request’s I/O operations failed. The error status of each request should be checked to determine which one failed.
ENOSYSThe lio_listio function is not supported.
If the mode parameter is LIO_NOWAIT and the caller cancels
a request, the error status for this request returned by
aio_error is ECANCELED.
When the sources are compiled with _FILE_OFFSET_BITS == 64, this
function is in fact lio_listio64 since the LFS interface
transparently replaces the normal implementation.
Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem | See POSIX Safety Concepts.
This function is similar to the lio_listio function. The only
difference is that on 32 bit machines, the file descriptor should
be opened in the large file mode. Internally, lio_listio64 uses
functionality equivalent to lseek64 (see Setting the File Position of a Descriptor) to position the file descriptor correctly for the reading or
writing, as opposed to the lseek functionality used in
lio_listio.
When the sources are compiled with _FILE_OFFSET_BITS == 64, this
function is available under the name lio_listio and so
transparently replaces the interface for small files on 32 bit
machines.