[3.7] bpo-31368: Enhance os.preadv() documentation (GH-7254) by miss-islington · Pull Request #7258 · python/cpython
.. function:: pread(fd, buffersize, offset) .. function:: pread(fd, n, offset)
Read from a file descriptor, *fd*, at a position of *offset*. It will read up to *buffersize* number of bytes. The file offset remains unchanged. Read at most *n* bytes from file descriptor *fd* at a position of *offset*, leaving the file offset unchanged.
Return a bytestring containing the bytes read. If the end of the file referred to by *fd* has been reached, an empty bytes object is returned.
Availability: Unix.
.. versionadded:: 3.3
.. function:: preadv(fd, buffers, offset, flags=0)
Read from a file descriptor *fd* at a position of *offset* into mutable :term:`bytes-like objects <bytes-like object>` *buffers*, leaving the file offset unchanged. Transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data.
The flags argument contains a bitwise OR of zero or more of the following flags:
- :data:`RWF_HIPRI` - :data:`RWF_NOWAIT`
Return the total number of bytes actually read which can be less than the total capacity of all the objects.
The operating system may set a limit (:func:`sysconf` value ``'SC_IOV_MAX'``) on the number of buffers that can be used.
Combine the functionality of :func:`os.readv` and :func:`os.pread`.
Availability: Linux 2.6.30 and newer, FreeBSD 6.0 and newer, OpenBSD 2.7 and newer. Using flags requires Linux 4.6 or newer.
.. versionadded:: 3.7
.. data:: RWF_NOWAIT
Do not wait for data which is not immediately available. If this flag is specified, the system call will return instantly if it would have to read data from the backing storage or wait for a lock.
If some data was successfully read, it will return the number of bytes read. If no bytes were read, it will return ``-1`` and set errno to :data:`errno.EAGAIN`.
Availability: Linux 4.14 and newer.
.. versionadded:: 3.7
.. data:: RWF_HIPRI
High priority read/write. Allows block-based filesystems to use polling of the device, which provides lower latency, but may use additional resources.
Currently, on Linux, this feature is usable only on a file descriptor opened using the :data:`O_DIRECT` flag.
Availability: Linux 4.6 and newer.
.. versionadded:: 3.7
.. function:: pwrite(fd, str, offset)
Write *bytestring* to a file descriptor, *fd*, from *offset*, leaving the file offset unchanged. Write the bytestring in *str* to file descriptor *fd* at position of *offset*, leaving the file offset unchanged.
Return the number of bytes actually written.
Availability: Unix.
.. function:: pwritev(fd, buffers, offset, flags=0)
Combines the functionality of :func:`os.writev` and :func:`os.pwrite`. It writes the contents of *buffers* to file descriptor *fd* at offset *offset*. *buffers* must be a sequence of :term:`bytes-like objects <bytes-like object>`. Buffers are processed in array order. Entire contents of first buffer is written before proceeding to second, and so on. The operating system may set a limit (sysconf() value SC_IOV_MAX) on the number of buffers that can be used. :func:`~os.pwritev` writes the contents of each object to the file descriptor and returns the total number of bytes written. Write the *buffers* contents to file descriptor *fd* at a offset *offset*, leaving the file offset unchanged. *buffers* must be a sequence of :term:`bytes-like objects <bytes-like object>`. Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on.
The *flags* argument contains a bitwise OR of zero or more of the following The flags argument contains a bitwise OR of zero or more of the following flags:
- RWF_DSYNC - RWF_SYNC - :data:`RWF_DSYNC` - :data:`RWF_SYNC`
Using non-zero flags requires Linux 4.7 or newer. Return the total number of bytes actually written.
Availability: Linux (version 2.6.30), FreeBSD 6.0 and newer, OpenBSD (version 2.7 and newer). The operating system may set a limit (:func:`sysconf` value ``'SC_IOV_MAX'``) on the number of buffers that can be used.
Combine the functionality of :func:`os.writev` and :func:`os.pwrite`.
Availability: Linux 2.6.30 and newer, FreeBSD 6.0 and newer, OpenBSD 2.7 and newer. Using flags requires Linux 4.7 or newer.
.. versionadded:: 3.7
.. data:: RWF_DSYNC
Provide a per-write equivalent of the O_DSYNC open(2) flag. This flag is meaningful only for pwritev2(), and its effect applies only to the data range written by the system call. Provide a per-write equivalent of the :data:`O_DSYNC` ``open(2)`` flag. This flag effect applies only to the data range written by the system call.
Availability: Linux (version 4.7). Availability: Linux 4.7 and newer.
.. versionadded:: 3.7
.. data:: RWF_SYNC
Provide a per-write equivalent of the O_SYNC open(2) flag. This flag is meaningful only for pwritev2(), and its effect applies only to the data range written by the system call. Provide a per-write equivalent of the :data:`O_SYNC` ``open(2)`` flag. This flag effect applies only to the data range written by the system call.
Availability: Linux (version 4.7). Availability: Linux 4.7 and newer.
.. versionadded:: 3.7
.. function:: read(fd, n)
Read at most *n* bytes from file descriptor *fd*. Return a bytestring containing the bytes read. If the end of the file referred to by *fd* has been reached, an empty bytes object is returned. Read at most *n* bytes from file descriptor *fd*.
Return a bytestring containing the bytes read. If the end of the file referred to by *fd* has been reached, an empty bytes object is returned.
.. note::
Read from a file descriptor *fd* into a number of mutable :term:`bytes-like objects <bytes-like object>` *buffers*. :func:`~os.readv` will transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data. :func:`~os.readv` returns the total number of bytes read (which may be less than the total capacity of all the objects). objects <bytes-like object>` *buffers*. Transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data.
Availability: Unix.
.. versionadded:: 3.3 Return the total number of bytes actually read which can be less than the total capacity of all the objects.
The operating system may set a limit (:func:`sysconf` value ``'SC_IOV_MAX'``) on the number of buffers that can be used.
.. function:: preadv(fd, buffers, offset, flags=0)
Combines the functionality of :func:`os.readv` and :func:`os.pread`. It reads from a file descriptor *fd* into a number of mutable :term:`bytes-like objects <bytes-like object>` *buffers*. As :func:`os.readv`, it will transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data. Its fourth argument, *offset*, specifies the file offset at which the input operation is to be performed. :func:`~os.preadv` return the total number of bytes read (which can be less than the total capacity of all the objects).
The flags argument contains a bitwise OR of zero or more of the following flags:
- RWF_HIPRI - RWF_NOWAIT
Using non-zero flags requires Linux 4.6 or newer.
Availability: Linux (version 2.6.30), FreeBSD 6.0 and newer, OpenBSD (version 2.7 and newer).
.. versionadded:: 3.7
.. data:: RWF_HIPRI
High priority read/write. Allows block-based filesystems to use polling of the device, which provides lower latency, but may use additional resources. (Currently, this feature is usable only on a file descriptor opened using the O_DIRECT flag.)
Availability: Linux (version 4.6).
.. versionadded:: 3.7
.. data:: RWF_NOWAIT
Do not wait for data which is not immediately available. If this flag is specified, the preadv2() system call will return instantly if it would have to read data from the backing storage or wait for a lock. If some data was successfully read, it will return the number of bytes read. If no bytes were read, it will return -1 and set errno to EAGAIN. Currently, this flag is meaningful only for preadv2().
Availability: Linux (version 4.14). Availability: Unix.
.. versionadded:: 3.7 .. versionadded:: 3.3
.. function:: tcgetpgrp(fd)
.. function:: write(fd, str)
Write the bytestring in *str* to file descriptor *fd*. Return the number of bytes actually written. Write the bytestring in *str* to file descriptor *fd*.
Return the number of bytes actually written.
.. note::
.. function:: writev(fd, buffers)
Write the contents of *buffers* to file descriptor *fd*. *buffers* must be a sequence of :term:`bytes-like objects <bytes-like object>`. Buffers are processed in array order. Entire contents of first buffer is written before proceeding to second, and so on. The operating system may set a limit (sysconf() value SC_IOV_MAX) on the number of buffers that can be used. Write the contents of *buffers* to file descriptor *fd*. *buffers* must be a sequence of :term:`bytes-like objects <bytes-like object>`. Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on.
Returns the total number of bytes actually written.
:func:`~os.writev` writes the contents of each object to the file descriptor and returns the total number of bytes written. The operating system may set a limit (:func:`sysconf` value ``'SC_IOV_MAX'``) on the number of buffers that can be used.
Availability: Unix.