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Diffstat (limited to 'Doc/library/fcntl.rst')
| -rw-r--r-- | Doc/library/fcntl.rst | 64 |
1 files changed, 32 insertions, 32 deletions
diff --git a/Doc/library/fcntl.rst b/Doc/library/fcntl.rst index 8e932fb954..432140f279 100644 --- a/Doc/library/fcntl.rst +++ b/Doc/library/fcntl.rst @@ -28,41 +28,41 @@ descriptor. The module defines the following functions: -.. function:: fcntl(fd, op[, arg]) +.. function:: fcntl(fd, cmd, arg=0) - Perform the operation *op* on file descriptor *fd* (file objects providing + Perform the operation *cmd* on file descriptor *fd* (file objects providing a :meth:`~io.IOBase.fileno` method are accepted as well). The values used - for *op* are operating system dependent, and are available as constants + for *cmd* are operating system dependent, and are available as constants in the :mod:`fcntl` module, using the same names as used in the relevant C - header files. The argument *arg* is optional, and defaults to the integer - value ``0``. When present, it can either be an integer value, or a string. - With the argument missing or an integer value, the return value of this function - is the integer return value of the C :c:func:`fcntl` call. When the argument is - a string it represents a binary structure, e.g. created by :func:`struct.pack`. - The binary data is copied to a buffer whose address is passed to the C - :c:func:`fcntl` call. The return value after a successful call is the contents - of the buffer, converted to a string object. The length of the returned string - will be the same as the length of the *arg* argument. This is limited to 1024 - bytes. If the information returned in the buffer by the operating system is - larger than 1024 bytes, this is most likely to result in a segmentation - violation or a more subtle data corruption. + header files. The argument *arg* can either be an integer value, or a + :class:`bytes` object. With an integer value, the return value of this + function is the integer return value of the C :c:func:`fcntl` call. When + the argument is bytes it represents a binary structure, e.g. created by + :func:`struct.pack`. The binary data is copied to a buffer whose address is + passed to the C :c:func:`fcntl` call. The return value after a successful + call is the contents of the buffer, converted to a :class:`bytes` object. + The length of the returned object will be the same as the length of the + *arg* argument. This is limited to 1024 bytes. If the information returned + in the buffer by the operating system is larger than 1024 bytes, this is + most likely to result in a segmentation violation or a more subtle data + corruption. If the :c:func:`fcntl` fails, an :exc:`OSError` is raised. -.. function:: ioctl(fd, op[, arg[, mutate_flag]]) +.. function:: ioctl(fd, request, arg=0, mutate_flag=True) This function is identical to the :func:`~fcntl.fcntl` function, except that the argument handling is even more complicated. - The op parameter is limited to values that can fit in 32-bits. - Additional constants of interest for use as the *op* argument can be + The *request* parameter is limited to values that can fit in 32-bits. + Additional constants of interest for use as the *request* argument can be found in the :mod:`termios` module, under the same names as used in the relevant C header files. - The parameter *arg* can be one of an integer, absent (treated identically to the - integer ``0``), an object supporting the read-only buffer interface (most likely - a plain Python string) or an object supporting the read-write buffer interface. + The parameter *arg* can be one of an integer, an object supporting the + read-only buffer interface (like :class:`bytes`) or an object supporting + the read-write buffer interface (like :class:`bytearray`). In all but the last case, behaviour is as for the :func:`~fcntl.fcntl` function. @@ -72,7 +72,7 @@ The module defines the following functions: If it is false, the buffer's mutability is ignored and behaviour is as for a read-only buffer, except that the 1024 byte limit mentioned above is avoided -- - so long as the buffer you pass is as least as long as what the operating system + so long as the buffer you pass is at least as long as what the operating system wants to put there, things should work. If *mutate_flag* is true (the default), then the buffer is (in effect) passed @@ -97,25 +97,25 @@ The module defines the following functions: array('h', [13341]) -.. function:: flock(fd, op) +.. function:: flock(fd, operation) - Perform the lock operation *op* on file descriptor *fd* (file objects providing + Perform the lock operation *operation* on file descriptor *fd* (file objects providing a :meth:`~io.IOBase.fileno` method are accepted as well). See the Unix manual :manpage:`flock(2)` for details. (On some systems, this function is emulated using :c:func:`fcntl`.) -.. function:: lockf(fd, operation, [length, [start, [whence]]]) +.. function:: lockf(fd, cmd, len=0, start=0, whence=0) This is essentially a wrapper around the :func:`~fcntl.fcntl` locking calls. - *fd* is the file descriptor of the file to lock or unlock, and *operation* + *fd* is the file descriptor of the file to lock or unlock, and *cmd* is one of the following values: * :const:`LOCK_UN` -- unlock * :const:`LOCK_SH` -- acquire a shared lock * :const:`LOCK_EX` -- acquire an exclusive lock - When *operation* is :const:`LOCK_SH` or :const:`LOCK_EX`, it can also be + When *cmd* is :const:`LOCK_SH` or :const:`LOCK_EX`, it can also be bitwise ORed with :const:`LOCK_NB` to avoid blocking on lock acquisition. If :const:`LOCK_NB` is used and the lock cannot be acquired, an :exc:`OSError` will be raised and the exception will have an *errno* @@ -124,7 +124,7 @@ The module defines the following functions: systems, :const:`LOCK_EX` can only be used if the file descriptor refers to a file opened for writing. - *length* is the number of bytes to lock, *start* is the byte offset at + *len* is the number of bytes to lock, *start* is the byte offset at which the lock starts, relative to *whence*, and *whence* is as with :func:`io.IOBase.seek`, specifically: @@ -133,7 +133,7 @@ The module defines the following functions: * :const:`2` -- relative to the end of the file (:data:`os.SEEK_END`) The default for *start* is 0, which means to start at the beginning of the file. - The default for *length* is 0 which means to lock to the end of the file. The + The default for *len* is 0 which means to lock to the end of the file. The default for *whence* is also 0. Examples (all on a SVR4 compliant system):: @@ -147,9 +147,9 @@ Examples (all on a SVR4 compliant system):: rv = fcntl.fcntl(f, fcntl.F_SETLKW, lockdata) Note that in the first example the return value variable *rv* will hold an -integer value; in the second example it will hold a string value. The structure -lay-out for the *lockdata* variable is system dependent --- therefore using the -:func:`flock` call may be better. +integer value; in the second example it will hold a :class:`bytes` object. The +structure lay-out for the *lockdata* variable is system dependent --- therefore +using the :func:`flock` call may be better. .. seealso:: |