ioctl.html

unix 下的C开发手册,还用详细的例程。

<dt>I_NREAD<dd>
Counts the number of data bytes in the data part of the first message on the
STREAM head read queue and places this value in the
<b>int</b>
pointed to by
<i>arg</i>.  The return value for the command is the number of messages on the
STREAM head read queue.  For example, if 0 is returned in <i>arg</i>, but
the
<i>ioctl()</i>
return value is greater than 0, this indicates that a zero-length message
is next on the queue.
<p>
<dt>I_FDINSERT<dd>
Creates a message from specified buffer(s), adds information about another
STREAM, and sends the message downstream.  The message contains a control part
and an optional data part.  The data and control parts to be sent are
distinguished by placement in separate buffers, as described below.  The
<i>arg</i> argument points to a <b>strfdinsert</b> structure.
<p>
The <b>len</b> member in the <b>ctlbuf strbuf</b> structure must be set to the
size of a
<b>t_uscalar_t</b>
plus the number of bytes of control information to be sent
with the message.  The <b>fildes</b> member specifies the file descriptor of
the other STREAM, and the <b>offset</b> member,
which must be suitably aligned for use as a
<b>t_uscalar_t</b>,
specifies the offset from the start of the control buffer where
I_FDINSERT will store a
<b>t_uscalar_t</b>
whose interpretation is specific to the STREAM
end.  The <b>len</b> member in the <b>databuf strbuf</b> structure must be set
to the number of bytes of data information to be sent with the message, or to
0 if no data part is to be sent.
<p>
The <b>flags</b> member specifies the type of message to be created.  A normal
message is created if <b>flags</b> is set to 0, and a high-priority message is
created if <b>flags</b> is set to RS_HIPRI.  For non-priority messages,
I_FDINSERT will block if the STREAM write queue is full due to internal flow
control conditions.  For priority messages, I_FDINSERT does not block on this
condition.  For non-priority messages, I_FDINSERT does not block when the
write queue is full and O_NONBLOCK is set.  Instead, it fails and sets
<i>errno</i> to [EAGAIN].
<p>
I_FDINSERT also blocks, unless prevented by lack of internal resources,
waiting for the availability of message blocks in the STREAM, regardless of
priority or whether O_NONBLOCK has been specified.  No partial message is
sent.
<p>
The
<i>ioctl()</i>
function with the I_FDINSERT command will fail if:
<dl compact>

<dt>[EAGAIN]<dd>
A non-priority message is specified, the O_NONBLOCK flag is set, and the
STREAM write queue is full due to internal flow control conditions.

<dt>[EAGAIN] or [ENOSR]<dd>

Buffers can not be allocated for the message that is to be created.

<dt>[EINVAL]<dd>
One of the following:
<ul>

<li>
The <i>fildes</i> member of the <b>strfdinsert</b> structure
is not a valid, open STREAM file descriptor.

<li>
The size of a
<b>t_uscalar_t</b>
plus <i>offset</i> is greater than the <i>len</i> member
for the buffer specified through <i>ctlbuf</i>.

<li>
The <i>offset</i> member does not specify a properly-aligned
location in the data buffer.

<li>
An undefined value is stored in <b>flags</b>.

</ul>

<dt>[ENXIO]<dd>
Hangup received on the STREAM identified by either the
<i>fildes</i>
argument or the <i>fildes</i> member of the <b>strfdinsert</b> structure.

<dt>[ERANGE]<dd>
The <i>len</i> member for the buffer specified through <i>databuf</i> does
not fall within the range specified by the maximum and minimum packet
sizes of the topmost STREAM module or the <i>len</i> member for
the buffer specified through <i>databuf</i> is larger than the maximum
configured size of the data part of a message; or the <i>len</i> member
for the buffer specified through <i>ctlbuf</i> is larger than the
maximum configured size of the control part of a message.

</dl>
<p>
<dt>I_STR<dd>
Constructs an internal STREAMS
<i>ioctl()</i>
message from the data pointed to by <i>arg</i>, and sends that message
downstream.
<p>
This mechanism is provided to send
<i>ioctl()</i>
requests to downstream modules and drivers.  It allows information to be sent
with
<i>ioctl()</i>,
and returns to the process any information sent upstream by the downstream
recipient.  I_STR blocks until the system responds with either a positive or
negative acknowledgement message, or until the request "times out" after some
period of time.  If the request times out, it fails with <i>errno</i> set to
[ETIME].
<p>
At most, one I_STR can be active on a STREAM.  Further I_STR calls will block
until the active I_STR completes at the STREAM head.  The default timeout
interval for these requests is 15 seconds.  The O_NONBLOCK
flag has no effect on this call.
<p>
To send requests downstream, <i>arg</i> must point to a <b>strioctl</b>
structure.
<p>
The <b>ic_cmd</b> member is the internal
<i>ioctl()</i>
command intended for a downstream
module or driver and <b>ic_timout</b> is the number of seconds (-1 =
infinite, 0 = use implementation-dependent timeout
interval, &gt;0 = as specified) an I_STR
request will wait for acknowledgement before timing out.
<b>ic_len</b> is the number of bytes in the data argument, and
<b>ic_dp</b> is a pointer to the data argument.
The <b>ic_len</b> member has two uses:  on input, it contains the length of the
data argument passed in, and on return from the command, it contains the
number of bytes being returned to the process (the buffer pointed to by
<b>ic_dp</b> should be large enough to contain the maximum amount of data that
any module or the driver in the STREAM can return).
<p>
The STREAM head will convert the information pointed to by the
<b>strioctl</b> structure to an internal
<i>ioctl()</i>
command message and send it downstream.
<p>
The
<i>ioctl()</i>
function with the I_STR command will fail if:
<dl compact>

<dt>[EAGAIN] or [ENOSR]<dd>

Unable to allocate buffers for the
<i>ioctl()</i>
message.

<dt>[EINVAL]<dd>
The <i>ic_len</i> member
is less than 0 or larger than the maximum configured size of the
data part of a message, or <i>ic_timout</i> is less than -1.

<dt>[ENXIO]<dd>
Hangup received on <i>fildes</i>.

<dt>[ETIME]<dd>
A downstream
<i>ioctl()</i>
timed out before acknowledgement was received.

</dl>
<p>
An I_STR can also fail while waiting for an acknowledgement if a message
indicating an error or a hangup is received at the STREAM head.  In addition,
an error code can be returned in the positive or negative acknowledgement
message, in the event the
<i>ioctl()</i>
command sent downstream fails.  For these cases, I_STR fails with <i>errno</i>
set to the value in the message.
<p>
<dt>I_SWROPT<dd>
Sets the write mode using the value of the argument <i>arg</i>.
Valid bit settings for <i>arg</i> are:
<dl compact>

<dt>SNDZERO<dd>
Send a zero-length message downstream when a
<i><a href="write.html">write()</a></i>
of 0 bytes occurs.  To not send a zero-length message when a
<i><a href="write.html">write()</a></i>
of 0 bytes occurs, this bit must not be set in <i>arg</i>
(for example, <i>arg</i> would be set to 0).

</dl>
<p>
The
<i>ioctl()</i>
function with the I_SWROPT command will fail if:
<dl compact>

<dt>[EINVAL]<dd>
<i>arg</i> is not the above value.

</dl>
<p>
<dt>I_GWROPT<dd>
Returns the current write mode setting, as described above, in the <b>int</b>
that is pointed to by the argument <i>arg</i>.
<p>
<dt>I_SENDFD<dd>
I_SENDFD creates a new reference to the open file description associated with
the file descriptor
<i>arg,</i>
and writes a message on the STREAMS-based pipe
<i>fildes</i>
containing this reference, together with the user ID and group ID of the
calling process.
<p>
The
<i>ioctl()</i>
function with the I_SENDFD command will fail if:
<dl compact>

<dt>[EAGAIN]<dd>
The sending STREAM is unable to allocate a message block to contain the file
pointer; or the read queue of the receiving STREAM head is full and
cannot accept the message sent by I_SENDFD.

<dt>[EBADF]<dd>
The <i>arg</i> argument is not a valid, open file descriptor.

<dt>[EINVAL]<dd>
The <i>fildes</i> argument is not connected to a STREAM pipe.

<dt>[ENXIO]<dd>
Hangup received on <i>fildes</i>.

</dl>
<p>
<dt>I_RECVFD<dd>
Retrieves the reference to an open file description from a message written to
a STREAMS-based pipe using the I_SENDFD command, and allocates a new file
descriptor in the calling process that refers to this open file description.
The <i>arg</i> argument is a pointer to
an <b>strrecvfd</b> data structure as defined in
<i><a href="stropts.h.html">&lt;stropts.h&gt;</a></i>.
<p>
The <b>fd</b> member is a file descriptor.  The <b>uid</b> and <b>gid</b> members
are the effective user ID and effective group ID, respectively, of the sending
process.
<p>
If O_NONBLOCK is not set I_RECVFD blocks until a message is present at the
STREAM head.  If O_NONBLOCK is set, I_RECVFD fails with <i>errno</i> set to
[EAGAIN] if no message is present at the STREAM head.
<p>
If the message at the STREAM head is a message sent by an I_SENDFD, a new file
descriptor is allocated for the open file descriptor referenced in the
message.  The new file descriptor is placed in the <b>fd</b> member of the
<b>strrecvfd</b> structure pointed to by <i>arg</i>.
<p>
The
<i>ioctl()</i>
function with the I_RECVFD command will fail if:
<dl compact>

<dt>[EAGAIN]<dd>
A message is not present at the STREAM head read queue and the O_NONBLOCK flag
is set.

<dt>[EBADMSG]<dd>
The message at the STREAM head read queue is not
a message containing a passed file descriptor.

<dt>[EMFILE]<dd>
The process has the maximum number of file descriptors currently open that
it is allowed.

<dt>[ENXIO]<dd>
Hangup received on <i>fildes</i>.

</dl>
<p>
<dt>I_LIST<dd>
This request allows the process to list all the module names on the STREAM, up
to and including the topmost driver name.  If <i>arg</i> is a null pointer, the
return value is the number of modules, including the driver, that are on the
STREAM pointed to by <i>fildes</i>.  This lets the process allocate enough
space for the module names.  Otherwise, it should point to an <b>str_list</b>
structure.
<p>
The <b>sl_nmods</b> member indicates the number of entries the process has
allocated in the array.  Upon return, the <b>sl_modlist</b> member of the
<b>str_list</b> structure contains the list of module names, and the number of
entries that have been filled into the <b>sl_modlist</b> array is found in the
<b>sl_nmods</b> member (the number includes the number of modules including the
driver).  The return value from
<i>ioctl()</i>
is 0.  The entries are filled in starting at the top of the STREAM and
continuing downstream until either the end of the STREAM is reached, or
the number of requested modules (<b>sl_nmods</b>) is satisfied.
<p>
The
<i>ioctl()</i>
function with the I_LIST command will fail if:
<dl compact>

<dt>[EINVAL]<dd>
The <b>sl_nmods</b> member is less than 1.

<dt>[EAGAIN] or [ENOSR]<dd>

Unable to allocate buffers.

</dl>
<p>
<dt>I_ATMARK<dd>
This request allows the process to see if the message at the head of the STREAM
head read queue is marked by some module downstream.  The <i>arg</i>
argument determines how the checking is done when there may be multiple marked
messages on the STREAM head read queue.  It may take on the following values:
<dl compact>

<dt>ANYMARK<dd>
Check if the message is marked.

<dt>LASTMARK<dd>
Check if the message is the last one marked on the queue.

</dl>
<p>
The bitwise inclusive OR of the flags ANYMARK and LASTMARK is permitted.
<p>
The return value is 1 if the mark condition is satisfied and 0 otherwise.
<p>
The
<i>ioctl()</i>
function with the I_ATMARK command will fail if:
<dl compact>

<dt>[EINVAL]<dd>
Invalid <i>arg</i> value.