CLOSE(9E) Driver Entry Points CLOSE(9E)

NAME

close - relinquish access to a device

SYNOPSIS

Block and Character

#include <sys/types.h>
#include <sys/file.h>
#include <sys/errno.h>
#include <sys/open.h>
#include <sys/cred.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>


int prefixclose(dev_t dev, int flag, int otyp, cred_t *cred_p);

STREAMS

#include <sys/types.h>
#include <sys/stream.h>
#include <sys/file.h>
#include <sys/errno.h>
#include <sys/open.h>
#include <sys/cred.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>


int prefixclose(queue_t *q, int flag, cred_t *cred_p);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI). This entry point is required
for block devices.

PARAMETERS

Block and Character

dev
Device number.


flag
File status flag, as set by the open(2) or modified by the
fcntl(2) system calls. The flag is for information only--the
file should always be closed completely. Possible values are:
FEXCL, FNDELAY, FREAD, FKLYR, and FWRITE. Refer to open(9E)
for more information.


otyp
Parameter supplied so that the driver can determine how many
times a device was opened and for what reasons. The flags
assume the open() routine may be called many times, but the
close() routine should only be called on the last close() of
a device.

OTYP_BLK
Close was through block interface for the device.


OTYP_CHR
Close was through the raw/character interface for
the device.


OTYP_LYR
Close a layered process (a higher-level driver
called the close() routine of the device).


*cred_p
Pointer to the user credential structure.

STREAMS

*q
Pointer to queue(9S) structure used to reference the read
side of the driver. (A queue is the central node of a
collection of structures and routines pointed to by a queue.)


flag
File status flag.


*cred_p
Pointer to the user credential structure.

DESCRIPTION

For STREAMS drivers, the close() routine is called by the kernel through
the cb_ops(9S) table entry for the device. (Modules use the fmodsw
table.) A non-null value in the d_str field of the cb_ops entry points
to a streamtab structure, which points to a qinit(9S) containing a
pointer to the close() routine. Non-STREAMS close() routines are called
directly from the cb_ops table.


close() ends the connection between the user process and the device, and
prepares the device (hardware and software) so that it is ready to be
opened again.


A device may be opened simultaneously by multiple processes and the
open() driver routine is called for each open. For all otyp values other
than OTYP_LYR, the kernel calls the close() routine when the last-
reference occurs. For OTYP_LYR each close operation will call the driver.


Kernel accounting for last-reference occurs at (dev, otyp) granularity.
Note that a device is referenced once its associated open(9E) routine is
entered, and thus open(9E)'s which have not yet completed will prevent
close() from being called. The driver's close() call associated with
the last-reference going away is typically issued as result of a
close(2), exit(2), munmap(2), or umount(2). However, a failed open(9E)
call can cause this last-reference close() call to be issued as a result
of an open(2) or mount(2).


The kernel provides open() close() exclusion guarantees to the driver at
the same devp, otyp granularity as last-reference accounting. The kernel
delays new calls to the open() driver routine while the last-reference
close() call is executing. For example, a driver that blocks in close()
will not see new calls to open() until it returns from close(). This
effectively delays invocation of other cb_ops(9S) driver entry points
that also depend on an open(9E) established device reference. If the
driver has indicated that an EINTR return is safe via the
D_OPEN_RETURNS_EINTR cb_flag, then a delayed open() may be interrupted by
a signal, resulting in an EINTR return from open() prior to calling
open(9E).


Last-reference accounting and open() close() exclusion typically simplify
driver writing. In some cases, however, they might be an impediment for
certain types of drivers. To overcome any impediment, the driver can
change minor numbers in open(9E), as described below, or implement
multiple minor nodes for the same device. Both techniques give the driver
control over when close() calls occur and whether additional open() calls
will be delayed while close() is executing.


In general, a close() routine should always check the validity of the
minor number component of the dev parameter. The routine should also
check permissions as necessary, by using the user credential structure
(if pertinent), and the appropriateness of the flag and otyp parameter
values.


close() could perform any of the following general functions:

o disable interrupts

o hang up phone lines

o rewind a tape

o deallocate buffers from a private buffering scheme

o unlock an unsharable device (that was locked in the open()
routine)

o flush buffers

o notify a device of the close

o deallocate any resources allocated on open


The close() routines of STREAMS drivers and modules are called when a
stream is dismantled or a module popped. The steps for dismantling a
stream are performed in the following order. First, any multiplexor links
present are unlinked and the lower streams are closed. Next, the
following steps are performed for each module or driver on the stream,
starting at the head and working toward the tail:

1. The write queue is given a chance to drain.

2. The close() routine is called.

3. The module or driver is removed from the stream.

RETURN VALUES

close() should return 0 for success, or the appropriate error number.
Return errors rarely occur, but if a failure is detected, the driver
should decide whether the severity of the problem warrants either
displaying a message on the console or, in worst cases, triggering a
system panic. Generally, a failure in a close() routine occurs because
a problem occurred in the associated device.

NOTES

If you use qwait_sig(9F), cv_wait_sig(9F) or cv_timedwait_sig(9F), you
should note that close() may be called in contexts in which signals
cannot be received. The ddi_can_receive_sig(9F) function is provided to
determine when this hazard exists.

SEE ALSO

close(2), fcntl(2), open(2), umount(2), detach(9E), open(9E),
ddi_can_receive_sig(9F), cb_ops(9S), qinit(9S), queue(9S)


Writing Device Drivers


STREAMS Programming Guide

April 24, 2008 CLOSE(9E)