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open(9e)
open(9E) Driver Entry Points open(9E)
NAME
open - gain 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 prefixopen(dev_t *devp, int flag, int otyp,
cred_t *cred_p);
STREAMS
#include <sys/file.h>
#include <sys/stream.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
int prefixopen(queue_t *q, dev_t *devp, int oflag, int sflag,
cred_t *cred_p);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI). This entry point is
required, but it can be nulldev(9F)
PARAMETERS
Block and Character
devp Pointer to a device number.
flag A bit field passed from the user program open(2) system call
that instructs the driver on how to open the file. Valid set‐
tings are:
FEXCL Open the device with exclusive access; fail all
other attempts to open the device.
FNDELAY Open the device and return immediately. Do not
block the open even if something is wrong.
FREAD Open the device with read-only permission, If ORed
with FWRITE, allow both read and write access.
FWRITE Open a device with write-only permission. If ORed
with FREAD, allow both read and write access.
otyp Parameter supplied for driver to determine how many times a
device was opened and for what reasons. For OTYP_BLK and
OTYP_CHR, the open() function can be called many times, but
the close(9E) function is called only when the last reference
to a device is removed. If the device is accessed through
file descriptors, it is done by a call to close(2) or
exit(2). If the device is accessed through memory mapping, it
is done by a call to munmap(2) or exit(2). For OTYP_LYR,
there is exactly one close(9E) for each open() operation that
is called. This permits software drivers to exist above hard‐
ware drivers and removes any ambiguity from the hardware
driver regarding how a device is used.
OTYP_BLK Open occurred through block interface for the
device.
OTYP_CHR Open occurred through the raw/character interface
for the device.
OTYP_LYR Open a layered process. This flag is used when
one driver calls another driver's open() or
close(9E) function. The calling driver ensures
that there is one-layered close for each layered
open. This flag applies to both block and charac‐
ter devices.
cred_p Pointer to the user credential structure.
STREAMS
q A pointer to the read queue.
devp Pointer to a device number. For STREAMS modules, devp always
points to the device number associated with the driver at the
end (tail) of the stream.
oflag Valid oflag values are FEXCL, FNDELAY, FREAD, and FWRITEL —
the same as those listed above for flag.. For STREAMS mod‐
ules, oflag is always set to 0.
sflag Valid values are as follows:
CLONEOPEN Indicates that the open() function is called
through the clone driver. The driver should
return a unique device number.
MODOPEN Modules should be called with sflag set to this
value. Modules should return an error if they
are called with sflag set to a different value.
Drivers should return an error if they are
called with sflag set to this value.
0 Indicates a driver is opened directly, without
calling the clone driver.
cred_p Pointer to the user credential structure.
DESCRIPTION
The driver's open() function is called by the kernel during an open(2)
or a mount(2) on the special file for the device. A device can be
opened simultaneously by multiple processes and the open() driver oper‐
ation is called for each open. Note that a device is referenced once
its associated open(9E) function is entered, and thus open(9E) opera‐
tions which have not yet completed will prevent close(9E) from being
called. The function should verify that the minor number component of
*devp is valid, that the type of access requested by otyp and flag is
appropriate for the device, and, if required, check permissions using
the user credentials pointed to by cred_p.
The kernel provides open() close() exclusion guarantees to the driver
at *devp, otyp granularity. This delays new open() calls to the driver
while a last-reference close() call is executing. If the driver has
indicated that an EINTR returns safe via the D_OPEN_RETURNS_EINTR
cb_ops(9S) cb_flag, a delayed open() may be interrupted by a signal
that results in an EINTR return.
Last-reference accounting and open() close() exclusion typically sim‐
plify driver writing. In some cases, however, they might be an impedi‐
ment 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 addi‐
tional open() calls will be delayed while close() is executing.
The open() function is passed a pointer to a device number so that the
driver can change the minor number. This allows drivers to dynamically
create minor instances of the device. An example of this might be a
pseudo-terminal driver that creates a new pseudo-terminal whenever it
is opened. A driver that chooses the minor number dynamically, normally
creates only one minor device node in attach(9E) with ddi_cre‐
ate_minor_node(9F). It then changes the minor number component of *devp
using makedevice(9F) and getmajor(9F). The driver needs to keep track
of available minor numbers internally. A driver that dynamically cre‐
ates minor numbers might want to avoid returning the original minor
number since returning the original minor will result in postponed
dynamic opens when original minor close() call occurs.
*devp = makedevice(getmajor(*devp), new_minor);
RETURN VALUES
The open() function should return 0 for success, or the appropriate
error number.
SEE ALSO
close(2), exit(2), mmap(2), mount(2), munmap(2), open(2), attach(9E),
close(9E), Intro(9E), ddi_create_minor_node(9F), getmajor(9F), getmi‐
nor(9F), makedevice(9F), nulldev(9F), cb_ops(9S)
Writing Device Drivers in Oracle Solaris 11.4
STREAMS Programming Guide
WARNINGS
Do not attempt to change the major number.
When a driver modifies the device number passed in, it must not change
the major number portion of the device number. Unless CLONEOPEN is
specified, the modified device number must map to the same driver
instance indicated by the driver's getinfo(9e) implementation. In other
words, cloning across different drivers is not supported. Cloning
across different instances of the same driver in only permitted if the
driver specified in CLONE_DEV in ddi_create_minor_node(9F) is not sup‐
ported.
Oracle Solaris 11.4 24 Apr 2008 open(9E)