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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH open 9E "24 Apr 2008" "SunOS 5.11" "Driver Entry Points" .SH NAME open \- gain access to a device .SH SYNOPSIS .SS "Block and Character" .LP .nf #include #include #include #include #include #include #include \fBint prefix\fR\fBopen\fR(\fBdev_t *\fR\fIdevp\fR, \fBint\fR \fIflag\fR, \fBint\fR \fIotyp\fR, \fBcred_t *\fR\fIcred_p\fR); .fi .SS "STREAMS" .LP .nf #include #include #include #include \fBint prefix\fR\fBopen\fR(\fBqueue_t *\fR\fIq\fR, \fBdev_t *\fR\fIdevp\fR, \fBint\fR \fIoflag\fR, \fBint\fR \fIsflag\fR, \fBcred_t *\fR\fIcred_p\fR); .fi .SH INTERFACE LEVEL .sp .LP Architecture independent level 1 (DDI/DKI). This entry point is required, but it can be \fBnulldev\fR(9F) .SH PARAMETERS .SS "Block and Character" .sp .ne 2 .mk .na \fB\fIdevp\fR\fR .ad .RS 10n .rt Pointer to a device number. .RE .sp .ne 2 .mk .na \fB\fIflag\fR\fR .ad .RS 10n .rt A bit field passed from the user program \fBopen\fR(2) system call that instructs the driver on how to open the file. Valid settings are: .sp .ne 2 .mk .na \fB\fBFEXCL\fR\fR .ad .RS 11n .rt Open the device with exclusive access; fail all other attempts to open the device. .RE .sp .ne 2 .mk .na \fB\fBFNDELAY\fR\fR .ad .RS 11n .rt Open the device and return immediately. Do not block the open even if something is wrong. .RE .sp .ne 2 .mk .na \fB\fBFREAD\fR\fR .ad .RS 11n .rt Open the device with read-only permission, If \fBOR\fRed with \fBFWRITE\fR, allow both read and write access. .RE .sp .ne 2 .mk .na \fB\fBFWRITE\fR\fR .ad .RS 11n .rt Open a device with write-only permission. If ORed with \fBFREAD\fR, allow both read and write access. .RE .RE .sp .ne 2 .mk .na \fB\fIotyp\fR\fR .ad .RS 10n .rt Parameter supplied for driver to determine how many times a device was opened and for what reasons. For \fBOTYP_BLK\fR and \fBOTYP_CHR\fR, the \fBopen()\fR function can be called many times, but the \fBclose\fR(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 \fBclose\fR(2) or \fBexit\fR(2). If the device is accessed through memory mapping, it is done by a call to \fBmunmap\fR(2) or \fBexit\fR(2). For \fBOTYP_LYR\fR, there is exactly one \fBclose\fR(9E) for each \fBopen()\fR operation that is called. This permits software drivers to exist above hardware drivers and removes any ambiguity from the hardware driver regarding how a device is used. .sp .ne 2 .mk .na \fB\fBOTYP_BLK\fR\fR .ad .RS 12n .rt Open occurred through block interface for the device. .RE .sp .ne 2 .mk .na \fB\fBOTYP_CHR\fR\fR .ad .RS 12n .rt Open occurred through the raw/character interface for the device. .RE .sp .ne 2 .mk .na \fB\fBOTYP_LYR\fR\fR .ad .RS 12n .rt Open a layered process. This flag is used when one driver calls another driver's \fBopen()\fR or \fBclose\fR(9E) function. The calling driver ensures that there is one-layered close for each layered open. This flag applies to both block and character devices. .RE .RE .sp .ne 2 .mk .na \fB\fIcred_p\fR\fR .ad .RS 10n .rt Pointer to the user credential structure. .RE .SS "STREAMS" .sp .ne 2 .mk .na \fB\fIq\fR\fR .ad .RS 10n .rt A pointer to the read \fBqueue\fR. .RE .sp .ne 2 .mk .na \fB\fIdevp\fR\fR .ad .RS 10n .rt Pointer to a device number. For \fBSTREAMS \fRmodules, \fIdevp\fR always points to the device number associated with the driver at the end (tail) of the stream. .RE .sp .ne 2 .mk .na \fB\fIoflag\fR\fR .ad .RS 10n .rt Valid \fIoflag\fR values are \fBFEXCL\fR, \fBFNDELAY\fR, \fBFREAD\fR, and \fBFWRITEL\fR \(em the same as those listed above for \fIflag.\fR. For \fBSTREAMS\fR modules, \fIoflag\fR is always set to \fB0\fR. .RE .sp .ne 2 .mk .na \fB\fIsflag\fR\fR .ad .RS 10n .rt Valid values are as follows: .sp .ne 2 .mk .na \fB\fBCLONEOPEN\fR\fR .ad .RS 13n .rt Indicates that the \fBopen()\fR function is called through the clone driver. The driver should return a unique device number. .RE .sp .ne 2 .mk .na \fB\fBMODOPEN\fR\fR .ad .RS 13n .rt Modules should be called with \fIsflag\fR set to this value. Modules should return an error if they are called with \fIsflag\fR set to a different value. Drivers should return an error if they are called with \fIsflag\fR set to this value. .RE .sp .ne 2 .mk .na \fB\fB0\fR\fR .ad .RS 13n .rt Indicates a driver is opened directly, without calling the clone driver. .RE .RE .sp .ne 2 .mk .na \fB\fIcred_p\fR\fR .ad .RS 10n .rt Pointer to the user credential structure. .RE .SH DESCRIPTION .sp .LP The driver's \fBopen()\fR function is called by the kernel during an \fBopen\fR(2) or a \fBmount\fR(2) on the special file for the device. A device can be opened simultaneously by multiple processes and the \fBopen()\fR driver operation is called for each open. Note that a device is referenced once its associated \fBopen\fR(9E) function is entered, and thus \fBopen\fR(9E) operations which have not yet completed will prevent \fBclose\fR(9E) from being called. The function should verify that the minor number component of \fI*devp\fR is valid, that the type of access requested by \fIotyp\fR and \fIflag\fR is appropriate for the device, and, if required, check permissions using the user credentials pointed to by \fIcred_p\fR. .sp .LP The kernel provides \fBopen()\fR \fBclose()\fR exclusion guarantees to the driver at *\fIdevp\fR, \fIotyp\fR granularity. This delays new \fBopen()\fR calls to the driver while a last-reference \fBclose()\fR call is executing. If the driver has indicated that an \fBEINTR\fR returns safe via the \fBD_OPEN_RETURNS_EINTR\fR \fBcb_ops\fR(9S) \fBcb_flag\fR, a delayed \fBopen()\fR may be interrupted by a signal that results in an \fBEINTR\fR return. .sp .LP Last-reference accounting and \fBopen()\fR \fBclose()\fR 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 \fBopen\fR(9E), as described below, or implement multiple minor nodes for the same device. Both techniques give the driver control over when \fBclose()\fR calls occur and whether additional \fBopen()\fR calls will be delayed while \fBclose()\fR is executing. .sp .LP The \fBopen()\fR 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 \fBattach\fR(9E) with \fBddi_create_minor_node\fR(9F). It then changes the minor number component of \fI*devp\fR using \fBmakedevice\fR(9F) and \fBgetmajor\fR(9F). The driver needs to keep track of available minor numbers internally. A driver that dynamically creates 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 \fBclose()\fR call occurs. .sp .in +2 .nf *devp = makedevice(getmajor(*devp), new_minor); .fi .in -2 .SH RETURN VALUES .sp .LP The \fBopen()\fR function should return \fB0\fR for success, or the appropriate error number. .SH SEE ALSO .sp .LP \fBclose\fR(2), \fBexit\fR(2), \fBmmap\fR(2), \fBmount\fR(2), \fBmunmap\fR(2), \fBopen\fR(2), \fBIntro\fR(9E), \fBattach\fR(9E), \fBclose\fR(9E), \fBddi_create_minor_node\fR(9F), \fBgetmajor\fR(9F), \fBgetminor\fR(9F), \fBmakedevice\fR(9F), \fBnulldev\fR(9F), \fBcb_ops\fR(9S) .sp .LP \fIWriting Device Drivers\fR .sp .LP \fISTREAMS Programming Guide\fR .SH WARNINGS .sp .LP Do not attempt to change the major number. .sp .LP 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 \fBCLONE_DEV\fR in \fBddi_create_minor_node\fR(9F) is not supported.