clone.7 (2010 09)

clone(7) clone(7)

NAME

clone - opens a major and minor device pair on a STREAMS driver

DESCRIPTION

The

clone driver is a "pass through" device driver that allows other drivers to select unique minor dev-

ice numbers on each open(). In effect, the driver passes an open operation through to the other driver.

This mechanism allows for multiple instantiations of a driver, each with a different minor number,

through a single device ﬁle.

When the

clone driver is opened, it is passed a major and minor device number by the operating sys-

tem. The major number is the clone

driver’s major number (72), and the minor number is the major

number of the driver the user wishes to clone (referred to here as the target driver). The clone driver

calls the open routine of the target driver with the

CLONEOPEN ﬂag which speciﬁes a clone open. The

target driver’s open routine allocates an unused minor number. The target driver must use

makedev to

make a new device number for the newly created device, and must set

*devp to the new device number

returned by

makedev. The new device number is returned to the

clone open through *devp. The

clone open then returns to the user a ﬁle descriptor that points to the new instantiation of the target

driver.

The

echo driver is an example of a clonable driver.

Notes

It is not possible to do multiple opens of a device with the same major and minor number using the

clone driver. This is because the clone driver is only given the major number of the driver to be

cloned, and that driver will then select a minor number which has not been opened.

When called with a pathname which corresponds to the clonable driver,

stat() will return different

results than fstat() when it is called on a ﬁle descriptor returned from open() of the same clonable

driver pathname.

RETURN VALUES

If the

clone driver is given an invalid minor number, or if the driver indicated is not a clonable driver,

the open() fails and errno is set to [ENXIO].

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clone(7) clone(7) NAME clone - opens a major and minor device pair on a STREAMS driver DESCRIPTION The clone driver is a "pass through" device driver that allows other drivers to select unique minor device numbers on each open(). In effect, the driver passes an open operation through to the other driver. This mechanism allows for multiple instantiations of a driver, each with a different minor number, through a single device file.
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(Notes) A (Notes) cA 2 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010