.\"	$NetBSD: devsw_attach.9,v 1.3 2017/04/30 12:30:00 pgoyette Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Kamil Rytarowski.
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.Dd April 30, 2017
.Dt DEVSW 9
.Os
.Sh NAME
.Nm devsw ,
.Nm devsw_attach ,
.Nm devsw_detach ,
.Nm bdevsw_lookup ,
.Nm cdevsw_lookup ,
.Nm bdevsw_lookup_major ,
.Nm cdevsw_lookup_major
.Nd character and block device switch functions
.Sh SYNOPSIS
.In sys/conf.h
.Ft int
.Fo devsw_attach
.Fa "const char *devname"
.Fa "const struct bdevsw *bev"
.Fa "devmajor_t *bmajor"
.Fa "const struct cdevsw *cdev"
.Fa "devmajor_t *cmajor"
.Fc
.Ft int
.Fo devsw_detach
.Fa "const struct bdevsw *bdev"
.Fa "const struct cdevsw *cdev"
.Fc
.Ft "const struct bdevsw *"
.Fo bdevsw_lookup
.Fa "dev_t dev"
.Fc
.Ft "const struct cdevsw *"
.Fo cdevsw_lookup
.Fa "dev_t dev"
.Fc
.Ft devmajor_t
.Fo bdevsw_lookup_major
.Fa "const struct bdevsw *bdev"
.Fc
.Ft devmajor_t
.Fo cdevsw_lookup_major
.Fa "const struct cdevsw *cdev"
.Fc
.Sh DESCRIPTION
If a device driver has character device interfaces accessed from
userland, the driver must define a
.Em cdevsw
structure.
If the driver also has block device interfaces, the driver must
additionally define a
.Em bdevsw
structure.
These structures are constant, and are defined within the
.Xr driver 9 .
.Pp
For drivers which are included in the kernel via
.Xr config 1 ,
the
.Em cdevsw
and
.Em bdevsw
structures are automatically linked into the configuration database.
For drivers which are separately loaded, the
.Fn devsw_attach
function creates the necessary linkage and associates the
.Em cdev
and optional
.Em bdev
with the
.Xr driver 9 .
If there is no block device interface needed,
.Em bdev
should be set to
.Dv NULL
and
.Em bmajor
to
.Dv \-1 .
The
.Em devname ,
major number, and device type
(character or block)
must correspond to the device file which will be opened by user programs.
By passing
.Dv \-1
to the function for the
.Em cmajor
or
.Em bmajor ,
the major number can be automatically generated.
It can then be returned to userspace (for example, using
.Xr sysctl 8 )
for creation of the device node.
.Pp
The
.Fn devsw_detach
function is used to detach the
.Em bdev
and
.Em cdev
structures.
.Fn devsw_detach
should be called before a loaded device driver is unloaded.
.Pp
The
.Fn bdevsw_lookup
and
.Fn cdevsw_lookup
functions return
.Em "const struct bdevsw *"
and
.Em "const struct cdevsw *"
for the given
.Em dev .
.Pp
The
.Fn bdevsw_lookup_major
and
.Fn cdevsw_lookup_major
functions return
.Em "devmajor_t"
for the given
.Em "const struct bdevsw *"
or
.Em "const struct cdevsw *" .
.Sh RETURN VALUES
Upon successful completion,
.Fn devsw_attach
and
.Fn devsw_detach
return 0.
Otherwise they return an error value.
.Pp
In case of failure,
.Fn bdevsw_lookup
and
.Fn cdevsw_lookup
return the
.Dv NULL
value.
.Pp
The
.Fn bdevsw_lookup_major
and
.Fn cdevsw_lookup_major
functions return
.Dv NODEVMAJOR
for an unsuccessful completion.
.Sh SEE ALSO
.Xr driver 9