.\" Copyright (c) 1999 Chris Costello
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.\" $FreeBSD: src/share/man/man9/make_dev.9,v 1.2.2.3 2001/12/17 11:30:18 ru Exp $
.\"
.Dd June 27, 2020
.Dt MAKE_DEV 9
.Os
.Sh NAME
.Nm destroy_dev ,
.Nm destroy_only_dev ,
.Nm devfs_scan_callback ,
.Nm dev_ops_intercept ,
.Nm dev_ops_remove_all ,
.Nm dev_ops_remove_minor ,
.Nm dev_ops_restore ,
.Nm make_dev ,
.Nm make_dev_alias ,
.Nm make_dev_covering ,
.Nm make_only_dev ,
.Nm reference_dev ,
.Nm release_dev
.Nd "device entry manipulation functions"
.Sh SYNOPSIS
.In sys/types.h
.In sys/conf.h
.In sys/devfs.h
.Ft void
.Fn destroy_dev "cdev_t dev"
.Ft void
.Fn destroy_only_dev "cdev_t dev"
.Ft int
.Fn devfs_scan_callback "devfs_scan_t *callback" "void *arg"
.Ft struct dev_ops *
.Fn dev_ops_intercept "cdev_t dev" "struct dev_ops *iops"
.Ft int
.Fn dev_ops_remove_all "struct dev_ops *ops"
.Ft void
.Fn dev_ops_restore "cdev_t dev" "struct dev_ops *oops"
.Ft int
.Fn dev_ops_remove_minor "struct dev_ops *ops" "int minor"
.Ft cdev_t
.Fn make_dev "struct dev_ops *ops" "int minor" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
.Ft int
.Fn make_dev_alias "cdev_t target" "const char *fmt" ...
.Ft cdev_t
.Fn make_dev_covering "struct dev_ops *ops" "struct dev_ops *bops" "int minor" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
.Ft cdev_t
.Fn make_only_dev "struct dev_ops *ops" "int minor" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
.Ft cdev_t
.Fn reference_dev "cdev_t dev"
.Ft void
.Fn release_dev "cdev_t dev"
.Sh DESCRIPTION
The
.Fn make_dev
function creates a
.Vt cdev_t
structure for a new device and makes the device name visible in the
.Xr devfs 5
mount points.
The device's name must be unique.
The name is the expansion of
.Fa fmt
and following arguments as
.Xr kprintf 9
would print it.
The name determines its path under
.Pa /dev .
The permissions of the file specified in
.Fa perms
are defined in
.In sys/stat.h :
.Pp
.Bd -literal -offset indent -compact
#define S_IRWXU 0000700    /* RWX mask for owner */
#define S_IRUSR 0000400    /* R for owner */
#define S_IWUSR 0000200    /* W for owner */
#define S_IXUSR 0000100    /* X for owner */

#define S_IRWXG 0000070    /* RWX mask for group */
#define S_IRGRP 0000040    /* R for group */
#define S_IWGRP 0000020    /* W for group */
#define S_IXGRP 0000010    /* X for group */

#define S_IRWXO 0000007    /* RWX mask for other */
#define S_IROTH 0000004    /* R for other */
#define S_IWOTH 0000002    /* W for other */
#define S_IXOTH 0000001    /* X for other */

#define S_ISUID 0004000    /* set user id on execution */
#define S_ISGID 0002000    /* set group id on execution */
#define S_ISVTX 0001000    /* sticky bit */
#if __BSD_VISIBLE
#define S_ISTXT 0001000
#endif
.Ed
.Pp
The
.Fa ops
argument is a pointer to a
.Vt dev_ops
data structure, which is defined as follows:
.Bd -literal
struct dev_ops {
        struct {
                const char      *name;  /* base name, e.g. 'da' */
                int              maj;   /* major device number */
                u_int            flags; /* D_XXX flags */
                void            *data;  /* custom driver data */
                int              refs;  /* ref count */
                int              id;
        } head;

#define dev_ops_first_field     d_default
        d_default_t     *d_default;
        d_open_t        *d_open;
        d_close_t       *d_close;
        d_read_t        *d_read;
        d_write_t       *d_write;
        d_ioctl_t       *d_ioctl;
        d_mmap_t        *d_mmap;
        d_strategy_t    *d_strategy;
        d_dump_t        *d_dump;
        d_psize_t       *d_psize;
        d_kqfilter_t    *d_kqfilter;
        d_clone_t       *d_clone;       /* clone from base dev_ops */
        d_revoke_t      *d_revoke;
#define dev_ops_last_field      d_revoke
};
.Ed
.Pp
While one can and should initialize the
.Fa name
and
.Fa maj
fields, they are effectively ignored.
Device major numbers are assigned automatically out of an internal pool of
major numbers, so there is no need to specify a unique major number in the
.Vt dev_ops
structure.
.Pp
Every member of the
.Fn d_xxx_t
family is defined as:
.Bd -literal
typedef int d_xxx_t (struct dev_xxx_args *ap);
.Ed
.Pp
Therefore, if one wants to implement a
.Fn mydev_open
function, this is the way:
.Bd -literal
d_open_t mydev_open;

int
mydev_open(struct dev_open_args *ap)
{
}
.Ed
.Pp
.Fn make_dev_covering
is equivalent to
.Fn make_dev ,
except that it also takes an argument
.Fa bops
which is set as the ops of the backing device for the newly created device.
This function should be used whenever a device is created covering
another raw device, as the disk subsystem does.
.Pp
.Fn make_only_dev
creates a
.Vt cdev_t
structure and initializes it in the same way as
.Fn make_dev
would, but the device will not appear in the
.Xr devfs 5
namespace.
This function is usually used in the clone handler of an autoclone device
created by
.Fn make_autoclone_dev .
.Pp
.Fn destroy_dev
takes the returned
.Vt cdev_t
from
.Fn make_dev
and destroys the registration for that device.
It should not be used to destroy a
.Vt cdev_t
created by
.Fn make_only_dev .
.Pp
.Fn destroy_only_dev
takes the returned
.Vt cdev_t
from
.Fn make_only_dev
and destroys the registration for that device.
It should not be used to destroy a
.Vt cdev_t
created by
.Fn make_dev .
.Pp
.Fn make_dev_alias
creates an automatic
.Xr devfs 5
link (alias) with the given name to the
.Vt cdev_t
specified by
.Fa target .
The
.Vt cdev_t
must have been created either by
.Fn make_dev
or bt a clone handler.
Aliases are alternative names for devices in the
.Xr devfs 5
namespace.
The lifetime of an alias is that of its associated
.Vt cdev_t .
Once the
.Vt cdev_t
is removed or destroyed, the alias is also destroyed and its name is
removed from the
.Xr devfs 5
namespace.
.Pp
.Fn reference_dev
adds a reference to
.Fa dev .
Callers generally add their own references when they are going to store a device
node in a variable for long periods of time, to prevent a disassociation from
freeing the node.
.Pp
.Fn release_dev
releases a reference on
.Fa dev .
The device will be terminated when the last reference has been released.
.Pp
.Fn dev_ops_intercept
intercepts the device operations vector of
.Fa dev
with
.Fa iops .
The old
.Vt dev_ops
is returned which may be used in a subsequent
.Fn dev_ops_restore
call.
The function sets the
.Dv SI_INTERCEPTED
flag in
.Fa dev .
.Pp
.Fn dev_ops_restore
restores the device operations vector of
.Fa dev
to
.Fa oops .
Also it unsets the
.Dv SI_INTERCEPTED
flag in
.Fa dev .
.Pp
.Fn dev_ops_remove_all
destroys all the
.Vt cdev_t
with the given
.Fa ops
and removes the devices from the
.Xr devfs 5
namespace.
This function is useful when uninitializing a driver.
.Pp
.Fn dev_ops_remove_minor
destroys all the
.Vt cdev_t
with the given
.Fa ops
and
.Fa minor
and removes the devices from the
.Xr devfs 5
namespace.
.Pp
.Fn devfs_scan_callback
calls the given
.Fa callback
function for every device registered in
.Xr devfs 5 .
The
.Fa callback
function has the following form:
.Bd -literal
devfs_scan_t mydev_scan_callback;

void
mydev_scan_callback(char *name, cdev_t dev, bool is_alias, void *arg)
{
};
.Ed
.Pp
The
.Fa name
argument is the alias' name (if
.Fa is_alias
is
.Dv true )
or the
.Vt cdev Ap s
.Fa si_name
field.
.Sh SEE ALSO
.Xr devfs 5 ,
.Xr make_autoclone_dev 9
.Sh HISTORY
The
.Fn make_dev
and
.Fn destroy_dev
functions first appeared in
.Fx 4.0 .
.Pp
A major overhaul of these functions occurred in
.Dx 2.3
with the addition of
.Xr devfs 5 .