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.Dd February 2, 2023 .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 n 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 void .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 .Vt cdevsw structure. If the driver also has block device interfaces, the driver must additionally define a .Vt bdevsw structure. These structures are constant, and are defined within the .Xr driver 9 .
p For drivers which are included in the kernel via .Xr config 1 , the .Vt cdevsw and .Vt 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 .Fa cdev and optional .Fa bdev with the .Xr driver 9 . If there is no block device interface needed, .Fa bdev should be set to .Dv NULL and .Fa bmajor to .Dv NODEVMAJOR . The .Fa 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 NODEVMAJOR to the function for the .Fa cmajor or .Fa bmajor , the major number can be automatically generated. It can then be returned to userspace
o for example, using .Xr sysctl 8
c for creation of the device node.
p The .Fn devsw_detach function is used to detach the .Fa bdev and .Fa cdev structures. .Fn devsw_detach should be called before a loaded device driver is unloaded. The caller must ensure that there are no open instances of the device, and that the device's .Fa d_open function will fail, before calling .Fn devsw_detach .
p The .Fn bdevsw_lookup and .Fn cdevsw_lookup functions return .Vt "const struct bdevsw *" and .Vt "const struct cdevsw *" for the given .Fa dev .
p The .Fn bdevsw_lookup_major and .Fn cdevsw_lookup_major functions return .Vt "devmajor_t" for the given .Vt "const struct bdevsw *" or .Vt "const struct cdevsw *" . .Sh RETURN VALUES Upon successful completion, .Fn devsw_attach returns 0. Otherwise it returns an error value.
p In case of failure, .Fn bdevsw_lookup and .Fn cdevsw_lookup return the .Dv NULL value.
p The .Fn bdevsw_lookup_major and .Fn cdevsw_lookup_major functions return .Dv NODEVMAJOR for an unsuccessful completion. .Sh SEE ALSO .Xr driver 9