48ce5d4cac
Immediate problem fixed by the new KPI is the long-standing race between device creation and assignments to cdev->si_drv1 and cdev->si_drv2, which allows the window where cdevsw methods might be called with si_drv1,2 fields not yet set. Devices typically checked for NULL and returned spurious errors to usermode, and often left some methods unchecked. The new function interface is designed to be extensible, which should allow to add more features to make_dev_s(9) without inventing yet another name for function to create devices, while maintaining KPI and even KBI backward-compatibility. Reviewed by: hps, jhb Sponsored by: The FreeBSD Foundation MFC after: 3 weeks Differential revision: https://reviews.freebsd.org/D4746
494 lines
12 KiB
Groff
494 lines
12 KiB
Groff
.\" Copyright (c) 1999 Chris Costello
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd Jan 3, 2016
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.Dt MAKE_DEV 9
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.Os
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.Sh NAME
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.Nm make_dev ,
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.Nm make_dev_cred ,
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.Nm make_dev_credf ,
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.Nm make_dev_p ,
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.Nm make_dev_s ,
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.Nm make_dev_alias ,
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.Nm make_dev_alias_p ,
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.Nm destroy_dev ,
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.Nm destroy_dev_sched ,
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.Nm destroy_dev_sched_cb ,
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.Nm destroy_dev_drain ,
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.Nm dev_depends
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.Nd manage
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.Vt cdev Ns 's
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and DEVFS registration for devices
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/conf.h
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.Ft void
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.Fn make_dev_args_init "struct make_dev_args *args"
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.Ft int
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.Fn make_dev_s "struct make_dev_args *args" "struct cdev **cdev" "const char *fmt" ...
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.Ft int
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.Fn make_dev_alias_p "int flags" "struct cdev **cdev" "struct cdev *pdev" "const char *fmt" ...
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.Ft void
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.Fn destroy_dev "struct cdev *dev"
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.Ft void
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.Fn destroy_dev_sched "struct cdev *dev"
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.Ft void
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.Fn destroy_dev_sched_cb "struct cdev *dev" "void (*cb)(void *)" "void *arg"
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.Ft void
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.Fn destroy_dev_drain "struct cdevsw *csw"
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.Ft void
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.Fn dev_depends "struct cdev *pdev" "struct cdev *cdev"
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.Pp
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LEGACY INTERFACES
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.Ft struct cdev *
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.Fn make_dev "struct cdevsw *cdevsw" "int unit" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
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.Ft struct cdev *
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.Fn make_dev_cred "struct cdevsw *cdevsw" "int unit" "struct ucred *cr" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
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.Ft struct cdev *
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.Fn make_dev_credf "int flags" "struct cdevsw *cdevsw" "int unit" "struct ucred *cr" "uid_t uid" "gid_t gid" "int perms" "const char *fmt" ...
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.Ft int
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.Fn make_dev_p "int flags" "struct cdev **cdev" "struct cdevsw *devsw" "struct ucred *cr" "uid_t uid" "gid_t gid" "int mode" "const char *fmt" ...
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.Ft struct cdev *
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.Fn make_dev_alias "struct cdev *pdev" "const char *fmt" ...
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.Sh DESCRIPTION
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The
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.Fn make_dev_s
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function creates a
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.Fa cdev
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structure for a new device, which is returned into the
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.Fa cdev
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argument.
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It also notifies
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.Xr devfs 5
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of the presence of the new device, that causes corresponding nodes
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to be created.
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Besides this, a
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.Xr devctl 4
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notification is sent.
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The function takes the structure
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.Va struct make_dev_args args ,
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which specifies the parameters for the device creation:
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.Pp
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.Bd -literal -offset indent -compact
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struct make_dev_args {
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size_t mda_size;
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int mda_flags;
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struct cdevsw *mda_devsw;
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struct ucred *mda_cr;
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uid_t mda_uid;
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gid_t mda_gid;
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int mda_mode;
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int mda_unit;
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void *mda_si_drv1;
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void *mda_si_drv2;
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};
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.Ed
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Before use and filling with the desired values, the structure must be
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initialized by the
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.Fn make_dev_args_init
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function, which ensures that future kernel interface expansion does
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not affect driver source code or binary interface.
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.Pp
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The created device will be owned by
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.Va args.mda_uid ,
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with the group ownership as
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.Va args.mda_gid .
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The name is the expansion of
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.Va fmt
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and following arguments as
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.Xr printf 9
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would print it.
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The name determines its path under
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.Pa /dev
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or other
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.Xr devfs 5
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mount point and may contain slash
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.Ql /
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characters to denote subdirectories.
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The permissions of the file specified in
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.Va args.mda_mode
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are defined in
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.In sys/stat.h :
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.Pp
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.Bd -literal -offset indent -compact
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#define S_IRWXU 0000700 /* RWX mask for owner */
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#define S_IRUSR 0000400 /* R for owner */
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#define S_IWUSR 0000200 /* W for owner */
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#define S_IXUSR 0000100 /* X for owner */
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#define S_IRWXG 0000070 /* RWX mask for group */
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#define S_IRGRP 0000040 /* R for group */
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#define S_IWGRP 0000020 /* W for group */
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#define S_IXGRP 0000010 /* X for group */
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#define S_IRWXO 0000007 /* RWX mask for other */
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#define S_IROTH 0000004 /* R for other */
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#define S_IWOTH 0000002 /* W for other */
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#define S_IXOTH 0000001 /* X for other */
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#define S_ISUID 0004000 /* set user id on execution */
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#define S_ISGID 0002000 /* set group id on execution */
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#define S_ISVTX 0001000 /* sticky bit */
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#ifndef _POSIX_SOURCE
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#define S_ISTXT 0001000
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#endif
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.Ed
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.Pp
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The
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.Va args.mda_cr
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argument specifies credentials that will be stored in the
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.Fa si_cred
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member of the initialized
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.Fa struct cdev .
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.Pp
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The
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.Va args.mda_flags
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argument alters the operation of
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.Fn make_dev_s.
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The following values are currently accepted:
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.Pp
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.Bl -tag -width "It Dv MAKEDEV_CHECKNAME" -compact -offset indent
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.It Dv MAKEDEV_REF
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reference the created device
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.It Dv MAKEDEV_NOWAIT
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do not sleep, the call may fail
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.It Dv MAKEDEV_WAITOK
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allow the function to sleep to satisfy malloc
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.It Dv MAKEDEV_ETERNAL
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created device will be never destroyed
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.It Dv MAKEDEV_CHECKNAME
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return an error if the device name is invalid or already exists
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.El
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.Pp
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Only
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.Dv MAKEDEV_NOWAIT ,
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.Dv MAKEDEV_WAITOK
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and
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.Dv MAKEDEV_CHECKNAME
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values are accepted for the
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.Fn make_dev_alias_p
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function.
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.Pp
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The
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.Dv MAKEDEV_WAITOK
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flag is assumed if none of
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.Dv MAKEDEV_WAITOK ,
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.Dv MAKEDEV_NOWAIT
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is specified.
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.Pp
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The
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.Xr dev_clone 9
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event handler shall specify
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.Dv MAKEDEV_REF
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flag when creating a device in response to lookup, to avoid race where
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the device created is destroyed immediately after
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.Xr devfs_lookup 9
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drops his reference to cdev.
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.Pp
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The
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.Dv MAKEDEV_ETERNAL
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flag allows the kernel to not acquire some locks when translating system
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calls into the cdevsw methods calls.
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It is responsibility of the driver author to make sure that
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.Fn destroy_dev
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is never called on the returned cdev.
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For the convenience, use the
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.Dv MAKEDEV_ETERNAL_KLD
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flag for the code that can be compiled into kernel or loaded
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(and unloaded) as loadable module.
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.Pp
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A panic will occur if the
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.Dv MAKEDEV_CHECKNAME
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flag is not specified
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and the device name is invalid or already exists.
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.Pp
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The
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.Fn make_dev_p
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use of the form
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.Bd -literal -offset indent
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struct cdev *dev;
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int res;
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res = make_dev_p(flags, &dev, cdevsw, cred, uid, gid, perms, name);
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.Ed
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is equivalent to the code
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.Bd -literal -offset indent
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struct cdev *dev;
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struct make_dev_args args;
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int res;
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make_dev_args_init(&args);
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args.mda_flags = flags;
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args.mda_devsw = cdevsw;
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args.mda_cred = cred;
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args.mda_uid = uid;
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args.mda_gid = gid;
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args.mda_mode = perms;
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res = make_dev_s(&args, &dev, name);
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.Ed
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.Pp
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Similarly, the
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.Fn make_dev_credf
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function call is equivalent to
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.Bd -literal -offset indent
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(void) make_dev_s(&args, &dev, name);
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.Ed
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In other words,
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.Fn make_dev_credf
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does not allow the caller to obtain the return value, and in
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kernels compiled with the
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.Va INVARIANTS
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options, the function asserts that the device creation succeeded.
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.Pp
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The
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.Fn make_dev_cred
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function is equivalent to the call
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.Bd -literal -offset indent
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make_dev_credf(0, cdevsw, unit, cr, uid, gid, perms, fmt, ...);
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.Ed
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.Pp
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The
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.Fn make_dev
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function call is the same as
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.Bd -literal -offset indent
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make_dev_credf(0, cdevsw, unit, NULL, uid, gid, perms, fmt, ...);
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.Ed
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.Pp
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The
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.Fn make_dev_alias_p
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function takes the returned
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.Ft cdev
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from
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.Fn make_dev
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and makes another (aliased) name for this device.
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It is an error to call
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.Fn make_dev_alias_p
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prior to calling
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.Fn make_dev .
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.Pp
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The
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.Fn make_dev_alias
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function is similar to
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.Fn make_dev_alias
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but it returns the resulting aliasing
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.Ft *cdev
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and may not return an error.
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.Pp
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The
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.Fa cdev
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returned by
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.Fn make_dev_s
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and
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.Fn make_dev_alias_p
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has two fields,
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.Fa si_drv1
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and
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.Fa si_drv2 ,
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that are available to store state.
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Both fields are of type
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.Ft void * ,
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and can be initialized simultaneously with the
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.Va cdev
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allocation by filling
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.Va args.mda_si_drv1
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and
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.Va args.mda_si_drv2
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members of the
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.Fn make_dev_s
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argument structure, or filled after the
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.Va cdev
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is allocated, if using legacy interfaces.
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In the latter case, the driver should handle the race of
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accessing uninitialized
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.Va si_drv1
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and
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.Va si_drv2
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itself.
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These are designed to replace the
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.Fa unit
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argument to
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.Fn make_dev ,
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which can be obtained with
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.Fn dev2unit .
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.Pp
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The
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.Fn destroy_dev
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function takes the returned
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.Fa cdev
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from
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.Fn make_dev
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and destroys the registration for that device.
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The notification is sent to
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.Xr devctl 4
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about the destruction event.
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Do not call
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.Fn destroy_dev
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on devices that were created with
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.Fn make_dev_alias .
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.Pp
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The
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.Fn dev_depends
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function establishes a parent-child relationship between two devices.
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The net effect is that a
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.Fn destroy_dev
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of the parent device will also result in the destruction of the
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child device(s),
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if any exist.
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A device may simultaneously be a parent and a child,
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so it is possible to build a complete hierarchy.
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.Pp
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The
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.Fn destroy_dev_sched_cb
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function schedules execution of the
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.Fn destroy_dev
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for the specified
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.Fa cdev
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in the safe context.
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After
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.Fn destroy_dev
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is finished, and if the supplied
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.Fa cb
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is not
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.Dv NULL ,
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the callback
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.Fa cb
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is called, with argument
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.Fa arg .
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The
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.Fn destroy_dev_sched
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function is the same as
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.Bd -literal -offset indent
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destroy_dev_sched_cb(cdev, NULL, NULL);
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.Ed
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.Pp
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The
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.Fn d_close
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driver method cannot call
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.Fn destroy_dev
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directly.
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Doing so causes deadlock when
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.Fn destroy_dev
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waits for all threads to leave the driver methods.
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Also, because
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.Fn destroy_dev
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sleeps, no non-sleepable locks may be held over the call.
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The
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.Fn destroy_dev_sched
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family of functions overcome these issues.
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.Pp
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The device driver may call the
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.Fn destroy_dev_drain
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function to wait until all devices that have supplied
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.Fa csw
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as cdevsw, are destroyed.
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This is useful when driver knows that
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.Fn destroy_dev_sched
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is called for all instantiated devices, but need to postpone module
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unload until
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.Fn destroy_dev
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is actually finished for all of them.
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.Sh RETURN VALUES
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If successful,
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.Fn make_dev_s
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and
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.Fn make_dev_p
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will return 0, otherwise they will return an error.
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If successful,
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.Fn make_dev_credf
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will return a valid
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.Fa cdev
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pointer, otherwise it will return
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.Dv NULL .
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.Sh ERRORS
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The
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.Fn make_dev_s ,
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.Fn make_dev_p
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and
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.Fn make_dev_alias_p
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calls will fail and the device will be not registered if:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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The
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.Dv MAKEDEV_NOWAIT
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flag was specified and a memory allocation request could not be satisfied.
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.It Bq Er ENAMETOOLONG
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The
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.Dv MAKEDEV_CHECKNAME
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flag was specified and the provided device name is longer than
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.Dv SPECNAMELEN .
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.It Bq Er EINVAL
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The
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.Dv MAKEDEV_CHECKNAME
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flag was specified and the provided device name is empty, contains a
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.Qq \&.
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or
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.Qq ..
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path component or ends with
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.Ql / .
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.It Bq Er EINVAL
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The
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.Dv MAKEDEV_CHECKNAME
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flag was specified and the provided device name contains invalid characters.
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.It Bq Er EEXIST
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The
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.Dv MAKEDEV_CHECKNAME
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|
flag was specified and the provided device name already exists.
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.El
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.Sh SEE ALSO
|
|
.Xr devctl 4 ,
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|
.Xr devfs 5 ,
|
|
.Xr destroy_dev_drain 9 ,
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.Xr dev_clone 9
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|
.Sh HISTORY
|
|
The
|
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.Fn make_dev
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and
|
|
.Fn destroy_dev
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|
functions first appeared in
|
|
.Fx 4.0 .
|
|
The function
|
|
.Fn make_dev_alias
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|
first appeared in
|
|
.Fx 4.1 .
|
|
The function
|
|
.Fn dev_depends
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|
first appeared in
|
|
.Fx 5.0 .
|
|
The functions
|
|
.Fn make_dev_credf ,
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.Fn destroy_dev_sched ,
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|
.Fn destroy_dev_sched_cb
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|
first appeared in
|
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.Fx 7.0 .
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|
The function
|
|
.Fn make_dev_p
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|
first appeared in
|
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.Fx 8.2 .
|
|
The function
|
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.Fn make_dev_s
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|
first appeared in
|
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.Fx 11.0 .
|