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MAKE_DEV(9)            FreeBSD Kernel Developer's Manual           MAKE_DEV(9)

NAME
     make_dev, make_dev_cred, make_dev_credf, make_dev_p, make_dev_s,
     make_dev_alias, make_dev_alias_p, destroy_dev, destroy_dev_sched,
     destroy_dev_sched_cb, destroy_dev_drain, dev_depends - manage cdev's and
     DEVFS registration for devices

SYNOPSIS
     #include <sys/param.h>
     #include <sys/conf.h>

     void
     make_dev_args_init(struct make_dev_args *args);

     int
     make_dev_s(struct make_dev_args *args, struct cdev **cdev,
         const char *fmt, ...);

     int
     make_dev_alias_p(int flags, struct cdev **cdev, struct cdev *pdev,
         const char *fmt, ...);

     void
     destroy_dev(struct cdev *dev);

     void
     destroy_dev_sched(struct cdev *dev);

     void
     destroy_dev_sched_cb(struct cdev *dev, void (*cb)(void *), void *arg);)(void *), void *arg);

     void
     destroy_dev_drain(struct cdevsw *csw);

     void
     dev_depends(struct cdev *pdev, struct cdev *cdev);

     LEGACY INTERFACES
     struct cdev *
     make_dev(struct cdevsw *cdevsw, int unit, uid_t uid, gid_t gid,
         int perms, const char *fmt, ...);

     struct cdev *
     make_dev_cred(struct cdevsw *cdevsw, int unit, struct ucred *cr,
         uid_t uid, gid_t gid, int perms, const char *fmt, ...);

     struct cdev *
     make_dev_credf(int flags, struct cdevsw *cdevsw, int unit,
         struct ucred *cr, uid_t uid, gid_t gid, int perms, const char *fmt,
         ...);

     int
     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,
         ...);

     struct cdev *
     make_dev_alias(struct cdev *pdev, const char *fmt, ...);

DESCRIPTION
     The make_dev_s() function creates a cdev structure for a new device,
     which is returned into the cdev argument.  It also notifies devfs(5) of
     the presence of the new device, that causes corresponding nodes to be
     created.  Besides this, a devctl(4) notification is sent.  The function
     takes the structure struct make_dev_args args, which specifies the
     parameters for the device creation:

           struct make_dev_args {
                   size_t           mda_size;
                   int              mda_flags;
                   struct cdevsw   *mda_devsw;
                   struct ucred    *mda_cr;
                   uid_t            mda_uid;
                   gid_t            mda_gid;
                   int              mda_mode;
                   int              mda_unit;
                   void            *mda_si_drv1;
                   void            *mda_si_drv2;
           };
     Before use and filling with the desired values, the structure must be
     initialized by the make_dev_args_init() function, which ensures that
     future kernel interface expansion does not affect driver source code or
     binary interface.

     The created device will be owned by args.mda_uid, with the group
     ownership as args.mda_gid.  The name is the expansion of fmt and
     following arguments as printf(9) would print it.  The name determines its
     path under /dev or other devfs(5) mount point and may contain slash `/'
     characters to denote subdirectories.  The permissions of the file
     specified in args.mda_mode are defined in <sys/stat.h>:

           #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 */
           #ifndef _POSIX_SOURCE
           #define S_ISTXT 0001000
           #endif

     The args.mda_cr argument specifies credentials that will be stored in the
     si_cred member of the initialized struct cdev.

     The args.mda_flags argument alters the operation of make_dev_s.() The
     following values are currently accepted:

           MAKEDEV_REF              reference the created device
           MAKEDEV_NOWAIT           do not sleep, the call may fail
           MAKEDEV_WAITOK           allow the function to sleep to satisfy
                                    malloc
           MAKEDEV_ETERNAL          created device will be never destroyed
           MAKEDEV_CHECKNAME        return an error if the device name is
                                    invalid or already exists

     Only MAKEDEV_NOWAIT, MAKEDEV_WAITOK and MAKEDEV_CHECKNAME values are
     accepted for the make_dev_alias_p() function.

     The MAKEDEV_WAITOK flag is assumed if none of MAKEDEV_WAITOK,
     MAKEDEV_NOWAIT is specified.

     The dev_clone(9) event handler shall specify MAKEDEV_REF flag when
     creating a device in response to lookup, to avoid race where the device
     created is destroyed immediately after devfs_lookup(9) drops his
     reference to cdev.

     The MAKEDEV_ETERNAL flag allows the kernel to not acquire some locks when
     translating system calls into the cdevsw methods calls.  It is
     responsibility of the driver author to make sure that destroy_dev() is
     never called on the returned cdev.  For the convenience, use the
     MAKEDEV_ETERNAL_KLD flag for the code that can be compiled into kernel or
     loaded (and unloaded) as loadable module.

     A panic will occur if the MAKEDEV_CHECKNAME flag is not specified and the
     device name is invalid or already exists.

     The make_dev_p() use of the form

           struct cdev *dev;
           int res;
           res = make_dev_p(flags, &dev, cdevsw, cred, uid, gid, perms, name);
     is equivalent to the code

           struct cdev *dev;
           struct make_dev_args args;
           int res;

           make_dev_args_init(&args);
           args.mda_flags = flags;
           args.mda_devsw = cdevsw;
           args.mda_cred = cred;
           args.mda_uid = uid;
           args.mda_gid = gid;
           args.mda_mode = perms;
           res = make_dev_s(&args, &dev, name);

     Similarly, the make_dev_credf() function call is equivalent to

                   (void) make_dev_s(&args, &dev, name);
     In other words, make_dev_credf() does not allow the caller to obtain the
     return value, and in kernels compiled with the INVARIANTS options, the
     function asserts that the device creation succeeded.

     The make_dev_cred() function is equivalent to the call

           make_dev_credf(0, cdevsw, unit, cr, uid, gid, perms, fmt, ...);

     The make_dev() function call is the same as

           make_dev_credf(0, cdevsw, unit, NULL, uid, gid, perms, fmt, ...);

     The make_dev_alias_p() function takes the returned cdev from make_dev()
     and makes another (aliased) name for this device.  It is an error to call
     make_dev_alias_p() prior to calling make_dev().

     The make_dev_alias() function is similar to make_dev_alias() but it
     returns the resulting aliasing *cdev and may not return an error.

     The cdev returned by make_dev_s() and make_dev_alias_p() has two fields,
     si_drv1 and si_drv2, that are available to store state.  Both fields are
     of type void *, and can be initialized simultaneously with the cdev
     allocation by filling args.mda_si_drv1 and args.mda_si_drv2 members of
     the make_dev_s() argument structure, or filled after the cdev is
     allocated, if using legacy interfaces.  In the latter case, the driver
     should handle the race of accessing uninitialized si_drv1 and si_drv2
     itself.  These are designed to replace the unit argument to make_dev(),
     which can be obtained with dev2unit().

     The destroy_dev() function takes the returned cdev from make_dev() and
     destroys the registration for that device.  The notification is sent to
     devctl(4) about the destruction event.  Do not call destroy_dev() on
     devices that were created with make_dev_alias().

     The dev_depends() function establishes a parent-child relationship
     between two devices.  The net effect is that a destroy_dev() of the
     parent device will also result in the destruction of the child device(s),
     if any exist.  A device may simultaneously be a parent and a child, so it
     is possible to build a complete hierarchy.

     The destroy_dev_sched_cb() function schedules execution of the
     destroy_dev() for the specified cdev in the safe context.  After
     destroy_dev() is finished, and if the supplied cb is not NULL, the
     callback cb is called, with argument arg.  The destroy_dev_sched()
     function is the same as

           destroy_dev_sched_cb(cdev, NULL, NULL);

     The d_close() driver method cannot call destroy_dev() directly.  Doing so
     causes deadlock when destroy_dev() waits for all threads to leave the
     driver methods.  Also, because destroy_dev() sleeps, no non-sleepable
     locks may be held over the call.  The destroy_dev_sched() family of
     functions overcome these issues.

     The device driver may call the destroy_dev_drain() function to wait until
     all devices that have supplied csw as cdevsw, are destroyed.  This is
     useful when driver knows that destroy_dev_sched() is called for all
     instantiated devices, but need to postpone module unload until
     destroy_dev() is actually finished for all of them.

RETURN VALUES
     If successful, make_dev_s() and make_dev_p() will return 0, otherwise
     they will return an error.  If successful, make_dev_credf() will return a
     valid cdev pointer, otherwise it will return NULL.

ERRORS
     The make_dev_s(), make_dev_p() and make_dev_alias_p() calls will fail and
     the device will be not registered if:

     [ENOMEM]           The MAKEDEV_NOWAIT flag was specified and a memory
                        allocation request could not be satisfied.

     [ENAMETOOLONG]     The MAKEDEV_CHECKNAME flag was specified and the
                        provided device name is longer than SPECNAMELEN.

     [EINVAL]           The MAKEDEV_CHECKNAME flag was specified and the
                        provided device name is empty, contains a "." or ".."
                        path component or ends with `/'.

     [EINVAL]           The MAKEDEV_CHECKNAME flag was specified and the
                        provided device name contains invalid characters.

     [EEXIST]           The MAKEDEV_CHECKNAME flag was specified and the
                        provided device name already exists.

SEE ALSO
     devctl(4), devfs(5), dev_clone(9)

HISTORY
     The make_dev() and destroy_dev() functions first appeared in FreeBSD 4.0.
     The function make_dev_alias() first appeared in FreeBSD 4.1.  The
     function dev_depends() first appeared in FreeBSD 5.0.  The functions
     make_dev_credf(), destroy_dev_sched(), destroy_dev_sched_cb() first
     appeared in FreeBSD 7.0.  The function make_dev_p() first appeared in
     FreeBSD 8.2.  The function make_dev_s() first appeared in FreeBSD 11.0.

FreeBSD 11.1-RELEASE-p4          March 2, 2016         FreeBSD 11.1-RELEASE-p4
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