MFC r326851:
In devfs_lookupx() dotdot lookup case, avoid dereferencing
dvp->v_mount after dvp is unlocked.

MFC r301928:
Only access vp->v_rdev for VCHR vnodes in devfs_reclaim().

MFC r298732:
sys/devfs: unsign an index to prevent signed integer overflow.

cdp_maxdirent in struct:cdev_priv is of type u_int. Use the same
type for the corresponding index in devfs_revoke().

MFC r293059:
Hide transient EBADF errors caused by the parallel revoke(2) or forced
unmount of devfs mounts, by restarting the failed syscall.

MFC 286974,291653:

286974:
Remove reference to non-existent kern_openat(9).

291653:
The cdevpriv_dtr_t typedef was not able to be used in a function prototype
like the various d_*_t typedefs since it declared a function pointer rather
than a function. Add a new d_priv_dtor_t typedef that declares the function
and can be used as a function prototype. The previous typedef wasn't
useful outside of the cdevpriv implementation, so retire it.

The name d_priv_dtor_t was chosen to be more consistent with cdev methods
since it is commonly used in place of d_close_t even though it is not a
direct pointer in struct cdevsw.

MFC r293042:
Minor style cleanup.

MFC r292621:
Keep devfs mount locked for the whole duration of the devfs_setattr(),
and ensure that our dirent is instantiated.

MFC r287033:

After r286237 it should be fine to call vgone(9) on a busy GEOM vnode;
remove KASSERT that would prevent forced devfs unmount from working.

Sponsored by: The FreeBSD Foundation

MFC r280308 (by delphij):
Disable timestamping on devfs read/write operations by default.

MFC r280949:
Refine r280308. Use seconds precision for devfs timestamps by default.

MFC r279362:
The VNASSERT in vflush() FORCECLOSE case is trying to panic early to
prevent errors from yanking devices out from under filesystems. Only
care about special vnodes on devfs, special nodes on other kinds of
filesystems do not have special properties.

MFC r277390:
Ignore devfs directory entries for devices being destroyed.

MFC r273131:
When vnode bypass cannot be performed on the cdev file descriptor for
read/write/poll/ioctl, call standard vnode filedescriptor fop.

MFC r267564:
In msdosfs_setattr(), add a check for result of the utimes(2) permissions test.
Refactor the permission checks for utimes(2).

MFC r256502:
Similar to debug.iosize_max_clamp sysctl, introduce
devfs_iosize_max_clamp sysctl, which allows/disables SSIZE_MAX-sized
i/o requests on the devfs files.

Approved by: re (glebius)

MFC r256501:
Remove two instances of ARGSUSED comment, and wrap lines nearby the
code that is to be changed.

Approved by: re (glebius)

MFC r280308 (by delphij):
Disable timestamping on devfs read/write operations by default.

MFC r280949:
Refine r280308. Use seconds precision for devfs timestamps by default.

MFC r279362:
The VNASSERT in vflush() FORCECLOSE case is trying to panic early to
prevent errors from yanking devices out from under filesystems. Only
care about special vnodes on devfs, special nodes on other kinds of
filesystems do not have special properties.

MFC r277390:
Ignore devfs directory entries for devices being destroyed.

MFC r273131:
When vnode bypass cannot be performed on the cdev file descriptor for
read/write/poll/ioctl, call standard vnode filedescriptor fop.

MFC r267564:
In msdosfs_setattr(), add a check for result of the utimes(2) permissions test.
Refactor the permission checks for utimes(2).

MFC r256502:
Similar to debug.iosize_max_clamp sysctl, introduce
devfs_iosize_max_clamp sysctl, which allows/disables SSIZE_MAX-sized
i/o requests on the devfs files.

Approved by: re (glebius)

MFC r256501:
Remove two instances of ARGSUSED comment, and wrap lines nearby the
code that is to be changed.

Approved by: re (glebius)