s/a_fdidx/a_fp/ for VOP_OPEN comments that inline struct vop_open_args
definition.

MFC r193924:
Fix r193923 by noting that type of a_fp is struct file *, not int.

Do not use casts (int *)0 and (struct thread *)0 for the arguments of
vn_rdwr, use NULL.

  Add support for inode sizes other than 128 bytes.
  Cleanup.

Fix two issues with bufdaemon, often causing the processes to hang in
the "nbufkv" sleep.

Do not retry request for the new block from ffs_bufwrite() when write is done
from bufdaemon and there is a buffer shortage.

In getnewbuf(), help bufdaemon to flush dirty buffers owned by the vnode
locked by curthread.

For MFC, default value for sysctl vfs.flushbufqtarget is set to -1,
disabling the helpers. The TDP_BUFNEED flag value from HEAD conflicts
with TDP_UPCALLING KSE bit, so it is moved to the end of allocated bits.

According to phk@, VOP_STRATEGY should never, _ever_, return
anything other than 0.  Make it so.  This fixes
"panic: VOP_STRATEGY failed bp=0xc320dd90 vp=0xc3b9f648",
encountered when writing to an orphaned filesystem.  Reason
for the panic was the following assert:
KASSERT(i == 0, ("VOP_STRATEGY failed bp=%p vp=%p", bp, bp->b_vp));
at vfs_bio:bufstrategy().

Reviewed by:	scottl, phk
Approved by:	rwatson (mentor)
Sponsored by:	FreeBSD Foundation

Garbage-collect vn_write_suspend_wait().

Initialize birthtime fields in vn_stat() to prevent stat(2) from
returning uninitialized birthtime. Most file systems don't initialize
birthtime properly in their VOP_GETTATTR().

MFC r183212:
Initialize va_flags and va_filerev properly in VOP_GETATTR(). Don't
initialize va_vaflags and va_spare because they are not part of the
VOP_GETATTR() API. Also don't initialize birthtime to ctime or zero.

MFC rr183213:
Initialize va_rdev to NODEV and va_fsid to VNOVAL before the
VOP_GETATTR() call in vn_stat(). Thus if a file system doesn't
initialize those fields in VOP_GETATTR() they will have a sane default
value.

MFC r183214:
Initialize va_rdev to NODEV instead of 0 or VNOVAL in VOP_GETATTR().
NODEV is more appropriate when va_rdev doesn't have a meaningful value.

MFC r183215:
fdescfs, devfs, mqueuefs, nfs, portalfs, pseudofs, tmpfs and xfs
initialize the vattr structure in VOP_GETATTR() with VATTR_NULL(),
vattr_null() or by zeroing it. Remove these to allow preinitialization
of fields work in vn_stat(). This is needed to get birthtime initialized
correctly.

Do not incorrectly add the low 5 bits of the offset to the resulting
position of the found zero bit.

Move the head of byte-level advisory lock list from the
filesystem-specific vnode data to the struct vnode. Provide the
default implementation for the vop_advlock and vop_advlockasync.
Purge the locks on the vnode reclaim by using the lf_purgelocks().
The default implementation is augmented for the nfs and smbfs.
In the nfs_advlock, push the Giant inside the nfs_dolock.

Before the change, the vop_advlock and vop_advlockasync have taken the
unlocked vnode and dereferenced the fs-private inode data, racing with
with the vnode reclamation due to forced unmount. Now, the vop_getattr
under the shared vnode lock is used to obtain the inode size, and
later, in the lf_advlockasync, after locking the vnode interlock, the
VI_DOOMED flag is checked to prevent an operation on the doomed vnode.

MFC r178247:
Fix compilation with LOCKF_DEBUG.

As was announced on the stable@, the MFC changes the VFS KBI on RELENG_7.

Approved by:	re (kensmith)

so that filesystems will consider 'nonofoo' a valid option.