`b_dev' value of NODEV happens and is normal if the buffer is on its way
to the underlying device strategy function for the first time.
Also, MFS sillily uses a major device number (255) which cannot be used
to index bdevsw[]. Check marked with XXXs.
call biowait() but return `success' immediately. We can return `success'
because buffers with recorded errors are not returned by getblk().
(Takes care of PR#3694).
* When a delayed write buffer falls off the LRU queue, arrange for it to go on
the AGE queue after being flushed out to disk.
* When a delayed write buffer is synced, leave it in its relative position in
the LRU queue.
of using it directly, use a local, and set that local to be curproc
if curproc is not NULL else a pointer to process 0's proc struct.
If syncing disks while handling a panic that occurred while 'curproc'
was NULL, the old code would dereference NULL and die.
delayed write is logically converted to a sync write, mirroring the async case.
In bdwrite(), move the tape case earlier to avoid needless reassignbuf()s.
bawrite(). it's logically more correct (doesn't return an error code,
because it's async; bdwrite is also async), it still writes things
in-order, it makes sure the proper accountins is done (see the
wasdelayed cases in bwrite()), and it allows writes to vnodes on volumes
mountd with the MNT_ASYNC to be converted into delayed writes the way
God, err, Kirk intended. Convert synchronous bwrite()s on MNT_ASYNC
file systems to delayed writes.
explained in comments), which can cause a race condition. amazingly,
the _only_ time i've ever seen or heard of this problem was in some
comments and sources by Rick Macklem, and when running against the
a DEC OSF/1 NFS server running on an Alpha.
structural changes should happen, as it now does the right thing
w.r.t. buffer resizing and having lots of buffers vs. relatively
little buffer space. Ports can now "do the standard thing", re:
nbuf and bufpages, which is make nbuf = bufpages by default.
