svclock.c

讲述linux的初始化过程

					       * is a NLMv1,3 request */
#else
			/* no applicable NLM status */
#endif
		case EAGAIN:
			return nlm_lck_denied;
		default:			/* includes ENOLCK */
			return nlm_lck_denied_nolocks;
		}
	}

	if (!wait) {
		up(&file->f_sema);
		return nlm_lck_denied;
	}

	/* If we don't have a block, create and initialize it. Then
	 * retry because we may have slept in kmalloc. */
	if (block == NULL) {
		dprintk("lockd: blocking on this lock (allocating).\n");
		if (!(block = nlmsvc_create_block(rqstp, file, lock, cookie)))
			return nlm_lck_denied_nolocks;
		goto again;
	}

	/* Append to list of blocked */
	nlmsvc_insert_block(block, NLM_NEVER);

	if (list_empty(&block->b_call.a_args.lock.fl.fl_block)) {
		/* Now add block to block list of the conflicting lock
		   if we haven't done so. */
		dprintk("lockd: blocking on this lock.\n");
		posix_block_lock(conflock, &block->b_call.a_args.lock.fl);
	}

	up(&file->f_sema);
	return nlm_lck_blocked;
}

/*
 * Test for presence of a conflicting lock.
 */
u32
nlmsvc_testlock(struct nlm_file *file, struct nlm_lock *lock,
				       struct nlm_lock *conflock)
{
	struct file_lock	*fl;

	dprintk("lockd: nlmsvc_testlock(%04x/%ld, ty=%d, %Ld-%Ld)\n",
				file->f_file.f_dentry->d_inode->i_dev,
				file->f_file.f_dentry->d_inode->i_ino,
				lock->fl.fl_type,
				(long long)lock->fl.fl_start,
				(long long)lock->fl.fl_end);

	if ((fl = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
		dprintk("lockd: conflicting lock(ty=%d, %Ld-%Ld)\n",
				fl->fl_type, (long long)fl->fl_start,
				(long long)fl->fl_end);
		conflock->caller = "somehost";	/* FIXME */
		conflock->oh.len = 0;		/* don't return OH info */
		conflock->fl = *fl;
		return nlm_lck_denied;
	}

	return nlm_granted;
}

/*
 * Remove a lock.
 * This implies a CANCEL call: We send a GRANT_MSG, the client replies
 * with a GRANT_RES call which gets lost, and calls UNLOCK immediately
 * afterwards. In this case the block will still be there, and hence
 * must be removed.
 */
u32
nlmsvc_unlock(struct nlm_file *file, struct nlm_lock *lock)
{
	int	error;

	dprintk("lockd: nlmsvc_unlock(%04x/%ld, pi=%d, %Ld-%Ld)\n",
				file->f_file.f_dentry->d_inode->i_dev,
				file->f_file.f_dentry->d_inode->i_ino,
				lock->fl.fl_pid,
				(long long)lock->fl.fl_start,
				(long long)lock->fl.fl_end);

	/* First, cancel any lock that might be there */
	nlmsvc_cancel_blocked(file, lock);

	lock->fl.fl_type = F_UNLCK;
	error = posix_lock_file(&file->f_file, &lock->fl, 0);

	return (error < 0)? nlm_lck_denied_nolocks : nlm_granted;
}

/*
 * Cancel a previously blocked request.
 *
 * A cancel request always overrides any grant that may currently
 * be in progress.
 * The calling procedure must check whether the file can be closed.
 */
u32
nlmsvc_cancel_blocked(struct nlm_file *file, struct nlm_lock *lock)
{
	struct nlm_block	*block;

	dprintk("lockd: nlmsvc_cancel(%04x/%ld, pi=%d, %Ld-%Ld)\n",
				file->f_file.f_dentry->d_inode->i_dev,
				file->f_file.f_dentry->d_inode->i_ino,
				lock->fl.fl_pid,
				(long long)lock->fl.fl_start,
				(long long)lock->fl.fl_end);

	down(&file->f_sema);
	if ((block = nlmsvc_lookup_block(file, lock, 1)) != NULL)
		nlmsvc_delete_block(block, 1);
	up(&file->f_sema);
	return nlm_granted;
}

/*
 * Unblock a blocked lock request. This is a callback invoked from the
 * VFS layer when a lock on which we blocked is removed.
 *
 * This function doesn't grant the blocked lock instantly, but rather moves
 * the block to the head of nlm_blocked where it can be picked up by lockd.
 */
static void
nlmsvc_notify_blocked(struct file_lock *fl)
{
	struct nlm_block	**bp, *block;

	dprintk("lockd: VFS unblock notification for block %p\n", fl);
	posix_unblock_lock(fl);
	for (bp = &nlm_blocked; (block = *bp); bp = &block->b_next) {
		if (nlm_compare_locks(&block->b_call.a_args.lock.fl, fl)) {
			nlmsvc_insert_block(block, 0);
			svc_wake_up(block->b_daemon);
			return;
		}
	}

	printk(KERN_WARNING "lockd: notification for unknown block!\n");
}

/*
 * Try to claim a lock that was previously blocked.
 *
 * Note that we use both the RPC_GRANTED_MSG call _and_ an async
 * RPC thread when notifying the client. This seems like overkill...
 * Here's why:
 *  -	we don't want to use a synchronous RPC thread, otherwise
 *	we might find ourselves hanging on a dead portmapper.
 *  -	Some lockd implementations (e.g. HP) don't react to
 *	RPC_GRANTED calls; they seem to insist on RPC_GRANTED_MSG calls.
 */
static void
nlmsvc_grant_blocked(struct nlm_block *block)
{
	struct nlm_file		*file = block->b_file;
	struct nlm_lock		*lock = &block->b_call.a_args.lock;
	struct file_lock	*conflock;
	int			error;

	dprintk("lockd: grant blocked lock %p\n", block);

	/* First thing is lock the file */
	down(&file->f_sema);

	/* Unlink block request from list */
	nlmsvc_remove_block(block);

	/* If b_granted is true this means we've been here before.
	 * Just retry the grant callback, possibly refreshing the RPC
	 * binding */
	if (block->b_granted) {
		nlm_rebind_host(block->b_host);
		goto callback;
	}

	/* Try the lock operation again */
	if ((conflock = posix_test_lock(&file->f_file, &lock->fl)) != NULL) {
		/* Bummer, we blocked again */
		dprintk("lockd: lock still blocked\n");
		nlmsvc_insert_block(block, NLM_NEVER);
		posix_block_lock(conflock, &lock->fl);
		up(&file->f_sema);
		return;
	}

	/* Alright, no conflicting lock. Now lock it for real. If the
	 * following yields an error, this is most probably due to low
	 * memory. Retry the lock in a few seconds.
	 */
	if ((error = posix_lock_file(&file->f_file, &lock->fl, 0)) < 0) {
		printk(KERN_WARNING "lockd: unexpected error %d in %s!\n",
				-error, __FUNCTION__);
		nlmsvc_insert_block(block, 10 * HZ);
		up(&file->f_sema);
		return;
	}

callback:
	/* Lock was granted by VFS. */
	dprintk("lockd: GRANTing blocked lock.\n");
	block->b_granted = 1;
	block->b_incall  = 1;

	/* Schedule next grant callback in 30 seconds */
	nlmsvc_insert_block(block, 30 * HZ);

	/* Call the client */
	nlm_get_host(block->b_call.a_host);
	if (nlmsvc_async_call(&block->b_call, NLMPROC_GRANTED_MSG,
						nlmsvc_grant_callback) < 0)
		nlm_release_host(block->b_call.a_host);
	up(&file->f_sema);
}

/*
 * This is the callback from the RPC layer when the NLM_GRANTED_MSG
 * RPC call has succeeded or timed out.
 * Like all RPC callbacks, it is invoked by the rpciod process, so it
 * better not sleep. Therefore, we put the blocked lock on the nlm_blocked
 * chain once more in order to have it removed by lockd itself (which can
 * then sleep on the file semaphore without disrupting e.g. the nfs client).
 */
static void
nlmsvc_grant_callback(struct rpc_task *task)
{
	struct nlm_rqst		*call = (struct nlm_rqst *) task->tk_calldata;
	struct nlm_block	*block;
	unsigned long		timeout;

	dprintk("lockd: GRANT_MSG RPC callback\n");
	dprintk("callback: looking for cookie %x \n", 
		*(unsigned int *)(call->a_args.cookie.data));
	if (!(block = nlmsvc_find_block(&call->a_args.cookie))) {
		dprintk("lockd: no block for cookie %x\n", *(u32 *)(call->a_args.cookie.data));
		return;
	}

	/* Technically, we should down the file semaphore here. Since we
	 * move the block towards the head of the queue only, no harm
	 * can be done, though. */
	if (task->tk_status < 0) {
		/* RPC error: Re-insert for retransmission */
		timeout = 10 * HZ;
	} else if (block->b_done) {
		/* Block already removed, kill it for real */
		timeout = 0;
	} else {
		/* Call was successful, now wait for client callback */
		timeout = 60 * HZ;
	}
	nlmsvc_insert_block(block, timeout);
	svc_wake_up(block->b_daemon);
	block->b_incall = 0;

	nlm_release_host(call->a_host);
}

/*
 * We received a GRANT_RES callback. Try to find the corresponding
 * block.
 */
void
nlmsvc_grant_reply(struct nlm_cookie *cookie, u32 status)
{
	struct nlm_block	*block;
	struct nlm_file		*file;

	if (!(block = nlmsvc_find_block(cookie)))
		return;
	file = block->b_file;

	file->f_count++;
	down(&file->f_sema);
	if ((block = nlmsvc_find_block(cookie)) != NULL) {
		if (status == NLM_LCK_DENIED_GRACE_PERIOD) {
			/* Try again in a couple of seconds */
			nlmsvc_insert_block(block, 10 * HZ);
			block = NULL;
		} else {
			/* Lock is now held by client, or has been rejected.
			 * In both cases, the block should be removed. */
			file->f_count++;
			up(&file->f_sema);
			if (status == NLM_LCK_GRANTED)
				nlmsvc_delete_block(block, 0);
			else
				nlmsvc_delete_block(block, 1);
		}
	}
	if (!block)
		up(&file->f_sema);
	nlm_release_file(file);
}

/*
 * Retry all blocked locks that have been notified. This is where lockd
 * picks up locks that can be granted, or grant notifications that must
 * be retransmitted.
 */
unsigned long
nlmsvc_retry_blocked(void)
{
	struct nlm_block	*block;

	dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
			nlm_blocked,
			nlm_blocked? nlm_blocked->b_when : 0);
	while ((block = nlm_blocked)) {
		if (block->b_when == NLM_NEVER)
			break;
	        if (time_after(block->b_when,jiffies))
			break;
		dprintk("nlmsvc_retry_blocked(%p, when=%ld, done=%d)\n",
			block, block->b_when, block->b_done);
		if (block->b_done)
			nlmsvc_delete_block(block, 0);
		else
			nlmsvc_grant_blocked(block);
	}

	if ((block = nlm_blocked) && block->b_when != NLM_NEVER)
		return (block->b_when - jiffies);

	return MAX_SCHEDULE_TIMEOUT;
}