svclock.c

ARM 嵌入式 系统 设计与实例开发 实验教材 二源码

/*
 * linux/fs/lockd/svclock.c
 *
 * Handling of server-side locks, mostly of the blocked variety.
 * This is the ugliest part of lockd because we tread on very thin ice.
 * GRANT and CANCEL calls may get stuck, meet in mid-flight, etc.
 * IMNSHO introducing the grant callback into the NLM protocol was one
 * of the worst ideas Sun ever had. Except maybe for the idea of doing
 * NFS file locking at all.
 *
 * I'm trying hard to avoid race conditions by protecting most accesses
 * to a file's list of blocked locks through a semaphore. The global
 * list of blocked locks is not protected in this fashion however.
 * Therefore, some functions (such as the RPC callback for the async grant
 * call) move blocked locks towards the head of the list *while some other
 * process might be traversing it*. This should not be a problem in
 * practice, because this will only cause functions traversing the list
 * to visit some blocks twice.
 *
 * Copyright (C) 1996, Olaf Kirch <[e-mail]>
 */

#include <linux/config.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp_lock.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/svc.h>
#include <linux/lockd/nlm.h>
#include <linux/lockd/lockd.h>

#define NLMDBG_FACILITY		NLMDBG_SVCLOCK

#ifdef CONFIG_LOCKD_V4
#define nlm_deadlock	nlm4_deadlock
#else
#define nlm_deadlock	nlm_lck_denied
#endif

static void	nlmsvc_insert_block(struct nlm_block *block, unsigned long);
static int	nlmsvc_remove_block(struct nlm_block *block);
static void	nlmsvc_grant_callback(struct rpc_task *task);
static void	nlmsvc_notify_blocked(struct file_lock *);

/*
 * The list of blocked locks to retry
 */
static struct nlm_block *	nlm_blocked;

/*
 * Insert a blocked lock into the global list
 */
static void
nlmsvc_insert_block(struct nlm_block *block, unsigned long when)
{
	struct nlm_block **bp, *b;

	dprintk("lockd: nlmsvc_insert_block(%p, %ld)\n", block, when);
	if (block->b_queued)
		nlmsvc_remove_block(block);
	bp = &nlm_blocked;
	if (when != NLM_NEVER) {
		if ((when += jiffies) == NLM_NEVER)
			when ++;
		while ((b = *bp) && time_before_eq(b->b_when,when))
			bp = &b->b_next;
	} else
		while ((b = *bp))
			bp = &b->b_next;

	block->b_queued = 1;
	block->b_when = when;
	block->b_next = b;
	*bp = block;
}

/*
 * Remove a block from the global list
 */
static int
nlmsvc_remove_block(struct nlm_block *block)
{
	struct nlm_block **bp, *b;

	if (!block->b_queued)
		return 1;
	for (bp = &nlm_blocked; (b = *bp); bp = &b->b_next) {
		if (b == block) {
			*bp = block->b_next;
			block->b_queued = 0;
			return 1;
		}
	}

	return 0;
}

/*
 * Find a block for a given lock and optionally remove it from
 * the list.
 */
static struct nlm_block *
nlmsvc_lookup_block(struct nlm_file *file, struct nlm_lock *lock, int remove)
{
	struct nlm_block	**head, *block;
	struct file_lock	*fl;

	dprintk("lockd: nlmsvc_lookup_block f=%p pd=%d %Ld-%Ld ty=%d\n",
				file, lock->fl.fl_pid,
				(long long)lock->fl.fl_start,
				(long long)lock->fl.fl_end, lock->fl.fl_type);
	for (head = &nlm_blocked; (block = *head); head = &block->b_next) {
		fl = &block->b_call.a_args.lock.fl;
		dprintk("lockd: check f=%p pd=%d %Ld-%Ld ty=%d cookie=%x\n",
				block->b_file, fl->fl_pid,
				(long long)fl->fl_start,
				(long long)fl->fl_end, fl->fl_type,
				*(unsigned int*)(block->b_call.a_args.cookie.data));
		if (block->b_file == file && nlm_compare_locks(fl, &lock->fl)) {
			if (remove) {
				*head = block->b_next;
				block->b_queued = 0;
			}
			return block;
		}
	}

	return NULL;
}

static inline int nlm_cookie_match(struct nlm_cookie *a, struct nlm_cookie *b)
{
	if(a->len != b->len)
		return 0;
	if(memcmp(a->data,b->data,a->len))
		return 0;
	return 1;
}

/*
 * Find a block with a given NLM cookie.
 */
static inline struct nlm_block *
nlmsvc_find_block(struct nlm_cookie *cookie)
{
	struct nlm_block *block;

	for (block = nlm_blocked; block; block = block->b_next) {
		dprintk("cookie: head of blocked queue %p, block %p\n", 
			nlm_blocked, block);
		if (nlm_cookie_match(&block->b_call.a_args.cookie,cookie))
			break;
	}

	return block;
}

/*
 * Create a block and initialize it.
 *
 * Note: we explicitly set the cookie of the grant reply to that of
 * the blocked lock request. The spec explicitly mentions that the client
 * should _not_ rely on the callback containing the same cookie as the
 * request, but (as I found out later) that's because some implementations
 * do just this. Never mind the standards comittees, they support our
 * logging industries.
 */
static inline struct nlm_block *
nlmsvc_create_block(struct svc_rqst *rqstp, struct nlm_file *file,
				struct nlm_lock *lock, struct nlm_cookie *cookie)
{
	struct nlm_block	*block;
	struct nlm_host		*host;
	struct nlm_rqst		*call;

	/* Create host handle for callback */
	host = nlmclnt_lookup_host(&rqstp->rq_addr,
				rqstp->rq_prot, rqstp->rq_vers);
	if (host == NULL)
		return NULL;

	/* Allocate memory for block, and initialize arguments */
	if (!(block = (struct nlm_block *) kmalloc(sizeof(*block), GFP_KERNEL)))
		goto failed;
	memset(block, 0, sizeof(*block));
	locks_init_lock(&block->b_call.a_args.lock.fl);
	locks_init_lock(&block->b_call.a_res.lock.fl);

	if (!nlmclnt_setgrantargs(&block->b_call, lock))
		goto failed_free;

	/* Set notifier function for VFS, and init args */
	block->b_call.a_args.lock.fl.fl_notify = nlmsvc_notify_blocked;
	block->b_call.a_args.cookie = *cookie;	/* see above */

	dprintk("lockd: created block %p...\n", block);

	/* Create and initialize the block */
	block->b_daemon = rqstp->rq_server;
	block->b_host   = host;
	block->b_file   = file;

	/* Add to file's list of blocks */
	block->b_fnext  = file->f_blocks;
	file->f_blocks  = block;

	/* Set up RPC arguments for callback */
	call = &block->b_call;
	call->a_host    = host;
	call->a_flags   = RPC_TASK_ASYNC;

	return block;

failed_free:
	kfree(block);
failed:
	nlm_release_host(host);
	return NULL;
}

/*
 * Delete a block. If the lock was cancelled or the grant callback
 * failed, unlock is set to 1.
 * It is the caller's responsibility to check whether the file
 * can be closed hereafter.
 */
static void
nlmsvc_delete_block(struct nlm_block *block, int unlock)
{
	struct file_lock	*fl = &block->b_call.a_args.lock.fl;
	struct nlm_file		*file = block->b_file;
	struct nlm_block	**bp;

	dprintk("lockd: deleting block %p...\n", block);

	/* Remove block from list */
	nlmsvc_remove_block(block);

	/* If granted, unlock it, else remove from inode block list */
	if (unlock && block->b_granted) {
		dprintk("lockd: deleting granted lock\n");
		fl->fl_type = F_UNLCK;
		posix_lock_file(&block->b_file->f_file, fl, 0);
		block->b_granted = 0;
	} else {
		dprintk("lockd: unblocking blocked lock\n");
		posix_unblock_lock(fl);
	}

	/* If the block is in the middle of a GRANT callback,
	 * don't kill it yet. */
	if (block->b_incall) {
		nlmsvc_insert_block(block, NLM_NEVER);
		block->b_done = 1;
		return;
	}

	/* Remove block from file's list of blocks */
	for (bp = &file->f_blocks; *bp; bp = &(*bp)->b_fnext) {
		if (*bp == block) {
			*bp = block->b_fnext;
			break;
		}
	}

	if (block->b_host)
		nlm_release_host(block->b_host);
	nlmclnt_freegrantargs(&block->b_call);
	kfree(block);
}

/*
 * Loop over all blocks and perform the action specified.
 * (NLM_ACT_CHECK handled by nlmsvc_inspect_file).
 */
int
nlmsvc_traverse_blocks(struct nlm_host *host, struct nlm_file *file, int action)
{
	struct nlm_block	*block, *next;

	down(&file->f_sema);
	for (block = file->f_blocks; block; block = next) {
		next = block->b_fnext;
		if (action == NLM_ACT_MARK)
			block->b_host->h_inuse = 1;
		else if (action == NLM_ACT_UNLOCK) {
			if (host == NULL || host == block->b_host)
				nlmsvc_delete_block(block, 1);
		}
	}
	up(&file->f_sema);
	return 0;
}

/*
 * Attempt to establish a lock, and if it can't be granted, block it
 * if required.
 */
u32
nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
			struct nlm_lock *lock, int wait, struct nlm_cookie *cookie)
{
	struct file_lock	*conflock;
	struct nlm_block	*block;
	int			error;

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

	/* Lock file against concurrent access */
	down(&file->f_sema);

	/* Get existing block (in case client is busy-waiting) */
	block = nlmsvc_lookup_block(file, lock, 0);

	lock->fl.fl_flags |= FL_LOCKD;

again:
	if (!(conflock = posix_test_lock(&file->f_file, &lock->fl))) {
		error = posix_lock_file(&file->f_file, &lock->fl, 0);

		if (block)
			nlmsvc_delete_block(block, 0);
		up(&file->f_sema);

		dprintk("lockd: posix_lock_file returned %d\n", -error);
		switch(-error) {
		case 0:
			return nlm_granted;