/* -*- linux-c -*- --------------------------------------------------------- *
 *
 * drivers/staging/autofs/dirhash.c
 *
 *  Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * ------------------------------------------------------------------------- */

#include "autofs_i.h"

/* Functions for maintenance of expiry queue */

static void autofs_init_usage(struct autofs_dirhash *dh,
			      struct autofs_dir_ent *ent)
{
	list_add_tail(&ent->exp, &dh->expiry_head);
	ent->last_usage = jiffies;
}

static void autofs_delete_usage(struct autofs_dir_ent *ent)
{
	list_del(&ent->exp);
}

void autofs_update_usage(struct autofs_dirhash *dh,
			 struct autofs_dir_ent *ent)
{
	autofs_delete_usage(ent);   /* Unlink from current position */
	autofs_init_usage(dh, ent);  /* Relink at queue tail */
}

struct autofs_dir_ent *autofs_expire(struct super_block *sb,
				     struct autofs_sb_info *sbi,
				     struct vfsmount *mnt)
{
	struct autofs_dirhash *dh = &sbi->dirhash;
	struct autofs_dir_ent *ent;
	unsigned long timeout = sbi->exp_timeout;

	while (1) {
		struct path path;
		int umount_ok;

		if (list_empty(&dh->expiry_head) || sbi->catatonic)
			return NULL;	/* No entries */
		/* We keep the list sorted by last_usage and want old stuff */
		ent = list_entry(dh->expiry_head.next,
						struct autofs_dir_ent, exp);
		if (jiffies - ent->last_usage < timeout)
			break;
		/* Move to end of list in case expiry isn't desirable */
		autofs_update_usage(dh, ent);

		/* Check to see that entry is expirable */
		if (ent->ino < AUTOFS_FIRST_DIR_INO)
			return ent; /* Symlinks are always expirable */

		/* Get the dentry for the autofs subdirectory */
		path.dentry = ent->dentry;

		if (!path.dentry) {
			/* Should only happen in catatonic mode */
			printk(KERN_DEBUG "autofs: dentry == NULL but inode \
				range is directory, entry %s\n", ent->name);
			autofs_delete_usage(ent);
			continue;
		}

		if (!path.dentry->d_inode) {
			dput(path.dentry);
			printk(KERN_DEBUG "autofs: negative dentry on expiry queue: %s\n",
			       ent->name);
			autofs_delete_usage(ent);
			continue;
		}

		/* Make sure entry is mounted and unused; note that dentry will
		   point to the mounted-on-top root. */
		if (!S_ISDIR(path.dentry->d_inode->i_mode) ||
		    !d_mountpoint(path.dentry)) {
			DPRINTK(("autofs: not expirable \
				(not a mounted directory): %s\n", ent->name));
			continue;
		}
		path.mnt = mnt;
		path_get(&path);
		if (!follow_down_one(&path)) {
			path_put(&path);
			DPRINTK(("autofs: not expirable\
			(not a mounted directory): %s\n", ent->name));
			continue;
		}
		follow_down(&path, false);  // TODO: need to check error
		umount_ok = may_umount(path.mnt);
		path_put(&path);

		if (umount_ok) {
			DPRINTK(("autofs: signaling expire on %s\n",
								ent->name));
			return ent; /* Expirable! */
		}

		DPRINTK(("autofs: didn't expire due to may_umount: %s\n",
								ent->name));
	}
	return NULL;		/* No expirable entries */
}

void autofs_initialize_hash(struct autofs_dirhash *dh)
{
	memset(&dh->h, 0, AUTOFS_HASH_SIZE*sizeof(struct autofs_dir_ent *));
	INIT_LIST_HEAD(&dh->expiry_head);
}

struct autofs_dir_ent *autofs_hash_lookup(const struct autofs_dirhash *dh,
						struct qstr *name)
{
	struct autofs_dir_ent *dhn;

	DPRINTK(("autofs_hash_lookup: hash = 0x%08x, name = ", name->hash));
	autofs_say(name->name, name->len);

	for (dhn = dh->h[(unsigned) name->hash % AUTOFS_HASH_SIZE];
		dhn;
		dhn = dhn->next) {
		if (name->hash == dhn->hash &&
		     name->len == dhn->len &&
		     !memcmp(name->name, dhn->name, name->len))
			break;
	}

	return dhn;
}

void autofs_hash_insert(struct autofs_dirhash *dh, struct autofs_dir_ent *ent)
{
	struct autofs_dir_ent **dhnp;

	DPRINTK(("autofs_hash_insert: hash = 0x%08x, name = ", ent->hash));
	autofs_say(ent->name, ent->len);

	autofs_init_usage(dh, ent);
	if (ent->dentry)
		dget(ent->dentry);

	dhnp = &dh->h[(unsigned) ent->hash % AUTOFS_HASH_SIZE];
	ent->next = *dhnp;
	ent->back = dhnp;
	*dhnp = ent;
	if (ent->next)
		ent->next->back = &(ent->next);
}

void autofs_hash_delete(struct autofs_dir_ent *ent)
{
	*(ent->back) = ent->next;
	if (ent->next)
		ent->next->back = ent->back;

	autofs_delete_usage(ent);

	if (ent->dentry)
		dput(ent->dentry);
	kfree(ent->name);
	kfree(ent);
}

/*
 * Used by readdir().  We must validate "ptr", so we can't simply make it
 * a pointer.  Values below 0xffff are reserved; calling with any value
 * <= 0x10000 will return the first entry found.
 *
 * "last" can be NULL or the value returned by the last search *if* we
 * want the next sequential entry.
 */
struct autofs_dir_ent *autofs_hash_enum(const struct autofs_dirhash *dh,
					off_t *ptr, struct autofs_dir_ent *last)
{
	int bucket, ecount, i;
	struct autofs_dir_ent *ent;

	bucket = (*ptr >> 16) - 1;
	ecount = *ptr & 0xffff;

	if (bucket < 0)
		bucket = ecount = 0;

	DPRINTK(("autofs_hash_enum: bucket %d, entry %d\n", bucket, ecount));

	ent = last ? last->next : NULL;

	if (ent) {
		ecount++;
	} else {
		while  (bucket < AUTOFS_HASH_SIZE) {
			ent = dh->h[bucket];
			for (i = ecount ; ent && i ; i--)
				ent = ent->next;

			if (ent) {
				ecount++; /* Point to *next* entry */
				break;
			}

			bucket++; ecount = 0;
		}
	}

#ifdef DEBUG
	if (!ent)
		printk(KERN_DEBUG "autofs_hash_enum: nothing found\n");
	else {
		printk(KERN_DEBUG "autofs_hash_enum: found hash %08x, name",
								ent->hash);
		autofs_say(ent->name, ent->len);
	}
#endif

	*ptr = ((bucket+1) << 16) + ecount;
	return ent;
}

/* Iterate over all the ents, and remove all dentry pointers.  Used on
   entering catatonic mode, in order to make the filesystem unmountable. */
void autofs_hash_dputall(struct autofs_dirhash *dh)
{
	int i;
	struct autofs_dir_ent *ent;

	for (i = 0 ; i < AUTOFS_HASH_SIZE ; i++) {
		for (ent = dh->h[i] ; ent ; ent = ent->next) {
			if (ent->dentry) {
				dput(ent->dentry);
				ent->dentry = NULL;
			}
		}
	}
}

/* Delete everything.  This is used on filesystem destruction, so we
   make no attempt to keep the pointers valid */
void autofs_hash_nuke(struct autofs_sb_info *sbi)
{
	int i;
	struct autofs_dir_ent *ent, *nent;

	for (i = 0 ; i < AUTOFS_HASH_SIZE ; i++) {
		for (ent = sbi->dirhash.h[i] ; ent ; ent = nent) {
			nent = ent->next;
			if (ent->dentry)
				dput(ent->dentry);
			kfree(ent->name);
			kfree(ent);
		}
	}
}