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/*

 * NET3:        Garbage Collector For AF_UNIX sockets

 *

 * Garbage Collector:

 *      Copyright (C) Barak A. Pearlmutter.

 *      Released under the GPL version 2 or later.

 *

 * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.

 * If it doesn't work blame me, it worked when Barak sent it.

 *

 * Assumptions:

 *

 *  - object w/ a bit

 *  - free list

 *

 * Current optimizations:

 *

 *  - explicit stack instead of recursion

 *  - tail recurse on first born instead of immediate push/pop

 *  - we gather the stuff that should not be killed into tree

 *    and stack is just a path from root to the current pointer.

 *

 *  Future optimizations:

 *

 *  - don't just push entire root set; process in place

 *

 *      This program is free software; you can redistribute it and/or

 *      modify it under the terms of the GNU General Public License

 *      as published by the Free Software Foundation; either version

 *      2 of the License, or (at your option) any later version.

 *

 *  Fixes:

 *      Alan Cox        07 Sept 1997    Vmalloc internal stack as needed.

 *                                      Cope with changing max_files.

 *      Al Viro         11 Oct 1998

 *              Graph may have cycles. That is, we can send the descriptor

 *              of foo to bar and vice versa. Current code chokes on that.

 *              Fix: move SCM_RIGHTS ones into the separate list and then

 *              skb_free() them all instead of doing explicit fput's.

 *              Another problem: since fput() may block somebody may

 *              create a new unix_socket when we are in the middle of sweep

 *              phase. Fix: revert the logic wrt MARKED. Mark everything

 *              upon the beginning and unmark non-junk ones.

 *

 *              [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS

 *              sent to connect()'ed but still not accept()'ed sockets.

 *              Fixed. Old code had slightly different problem here:

 *              extra fput() in situation when we passed the descriptor via

 *              such socket and closed it (descriptor). That would happen on

 *              each unix_gc() until the accept(). Since the struct file in

 *              question would go to the free list and might be reused...

 *              That might be the reason of random oopses on filp_close()

 *              in unrelated processes.

 *

 *      AV              28 Feb 1999

 *              Kill the explicit allocation of stack. Now we keep the tree

 *              with root in dummy + pointer (gc_current) to one of the nodes.

 *              Stack is represented as path from gc_current to dummy. Unmark

 *              now means "add to tree". Push == "make it a son of gc_current".

 *              Pop == "move gc_current to parent". We keep only pointers to

 *              parents (->gc_tree).

 *      AV              1 Mar 1999

 *              Damn. Added missing check for ->dead in listen queues scanning.

 *

 */

#include <linux/kernel.h>

#include <linux/sched.h>

#include <linux/string.h>

#include <linux/socket.h>

#include <linux/un.h>

#include <linux/net.h>

#include <linux/fs.h>

#include <linux/slab.h>

#include <linux/skbuff.h>

#include <linux/netdevice.h>

#include <linux/file.h>

#include <linux/proc_fs.h>

#include <linux/tcp.h>

#include <net/sock.h>

#include <net/af_unix.h>

#include <net/scm.h>

/* Internal data structures and random procedures: */

#define GC_HEAD         ((unix_socket *)(-1))

#define GC_ORPHAN       ((unix_socket *)(-3))

static unix_socket *gc_current=GC_HEAD; /* stack of objects to mark */

atomic_t unix_tot_inflight = ATOMIC_INIT(0);

extern inline unix_socket *unix_get_socket(struct file *filp)

{

        unix_socket * u_sock = NULL;

        struct inode *inode = filp->f_dentry->d_inode;

        /*

         *      Socket ?

         */

        if (inode->i_sock) {

                struct socket * sock = &inode->u.socket_i;

                struct sock * s = sock->sk;

                /*

                 *      PF_UNIX ?

                 */

                if (s && sock->ops && sock->ops->family == PF_UNIX)

                        u_sock = s;

        }

        return u_sock;

}

/*

 *      Keep the number of times in flight count for the file

 *      descriptor if it is for an AF_UNIX socket.

 */

void unix_inflight(struct file *fp)

{

        unix_socket *s=unix_get_socket(fp);

        if(s) {

                atomic_inc(&s->protinfo.af_unix.inflight);

                atomic_inc(&unix_tot_inflight);

        }

}

void unix_notinflight(struct file *fp)

{

        unix_socket *s=unix_get_socket(fp);

        if(s) {

                atomic_dec(&s->protinfo.af_unix.inflight);

                atomic_dec(&unix_tot_inflight);

        }

}

/*

 *      Garbage Collector Support Functions

 */

extern inline unix_socket *pop_stack(void)

{

        unix_socket *p=gc_current;

        gc_current = p->protinfo.af_unix.gc_tree;

        return p;

}

extern inline int empty_stack(void)

{

        return gc_current == GC_HEAD;

}

extern inline void maybe_unmark_and_push(unix_socket *x)

{

        if (x->protinfo.af_unix.gc_tree != GC_ORPHAN)

                return;

        sock_hold(x);

        x->protinfo.af_unix.gc_tree = gc_current;

        gc_current = x;

}

/* The external entry point: unix_gc() */

void unix_gc(void)

{

        static DECLARE_MUTEX(unix_gc_sem);

        int i;

        unix_socket *s;

        struct sk_buff_head hitlist;

        struct sk_buff *skb;

        /*

         *      Avoid a recursive GC.

         */

        if (down_trylock(&unix_gc_sem))

                return;

        read_lock(&unix_table_lock);

        forall_unix_sockets(i, s)

        {

                s->protinfo.af_unix.gc_tree=GC_ORPHAN;

        }

        /*

         *      Everything is now marked

         */

        /* Invariant to be maintained:

                - everything unmarked is either:

                -- (a) on the stack, or

                -- (b) has all of its children unmarked

                - everything on the stack is always unmarked

                - nothing is ever pushed onto the stack twice, because:

                -- nothing previously unmarked is ever pushed on the stack

         */

        /*

         *      Push root set

         */

        forall_unix_sockets(i, s)

        {

                int open_count = 0;

                /*

                 *      If all instances of the descriptor are not

                 *      in flight we are in use.

                 *

                 *      Special case: when socket s is embrion, it may be

                 *      hashed but still not in queue of listening socket.

                 *      In this case (see unix_create1()) we set artificial

                 *      negative inflight counter to close race window.

                 *      It is trick of course and dirty one.

                 */

                if(s->socket && s->socket->file)

                        open_count = file_count(s->socket->file);

                if (open_count > atomic_read(&s->protinfo.af_unix.inflight))

                        maybe_unmark_and_push(s);

        }

        /*

         *      Mark phase

         */

        while (!empty_stack())

        {

                unix_socket *x = pop_stack();

                unix_socket *sk;

                spin_lock(&x->receive_queue.lock);

                skb=skb_peek(&x->receive_queue);

                /*

                 *      Loop through all but first born

                 */

                while(skb && skb != (struct sk_buff *)&x->receive_queue)

                {

                        /*

                         *      Do we have file descriptors ?

                         */

                        if(UNIXCB(skb).fp)

                        {

                                /*

                                 *      Process the descriptors of this socket

                                 */

                                int nfd=UNIXCB(skb).fp->count;

                                struct file **fp = UNIXCB(skb).fp->fp;

                                while(nfd--)

                                {

                                        /*

                                         *      Get the socket the fd matches if

                                         *      it indeed does so

                                         */

                                        if((sk=unix_get_socket(*fp++))!=NULL)

                                        {

                                                maybe_unmark_and_push(sk);

                                        }

                                }

                        }

                        /* We have to scan not-yet-accepted ones too */

                        if (x->state == TCP_LISTEN) {

                                maybe_unmark_and_push(skb->sk);

                        }

                        skb=skb->next;

                }

                spin_unlock(&x->receive_queue.lock);

                sock_put(x);

        }

        skb_queue_head_init(&hitlist);

        forall_unix_sockets(i, s)

        {

                if (s->protinfo.af_unix.gc_tree == GC_ORPHAN)

                {

                        struct sk_buff *nextsk;

                        spin_lock(&s->receive_queue.lock);

                        skb=skb_peek(&s->receive_queue);

                        while(skb && skb != (struct sk_buff *)&s->receive_queue)

                        {

                                nextsk=skb->next;

                                /*

                                 *      Do we have file descriptors ?

                                 */

                                if(UNIXCB(skb).fp)

                                {

                                        __skb_unlink(skb, skb->list);

                                        __skb_queue_tail(&hitlist,skb);

                                }

                                skb=nextsk;

                        }

                        spin_unlock(&s->receive_queue.lock);

                }

                s->protinfo.af_unix.gc_tree = GC_ORPHAN;

        }

        read_unlock(&unix_table_lock);

        /*

         *      Here we are. Hitlist is filled. Die.

         */

        __skb_queue_purge(&hitlist);

        up(&unix_gc_sem);

}