/*
 *  linux/kernel/fork.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 *  'fork.c' contains the help-routines for the 'fork' system call
 * (see also system_call.s).
 * Fork is rather simple, once you get the hang of it, but the memory
 * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'
 */

#include <linux/init.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
#include <linux/malloc.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/module.h>

#include <asm/system.h>
#include <asm/pgtable.h>
#include <asm/mmu_context.h>
#include <asm/uaccess.h>

int nr_tasks=1;
int nr_running=1;
unsigned long int total_forks=0;        /* Handle normal Linux uptimes. */
int last_pid=0;

/* SLAB cache for mm_struct's. */
kmem_cache_t *mm_cachep;

/* SLAB cache for files structs */
kmem_cache_t *files_cachep; 

struct task_struct *pidhash[PIDHASH_SZ];
spinlock_t pidhash_lock = SPIN_LOCK_UNLOCKED;

struct task_struct **tarray_freelist = NULL;
spinlock_t taskslot_lock = SPIN_LOCK_UNLOCKED;

/* UID task count cache, to prevent walking entire process list every
 * single fork() operation.
 */
#define UIDHASH_SZ      (PIDHASH_SZ >> 2)

static struct uid_taskcount {
        struct uid_taskcount *next, **pprev;
        unsigned short uid;
        int task_count;
} *uidhash[UIDHASH_SZ];

#ifdef __SMP__
static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
#endif

kmem_cache_t *uid_cachep;

#define uidhashfn(uid)  (((uid >> 8) ^ uid) & (UIDHASH_SZ - 1))

static inline void uid_hash_insert(struct uid_taskcount *up, unsigned int hashent)
{
        spin_lock(&uidhash_lock);
        if((up->next = uidhash[hashent]) != NULL)
                uidhash[hashent]->pprev = &up->next;
        up->pprev = &uidhash[hashent];
        uidhash[hashent] = up;
        spin_unlock(&uidhash_lock);
}

static inline void uid_hash_remove(struct uid_taskcount *up)
{
        spin_lock(&uidhash_lock);
        if(up->next)
                up->next->pprev = up->pprev;
        *up->pprev = up->next;
        spin_unlock(&uidhash_lock);
}

static inline struct uid_taskcount *uid_find(unsigned short uid, unsigned int hashent)
{
        struct uid_taskcount *up;

        spin_lock(&uidhash_lock);
        for(up = uidhash[hashent]; (up && up->uid != uid); up = up->next)
                ;
        spin_unlock(&uidhash_lock);
        return up;
}

int charge_uid(struct task_struct *p, int count)
{
        unsigned int hashent = uidhashfn(p->uid);
        struct uid_taskcount *up = uid_find(p->uid, hashent);

        if(up) {
                int limit = p->rlim[RLIMIT_NPROC].rlim_cur;
                int newcnt = up->task_count + count;

                if(newcnt > limit)
                        return -EAGAIN;
                else if(newcnt == 0) {
                        uid_hash_remove(up);
                        kmem_cache_free(uid_cachep, up);
                        return 0;
                }
        } else {
                up = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
                if(!up)
                        return -EAGAIN;
                up->uid = p->uid;
                up->task_count = 0;
                uid_hash_insert(up, hashent);
        }
        up->task_count += count;
        return 0;
}

__initfunc(void uidcache_init(void))
{
        int i;

        uid_cachep = kmem_cache_create("uid_cache", sizeof(struct uid_taskcount),
                                       0,
                                       SLAB_HWCACHE_ALIGN, NULL, NULL);
        if(!uid_cachep)
                panic("Cannot create uid taskcount SLAB cache\n");

        for(i = 0; i < UIDHASH_SZ; i++)
                uidhash[i] = 0;
}

static inline int find_empty_process(void)
{
        struct task_struct **tslot;

        if(current->uid) {
                int error;

                if(nr_tasks >= NR_TASKS - MIN_TASKS_LEFT_FOR_ROOT)
                        return -EAGAIN;
                if((error = charge_uid(current, 1)) < 0)
                        return error;
        }
        tslot = get_free_taskslot();
        if(tslot)
                return tslot - &task[0];
        return -EAGAIN;
}

#ifdef __SMP__
/* Protects next_safe and last_pid. */
static spinlock_t lastpid_lock = SPIN_LOCK_UNLOCKED;
#endif

static int get_pid(unsigned long flags)
{
        static int next_safe = PID_MAX;
        struct task_struct *p;

        if (flags & CLONE_PID)
                return current->pid;

        spin_lock(&lastpid_lock);
        if((++last_pid) & 0xffff8000) {
                last_pid = 300;         /* Skip daemons etc. */
                goto inside;
        }
        if(last_pid >= next_safe) {
inside:
                next_safe = PID_MAX;
                read_lock(&tasklist_lock);
        repeat:
                for_each_task(p) {
                        if(p->pid == last_pid   ||
                           p->pgrp == last_pid  ||
                           p->session == last_pid) {
                                if(++last_pid >= next_safe) {
                                        if(last_pid & 0xffff8000)
                                                last_pid = 300;
                                        next_safe = PID_MAX;
                                        goto repeat;
                                }
                        }
                        if(p->pid > last_pid && next_safe > p->pid)
                                next_safe = p->pid;
                        if(p->pgrp > last_pid && next_safe > p->pgrp)
                                next_safe = p->pgrp;
                        if(p->session > last_pid && next_safe > p->session)
                                next_safe = p->session;
                }
                read_unlock(&tasklist_lock);
        }
        spin_unlock(&lastpid_lock);

        return last_pid;
}

static inline int dup_mmap(struct mm_struct * mm)
{
        struct vm_area_struct * mpnt, *tmp, **pprev;
        int retval;

        mm->mmap = mm->mmap_cache = NULL;
        flush_cache_mm(current->mm);
        pprev = &mm->mmap;
        for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
                struct dentry *dentry;

                retval = -ENOMEM;
                tmp = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
                if (!tmp)
                        goto fail_nomem;
                *tmp = *mpnt;
                tmp->vm_flags &= ~VM_LOCKED;
                tmp->vm_mm = mm;
                tmp->vm_next = NULL;
                dentry = tmp->vm_dentry;
                if (dentry) {
                        dget(dentry);
                        if (tmp->vm_flags & VM_DENYWRITE)
                                dentry->d_inode->i_writecount--;
      
                        /* insert tmp into the share list, just after mpnt */
                        if((tmp->vm_next_share = mpnt->vm_next_share) != NULL)
                                mpnt->vm_next_share->vm_pprev_share =
                                        &tmp->vm_next_share;
                        mpnt->vm_next_share = tmp;
                        tmp->vm_pprev_share = &mpnt->vm_next_share;
                }

                /* Copy the pages, but defer checking for errors */
                retval = copy_page_range(mm, current->mm, tmp);
                if (!retval && tmp->vm_ops && tmp->vm_ops->open)
                        tmp->vm_ops->open(tmp);

                /*
                 * Link in the new vma even if an error occurred,
                 * so that exit_mmap() can clean up the mess.
                 */
                if((tmp->vm_next = *pprev) != NULL)
                        (*pprev)->vm_pprev = &tmp->vm_next;
                *pprev = tmp;
                tmp->vm_pprev = pprev;

                pprev = &tmp->vm_next;
                if (retval)
                        goto fail_nomem;
        }
        flush_tlb_mm(current->mm);
        return 0;

fail_nomem:
        flush_tlb_mm(current->mm);
        return retval;
}

/*
 * Allocate and initialize an mm_struct.
 */
struct mm_struct * mm_alloc(void)
{
        struct mm_struct * mm;

        mm = kmem_cache_alloc(mm_cachep, SLAB_KERNEL);
        if (mm) {
                *mm = *current->mm;
                init_new_context(mm);
                mm->count = 1;
                mm->def_flags = 0;
                mm->mmap_sem = MUTEX;
                mm->pgd = NULL;
                mm->mmap = mm->mmap_cache = NULL;

                /* It has not run yet, so cannot be present in anyone's
                 * cache or tlb.
                 */
                mm->cpu_vm_mask = 0;
        }
        return mm;
}

/*
 * Decrement the use count and release all resources for an mm.
 */
void mmput(struct mm_struct *mm)
{
        if (!--mm->count) {
                exit_mmap(mm);
                free_page_tables(mm);
                kmem_cache_free(mm_cachep, mm);
        }
}

static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
        struct mm_struct * mm;
        int retval;

        if (clone_flags & CLONE_VM) {
                mmget(current->mm);
                SET_PAGE_DIR(tsk, current->mm->pgd);
                return 0;
        }

        retval = -ENOMEM;
        mm = mm_alloc();
        if (!mm)
                goto fail_nomem;

        tsk->mm = mm;
        tsk->min_flt = tsk->maj_flt = 0;
        tsk->cmin_flt = tsk->cmaj_flt = 0;
        tsk->nswap = tsk->cnswap = 0;
        retval = new_page_tables(tsk);
        if (retval)
                goto free_mm;
        retval = dup_mmap(mm);
        if (retval)
                goto free_mm;
        return 0;

free_mm:
        tsk->mm = NULL;
        mmput(mm);
fail_nomem:
        return retval;
}

static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
{
        if (clone_flags & CLONE_FS) {
                current->fs->count++;
                return 0;
        }
        tsk->fs = kmalloc(sizeof(*tsk->fs), GFP_KERNEL);
        if (!tsk->fs)
                return -1;
        tsk->fs->count = 1;
        tsk->fs->umask = current->fs->umask;
        tsk->fs->root = dget(current->fs->root);
        tsk->fs->pwd = dget(current->fs->pwd);
        return 0;
}

/* return value is only accurate by +-sizeof(long)*8 fds */ 
/* XXX make this architecture specific */
static inline int __copy_fdset(unsigned long *d, unsigned long *src)
{
        int i; 
        unsigned long *p = src; 
        unsigned long *max = src; 

        for (i = __FDSET_LONGS; i; --i) {
                if ((*d++ = *p++) != 0) 
                        max = p; 
        }
        return (max - src)*sizeof(long)*8; 
}

static inline int copy_fdset(fd_set *dst, fd_set *src)
{
        return __copy_fdset(dst->fds_bits, src->fds_bits);  
}

static inline int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
        int i;  
        struct files_struct *oldf, *newf;
        struct file **old_fds, **new_fds;

        oldf = current->files;
        if (clone_flags & CLONE_FILES) {
                oldf->count++;
                return 0;
        }

        newf = kmem_cache_alloc(files_cachep, SLAB_KERNEL);
        tsk->files = newf;
        if (!newf) 
                return -1;

        newf->count = 1;
        newf->close_on_exec = oldf->close_on_exec;
        i = copy_fdset(&newf->open_fds,&oldf->open_fds);

        old_fds = oldf->fd;
        new_fds = newf->fd;
        for (; i != 0; i--) {
                struct file * f = *old_fds;
                old_fds++;
                *new_fds = f;
                new_fds++;
                if (f)
                        f->f_count++;
        }
        return 0;
}

static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
        if (clone_flags & CLONE_SIGHAND) {
                atomic_inc(&current->sig->count);
                return 0;
        }
        tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
        if (!tsk->sig)
                return -1;
        spin_lock_init(&tsk->sig->siglock);
        atomic_set(&tsk->sig->count, 1);
        memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
        return 0;
}

/*
 *  Ok, this is the main fork-routine. It copies the system process
 * information (task[nr]) and sets up the necessary registers. It
 * also copies the data segment in its entirety.
 */
int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
{
        int nr;
        int error = -ENOMEM;
        struct task_struct *p;

        lock_kernel();
        p = alloc_task_struct();
        if (!p)
                goto bad_fork;

        error = -EAGAIN;
        nr = find_empty_process();
        if (nr < 0)
                goto bad_fork_free;

        *p = *current;

        if (p->exec_domain && p->exec_domain->module)
                __MOD_INC_USE_COUNT(p->exec_domain->module);
        if (p->binfmt && p->binfmt->module)
                __MOD_INC_USE_COUNT(p->binfmt->module);

        p->did_exec = 0;
        p->swappable = 0;
        p->state = TASK_UNINTERRUPTIBLE;
        p->flags &= ~(PF_PTRACED|PF_TRACESYS|PF_SUPERPRIV);
        p->flags |= PF_FORKNOEXEC;
        p->pid = get_pid(clone_flags);
        p->next_run = NULL;
        p->prev_run = NULL;
        p->p_pptr = p->p_opptr = current;
        p->p_cptr = NULL;
        init_waitqueue(&p->wait_chldexit);
        p->signal = 0;
        p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
        p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
        init_timer(&p->real_timer);
        p->real_timer.data = (unsigned long) p;
        p->leader = 0;          /* session leadership doesn't inherit */
        p->tty_old_pgrp = 0;
        p->times.tms_utime = p->times.tms_stime = 0;
        p->times.tms_cutime = p->times.tms_cstime = 0;
#ifdef __SMP__
        p->has_cpu = 0;
        p->processor = NO_PROC_ID;
#endif
        p->lock_depth = 0;
        p->start_time = jiffies;
        p->tarray_ptr = &task[nr];
        *p->tarray_ptr = p;
        SET_LINKS(p);
        hash_pid(p);
        nr_tasks++;

        error = -ENOMEM;
        /* copy all the process information */
        if (copy_files(clone_flags, p))
                goto bad_fork_cleanup;
        if (copy_fs(clone_flags, p))
                goto bad_fork_cleanup_files;
        if (copy_sighand(clone_flags, p))
                goto bad_fork_cleanup_fs;
        if (copy_mm(clone_flags, p))
                goto bad_fork_cleanup_sighand;
        error = copy_thread(nr, clone_flags, usp, p, regs);
        if (error)
                goto bad_fork_cleanup_sighand;
        p->semundo = NULL;

        /* ok, now we should be set up.. */
        p->swappable = 1;
        p->exit_signal = clone_flags & CSIGNAL;

        /*
         * "share" dynamic priority between parent and child, thus the
         * total amount of dynamic priorities in the system doesnt change,
         * more scheduling fairness. This is only important in the first
         * timeslice, on the long run the scheduling behaviour is unchanged.
         */
        current->counter >>= 1;
        p->counter = current->counter;

        if(p->pid) {
                wake_up_process(p);             /* do this last, just in case */
        } else {
                p->state = TASK_RUNNING;
                p->next_run = p->prev_run = p;
        }
        ++total_forks;
        error = p->pid;
        goto fork_out;

bad_fork_cleanup_sighand:
        exit_sighand(p);
bad_fork_cleanup_fs:
        exit_fs(p); /* blocking */
bad_fork_cleanup_files:
        exit_files(p); /* blocking */
bad_fork_cleanup:
        charge_uid(current, -1);
        if (p->exec_domain && p->exec_domain->module)
                __MOD_DEC_USE_COUNT(p->exec_domain->module);
        if (p->binfmt && p->binfmt->module)
                __MOD_DEC_USE_COUNT(p->binfmt->module);
        add_free_taskslot(p->tarray_ptr);
        unhash_pid(p);
        REMOVE_LINKS(p);
        nr_tasks--;
bad_fork_free:
        free_task_struct(p);
bad_fork:
fork_out:
        unlock_kernel();
        return error;
}

static void files_ctor(void *fp, kmem_cache_t *cachep, unsigned long flags)
{
        struct files_struct *f = fp;

        memset(f, 0, sizeof(*f));
}

__initfunc(void filescache_init(void))
{
        files_cachep = kmem_cache_create("files_cache", 
                                         sizeof(struct files_struct),
                                         0, 
                                         SLAB_HWCACHE_ALIGN,
                                         files_ctor, NULL);
        if (!files_cachep) 
                panic("Cannot create files cache"); 
}