求助

我是一个初学者，下面的代码我想分析一下wait函数，请高手指点一下！给出相应的框图！

#include <linux/config.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/completion.h>
#include <linux/namespace.h>
#include <linux/personality.h>
#include <linux/compiler.h>
#include <linux/mman.h>

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

int nr_threads;
int max_threads;
unsigned long total_forks;
int last_pid;

struct task_struct *pidhash[PIDHASH_SZ];

rwlock_t tasklist_lock __cacheline_aligned = RW_LOCK_UNLOCKED;  /* outer */

void add_wait_queue(wait_queue_head_t *q, wait_queue_t * wait)
{
unsigned long flags;

wait->flags &= ~WQ_FLAG_EXCLUSIVE;
wq_write_lock_irqsave(&q->lock, flags);
__add_wait_queue(q, wait);
wq_write_unlock_irqrestore(&q->lock, flags);
}

void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t * wait)
{
unsigned long flags;

wait->flags |= WQ_FLAG_EXCLUSIVE;
wq_write_lock_irqsave(&q->lock, flags);
__add_wait_queue_tail(q, wait);
wq_write_unlock_irqrestore(&q->lock, flags);
}

void remove_wait_queue(wait_queue_head_t *q, wait_queue_t * wait)
{
unsigned long flags;

wq_write_lock_irqsave(&q->lock, flags);
__remove_wait_queue(q, wait);
wq_write_unlock_irqrestore(&q->lock, flags);
}

void __init fork_init(unsigned long mempages)
{

max_threads = mempages / (THREAD_SIZE/PAGE_SIZE) / 8;

init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
}


spinlock_t lastpid_lock = SPIN_LOCK_UNLOCKED;

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

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

spin_lock(&lastpid_lock);
beginpid = last_pid;
if((++last_pid) & 0xffff8000) {
  last_pid = 300;  
  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->tgid == last_pid ||
      p->session == last_pid) {
    if(++last_pid >= next_safe) {
     if(last_pid & 0xffff8000)
      last_pid = 300;
     next_safe = PID_MAX;
    }
    if(unlikely(last_pid == beginpid))
     goto nomorepids;
    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->tgid > last_pid && next_safe > p->tgid)
    next_safe = p->tgid;
   if(p->session > last_pid && next_safe > p->session)
    next_safe = p->session;
  }
  read_unlock(&tasklist_lock);
}
pid = last_pid;
spin_unlock(&lastpid_lock);

return pid;

nomorepids:
read_unlock(&tasklist_lock);
spin_unlock(&lastpid_lock);
return 0;
}

static inline int dup_mmap(struct mm_struct * mm)
{
struct vm_area_struct * mpnt, *tmp, **pprev;
int retval;
unsigned long charge = 0;

flush_cache_mm(current->mm);
mm->locked_vm = 0;
mm->mmap = NULL;
mm->mmap_cache = NULL;
mm->map_count = 0;
mm->rss = 0;
mm->cpu_vm_mask = 0;
pprev = &mm->mmap;


spin_lock(&mmlist_lock);
list_add(&mm->mmlist, &current->mm->mmlist);
mmlist_nr++;
spin_unlock(&mmlist_lock);

for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
  struct file *file;

  retval = -ENOMEM;
  if(mpnt->vm_flags & VM_DONTCOPY)
   continue;

  /* FIXME: shared writable map accounting should be one off */
  if(mpnt->vm_flags & VM_ACCOUNT)
  {
   unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
   if(!vm_enough_memory(len))
    goto fail_nomem;
   charge += len;
  }
  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;
  file = tmp->vm_file;
  if (file) {
   struct inode *inode = file->f_dentry->d_inode;
   get_file(file);
   if (tmp->vm_flags & VM_DENYWRITE)
    atomic_dec(&inode->i_writecount);
      
   spin_lock(&inode->i_mapping->i_shared_lock);
   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;
   spin_unlock(&inode->i_mapping->i_shared_lock);
  }

  spin_lock(&mm->page_table_lock);
  *pprev = tmp;
  pprev = &tmp->vm_next;
  mm->map_count++;
  retval = copy_page_range(mm, current->mm, tmp);
  spin_unlock(&mm->page_table_lock);
  if (tmp->vm_ops && tmp->vm_ops->open)
   tmp->vm_ops->open(tmp);

  if (retval)
   goto fail_nomem;
}
retval = 0;
build_mmap_rb(mm);
out:
flush_tlb_mm(current->mm);
return retval;
fail_nomem:
vm_unacct_memory(charge);
goto out;
}

spinlock_t mmlist_lock __cacheline_aligned = SPIN_LOCK_UNLOCKED;
int mmlist_nr;

#define allocate_mm() (kmem_cache_alloc(mm_cachep, SLAB_KERNEL))
#define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))

static struct mm_struct * mm_init(struct mm_struct * mm)
{
atomic_set(&mm->mm_users, 1);
atomic_set(&mm->mm_count, 1);
init_rwsem(&mm->mmap_sem);
mm->page_table_lock = SPIN_LOCK_UNLOCKED;
mm->pgd = pgd_alloc(mm);
mm->def_flags = 0;
if (mm->pgd)
  return mm;
free_mm(mm);
return NULL;
}

struct mm_struct * mm_alloc(void)
{
struct mm_struct * mm;

mm = allocate_mm();
if (mm) {
  memset(mm, 0, sizeof(*mm));
  return mm_init(mm);
}
return NULL;
}

inline void __mmdrop(struct mm_struct *mm)
{
BUG_ON(mm == &init_mm);
pgd_free(mm->pgd);
destroy_context(mm);
free_mm(mm);
}

void mmput(struct mm_struct *mm)
{
if (atomic_dec_and_lock(&mm->mm_users, &mmlist_lock)) {
  list_del(&mm->mmlist);
  mmlist_nr--;
  spin_unlock(&mmlist_lock);
  exit_mmap(mm);
  mmdrop(mm);
}
}

void mm_release(void)
{
struct task_struct *tsk = current;
struct completion *vfork_done = tsk->vfork_done;

if (vfork_done) {
  tsk->vfork_done = NULL;
  complete(vfork_done);
}
}
static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
struct mm_struct * mm, *oldmm;
int retval;

tsk->min_flt = tsk->maj_flt = 0;
tsk->cmin_flt = tsk->cmaj_flt = 0;
tsk->nswap = tsk->cnswap = 0;

tsk->mm = NULL;
tsk->active_mm = NULL;

oldmm = current->mm;
if (!oldmm)
  return 0;
if (clone_flags & CLONE_VM) {
  atomic_inc(&oldmm->mm_users);
  mm = oldmm;
  goto good_mm;
}

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

memcpy(mm, oldmm, sizeof(*mm));
if (!mm_init(mm))
  goto fail_nomem;
if (init_new_context(tsk,mm))
  goto free_pt;

down_write(&oldmm->mmap_sem);
retval = dup_mmap(mm);
up_write(&oldmm->mmap_sem);

if (retval)
  goto free_pt;

copy_segments(tsk, mm);
good_mm:
tsk->mm = mm;
tsk->active_mm = mm;
return 0;

free_pt:
mmput(mm);
fail_nomem:
return retval;
}

static inline struct fs_struct *__copy_fs_struct(struct fs_struct *old)
{
struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
/* We don't need to lock fs - think why ;-) */
if (fs) {
  atomic_set(&fs->count, 1);
  fs->lock = RW_LOCK_UNLOCKED;
  fs->umask = old->umask;
  read_lock(&old->lock);
  fs->rootmnt = mntget(old->rootmnt);
  fs->root = dget(old->root);
  fs->pwdmnt = mntget(old->pwdmnt);
  fs->pwd = dget(old->pwd);
  if (old->altroot) {
   fs->altrootmnt = mntget(old->altrootmnt);
   fs->altroot = dget(old->altroot);
  } else {
   fs->altrootmnt = NULL;
   fs->altroot = NULL;
  }
  read_unlock(&old->lock);
}
return fs;
}

struct fs_struct *copy_fs_struct(struct fs_struct *old)
{
return __copy_fs_struct(old);
}

static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
{
if (clone_flags & CLONE_FS) {
  atomic_inc(&current->fs->count);
  return 0;
}
tsk->fs = __copy_fs_struct(current->fs);
if (!tsk->fs)
  return -1;
return 0;
}

static int count_open_files(struct files_struct *files, int size)
{
int i;

/* Find the last open fd */
for (i = size/(8*sizeof(long)); i > 0; ) {
  if (files->open_fds->fds_bits[--i])
   break;
}
i = (i+1) * 8 * sizeof(long);
return i;
}

static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
struct files_struct *oldf, *newf;
struct file **old_fds, **new_fds;
int open_files, nfds, size, i, error = 0;

oldf = current->files;
if (!oldf)
  goto out;

if (clone_flags & CLONE_FILES) {
  atomic_inc(&oldf->count);
  goto out;
}

tsk->files = NULL;
error = -ENOMEM;
newf = kmem_cache_alloc(files_cachep, SLAB_KERNEL);
if (!newf)
  goto out;

atomic_set(&newf->count, 1);

newf->file_lock     = RW_LOCK_UNLOCKED;
newf->next_fd     = 0;
newf->max_fds     = NR_OPEN_DEFAULT;
newf->max_fdset     = __FD_SETSIZE;
newf->close_on_exec = &newf->close_on_exec_init;
newf->open_fds     = &newf->open_fds_init;
newf->fd     = &newf->fd_array[0];

/* We don't yet have the oldf readlock, but even if the old
           fdset gets grown now, we'll only copy up to "size" fds */
size = oldf->max_fdset;
if (size > __FD_SETSIZE) {
  newf->max_fdset = 0;
  write_lock(&newf->file_lock);
  error = expand_fdset(newf, size-1);
  write_unlock(&newf->file_lock);
  if (error)
   goto out_release;
}
read_lock(&oldf->file_lock);

open_files = count_open_files(oldf, size);

nfds = NR_OPEN_DEFAULT;
if (open_files > nfds) {
  read_unlock(&oldf->file_lock);
  newf->max_fds = 0;
  write_lock(&newf->file_lock);
  error = expand_fd_array(newf, open_files-1);
  write_unlock(&newf->file_lock);
  if (error)
   goto out_release;
  nfds = newf->max_fds;
  read_lock(&oldf->file_lock);
}
old_fds = oldf->fd;
new_fds = newf->fd;

memcpy(newf->open_fds->fds_bits, oldf->open_fds->fds_bits, open_files/8);
memcpy(newf->close_on_exec->fds_bits, oldf->close_on_exec->fds_bits, open_files/8);

for (i = open_files; i != 0; i--) {
  struct file *f = *old_fds++;
  if (f)
   get_file(f);
  *new_fds++ = f;
}
read_unlock(&oldf->file_lock);

size = (newf->max_fds - open_files) * sizeof(struct file *);

memset(new_fds, 0, size);
if (newf->max_fdset > open_files) {
  int left = (newf->max_fdset-open_files)/8;
  int start = open_files / (8 * sizeof(unsigned long));
  
  memset(&newf->open_fds->fds_bits[start], 0, left);
  memset(&newf->close_on_exec->fds_bits[start], 0, left);
}

tsk->files = newf;
error = 0;
out:
return error;

out_release:
free_fdset (newf->close_on_exec, newf->max_fdset);
free_fdset (newf->open_fds, newf->max_fdset);
kmem_cache_free(files_cachep, newf);
goto out;
}

static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
struct signal_struct *sig;

if (clone_flags & CLONE_SIGHAND) {
  atomic_inc(&current->sig->count);
  return 0;
}
sig = kmem_cache_alloc(sigact_cachep, GFP_KERNEL);
tsk->sig = sig;
if (!sig)
  return -1;
spin_lock_init(&sig->siglock);
atomic_set(&sig->count, 1);
memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
return 0;
}

static inline void copy_flags(unsigned long clone_flags, struct task_struct *p)
{
unsigned long new_flags = p->flags;

new_flags &= ~(PF_SUPERPRIV | PF_USEDFPU);
new_flags |= PF_FORKNOEXEC;
if (!(clone_flags & CLONE_PTRACE))
  p->ptrace = 0;
p->flags = new_flags;
}


int do_fork(unsigned long clone_flags, unsigned long stack_start,
     struct pt_regs *regs, unsigned long stack_size)
{
int retval;
unsigned long flags;
struct task_struct *p;
struct completion vfork;

if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
  return -EINVAL;

retval = -EPERM;


if (clone_flags & CLONE_PID) {
  if (current->pid)
   goto fork_out;
}

retval = -ENOMEM;
p = alloc_task_struct();
if (!p)
  goto fork_out;

*p = *current;
p->tux_info = NULL;
p->cpus_allowed_mask &= p->cpus_allowed;

retval = -EAGAIN;

if (atomic_read(&p->user->processes) >= p->rlim[RLIMIT_NPROC].rlim_cur
               && !capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE))
  goto bad_fork_free;

atomic_inc(&p->user->__count);
atomic_inc(&p->user->processes);


if (nr_threads >= max_threads)
  goto bad_fork_cleanup_count;

get_exec_domain(p->exec_domain);

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

p->did_exec = 0;
p->swappable = 0;
p->state = TASK_UNINTERRUPTIBLE;

copy_flags(clone_flags, p);
p->pid = get_pid(clone_flags);
if (p->pid == 0 && current->pid != 0)
  goto bad_fork_cleanup;

INIT_LIST_HEAD(&p->run_list);

p->p_cptr = NULL;
init_waitqueue_head(&p->wait_chldexit);
p->vfork_done = NULL;
if (clone_flags & CLONE_VFORK) {
  p->vfork_done = &vfork;
  init_completion(&vfork);
}
spin_lock_init(&p->alloc_lock);

p->sigpending = 0;
init_sigpending(&p->pending);

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 CONFIG_SMP
{
  int i;

  /* ?? should we just memset this ?? */
  for(i = 0; i < smp_num_cpus; i++)
   p->per_cpu_utime[cpu_logical_map(i)] =
    p->per_cpu_stime[cpu_logical_map(i)] = 0;
  spin_lock_init(&p->sigmask_lock);
}
#endif
p->array = NULL;
p->lock_depth = -1;  /* -1 = no lock */
p->start_time = jiffies_64;

retval = -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;
if (copy_namespace(clone_flags, p))
  goto bad_fork_cleanup_mm;
retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
if (retval)
  goto bad_fork_cleanup_namespace;
p->semundo = NULL;

/* Our parent execution domain becomes current domain
    These must match for thread signalling to apply */
   
p->parent_exec_id = p->self_exec_id;

/* ok, now we should be set up.. */
p->swappable = 1;
p->exit_signal = clone_flags & CSIGNAL;
p->pdeath_signal = 0;


__save_flags(flags);
__cli();
if (!current->time_slice)
  BUG();
p->time_slice = (current->time_slice + 1) >> 1;
p->first_time_slice = 1;
current->time_slice >>= 1;
p->sleep_timestamp = jiffies;
if (!current->time_slice) {

  current->time_slice = 1;
  scheduler_tick(0,0);
}
__restore_flags(flags);


retval = p->pid;
p->tgid = retval;
INIT_LIST_HEAD(&p->thread_group);

/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);

/* CLONE_PARENT re-uses the old parent */
p->p_opptr = current->p_opptr;
p->p_pptr = current->p_pptr;
if (!(clone_flags & CLONE_PARENT)) {
  p->p_opptr = current;
  if (!(p->ptrace & PT_PTRACED))
   p->p_pptr = current;
}

if (clone_flags & CLONE_THREAD) {
  p->tgid = current->tgid;
  list_add(&p->thread_group, &current->thread_group);
}

SET_LINKS(p);
hash_pid(p);
nr_threads++;
write_unlock_irq(&tasklist_lock);

if (p->ptrace & PT_PTRACED)
  send_sig(SIGSTOP, p, 1);
wake_up_forked_process(p); /* do this last */
++total_forks;
if (clone_flags & CLONE_VFORK)
  wait_for_completion(&vfork);
else

  current->need_resched = 1;

fork_out:
return retval;

bad_fork_cleanup_namespace:
exit_namespace(p);
bad_fork_cleanup_mm:
exit_mm(p);
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:
put_exec_domain(p->exec_domain);
if (p->binfmt && p->binfmt->module)
  __MOD_DEC_USE_COUNT(p->binfmt->module);
bad_fork_cleanup_count:
atomic_dec(&p->user->processes);
free_uid(p->user);
bad_fork_free:
free_task_struct(p);
goto fork_out;
}

/* SLAB cache for signal_struct structures (tsk->sig) */
kmem_cache_t *sigact_cachep;

/* SLAB cache for files_struct structures (tsk->files) */
kmem_cache_t *files_cachep;

/* SLAB cache for fs_struct structures (tsk->fs) */
kmem_cache_t *fs_cachep;

/* SLAB cache for vm_area_struct structures */
kmem_cache_t *vm_area_cachep;

/* SLAB cache for mm_struct structures (tsk->mm) */
kmem_cache_t *mm_cachep;

void __init proc_caches_init(void)
{
sigact_cachep = kmem_cache_create("signal_act",
   sizeof(struct signal_struct), 0,
   SLAB_HWCACHE_ALIGN, NULL, NULL);
if (!sigact_cachep)
  panic("Cannot create signal action SLAB cache");

files_cachep = kmem_cache_create("files_cache",
    sizeof(struct files_struct), 0,
    SLAB_HWCACHE_ALIGN, NULL, NULL);
if (!files_cachep)
  panic("Cannot create files SLAB cache");

fs_cachep = kmem_cache_create("fs_cache",
    sizeof(struct fs_struct), 0,
    SLAB_HWCACHE_ALIGN, NULL, NULL);
if (!fs_cachep)
  panic("Cannot create fs_struct SLAB cache");

vm_area_cachep = kmem_cache_create("vm_area_struct",
   sizeof(struct vm_area_struct), 0,
   SLAB_HWCACHE_ALIGN, NULL, NULL);
if(!vm_area_cachep)
  panic("vma_init: Cannot alloc vm_area_struct SLAB cache");

mm_cachep = kmem_cache_create("mm_struct",
   sizeof(struct mm_struct), 0,
   SLAB_HWCACHE_ALIGN, NULL, NULL);
if(!mm_cachep)
  panic("vma_init: Cannot alloc mm_struct SLAB cache");
}