View of xos/fs/vfat_lock.c

/* Copyright (C) 2008  Emmanuel Varoquaux
 
   This file is part of XOS.
 
   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 3 of the License, or
   (at your option) any later version.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
 
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>. */
 
#include "vfat_lock_struct.h"
 
#include <panic.h>
#include <rw_lock.h>
#include <condition.h>
#include <kmalloc.h>
#include <errno.h>
#include <stddef.h>
 
/* Du fait de la petite taille du pool de verrous, on utilise un algorithme
 * simplifie inspire d'une table de hachage a adressage ouvert : la cle de
 * hachage donne simplement la "meilleure" place possible pour un id, et
 * constitue le point de depart de la recherche.
 *
 * Cette fonction est bloquante si l'id n'est pas dans la table et que la table
 * est pleine. Elle retourne NULL si l'attente a ete interrompue. */
static struct vfat_lock_struct *get(struct vfat_lock_pool_struct *lock_pool, unsigned long id)
{
  int start;
  struct vfat_lock_struct *nearest_free;
  struct vfat_lock_struct *lck;
 
  /* recherche d'un verrou pour l'identifiant id, et, en parallele, le verrou
     libre le plus proche de la cle de hachage */
  start = id % lock_pool->lock_table_size;
  nearest_free = NULL;
  lck = &lock_pool->lock_table[start];
  do {
    if (lck->id == id)
      return lck;
    if (!lck->count && !nearest_free)
      nearest_free = lck;
    if (++lck == &lock_pool->lock_table[lock_pool->lock_table_size])
      lck = &lock_pool->lock_table[0];
  }
  while (lck != &lock_pool->lock_table[start]);
 
  /* un verrou pour l'identifiant id n'a pas ete trouve, recherche d'un verrou
     libre */
  if (!(lck = nearest_free))
    do
      if (!condition_wait_interruptible(&lock_pool->free_condition))
        return NULL;
    while (!(lck = lock_pool->free));
  lck->id = id;
  return lck;
}
 
/* Identique a get() mais declenche une erreur si le verrou n'existe pas. */
static struct vfat_lock_struct *get_const(const struct vfat_lock_pool_struct *lock_pool, unsigned long id)
{
  int start;
  struct vfat_lock_struct *lck;
 
  /* recherche d'un verrou pour l'identifiant id */
  start = id % lock_pool->lock_table_size;
  lck = &lock_pool->lock_table[start];
  do {
    if (lck->id == id)
      return lck;
    if (++lck == &lock_pool->lock_table[lock_pool->lock_table_size])
      lck = &lock_pool->lock_table[0];
  }
  while (lck != &lock_pool->lock_table[start]);
 
  panic("Lock not found!");
}
 
static void del(struct vfat_lock_pool_struct *lock_pool, struct vfat_lock_struct *lock)
{
  lock_pool->free = lock;
  condition_signal(&lock_pool->free_condition);
}
 
int vfat_lock_pool_init(struct vfat_lock_pool_struct *lock_pool, unsigned int size)
{
  unsigned int i;
 
  if (!(lock_pool->lock_table = kmalloc(size * sizeof (struct vfat_lock_struct))))
    return -ENOMEM;
  lock_pool->lock_table_size = size;
  for (i = 0; i < lock_pool->lock_table_size; i++)
    lock_pool->lock_table[i].count = 0;
  condition_init(&lock_pool->free_condition);
  return 0;
}
 
void vfat_lock_pool_destroy(struct vfat_lock_pool_struct *lock_pool)
{
  kfree(lock_pool->lock_table, lock_pool->lock_table_size * sizeof (struct vfat_lock_struct));
}
 
int vfat_lock(struct vfat_lock_pool_struct *lock_pool, unsigned long id, int request)
{
  struct vfat_lock_struct *lck;
 
  if (!(lck = get(lock_pool, id)))
    return 0;
  lck->count++;
  switch (request) {
  case lr_read:
    if (!rw_lock_lock_read(&lck->rw_lock))
      goto interrupted;
    break;
  case lr_write:
    if (!rw_lock_lock_write(&lck->rw_lock))
      goto interrupted;
    break;
  }
  lck->request = request;
  return 1;
 
 interrupted:
  if (!--lck->count)
    del(lock_pool, lck);
  return 0;
}
 
void vfat_unlock(struct vfat_lock_pool_struct *lock_pool, unsigned long id)
{
  struct vfat_lock_struct *lck;
 
  lck = get_const(lock_pool, id);
  switch (lck->request) {
  case lr_read:
    rw_lock_unlock_read(&lck->rw_lock);
    break;
  case lr_write:
    rw_lock_unlock_write(&lck->rw_lock);
    break;
  }
  if (!--lck->count)
    del(lock_pool, lck);
}