fs/timerfd.c

   1 /*
   2  *  fs/timerfd.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  *
   7  *  Thanks to Thomas Gleixner for code reviews and useful comments.
   8  *
   9  */
  10
  11 #include <linux/file.h>
  12 #include <linux/poll.h>
  13 #include <linux/init.h>
  14 #include <linux/fs.h>
  15 #include <linux/sched.h>
  16 #include <linux/kernel.h>
  17 #include <linux/list.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/time.h>
  20 #include <linux/hrtimer.h>
  21 #include <linux/anon_inodes.h>
  22 #include <linux/timerfd.h>
  23
  24 struct timerfd_ctx {
  25         struct hrtimer tmr;
  26         ktime_t tintv;
  27         wait_queue_head_t wqh;
  28         int expired;
  29 };
  30
  31 /*
  32  * This gets called when the timer event triggers. We set the "expired"
  33  * flag, but we do not re-arm the timer (in case it's necessary,
  34  * tintv.tv64 != 0) until the timer is read.
  35  */
  36 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  37 {
  38         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
  39         unsigned long flags;
  40
  41         spin_lock_irqsave(&ctx->wqh.lock, flags);
  42         ctx->expired = 1;
  43         wake_up_locked(&ctx->wqh);
  44         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  45
  46         return HRTIMER_NORESTART;
  47 }
  48
  49 static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, int flags,
  50                           const struct itimerspec *ktmr)
  51 {
  52         enum hrtimer_mode htmode;
  53         ktime_t texp;
  54
  55         htmode = (flags & TFD_TIMER_ABSTIME) ?
  56                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
  57
  58         texp = timespec_to_ktime(ktmr->it_value);
  59         ctx->expired = 0;
  60         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
  61         hrtimer_init(&ctx->tmr, clockid, htmode);
  62         ctx->tmr.expires = texp;
  63         ctx->tmr.function = timerfd_tmrproc;
  64         if (texp.tv64 != 0)
  65                 hrtimer_start(&ctx->tmr, texp, htmode);
  66 }
  67
  68 static int timerfd_release(struct inode *inode, struct file *file)
  69 {
  70         struct timerfd_ctx *ctx = file->private_data;
  71
  72         hrtimer_cancel(&ctx->tmr);
  73         kfree(ctx);
  74         return 0;
  75 }
  76
  77 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
  78 {
  79         struct timerfd_ctx *ctx = file->private_data;
  80         unsigned int events = 0;
  81         unsigned long flags;
  82
  83         poll_wait(file, &ctx->wqh, wait);
  84
  85         spin_lock_irqsave(&ctx->wqh.lock, flags);
  86         if (ctx->expired)
  87                 events |= POLLIN;
  88         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  89
  90         return events;
  91 }
  92
  93 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
  94                             loff_t *ppos)
  95 {
  96         struct timerfd_ctx *ctx = file->private_data;
  97         ssize_t res;
  98         u32 ticks = 0;
  99         DECLARE_WAITQUEUE(wait, current);
 100
 101         if (count < sizeof(ticks))
 102                 return -EINVAL;
 103         spin_lock_irq(&ctx->wqh.lock);
 104         res = -EAGAIN;
 105         if (!ctx->expired && !(file->f_flags & O_NONBLOCK)) {
 106                 __add_wait_queue(&ctx->wqh, &wait);
 107                 for (res = 0;;) {
 108                         set_current_state(TASK_INTERRUPTIBLE);
 109                         if (ctx->expired) {
 110                                 res = 0;
 111                                 break;
 112                         }
 113                         if (signal_pending(current)) {
 114                                 res = -ERESTARTSYS;
 115                                 break;
 116                         }
 117                         spin_unlock_irq(&ctx->wqh.lock);
 118                         schedule();
 119                         spin_lock_irq(&ctx->wqh.lock);
 120                 }
 121                 __remove_wait_queue(&ctx->wqh, &wait);
 122                 __set_current_state(TASK_RUNNING);
 123         }
 124         if (ctx->expired) {
 125                 ctx->expired = 0;
 126                 if (ctx->tintv.tv64 != 0) {
 127                         /*
 128                          * If tintv.tv64 != 0, this is a periodic timer that
 129                          * needs to be re-armed. We avoid doing it in the timer
 130                          * callback to avoid DoS attacks specifying a very
 131                          * short timer period.
 132                          */
 133                         ticks = (u32)
 134                                 hrtimer_forward(&ctx->tmr,
 135                                                 hrtimer_cb_get_time(&ctx->tmr),
 136                                                 ctx->tintv);
 137                         hrtimer_restart(&ctx->tmr);
 138                 } else
 139                         ticks = 1;
 140         }
 141         spin_unlock_irq(&ctx->wqh.lock);
 142         if (ticks)
 143                 res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks);
 144         return res;
 145 }
 146
 147 static const struct file_operations timerfd_fops = {
 148         .release        = timerfd_release,
 149         .poll           = timerfd_poll,
 150         .read           = timerfd_read,
 151 };
 152
 153 asmlinkage long sys_timerfd(int ufd, int clockid, int flags,
 154                             const struct itimerspec __user *utmr)
 155 {
 156         int error;
 157         struct timerfd_ctx *ctx;
 158         struct file *file;
 159         struct inode *inode;
 160         struct itimerspec ktmr;
 161
 162         if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
 163                 return -EFAULT;
 164
 165         if (clockid != CLOCK_MONOTONIC &&
 166             clockid != CLOCK_REALTIME)
 167                 return -EINVAL;
 168         if (!timespec_valid(&ktmr.it_value) ||
 169             !timespec_valid(&ktmr.it_interval))
 170                 return -EINVAL;
 171
 172         if (ufd == -1) {
 173                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 174                 if (!ctx)
 175                         return -ENOMEM;
 176
 177                 init_waitqueue_head(&ctx->wqh);
 178
 179                 timerfd_setup(ctx, clockid, flags, &ktmr);
 180
 181                 /*
 182                  * When we call this, the initialization must be complete, since
 183                  * anon_inode_getfd() will install the fd.
 184                  */
 185                 error = anon_inode_getfd(&ufd, &inode, &file, "[timerfd]",
 186                                          &timerfd_fops, ctx);
 187                 if (error)
 188                         goto err_tmrcancel;
 189         } else {
 190                 file = fget(ufd);
 191                 if (!file)
 192                         return -EBADF;
 193                 ctx = file->private_data;
 194                 if (file->f_op != &timerfd_fops) {
 195                         fput(file);
 196                         return -EINVAL;
 197                 }
 198                 /*
 199                  * We need to stop the existing timer before reprogramming
 200                  * it to the new values.
 201                  */
 202                 for (;;) {
 203                         spin_lock_irq(&ctx->wqh.lock);
 204                         if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 205                                 break;
 206                         spin_unlock_irq(&ctx->wqh.lock);
 207                         cpu_relax();
 208                 }
 209                 /*
 210                  * Re-program the timer to the new value ...
 211                  */
 212                 timerfd_setup(ctx, clockid, flags, &ktmr);
 213
 214                 spin_unlock_irq(&ctx->wqh.lock);
 215                 fput(file);
 216         }
 217
 218         return ufd;
 219
 220 err_tmrcancel:
 221         hrtimer_cancel(&ctx->tmr);
 222         kfree(ctx);
 223         return error;
 224 }
 225