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/slab.h>
  18 #include <linux/list.h>
  19 #include <linux/spinlock.h>
  20 #include <linux/time.h>
  21 #include <linux/hrtimer.h>
  22 #include <linux/anon_inodes.h>
  23 #include <linux/timerfd.h>
  24 #include <linux/syscalls.h>
  25
  26 struct timerfd_ctx {
  27         struct hrtimer tmr;
  28         ktime_t tintv;
  29         wait_queue_head_t wqh;
  30         u64 ticks;
  31         int expired;
  32         int clockid;
  33 };
  34
  35 /*
  36  * This gets called when the timer event triggers. We set the "expired"
  37  * flag, but we do not re-arm the timer (in case it's necessary,
  38  * tintv.tv64 != 0) until the timer is accessed.
  39  */
  40 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  41 {
  42         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
  43         unsigned long flags;
  44
  45         spin_lock_irqsave(&ctx->wqh.lock, flags);
  46         ctx->expired = 1;
  47         ctx->ticks++;
  48         wake_up_locked(&ctx->wqh);
  49         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  50
  51         return HRTIMER_NORESTART;
  52 }
  53
  54 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
  55 {
  56         ktime_t remaining;
  57
  58         remaining = hrtimer_expires_remaining(&ctx->tmr);
  59         return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
  60 }
  61
  62 static void timerfd_setup(struct timerfd_ctx *ctx, int flags,
  63                           const struct itimerspec *ktmr)
  64 {
  65         enum hrtimer_mode htmode;
  66         ktime_t texp;
  67
  68         htmode = (flags & TFD_TIMER_ABSTIME) ?
  69                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
  70
  71         texp = timespec_to_ktime(ktmr->it_value);
  72         ctx->expired = 0;
  73         ctx->ticks = 0;
  74         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
  75         hrtimer_init(&ctx->tmr, ctx->clockid, htmode);
  76         hrtimer_set_expires(&ctx->tmr, texp);
  77         ctx->tmr.function = timerfd_tmrproc;
  78         if (texp.tv64 != 0)
  79                 hrtimer_start(&ctx->tmr, texp, htmode);
  80 }
  81
  82 static int timerfd_release(struct inode *inode, struct file *file)
  83 {
  84         struct timerfd_ctx *ctx = file->private_data;
  85
  86         hrtimer_cancel(&ctx->tmr);
  87         kfree(ctx);
  88         return 0;
  89 }
  90
  91 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
  92 {
  93         struct timerfd_ctx *ctx = file->private_data;
  94         unsigned int events = 0;
  95         unsigned long flags;
  96
  97         poll_wait(file, &ctx->wqh, wait);
  98
  99         spin_lock_irqsave(&ctx->wqh.lock, flags);
 100         if (ctx->ticks)
 101                 events |= POLLIN;
 102         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 103
 104         return events;
 105 }
 106
 107 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 108                             loff_t *ppos)
 109 {
 110         struct timerfd_ctx *ctx = file->private_data;
 111         ssize_t res;
 112         u64 ticks = 0;
 113
 114         if (count < sizeof(ticks))
 115                 return -EINVAL;
 116         spin_lock_irq(&ctx->wqh.lock);
 117         if (file->f_flags & O_NONBLOCK)
 118                 res = -EAGAIN;
 119         else
 120                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
 121         if (ctx->ticks) {
 122                 ticks = ctx->ticks;
 123                 if (ctx->expired && ctx->tintv.tv64) {
 124                         /*
 125                          * If tintv.tv64 != 0, this is a periodic timer that
 126                          * needs to be re-armed. We avoid doing it in the timer
 127                          * callback to avoid DoS attacks specifying a very
 128                          * short timer period.
 129                          */
 130                         ticks += hrtimer_forward_now(&ctx->tmr,
 131                                                      ctx->tintv) - 1;
 132                         hrtimer_restart(&ctx->tmr);
 133                 }
 134                 ctx->expired = 0;
 135                 ctx->ticks = 0;
 136         }
 137         spin_unlock_irq(&ctx->wqh.lock);
 138         if (ticks)
 139                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
 140         return res;
 141 }
 142
 143 static const struct file_operations timerfd_fops = {
 144         .release        = timerfd_release,
 145         .poll           = timerfd_poll,
 146         .read           = timerfd_read,
 147 };
 148
 149 static struct file *timerfd_fget(int fd)
 150 {
 151         struct file *file;
 152
 153         file = fget(fd);
 154         if (!file)
 155                 return ERR_PTR(-EBADF);
 156         if (file->f_op != &timerfd_fops) {
 157                 fput(file);
 158                 return ERR_PTR(-EINVAL);
 159         }
 160
 161         return file;
 162 }
 163
 164 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 165 {
 166         int ufd;
 167         struct timerfd_ctx *ctx;
 168
 169         /* Check the TFD_* constants for consistency.  */
 170         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 171         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 172
 173         if ((flags & ~TFD_CREATE_FLAGS) ||
 174             (clockid != CLOCK_MONOTONIC &&
 175              clockid != CLOCK_REALTIME))
 176                 return -EINVAL;
 177
 178         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 179         if (!ctx)
 180                 return -ENOMEM;
 181
 182         init_waitqueue_head(&ctx->wqh);
 183         ctx->clockid = clockid;
 184         hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
 185
 186         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 187                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 188         if (ufd < 0)
 189                 kfree(ctx);
 190
 191         return ufd;
 192 }
 193
 194 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 195                 const struct itimerspec __user *, utmr,
 196                 struct itimerspec __user *, otmr)
 197 {
 198         struct file *file;
 199         struct timerfd_ctx *ctx;
 200         struct itimerspec ktmr, kotmr;
 201
 202         if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
 203                 return -EFAULT;
 204
 205         if ((flags & ~TFD_SETTIME_FLAGS) ||
 206             !timespec_valid(&ktmr.it_value) ||
 207             !timespec_valid(&ktmr.it_interval))
 208                 return -EINVAL;
 209
 210         file = timerfd_fget(ufd);
 211         if (IS_ERR(file))
 212                 return PTR_ERR(file);
 213         ctx = file->private_data;
 214
 215         /*
 216          * We need to stop the existing timer before reprogramming
 217          * it to the new values.
 218          */
 219         for (;;) {
 220                 spin_lock_irq(&ctx->wqh.lock);
 221                 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 222                         break;
 223                 spin_unlock_irq(&ctx->wqh.lock);
 224                 cpu_relax();
 225         }
 226
 227         /*
 228          * If the timer is expired and it's periodic, we need to advance it
 229          * because the caller may want to know the previous expiration time.
 230          * We do not update "ticks" and "expired" since the timer will be
 231          * re-programmed again in the following timerfd_setup() call.
 232          */
 233         if (ctx->expired && ctx->tintv.tv64)
 234                 hrtimer_forward_now(&ctx->tmr, ctx->tintv);
 235
 236         kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 237         kotmr.it_interval = ktime_to_timespec(ctx->tintv);
 238
 239         /*
 240          * Re-program the timer to the new value ...
 241          */
 242         timerfd_setup(ctx, flags, &ktmr);
 243
 244         spin_unlock_irq(&ctx->wqh.lock);
 245         fput(file);
 246         if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
 247                 return -EFAULT;
 248
 249         return 0;
 250 }
 251
 252 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 253 {
 254         struct file *file;
 255         struct timerfd_ctx *ctx;
 256         struct itimerspec kotmr;
 257
 258         file = timerfd_fget(ufd);
 259         if (IS_ERR(file))
 260                 return PTR_ERR(file);
 261         ctx = file->private_data;
 262
 263         spin_lock_irq(&ctx->wqh.lock);
 264         if (ctx->expired && ctx->tintv.tv64) {
 265                 ctx->expired = 0;
 266                 ctx->ticks +=
 267                         hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
 268                 hrtimer_restart(&ctx->tmr);
 269         }
 270         kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 271         kotmr.it_interval = ktime_to_timespec(ctx->tintv);
 272         spin_unlock_irq(&ctx->wqh.lock);
 273         fput(file);
 274
 275         return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 276 }
 277