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 #include <linux/syscalls.h> 24 25 struct timerfd_ctx { 26 struct hrtimer tmr; 27 ktime_t tintv; 28 wait_queue_head_t wqh; 29 u64 ticks; 30 int expired; 31 int clockid; 32 }; 33 34 /* 35 * This gets called when the timer event triggers. We set the "expired" 36 * flag, but we do not re-arm the timer (in case it's necessary, 37 * tintv.tv64 != 0) until the timer is accessed. 38 */ 39 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) 40 { 41 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); 42 unsigned long flags; 43 44 spin_lock_irqsave(&ctx->wqh.lock, flags); 45 ctx->expired = 1; 46 ctx->ticks++; 47 wake_up_locked(&ctx->wqh); 48 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 49 50 return HRTIMER_NORESTART; 51 } 52 53 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) 54 { 55 ktime_t now, remaining; 56 57 now = ctx->tmr.base->get_time(); 58 remaining = ktime_sub(ctx->tmr.expires, now); 59 60 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining; 61 } 62 63 static void timerfd_setup(struct timerfd_ctx *ctx, int flags, 64 const struct itimerspec *ktmr) 65 { 66 enum hrtimer_mode htmode; 67 ktime_t texp; 68 69 htmode = (flags & TFD_TIMER_ABSTIME) ? 70 HRTIMER_MODE_ABS: HRTIMER_MODE_REL; 71 72 texp = timespec_to_ktime(ktmr->it_value); 73 ctx->expired = 0; 74 ctx->ticks = 0; 75 ctx->tintv = timespec_to_ktime(ktmr->it_interval); 76 hrtimer_init(&ctx->tmr, ctx->clockid, htmode); 77 ctx->tmr.expires = texp; 78 ctx->tmr.function = timerfd_tmrproc; 79 if (texp.tv64 != 0) 80 hrtimer_start(&ctx->tmr, texp, htmode); 81 } 82 83 static int timerfd_release(struct inode *inode, struct file *file) 84 { 85 struct timerfd_ctx *ctx = file->private_data; 86 87 hrtimer_cancel(&ctx->tmr); 88 kfree(ctx); 89 return 0; 90 } 91 92 static unsigned int timerfd_poll(struct file *file, poll_table *wait) 93 { 94 struct timerfd_ctx *ctx = file->private_data; 95 unsigned int events = 0; 96 unsigned long flags; 97 98 poll_wait(file, &ctx->wqh, wait); 99 100 spin_lock_irqsave(&ctx->wqh.lock, flags); 101 if (ctx->ticks) 102 events |= POLLIN; 103 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 104 105 return events; 106 } 107 108 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, 109 loff_t *ppos) 110 { 111 struct timerfd_ctx *ctx = file->private_data; 112 ssize_t res; 113 u64 ticks = 0; 114 DECLARE_WAITQUEUE(wait, current); 115 116 if (count < sizeof(ticks)) 117 return -EINVAL; 118 spin_lock_irq(&ctx->wqh.lock); 119 res = -EAGAIN; 120 if (!ctx->ticks && !(file->f_flags & O_NONBLOCK)) { 121 __add_wait_queue(&ctx->wqh, &wait); 122 for (res = 0;;) { 123 set_current_state(TASK_INTERRUPTIBLE); 124 if (ctx->ticks) { 125 res = 0; 126 break; 127 } 128 if (signal_pending(current)) { 129 res = -ERESTARTSYS; 130 break; 131 } 132 spin_unlock_irq(&ctx->wqh.lock); 133 schedule(); 134 spin_lock_irq(&ctx->wqh.lock); 135 } 136 __remove_wait_queue(&ctx->wqh, &wait); 137 __set_current_state(TASK_RUNNING); 138 } 139 if (ctx->ticks) { 140 ticks = ctx->ticks; 141 if (ctx->expired && ctx->tintv.tv64) { 142 /* 143 * If tintv.tv64 != 0, this is a periodic timer that 144 * needs to be re-armed. We avoid doing it in the timer 145 * callback to avoid DoS attacks specifying a very 146 * short timer period. 147 */ 148 ticks += hrtimer_forward_now(&ctx->tmr, 149 ctx->tintv) - 1; 150 hrtimer_restart(&ctx->tmr); 151 } 152 ctx->expired = 0; 153 ctx->ticks = 0; 154 } 155 spin_unlock_irq(&ctx->wqh.lock); 156 if (ticks) 157 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); 158 return res; 159 } 160 161 static const struct file_operations timerfd_fops = { 162 .release = timerfd_release, 163 .poll = timerfd_poll, 164 .read = timerfd_read, 165 }; 166 167 static struct file *timerfd_fget(int fd) 168 { 169 struct file *file; 170 171 file = fget(fd); 172 if (!file) 173 return ERR_PTR(-EBADF); 174 if (file->f_op != &timerfd_fops) { 175 fput(file); 176 return ERR_PTR(-EINVAL); 177 } 178 179 return file; 180 } 181 182 asmlinkage long sys_timerfd_create(int clockid, int flags) 183 { 184 int ufd; 185 struct timerfd_ctx *ctx; 186 187 if (flags) 188 return -EINVAL; 189 if (clockid != CLOCK_MONOTONIC && 190 clockid != CLOCK_REALTIME) 191 return -EINVAL; 192 193 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); 194 if (!ctx) 195 return -ENOMEM; 196 197 init_waitqueue_head(&ctx->wqh); 198 ctx->clockid = clockid; 199 hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS); 200 201 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx); 202 if (ufd < 0) 203 kfree(ctx); 204 205 return ufd; 206 } 207 208 asmlinkage long sys_timerfd_settime(int ufd, int flags, 209 const struct itimerspec __user *utmr, 210 struct itimerspec __user *otmr) 211 { 212 struct file *file; 213 struct timerfd_ctx *ctx; 214 struct itimerspec ktmr, kotmr; 215 216 if (copy_from_user(&ktmr, utmr, sizeof(ktmr))) 217 return -EFAULT; 218 219 if (!timespec_valid(&ktmr.it_value) || 220 !timespec_valid(&ktmr.it_interval)) 221 return -EINVAL; 222 223 file = timerfd_fget(ufd); 224 if (IS_ERR(file)) 225 return PTR_ERR(file); 226 ctx = file->private_data; 227 228 /* 229 * We need to stop the existing timer before reprogramming 230 * it to the new values. 231 */ 232 for (;;) { 233 spin_lock_irq(&ctx->wqh.lock); 234 if (hrtimer_try_to_cancel(&ctx->tmr) >= 0) 235 break; 236 spin_unlock_irq(&ctx->wqh.lock); 237 cpu_relax(); 238 } 239 240 /* 241 * If the timer is expired and it's periodic, we need to advance it 242 * because the caller may want to know the previous expiration time. 243 * We do not update "ticks" and "expired" since the timer will be 244 * re-programmed again in the following timerfd_setup() call. 245 */ 246 if (ctx->expired && ctx->tintv.tv64) 247 hrtimer_forward_now(&ctx->tmr, ctx->tintv); 248 249 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 250 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 251 252 /* 253 * Re-program the timer to the new value ... 254 */ 255 timerfd_setup(ctx, flags, &ktmr); 256 257 spin_unlock_irq(&ctx->wqh.lock); 258 fput(file); 259 if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr))) 260 return -EFAULT; 261 262 return 0; 263 } 264 265 asmlinkage long sys_timerfd_gettime(int ufd, struct itimerspec __user *otmr) 266 { 267 struct file *file; 268 struct timerfd_ctx *ctx; 269 struct itimerspec kotmr; 270 271 file = timerfd_fget(ufd); 272 if (IS_ERR(file)) 273 return PTR_ERR(file); 274 ctx = file->private_data; 275 276 spin_lock_irq(&ctx->wqh.lock); 277 if (ctx->expired && ctx->tintv.tv64) { 278 ctx->expired = 0; 279 ctx->ticks += 280 hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1; 281 hrtimer_restart(&ctx->tmr); 282 } 283 kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx)); 284 kotmr.it_interval = ktime_to_timespec(ctx->tintv); 285 spin_unlock_irq(&ctx->wqh.lock); 286 fput(file); 287 288 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0; 289 } 290 291