fs/eventfd.c

   1 /*
   2  *  fs/eventfd.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  */
   7
   8 #include <linux/file.h>
   9 #include <linux/poll.h>
  10 #include <linux/init.h>
  11 #include <linux/fs.h>
  12 #include <linux/sched.h>
  13 #include <linux/kernel.h>
  14 #include <linux/list.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/anon_inodes.h>
  17 #include <linux/eventfd.h>
  18
  19 struct eventfd_ctx {
  20         wait_queue_head_t wqh;
  21         /*
  22          * Every time that a write(2) is performed on an eventfd, the
  23          * value of the __u64 being written is added to "count" and a
  24          * wakeup is performed on "wqh". A read(2) will return the "count"
  25          * value to userspace, and will reset "count" to zero. The kernel
  26          * size eventfd_signal() also, adds to the "count" counter and
  27          * issue a wakeup.
  28          */
  29         __u64 count;
  30 };
  31
  32 /*
  33  * Adds "n" to the eventfd counter "count". Returns "n" in case of
  34  * success, or a value lower then "n" in case of coutner overflow.
  35  * This function is supposed to be called by the kernel in paths
  36  * that do not allow sleeping. In this function we allow the counter
  37  * to reach the ULLONG_MAX value, and we signal this as overflow
  38  * condition by returining a POLLERR to poll(2).
  39  */
  40 int eventfd_signal(struct file *file, int n)
  41 {
  42         struct eventfd_ctx *ctx = file->private_data;
  43         unsigned long flags;
  44
  45         if (n < 0)
  46                 return -EINVAL;
  47         spin_lock_irqsave(&ctx->wqh.lock, flags);
  48         if (ULLONG_MAX - ctx->count < n)
  49                 n = (int) (ULLONG_MAX - ctx->count);
  50         ctx->count += n;
  51         if (waitqueue_active(&ctx->wqh))
  52                 wake_up_locked(&ctx->wqh);
  53         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  54
  55         return n;
  56 }
  57
  58 static int eventfd_release(struct inode *inode, struct file *file)
  59 {
  60         kfree(file->private_data);
  61         return 0;
  62 }
  63
  64 static unsigned int eventfd_poll(struct file *file, poll_table *wait)
  65 {
  66         struct eventfd_ctx *ctx = file->private_data;
  67         unsigned int events = 0;
  68         unsigned long flags;
  69
  70         poll_wait(file, &ctx->wqh, wait);
  71
  72         spin_lock_irqsave(&ctx->wqh.lock, flags);
  73         if (ctx->count > 0)
  74                 events |= POLLIN;
  75         if (ctx->count == ULLONG_MAX)
  76                 events |= POLLERR;
  77         if (ULLONG_MAX - 1 > ctx->count)
  78                 events |= POLLOUT;
  79         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  80
  81         return events;
  82 }
  83
  84 static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
  85                             loff_t *ppos)
  86 {
  87         struct eventfd_ctx *ctx = file->private_data;
  88         ssize_t res;
  89         __u64 ucnt;
  90         DECLARE_WAITQUEUE(wait, current);
  91
  92         if (count < sizeof(ucnt))
  93                 return -EINVAL;
  94         spin_lock_irq(&ctx->wqh.lock);
  95         res = -EAGAIN;
  96         ucnt = ctx->count;
  97         if (ucnt > 0)
  98                 res = sizeof(ucnt);
  99         else if (!(file->f_flags & O_NONBLOCK)) {
 100                 __add_wait_queue(&ctx->wqh, &wait);
 101                 for (res = 0;;) {
 102                         set_current_state(TASK_INTERRUPTIBLE);
 103                         if (ctx->count > 0) {
 104                                 ucnt = ctx->count;
 105                                 res = sizeof(ucnt);
 106                                 break;
 107                         }
 108                         if (signal_pending(current)) {
 109                                 res = -ERESTARTSYS;
 110                                 break;
 111                         }
 112                         spin_unlock_irq(&ctx->wqh.lock);
 113                         schedule();
 114                         spin_lock_irq(&ctx->wqh.lock);
 115                 }
 116                 __remove_wait_queue(&ctx->wqh, &wait);
 117                 __set_current_state(TASK_RUNNING);
 118         }
 119         if (res > 0) {
 120                 ctx->count = 0;
 121                 if (waitqueue_active(&ctx->wqh))
 122                         wake_up_locked(&ctx->wqh);
 123         }
 124         spin_unlock_irq(&ctx->wqh.lock);
 125         if (res > 0 && put_user(ucnt, (__u64 __user *) buf))
 126                 return -EFAULT;
 127
 128         return res;
 129 }
 130
 131 static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
 132                              loff_t *ppos)
 133 {
 134         struct eventfd_ctx *ctx = file->private_data;
 135         ssize_t res;
 136         __u64 ucnt;
 137         DECLARE_WAITQUEUE(wait, current);
 138
 139         if (count < sizeof(ucnt))
 140                 return -EINVAL;
 141         if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
 142                 return -EFAULT;
 143         if (ucnt == ULLONG_MAX)
 144                 return -EINVAL;
 145         spin_lock_irq(&ctx->wqh.lock);
 146         res = -EAGAIN;
 147         if (ULLONG_MAX - ctx->count > ucnt)
 148                 res = sizeof(ucnt);
 149         else if (!(file->f_flags & O_NONBLOCK)) {
 150                 __add_wait_queue(&ctx->wqh, &wait);
 151                 for (res = 0;;) {
 152                         set_current_state(TASK_INTERRUPTIBLE);
 153                         if (ULLONG_MAX - ctx->count > ucnt) {
 154                                 res = sizeof(ucnt);
 155                                 break;
 156                         }
 157                         if (signal_pending(current)) {
 158                                 res = -ERESTARTSYS;
 159                                 break;
 160                         }
 161                         spin_unlock_irq(&ctx->wqh.lock);
 162                         schedule();
 163                         spin_lock_irq(&ctx->wqh.lock);
 164                 }
 165                 __remove_wait_queue(&ctx->wqh, &wait);
 166                 __set_current_state(TASK_RUNNING);
 167         }
 168         if (res > 0) {
 169                 ctx->count += ucnt;
 170                 if (waitqueue_active(&ctx->wqh))
 171                         wake_up_locked(&ctx->wqh);
 172         }
 173         spin_unlock_irq(&ctx->wqh.lock);
 174
 175         return res;
 176 }
 177
 178 static const struct file_operations eventfd_fops = {
 179         .release        = eventfd_release,
 180         .poll           = eventfd_poll,
 181         .read           = eventfd_read,
 182         .write          = eventfd_write,
 183 };
 184
 185 struct file *eventfd_fget(int fd)
 186 {
 187         struct file *file;
 188
 189         file = fget(fd);
 190         if (!file)
 191                 return ERR_PTR(-EBADF);
 192         if (file->f_op != &eventfd_fops) {
 193                 fput(file);
 194                 return ERR_PTR(-EINVAL);
 195         }
 196
 197         return file;
 198 }
 199
 200 asmlinkage long sys_eventfd(unsigned int count)
 201 {
 202         int error, fd;
 203         struct eventfd_ctx *ctx;
 204         struct file *file;
 205         struct inode *inode;
 206
 207         ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 208         if (!ctx)
 209                 return -ENOMEM;
 210
 211         init_waitqueue_head(&ctx->wqh);
 212         ctx->count = count;
 213
 214         /*
 215          * When we call this, the initialization must be complete, since
 216          * anon_inode_getfd() will install the fd.
 217          */
 218         error = anon_inode_getfd(&fd, &inode, &file, "[eventfd]",
 219                                  &eventfd_fops, ctx);
 220         if (!error)
 221                 return fd;
 222
 223         kfree(ctx);
 224         return error;
 225 }
 226