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 #include <linux/syscalls.h> 19 20 struct eventfd_ctx { 21 wait_queue_head_t wqh; 22 /* 23 * Every time that a write(2) is performed on an eventfd, the 24 * value of the __u64 being written is added to "count" and a 25 * wakeup is performed on "wqh". A read(2) will return the "count" 26 * value to userspace, and will reset "count" to zero. The kernel 27 * size eventfd_signal() also, adds to the "count" counter and 28 * issue a wakeup. 29 */ 30 __u64 count; 31 }; 32 33 /* 34 * Adds "n" to the eventfd counter "count". Returns "n" in case of 35 * success, or a value lower then "n" in case of coutner overflow. 36 * This function is supposed to be called by the kernel in paths 37 * that do not allow sleeping. In this function we allow the counter 38 * to reach the ULLONG_MAX value, and we signal this as overflow 39 * condition by returining a POLLERR to poll(2). 40 */ 41 int eventfd_signal(struct file *file, int n) 42 { 43 struct eventfd_ctx *ctx = file->private_data; 44 unsigned long flags; 45 46 if (n < 0) 47 return -EINVAL; 48 spin_lock_irqsave(&ctx->wqh.lock, flags); 49 if (ULLONG_MAX - ctx->count < n) 50 n = (int) (ULLONG_MAX - ctx->count); 51 ctx->count += n; 52 if (waitqueue_active(&ctx->wqh)) 53 wake_up_locked(&ctx->wqh); 54 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 55 56 return n; 57 } 58 59 static int eventfd_release(struct inode *inode, struct file *file) 60 { 61 kfree(file->private_data); 62 return 0; 63 } 64 65 static unsigned int eventfd_poll(struct file *file, poll_table *wait) 66 { 67 struct eventfd_ctx *ctx = file->private_data; 68 unsigned int events = 0; 69 unsigned long flags; 70 71 poll_wait(file, &ctx->wqh, wait); 72 73 spin_lock_irqsave(&ctx->wqh.lock, flags); 74 if (ctx->count > 0) 75 events |= POLLIN; 76 if (ctx->count == ULLONG_MAX) 77 events |= POLLERR; 78 if (ULLONG_MAX - 1 > ctx->count) 79 events |= POLLOUT; 80 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 81 82 return events; 83 } 84 85 static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count, 86 loff_t *ppos) 87 { 88 struct eventfd_ctx *ctx = file->private_data; 89 ssize_t res; 90 __u64 ucnt; 91 DECLARE_WAITQUEUE(wait, current); 92 93 if (count < sizeof(ucnt)) 94 return -EINVAL; 95 spin_lock_irq(&ctx->wqh.lock); 96 res = -EAGAIN; 97 ucnt = ctx->count; 98 if (ucnt > 0) 99 res = sizeof(ucnt); 100 else if (!(file->f_flags & O_NONBLOCK)) { 101 __add_wait_queue(&ctx->wqh, &wait); 102 for (res = 0;;) { 103 set_current_state(TASK_INTERRUPTIBLE); 104 if (ctx->count > 0) { 105 ucnt = ctx->count; 106 res = sizeof(ucnt); 107 break; 108 } 109 if (signal_pending(current)) { 110 res = -ERESTARTSYS; 111 break; 112 } 113 spin_unlock_irq(&ctx->wqh.lock); 114 schedule(); 115 spin_lock_irq(&ctx->wqh.lock); 116 } 117 __remove_wait_queue(&ctx->wqh, &wait); 118 __set_current_state(TASK_RUNNING); 119 } 120 if (res > 0) { 121 ctx->count = 0; 122 if (waitqueue_active(&ctx->wqh)) 123 wake_up_locked(&ctx->wqh); 124 } 125 spin_unlock_irq(&ctx->wqh.lock); 126 if (res > 0 && put_user(ucnt, (__u64 __user *) buf)) 127 return -EFAULT; 128 129 return res; 130 } 131 132 static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count, 133 loff_t *ppos) 134 { 135 struct eventfd_ctx *ctx = file->private_data; 136 ssize_t res; 137 __u64 ucnt; 138 DECLARE_WAITQUEUE(wait, current); 139 140 if (count < sizeof(ucnt)) 141 return -EINVAL; 142 if (copy_from_user(&ucnt, buf, sizeof(ucnt))) 143 return -EFAULT; 144 if (ucnt == ULLONG_MAX) 145 return -EINVAL; 146 spin_lock_irq(&ctx->wqh.lock); 147 res = -EAGAIN; 148 if (ULLONG_MAX - ctx->count > ucnt) 149 res = sizeof(ucnt); 150 else if (!(file->f_flags & O_NONBLOCK)) { 151 __add_wait_queue(&ctx->wqh, &wait); 152 for (res = 0;;) { 153 set_current_state(TASK_INTERRUPTIBLE); 154 if (ULLONG_MAX - ctx->count > ucnt) { 155 res = sizeof(ucnt); 156 break; 157 } 158 if (signal_pending(current)) { 159 res = -ERESTARTSYS; 160 break; 161 } 162 spin_unlock_irq(&ctx->wqh.lock); 163 schedule(); 164 spin_lock_irq(&ctx->wqh.lock); 165 } 166 __remove_wait_queue(&ctx->wqh, &wait); 167 __set_current_state(TASK_RUNNING); 168 } 169 if (res > 0) { 170 ctx->count += ucnt; 171 if (waitqueue_active(&ctx->wqh)) 172 wake_up_locked(&ctx->wqh); 173 } 174 spin_unlock_irq(&ctx->wqh.lock); 175 176 return res; 177 } 178 179 static const struct file_operations eventfd_fops = { 180 .release = eventfd_release, 181 .poll = eventfd_poll, 182 .read = eventfd_read, 183 .write = eventfd_write, 184 }; 185 186 struct file *eventfd_fget(int fd) 187 { 188 struct file *file; 189 190 file = fget(fd); 191 if (!file) 192 return ERR_PTR(-EBADF); 193 if (file->f_op != &eventfd_fops) { 194 fput(file); 195 return ERR_PTR(-EINVAL); 196 } 197 198 return file; 199 } 200 201 asmlinkage long sys_eventfd2(unsigned int count, int flags) 202 { 203 int fd; 204 struct eventfd_ctx *ctx; 205 206 /* Check the EFD_* constants for consistency. */ 207 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC); 208 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK); 209 210 if (flags & ~(EFD_CLOEXEC | EFD_NONBLOCK)) 211 return -EINVAL; 212 213 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); 214 if (!ctx) 215 return -ENOMEM; 216 217 init_waitqueue_head(&ctx->wqh); 218 ctx->count = count; 219 220 /* 221 * When we call this, the initialization must be complete, since 222 * anon_inode_getfd() will install the fd. 223 */ 224 fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx, 225 flags & (O_CLOEXEC | O_NONBLOCK)); 226 if (fd < 0) 227 kfree(ctx); 228 return fd; 229 } 230 231 asmlinkage long sys_eventfd(unsigned int count) 232 { 233 return sys_eventfd2(count, 0); 234 } 235 236