linux/fs/signalfd.c
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   1/*
   2 *  fs/signalfd.c
   3 *
   4 *  Copyright (C) 2003  Linus Torvalds
   5 *
   6 *  Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
   7 *      Changed ->read() to return a siginfo strcture instead of signal number.
   8 *      Fixed locking in ->poll().
   9 *      Added sighand-detach notification.
  10 *      Added fd re-use in sys_signalfd() syscall.
  11 *      Now using anonymous inode source.
  12 *      Thanks to Oleg Nesterov for useful code review and suggestions.
  13 *      More comments and suggestions from Arnd Bergmann.
  14 *  Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
  15 *      Retrieve multiple signals with one read() call
  16 *  Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
  17 *      Attach to the sighand only during read() and poll().
  18 */
  19
  20#include <linux/file.h>
  21#include <linux/poll.h>
  22#include <linux/init.h>
  23#include <linux/fs.h>
  24#include <linux/sched.h>
  25#include <linux/slab.h>
  26#include <linux/kernel.h>
  27#include <linux/signal.h>
  28#include <linux/list.h>
  29#include <linux/anon_inodes.h>
  30#include <linux/signalfd.h>
  31#include <linux/syscalls.h>
  32
  33struct signalfd_ctx {
  34        sigset_t sigmask;
  35};
  36
  37static int signalfd_release(struct inode *inode, struct file *file)
  38{
  39        kfree(file->private_data);
  40        return 0;
  41}
  42
  43static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  44{
  45        struct signalfd_ctx *ctx = file->private_data;
  46        unsigned int events = 0;
  47
  48        poll_wait(file, &current->sighand->signalfd_wqh, wait);
  49
  50        spin_lock_irq(&current->sighand->siglock);
  51        if (next_signal(&current->pending, &ctx->sigmask) ||
  52            next_signal(&current->signal->shared_pending,
  53                        &ctx->sigmask))
  54                events |= POLLIN;
  55        spin_unlock_irq(&current->sighand->siglock);
  56
  57        return events;
  58}
  59
  60/*
  61 * Copied from copy_siginfo_to_user() in kernel/signal.c
  62 */
  63static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  64                             siginfo_t const *kinfo)
  65{
  66        long err;
  67
  68        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  69
  70        /*
  71         * Unused members should be zero ...
  72         */
  73        err = __clear_user(uinfo, sizeof(*uinfo));
  74
  75        /*
  76         * If you change siginfo_t structure, please be sure
  77         * this code is fixed accordingly.
  78         */
  79        err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  80        err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  81        err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
  82        switch (kinfo->si_code & __SI_MASK) {
  83        case __SI_KILL:
  84                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
  85                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
  86                break;
  87        case __SI_TIMER:
  88                 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
  89                 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
  90                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
  91                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
  92                break;
  93        case __SI_POLL:
  94                err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
  95                err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
  96                break;
  97        case __SI_FAULT:
  98                err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
  99#ifdef __ARCH_SI_TRAPNO
 100                err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 101#endif
 102#ifdef BUS_MCEERR_AO
 103                /* 
 104                 * Other callers might not initialize the si_lsb field,
 105                 * so check explicitly for the right codes here.
 106                 */
 107                if (kinfo->si_code == BUS_MCEERR_AR ||
 108                    kinfo->si_code == BUS_MCEERR_AO)
 109                        err |= __put_user((short) kinfo->si_addr_lsb,
 110                                          &uinfo->ssi_addr_lsb);
 111#endif
 112                break;
 113        case __SI_CHLD:
 114                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 115                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 116                err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 117                err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 118                err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 119                break;
 120        case __SI_RT: /* This is not generated by the kernel as of now. */
 121        case __SI_MESGQ: /* But this is */
 122                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 123                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 124                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 125                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 126                break;
 127        default:
 128                /*
 129                 * This case catches also the signals queued by sigqueue().
 130                 */
 131                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 132                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 133                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 134                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 135                break;
 136        }
 137
 138        return err ? -EFAULT: sizeof(*uinfo);
 139}
 140
 141static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 142                                int nonblock)
 143{
 144        ssize_t ret;
 145        DECLARE_WAITQUEUE(wait, current);
 146
 147        spin_lock_irq(&current->sighand->siglock);
 148        ret = dequeue_signal(current, &ctx->sigmask, info);
 149        switch (ret) {
 150        case 0:
 151                if (!nonblock)
 152                        break;
 153                ret = -EAGAIN;
 154        default:
 155                spin_unlock_irq(&current->sighand->siglock);
 156                return ret;
 157        }
 158
 159        add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 160        for (;;) {
 161                set_current_state(TASK_INTERRUPTIBLE);
 162                ret = dequeue_signal(current, &ctx->sigmask, info);
 163                if (ret != 0)
 164                        break;
 165                if (signal_pending(current)) {
 166                        ret = -ERESTARTSYS;
 167                        break;
 168                }
 169                spin_unlock_irq(&current->sighand->siglock);
 170                schedule();
 171                spin_lock_irq(&current->sighand->siglock);
 172        }
 173        spin_unlock_irq(&current->sighand->siglock);
 174
 175        remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 176        __set_current_state(TASK_RUNNING);
 177
 178        return ret;
 179}
 180
 181/*
 182 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 183 * error code. The "count" parameter must be at least the size of a
 184 * "struct signalfd_siginfo".
 185 */
 186static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 187                             loff_t *ppos)
 188{
 189        struct signalfd_ctx *ctx = file->private_data;
 190        struct signalfd_siginfo __user *siginfo;
 191        int nonblock = file->f_flags & O_NONBLOCK;
 192        ssize_t ret, total = 0;
 193        siginfo_t info;
 194
 195        count /= sizeof(struct signalfd_siginfo);
 196        if (!count)
 197                return -EINVAL;
 198
 199        siginfo = (struct signalfd_siginfo __user *) buf;
 200        do {
 201                ret = signalfd_dequeue(ctx, &info, nonblock);
 202                if (unlikely(ret <= 0))
 203                        break;
 204                ret = signalfd_copyinfo(siginfo, &info);
 205                if (ret < 0)
 206                        break;
 207                siginfo++;
 208                total += ret;
 209                nonblock = 1;
 210        } while (--count);
 211
 212        return total ? total: ret;
 213}
 214
 215static const struct file_operations signalfd_fops = {
 216        .release        = signalfd_release,
 217        .poll           = signalfd_poll,
 218        .read           = signalfd_read,
 219        .llseek         = noop_llseek,
 220};
 221
 222SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 223                size_t, sizemask, int, flags)
 224{
 225        sigset_t sigmask;
 226        struct signalfd_ctx *ctx;
 227
 228        /* Check the SFD_* constants for consistency.  */
 229        BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 230        BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 231
 232        if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 233                return -EINVAL;
 234
 235        if (sizemask != sizeof(sigset_t) ||
 236            copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 237                return -EINVAL;
 238        sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 239        signotset(&sigmask);
 240
 241        if (ufd == -1) {
 242                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 243                if (!ctx)
 244                        return -ENOMEM;
 245
 246                ctx->sigmask = sigmask;
 247
 248                /*
 249                 * When we call this, the initialization must be complete, since
 250                 * anon_inode_getfd() will install the fd.
 251                 */
 252                ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 253                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 254                if (ufd < 0)
 255                        kfree(ctx);
 256        } else {
 257                struct file *file = fget(ufd);
 258                if (!file)
 259                        return -EBADF;
 260                ctx = file->private_data;
 261                if (file->f_op != &signalfd_fops) {
 262                        fput(file);
 263                        return -EINVAL;
 264                }
 265                spin_lock_irq(&current->sighand->siglock);
 266                ctx->sigmask = sigmask;
 267                spin_unlock_irq(&current->sighand->siglock);
 268
 269                wake_up(&current->sighand->signalfd_wqh);
 270                fput(file);
 271        }
 272
 273        return ufd;
 274}
 275
 276SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 277                size_t, sizemask)
 278{
 279        return sys_signalfd4(ufd, user_mask, sizemask, 0);
 280}
 281
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