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#include <linux/proc_fs.h>
  33
  34void signalfd_cleanup(struct sighand_struct *sighand)
  35{
  36        wait_queue_head_t *wqh = &sighand->signalfd_wqh;
  37        /*
  38         * The lockless check can race with remove_wait_queue() in progress,
  39         * but in this case its caller should run under rcu_read_lock() and
  40         * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return.
  41         */
  42        if (likely(!waitqueue_active(wqh)))
  43                return;
  44
  45        /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
  46        wake_up_poll(wqh, POLLHUP | POLLFREE);
  47}
  48
  49struct signalfd_ctx {
  50        sigset_t sigmask;
  51};
  52
  53static int signalfd_release(struct inode *inode, struct file *file)
  54{
  55        kfree(file->private_data);
  56        return 0;
  57}
  58
  59static unsigned int signalfd_poll(struct file *file, poll_table *wait)
  60{
  61        struct signalfd_ctx *ctx = file->private_data;
  62        unsigned int events = 0;
  63
  64        poll_wait(file, &current->sighand->signalfd_wqh, wait);
  65
  66        spin_lock_irq(&current->sighand->siglock);
  67        if (next_signal(&current->pending, &ctx->sigmask) ||
  68            next_signal(&current->signal->shared_pending,
  69                        &ctx->sigmask))
  70                events |= POLLIN;
  71        spin_unlock_irq(&current->sighand->siglock);
  72
  73        return events;
  74}
  75
  76/*
  77 * Copied from copy_siginfo_to_user() in kernel/signal.c
  78 */
  79static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
  80                             siginfo_t const *kinfo)
  81{
  82        long err;
  83
  84        BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
  85
  86        /*
  87         * Unused members should be zero ...
  88         */
  89        err = __clear_user(uinfo, sizeof(*uinfo));
  90
  91        /*
  92         * If you change siginfo_t structure, please be sure
  93         * this code is fixed accordingly.
  94         */
  95        err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
  96        err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
  97        err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
  98        switch (kinfo->si_code & __SI_MASK) {
  99        case __SI_KILL:
 100                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 101                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 102                break;
 103        case __SI_TIMER:
 104                 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
 105                 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
 106                 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 107                 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 108                break;
 109        case __SI_POLL:
 110                err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
 111                err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
 112                break;
 113        case __SI_FAULT:
 114                err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
 115#ifdef __ARCH_SI_TRAPNO
 116                err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
 117#endif
 118#ifdef BUS_MCEERR_AO
 119                /* 
 120                 * Other callers might not initialize the si_lsb field,
 121                 * so check explicitly for the right codes here.
 122                 */
 123                if (kinfo->si_code == BUS_MCEERR_AR ||
 124                    kinfo->si_code == BUS_MCEERR_AO)
 125                        err |= __put_user((short) kinfo->si_addr_lsb,
 126                                          &uinfo->ssi_addr_lsb);
 127#endif
 128                break;
 129        case __SI_CHLD:
 130                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 131                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 132                err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
 133                err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
 134                err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
 135                break;
 136        case __SI_RT: /* This is not generated by the kernel as of now. */
 137        case __SI_MESGQ: /* But this is */
 138                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 139                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 140                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 141                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 142                break;
 143        default:
 144                /*
 145                 * This case catches also the signals queued by sigqueue().
 146                 */
 147                err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 148                err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
 149                err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
 150                err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 151                break;
 152        }
 153
 154        return err ? -EFAULT: sizeof(*uinfo);
 155}
 156
 157static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
 158                                int nonblock)
 159{
 160        ssize_t ret;
 161        DECLARE_WAITQUEUE(wait, current);
 162
 163        spin_lock_irq(&current->sighand->siglock);
 164        ret = dequeue_signal(current, &ctx->sigmask, info);
 165        switch (ret) {
 166        case 0:
 167                if (!nonblock)
 168                        break;
 169                ret = -EAGAIN;
 170        default:
 171                spin_unlock_irq(&current->sighand->siglock);
 172                return ret;
 173        }
 174
 175        add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 176        for (;;) {
 177                set_current_state(TASK_INTERRUPTIBLE);
 178                ret = dequeue_signal(current, &ctx->sigmask, info);
 179                if (ret != 0)
 180                        break;
 181                if (signal_pending(current)) {
 182                        ret = -ERESTARTSYS;
 183                        break;
 184                }
 185                spin_unlock_irq(&current->sighand->siglock);
 186                schedule();
 187                spin_lock_irq(&current->sighand->siglock);
 188        }
 189        spin_unlock_irq(&current->sighand->siglock);
 190
 191        remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
 192        __set_current_state(TASK_RUNNING);
 193
 194        return ret;
 195}
 196
 197/*
 198 * Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
 199 * error code. The "count" parameter must be at least the size of a
 200 * "struct signalfd_siginfo".
 201 */
 202static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
 203                             loff_t *ppos)
 204{
 205        struct signalfd_ctx *ctx = file->private_data;
 206        struct signalfd_siginfo __user *siginfo;
 207        int nonblock = file->f_flags & O_NONBLOCK;
 208        ssize_t ret, total = 0;
 209        siginfo_t info;
 210
 211        count /= sizeof(struct signalfd_siginfo);
 212        if (!count)
 213                return -EINVAL;
 214
 215        siginfo = (struct signalfd_siginfo __user *) buf;
 216        do {
 217                ret = signalfd_dequeue(ctx, &info, nonblock);
 218                if (unlikely(ret <= 0))
 219                        break;
 220                ret = signalfd_copyinfo(siginfo, &info);
 221                if (ret < 0)
 222                        break;
 223                siginfo++;
 224                total += ret;
 225                nonblock = 1;
 226        } while (--count);
 227
 228        return total ? total: ret;
 229}
 230
 231#ifdef CONFIG_PROC_FS
 232static int signalfd_show_fdinfo(struct seq_file *m, struct file *f)
 233{
 234        struct signalfd_ctx *ctx = f->private_data;
 235        sigset_t sigmask;
 236
 237        sigmask = ctx->sigmask;
 238        signotset(&sigmask);
 239        render_sigset_t(m, "sigmask:\t", &sigmask);
 240
 241        return 0;
 242}
 243#endif
 244
 245static const struct file_operations signalfd_fops = {
 246#ifdef CONFIG_PROC_FS
 247        .show_fdinfo    = signalfd_show_fdinfo,
 248#endif
 249        .release        = signalfd_release,
 250        .poll           = signalfd_poll,
 251        .read           = signalfd_read,
 252        .llseek         = noop_llseek,
 253};
 254
 255SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 256                size_t, sizemask, int, flags)
 257{
 258        sigset_t sigmask;
 259        struct signalfd_ctx *ctx;
 260
 261        /* Check the SFD_* constants for consistency.  */
 262        BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
 263        BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
 264
 265        if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 266                return -EINVAL;
 267
 268        if (sizemask != sizeof(sigset_t) ||
 269            copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
 270                return -EINVAL;
 271        sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
 272        signotset(&sigmask);
 273
 274        if (ufd == -1) {
 275                ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 276                if (!ctx)
 277                        return -ENOMEM;
 278
 279                ctx->sigmask = sigmask;
 280
 281                /*
 282                 * When we call this, the initialization must be complete, since
 283                 * anon_inode_getfd() will install the fd.
 284                 */
 285                ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
 286                                       O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
 287                if (ufd < 0)
 288                        kfree(ctx);
 289        } else {
 290                struct fd f = fdget(ufd);
 291                if (!f.file)
 292                        return -EBADF;
 293                ctx = f.file->private_data;
 294                if (f.file->f_op != &signalfd_fops) {
 295                        fdput(f);
 296                        return -EINVAL;
 297                }
 298                spin_lock_irq(&current->sighand->siglock);
 299                ctx->sigmask = sigmask;
 300                spin_unlock_irq(&current->sighand->siglock);
 301
 302                wake_up(&current->sighand->signalfd_wqh);
 303                fdput(f);
 304        }
 305
 306        return ufd;
 307}
 308
 309SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 310                size_t, sizemask)
 311{
 312        return sys_signalfd4(ufd, user_mask, sizemask, 0);
 313}
 314
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