fs/select.c

   1 /*
   2  * This file contains the procedures for the handling of select and poll
   3  *
   4  * Created for Linux based loosely upon Mathius Lattner's minix
   5  * patches by Peter MacDonald. Heavily edited by Linus.
   6  *
   7  *  4 February 1994
   8  *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS
   9  *     flag set in its personality we do *not* modify the given timeout
  10  *     parameter to reflect time remaining.
  11  *
  12  *  24 January 2000
  13  *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation
  14  *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).
  15  */
  16
  17 #include <linux/slab.h>
  18 #include <linux/smp_lock.h>
  19 #include <linux/poll.h>
  20 #include <linux/personality.h> /* for STICKY_TIMEOUTS */
  21 #include <linux/file.h>
  22
  23 #include <asm/uaccess.h>
  24
  25 #define ROUND_UP(x,y) (((x)+(y)-1)/(y))
  26 #define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
  27
  28 struct poll_table_entry {
  29         struct file * filp;
  30         wait_queue_t wait;
  31         wait_queue_head_t * wait_address;
  32 };
  33
  34 struct poll_table_page {
  35         struct poll_table_page * next;
  36         struct poll_table_entry * entry;
  37         struct poll_table_entry entries[0];
  38 };
  39
  40 #define POLL_TABLE_FULL(table) \
  41         ((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))
  42
  43 /*
  44  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
  45  * I have rewritten this, taking some shortcuts: This code may not be easy to
  46  * follow, but it should be free of race-conditions, and it's practical. If you
  47  * understand what I'm doing here, then you understand how the linux
  48  * sleep/wakeup mechanism works.
  49  *
  50  * Two very simple procedures, poll_wait() and poll_freewait() make all the
  51  * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
  52  * as all select/poll functions have to call it to add an entry to the
  53  * poll table.
  54  */
  55
  56 void poll_freewait(poll_table* pt)
  57 {
  58         struct poll_table_page * p = pt->table;
  59         while (p) {
  60                 struct poll_table_entry * entry;
  61                 struct poll_table_page *old;
  62
  63                 entry = p->entry;
  64                 do {
  65                         entry--;
  66                         remove_wait_queue(entry->wait_address,&entry->wait);
  67                         fput(entry->filp);
  68                 } while (entry > p->entries);
  69                 old = p;
  70                 p = p->next;
  71                 free_page((unsigned long) old);
  72         }
  73 }
  74
  75 void __pollwait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
  76 {
  77         struct poll_table_page *table = p->table;
  78
  79         if (!table || POLL_TABLE_FULL(table)) {
  80                 struct poll_table_page *new_table;
  81
  82                 new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
  83                 if (!new_table) {
  84                         p->error = -ENOMEM;
  85                         __set_current_state(TASK_RUNNING);
  86                         return;
  87                 }
  88                 new_table->entry = new_table->entries;
  89                 new_table->next = table;
  90                 p->table = new_table;
  91                 table = new_table;
  92         }
  93
  94         /* Add a new entry */
  95         {
  96                 struct poll_table_entry * entry = table->entry;
  97                 table->entry = entry+1;
  98                 get_file(filp);
  99                 entry->filp = filp;
 100                 entry->wait_address = wait_address;
 101                 init_waitqueue_entry(&entry->wait, current);
 102                 add_wait_queue(wait_address,&entry->wait);
 103         }
 104 }
 105
 106 #define __IN(fds, n)            (fds->in + n)
 107 #define __OUT(fds, n)           (fds->out + n)
 108 #define __EX(fds, n)            (fds->ex + n)
 109 #define __RES_IN(fds, n)        (fds->res_in + n)
 110 #define __RES_OUT(fds, n)       (fds->res_out + n)
 111 #define __RES_EX(fds, n)        (fds->res_ex + n)
 112
 113 #define BITS(fds, n)            (*__IN(fds, n)|*__OUT(fds, n)|*__EX(fds, n))
 114
 115 static int max_select_fd(unsigned long n, fd_set_bits *fds)
 116 {
 117         unsigned long *open_fds;
 118         unsigned long set;
 119         int max;
 120
 121         /* handle last in-complete long-word first */
 122         set = ~(~0UL << (n & (__NFDBITS-1)));
 123         n /= __NFDBITS;
 124         open_fds = current->files->open_fds->fds_bits+n;
 125         max = 0;
 126         if (set) {
 127                 set &= BITS(fds, n);
 128                 if (set) {
 129                         if (!(set & ~*open_fds))
 130                                 goto get_max;
 131                         return -EBADF;
 132                 }
 133         }
 134         while (n) {
 135                 open_fds--;
 136                 n--;
 137                 set = BITS(fds, n);
 138                 if (!set)
 139                         continue;
 140                 if (set & ~*open_fds)
 141                         return -EBADF;
 142                 if (max)
 143                         continue;
 144 get_max:
 145                 do {
 146                         max++;
 147                         set >>= 1;
 148                 } while (set);
 149                 max += n * __NFDBITS;
 150         }
 151
 152         return max;
 153 }
 154
 155 #define BIT(i)          (1UL << ((i)&(__NFDBITS-1)))
 156 #define MEM(i,m)        ((m)+(unsigned)(i)/__NFDBITS)
 157 #define ISSET(i,m)      (((i)&*(m)) != 0)
 158 #define SET(i,m)        (*(m) |= (i))
 159
 160 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
 161 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
 162 #define POLLEX_SET (POLLPRI)
 163
 164 int do_select(int n, fd_set_bits *fds, long *timeout)
 165 {
 166         poll_table table, *wait;
 167         int retval, i, off;
 168         long __timeout = *timeout;
 169
 170         read_lock(&current->files->file_lock);
 171         retval = max_select_fd(n, fds);
 172         read_unlock(&current->files->file_lock);
 173
 174         if (retval < 0)
 175                 return retval;
 176         n = retval;
 177
 178         poll_initwait(&table);
 179         wait = &table;
 180         if (!__timeout)
 181                 wait = NULL;
 182         retval = 0;
 183         for (;;) {
 184                 set_current_state(TASK_INTERRUPTIBLE);
 185                 for (i = 0 ; i < n; i++) {
 186                         unsigned long bit = BIT(i);
 187                         unsigned long mask;
 188                         struct file *file;
 189
 190                         off = i / __NFDBITS;
 191                         if (!(bit & BITS(fds, off)))
 192                                 continue;
 193                         file = fget(i);
 194                         mask = POLLNVAL;
 195                         if (file) {
 196                                 mask = DEFAULT_POLLMASK;
 197                                 if (file->f_op && file->f_op->poll)
 198                                         mask = file->f_op->poll(file, wait);
 199                                 fput(file);
 200                         }
 201                         if ((mask & POLLIN_SET) && ISSET(bit, __IN(fds,off))) {
 202                                 SET(bit, __RES_IN(fds,off));
 203                                 retval++;
 204                                 wait = NULL;
 205                         }
 206                         if ((mask & POLLOUT_SET) && ISSET(bit, __OUT(fds,off))) {
 207                                 SET(bit, __RES_OUT(fds,off));
 208                                 retval++;
 209                                 wait = NULL;
 210                         }
 211                         if ((mask & POLLEX_SET) && ISSET(bit, __EX(fds,off))) {
 212                                 SET(bit, __RES_EX(fds,off));
 213                                 retval++;
 214                                 wait = NULL;
 215                         }
 216                 }
 217                 wait = NULL;
 218                 if (retval || !__timeout || signal_pending(current))
 219                         break;
 220                 if(table.error) {
 221                         retval = table.error;
 222                         break;
 223                 }
 224                 __timeout = schedule_timeout(__timeout);
 225         }
 226         current->state = TASK_RUNNING;
 227
 228         poll_freewait(&table);
 229
 230         /*
 231          * Up-to-date the caller timeout.
 232          */
 233         *timeout = __timeout;
 234         return retval;
 235 }
 236
 237 static void *select_bits_alloc(int size)
 238 {
 239         return kmalloc(6 * size, GFP_KERNEL);
 240 }
 241
 242 static void select_bits_free(void *bits, int size)
 243 {
 244         kfree(bits);
 245 }
 246
 247 /*
 248  * We can actually return ERESTARTSYS instead of EINTR, but I'd
 249  * like to be certain this leads to no problems. So I return
 250  * EINTR just for safety.
 251  *
 252  * Update: ERESTARTSYS breaks at least the xview clock binary, so
 253  * I'm trying ERESTARTNOHAND which restart only when you want to.
 254  */
 255 #define MAX_SELECT_SECONDS \
 256         ((unsigned long) (MAX_SCHEDULE_TIMEOUT / HZ)-1)
 257
 258 asmlinkage long
 259 sys_select(int n, fd_set *inp, fd_set *outp, fd_set *exp, struct timeval *tvp)
 260 {
 261         fd_set_bits fds;
 262         char *bits;
 263         long timeout;
 264         int ret, size, max_fdset;
 265
 266         timeout = MAX_SCHEDULE_TIMEOUT;
 267         if (tvp) {
 268                 time_t sec, usec;
 269
 270                 if ((ret = verify_area(VERIFY_READ, tvp, sizeof(*tvp)))
 271                     || (ret = __get_user(sec, &tvp->tv_sec))
 272                     || (ret = __get_user(usec, &tvp->tv_usec)))
 273                         goto out_nofds;
 274
 275                 ret = -EINVAL;
 276                 if (sec < 0 || usec < 0)
 277                         goto out_nofds;
 278
 279                 if ((unsigned long) sec < MAX_SELECT_SECONDS) {
 280                         timeout = ROUND_UP(usec, 1000000/HZ);
 281                         timeout += sec * (unsigned long) HZ;
 282                 }
 283         }
 284
 285         ret = -EINVAL;
 286         if (n < 0)
 287                 goto out_nofds;
 288
 289         /* max_fdset can increase, so grab it once to avoid race */
 290         max_fdset = current->files->max_fdset;
 291         if (n > max_fdset)
 292                 n = max_fdset;
 293
 294         /*
 295          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
 296          * since we used fdset we need to allocate memory in units of
 297          * long-words.
 298          */
 299         ret = -ENOMEM;
 300         size = FDS_BYTES(n);
 301         bits = select_bits_alloc(size);
 302         if (!bits)
 303                 goto out_nofds;
 304         fds.in      = (unsigned long *)  bits;
 305         fds.out     = (unsigned long *) (bits +   size);
 306         fds.ex      = (unsigned long *) (bits + 2*size);
 307         fds.res_in  = (unsigned long *) (bits + 3*size);
 308         fds.res_out = (unsigned long *) (bits + 4*size);
 309         fds.res_ex  = (unsigned long *) (bits + 5*size);
 310
 311         if ((ret = get_fd_set(n, inp, fds.in)) ||
 312             (ret = get_fd_set(n, outp, fds.out)) ||
 313             (ret = get_fd_set(n, exp, fds.ex)))
 314                 goto out;
 315         zero_fd_set(n, fds.res_in);
 316         zero_fd_set(n, fds.res_out);
 317         zero_fd_set(n, fds.res_ex);
 318
 319         ret = do_select(n, &fds, &timeout);
 320
 321         if (tvp && !(current->personality & STICKY_TIMEOUTS)) {
 322                 time_t sec = 0, usec = 0;
 323                 if (timeout) {
 324                         sec = timeout / HZ;
 325                         usec = timeout % HZ;
 326                         usec *= (1000000/HZ);
 327                 }
 328                 put_user(sec, &tvp->tv_sec);
 329                 put_user(usec, &tvp->tv_usec);
 330         }
 331
 332         if (ret < 0)
 333                 goto out;
 334         if (!ret) {
 335                 ret = -ERESTARTNOHAND;
 336                 if (signal_pending(current))
 337                         goto out;
 338                 ret = 0;
 339         }
 340
 341         set_fd_set(n, inp, fds.res_in);
 342         set_fd_set(n, outp, fds.res_out);
 343         set_fd_set(n, exp, fds.res_ex);
 344
 345 out:
 346         select_bits_free(bits, size);
 347 out_nofds:
 348         return ret;
 349 }
 350
 351 #define POLLFD_PER_PAGE  ((PAGE_SIZE) / sizeof(struct pollfd))
 352
 353 static void do_pollfd(unsigned int num, struct pollfd * fdpage,
 354         poll_table ** pwait, int *count)
 355 {
 356         int i;
 357
 358         for (i = 0; i < num; i++) {
 359                 int fd;
 360                 unsigned int mask;
 361                 struct pollfd *fdp;
 362
 363                 mask = 0;
 364                 fdp = fdpage+i;
 365                 fd = fdp->fd;
 366                 if (fd >= 0) {
 367                         struct file * file = fget(fd);
 368                         mask = POLLNVAL;
 369                         if (file != NULL) {
 370                                 mask = DEFAULT_POLLMASK;
 371                                 if (file->f_op && file->f_op->poll)
 372                                         mask = file->f_op->poll(file, *pwait);
 373                                 mask &= fdp->events | POLLERR | POLLHUP;
 374                                 fput(file);
 375                         }
 376                         if (mask) {
 377                                 *pwait = NULL;
 378                                 (*count)++;
 379                         }
 380                 }
 381                 fdp->revents = mask;
 382         }
 383 }
 384
 385 static int do_poll(unsigned int nfds, unsigned int nchunks, unsigned int nleft,
 386         struct pollfd *fds[], poll_table *wait, long timeout)
 387 {
 388         int count;
 389         poll_table* pt = wait;
 390
 391         for (;;) {
 392                 unsigned int i;
 393
 394                 set_current_state(TASK_INTERRUPTIBLE);
 395                 count = 0;
 396                 for (i=0; i < nchunks; i++)
 397                         do_pollfd(POLLFD_PER_PAGE, fds[i], &pt, &count);
 398                 if (nleft)
 399                         do_pollfd(nleft, fds[nchunks], &pt, &count);
 400                 pt = NULL;
 401                 if (count || !timeout || signal_pending(current))
 402                         break;
 403                 count = wait->error;
 404                 if (count)
 405                         break;
 406                 timeout = schedule_timeout(timeout);
 407         }
 408         current->state = TASK_RUNNING;
 409         return count;
 410 }
 411
 412 asmlinkage long sys_poll(struct pollfd * ufds, unsigned int nfds, long timeout)
 413 {
 414         int i, j, fdcount, err;
 415         struct pollfd **fds;
 416         poll_table table, *wait;
 417         int nchunks, nleft;
 418
 419         /* Do a sanity check on nfds ... */
 420         if (nfds > current->files->max_fdset && nfds > OPEN_MAX)
 421                 return -EINVAL;
 422
 423         if (timeout) {
 424                 /* Careful about overflow in the intermediate values */
 425                 if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
 426                         timeout = (unsigned long)(timeout*HZ+999)/1000+1;
 427                 else /* Negative or overflow */
 428                         timeout = MAX_SCHEDULE_TIMEOUT;
 429         }
 430
 431         poll_initwait(&table);
 432         wait = &table;
 433         if (!timeout)
 434                 wait = NULL;
 435
 436         err = -ENOMEM;
 437         fds = NULL;
 438         if (nfds != 0) {
 439                 fds = (struct pollfd **)kmalloc(
 440                         (1 + (nfds - 1) / POLLFD_PER_PAGE) * sizeof(struct pollfd *),
 441                         GFP_KERNEL);
 442                 if (fds == NULL)
 443                         goto out;
 444         }
 445
 446         nchunks = 0;
 447         nleft = nfds;
 448         while (nleft > POLLFD_PER_PAGE) { /* allocate complete PAGE_SIZE chunks */
 449                 fds[nchunks] = (struct pollfd *)__get_free_page(GFP_KERNEL);
 450                 if (fds[nchunks] == NULL)
 451                         goto out_fds;
 452                 nchunks++;
 453                 nleft -= POLLFD_PER_PAGE;
 454         }
 455         if (nleft) { /* allocate last PAGE_SIZE chunk, only nleft elements used */
 456                 fds[nchunks] = (struct pollfd *)__get_free_page(GFP_KERNEL);
 457                 if (fds[nchunks] == NULL)
 458                         goto out_fds;
 459         }
 460
 461         err = -EFAULT;
 462         for (i=0; i < nchunks; i++)
 463                 if (copy_from_user(fds[i], ufds + i*POLLFD_PER_PAGE, PAGE_SIZE))
 464                         goto out_fds1;
 465         if (nleft) {
 466                 if (copy_from_user(fds[nchunks], ufds + nchunks*POLLFD_PER_PAGE,
 467                                 nleft * sizeof(struct pollfd)))
 468                         goto out_fds1;
 469         }
 470
 471         fdcount = do_poll(nfds, nchunks, nleft, fds, wait, timeout);
 472
 473         /* OK, now copy the revents fields back to user space. */
 474         for(i=0; i < nchunks; i++)
 475                 for (j=0; j < POLLFD_PER_PAGE; j++, ufds++)
 476                         __put_user((fds[i] + j)->revents, &ufds->revents);
 477         if (nleft)
 478                 for (j=0; j < nleft; j++, ufds++)
 479                         __put_user((fds[nchunks] + j)->revents, &ufds->revents);
 480
 481         err = fdcount;
 482         if (!fdcount && signal_pending(current))
 483                 err = -EINTR;
 484
 485 out_fds1:
 486         if (nleft)
 487                 free_page((unsigned long)(fds[nchunks]));
 488 out_fds:
 489         for (i=0; i < nchunks; i++)
 490                 free_page((unsigned long)(fds[i]));
 491         if (nfds != 0)
 492                 kfree(fds);
 493 out:
 494         poll_freewait(&table);
 495         return err;
 496 }