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