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/syscalls.h>
  18 #include <linux/module.h>
  19 #include <linux/slab.h>
  20 #include <linux/smp_lock.h>
  21 #include <linux/poll.h>
  22 #include <linux/personality.h> /* for STICKY_TIMEOUTS */
  23 #include <linux/file.h>
  24 #include <linux/fs.h>
  25 #include <linux/rcupdate.h>
  26
  27 #include <asm/uaccess.h>
  28
  29 #define ROUND_UP(x,y) (((x)+(y)-1)/(y))
  30 #define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
  31
  32 struct poll_table_entry {
  33         struct file * filp;
  34         wait_queue_t wait;
  35         wait_queue_head_t * wait_address;
  36 };
  37
  38 struct poll_table_page {
  39         struct poll_table_page * next;
  40         struct poll_table_entry * entry;
  41         struct poll_table_entry entries[0];
  42 };
  43
  44 #define POLL_TABLE_FULL(table) \
  45         ((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))
  46
  47 /*
  48  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
  49  * I have rewritten this, taking some shortcuts: This code may not be easy to
  50  * follow, but it should be free of race-conditions, and it's practical. If you
  51  * understand what I'm doing here, then you understand how the linux
  52  * sleep/wakeup mechanism works.
  53  *
  54  * Two very simple procedures, poll_wait() and poll_freewait() make all the
  55  * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
  56  * as all select/poll functions have to call it to add an entry to the
  57  * poll table.
  58  */
  59 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
  60                        poll_table *p);
  61
  62 void poll_initwait(struct poll_wqueues *pwq)
  63 {
  64         init_poll_funcptr(&pwq->pt, __pollwait);
  65         pwq->error = 0;
  66         pwq->table = NULL;
  67 }
  68
  69 EXPORT_SYMBOL(poll_initwait);
  70
  71 void poll_freewait(struct poll_wqueues *pwq)
  72 {
  73         struct poll_table_page * p = pwq->table;
  74         while (p) {
  75                 struct poll_table_entry * entry;
  76                 struct poll_table_page *old;
  77
  78                 entry = p->entry;
  79                 do {
  80                         entry--;
  81                         remove_wait_queue(entry->wait_address,&entry->wait);
  82                         fput(entry->filp);
  83                 } while (entry > p->entries);
  84                 old = p;
  85                 p = p->next;
  86                 free_page((unsigned long) old);
  87         }
  88 }
  89
  90 EXPORT_SYMBOL(poll_freewait);
  91
  92 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
  93                        poll_table *_p)
  94 {
  95         struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
  96         struct poll_table_page *table = p->table;
  97
  98         if (!table || POLL_TABLE_FULL(table)) {
  99                 struct poll_table_page *new_table;
 100
 101                 new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
 102                 if (!new_table) {
 103                         p->error = -ENOMEM;
 104                         __set_current_state(TASK_RUNNING);
 105                         return;
 106                 }
 107                 new_table->entry = new_table->entries;
 108                 new_table->next = table;
 109                 p->table = new_table;
 110                 table = new_table;
 111         }
 112
 113         /* Add a new entry */
 114         {
 115                 struct poll_table_entry * entry = table->entry;
 116                 table->entry = entry+1;
 117                 get_file(filp);
 118                 entry->filp = filp;
 119                 entry->wait_address = wait_address;
 120                 init_waitqueue_entry(&entry->wait, current);
 121                 add_wait_queue(wait_address,&entry->wait);
 122         }
 123 }
 124
 125 #define FDS_IN(fds, n)          (fds->in + n)
 126 #define FDS_OUT(fds, n)         (fds->out + n)
 127 #define FDS_EX(fds, n)          (fds->ex + n)
 128
 129 #define BITS(fds, n)    (*FDS_IN(fds, n)|*FDS_OUT(fds, n)|*FDS_EX(fds, n))
 130
 131 static int max_select_fd(unsigned long n, fd_set_bits *fds)
 132 {
 133         unsigned long *open_fds;
 134         unsigned long set;
 135         int max;
 136         struct fdtable *fdt;
 137
 138         /* handle last in-complete long-word first */
 139         set = ~(~0UL << (n & (__NFDBITS-1)));
 140         n /= __NFDBITS;
 141         fdt = files_fdtable(current->files);
 142         open_fds = fdt->open_fds->fds_bits+n;
 143         max = 0;
 144         if (set) {
 145                 set &= BITS(fds, n);
 146                 if (set) {
 147                         if (!(set & ~*open_fds))
 148                                 goto get_max;
 149                         return -EBADF;
 150                 }
 151         }
 152         while (n) {
 153                 open_fds--;
 154                 n--;
 155                 set = BITS(fds, n);
 156                 if (!set)
 157                         continue;
 158                 if (set & ~*open_fds)
 159                         return -EBADF;
 160                 if (max)
 161                         continue;
 162 get_max:
 163                 do {
 164                         max++;
 165                         set >>= 1;
 166                 } while (set);
 167                 max += n * __NFDBITS;
 168         }
 169
 170         return max;
 171 }
 172
 173 #define BIT(i)          (1UL << ((i)&(__NFDBITS-1)))
 174 #define MEM(i,m)        ((m)+(unsigned)(i)/__NFDBITS)
 175 #define ISSET(i,m)      (((i)&*(m)) != 0)
 176 #define SET(i,m)        (*(m) |= (i))
 177
 178 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
 179 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
 180 #define POLLEX_SET (POLLPRI)
 181
 182 int do_select(int n, fd_set_bits *fds, long *timeout)
 183 {
 184         struct poll_wqueues table;
 185         poll_table *wait;
 186         int retval, i;
 187         long __timeout = *timeout;
 188
 189         rcu_read_lock();
 190         retval = max_select_fd(n, fds);
 191         rcu_read_unlock();
 192
 193         if (retval < 0)
 194                 return retval;
 195         n = retval;
 196
 197         poll_initwait(&table);
 198         wait = &table.pt;
 199         if (!__timeout)
 200                 wait = NULL;
 201         retval = 0;
 202         for (;;) {
 203                 unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
 204
 205                 set_current_state(TASK_INTERRUPTIBLE);
 206
 207                 inp = fds->in; outp = fds->out; exp = fds->ex;
 208                 rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
 209
 210                 for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
 211                         unsigned long in, out, ex, all_bits, bit = 1, mask, j;
 212                         unsigned long res_in = 0, res_out = 0, res_ex = 0;
 213                         struct file_operations *f_op = NULL;
 214                         struct file *file = NULL;
 215
 216                         in = *inp++; out = *outp++; ex = *exp++;
 217                         all_bits = in | out | ex;
 218                         if (all_bits == 0) {
 219                                 i += __NFDBITS;
 220                                 continue;
 221                         }
 222
 223                         for (j = 0; j < __NFDBITS; ++j, ++i, bit <<= 1) {
 224                                 if (i >= n)
 225                                         break;
 226                                 if (!(bit & all_bits))
 227                                         continue;
 228                                 file = fget(i);
 229                                 if (file) {
 230                                         f_op = file->f_op;
 231                                         mask = DEFAULT_POLLMASK;
 232                                         if (f_op && f_op->poll)
 233                                                 mask = (*f_op->poll)(file, retval ? NULL : wait);
 234                                         fput(file);
 235                                         if ((mask & POLLIN_SET) && (in & bit)) {
 236                                                 res_in |= bit;
 237                                                 retval++;
 238                                         }
 239                                         if ((mask & POLLOUT_SET) && (out & bit)) {
 240                                                 res_out |= bit;
 241                                                 retval++;
 242                                         }
 243                                         if ((mask & POLLEX_SET) && (ex & bit)) {
 244                                                 res_ex |= bit;
 245                                                 retval++;
 246                                         }
 247                                 }
 248                                 cond_resched();
 249                         }
 250                         if (res_in)
 251                                 *rinp = res_in;
 252                         if (res_out)
 253                                 *routp = res_out;
 254                         if (res_ex)
 255                                 *rexp = res_ex;
 256                 }
 257                 wait = NULL;
 258                 if (retval || !__timeout || signal_pending(current))
 259                         break;
 260                 if(table.error) {
 261                         retval = table.error;
 262                         break;
 263                 }
 264                 __timeout = schedule_timeout(__timeout);
 265         }
 266         __set_current_state(TASK_RUNNING);
 267
 268         poll_freewait(&table);
 269
 270         /*
 271          * Up-to-date the caller timeout.
 272          */
 273         *timeout = __timeout;
 274         return retval;
 275 }
 276
 277 static void *select_bits_alloc(int size)
 278 {
 279         return kmalloc(6 * size, GFP_KERNEL);
 280 }
 281
 282 static void select_bits_free(void *bits, int size)
 283 {
 284         kfree(bits);
 285 }
 286
 287 /*
 288  * We can actually return ERESTARTSYS instead of EINTR, but I'd
 289  * like to be certain this leads to no problems. So I return
 290  * EINTR just for safety.
 291  *
 292  * Update: ERESTARTSYS breaks at least the xview clock binary, so
 293  * I'm trying ERESTARTNOHAND which restart only when you want to.
 294  */
 295 #define MAX_SELECT_SECONDS \
 296         ((unsigned long) (MAX_SCHEDULE_TIMEOUT / HZ)-1)
 297
 298 asmlinkage long
 299 sys_select(int n, fd_set __user *inp, fd_set __user *outp, fd_set __user *exp, struct timeval __user *tvp)
 300 {
 301         fd_set_bits fds;
 302         char *bits;
 303         long timeout;
 304         int ret, size, max_fdset;
 305         struct fdtable *fdt;
 306
 307         timeout = MAX_SCHEDULE_TIMEOUT;
 308         if (tvp) {
 309                 time_t sec, usec;
 310
 311                 if (!access_ok(VERIFY_READ, tvp, sizeof(*tvp))
 312                     || __get_user(sec, &tvp->tv_sec)
 313                     || __get_user(usec, &tvp->tv_usec)) {
 314                         ret = -EFAULT;
 315                         goto out_nofds;
 316                 }
 317
 318                 ret = -EINVAL;
 319                 if (sec < 0 || usec < 0)
 320                         goto out_nofds;
 321
 322                 if ((unsigned long) sec < MAX_SELECT_SECONDS) {
 323                         timeout = ROUND_UP(usec, 1000000/HZ);
 324                         timeout += sec * (unsigned long) HZ;
 325                 }
 326         }
 327
 328         ret = -EINVAL;
 329         if (n < 0)
 330                 goto out_nofds;
 331
 332         /* max_fdset can increase, so grab it once to avoid race */
 333         rcu_read_lock();
 334         fdt = files_fdtable(current->files);
 335         max_fdset = fdt->max_fdset;
 336         rcu_read_unlock();
 337         if (n > max_fdset)
 338                 n = max_fdset;
 339
 340         /*
 341          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
 342          * since we used fdset we need to allocate memory in units of
 343          * long-words.
 344          */
 345         ret = -ENOMEM;
 346         size = FDS_BYTES(n);
 347         bits = select_bits_alloc(size);
 348         if (!bits)
 349                 goto out_nofds;
 350         fds.in      = (unsigned long *)  bits;
 351         fds.out     = (unsigned long *) (bits +   size);
 352         fds.ex      = (unsigned long *) (bits + 2*size);
 353         fds.res_in  = (unsigned long *) (bits + 3*size);
 354         fds.res_out = (unsigned long *) (bits + 4*size);
 355         fds.res_ex  = (unsigned long *) (bits + 5*size);
 356
 357         if ((ret = get_fd_set(n, inp, fds.in)) ||
 358             (ret = get_fd_set(n, outp, fds.out)) ||
 359             (ret = get_fd_set(n, exp, fds.ex)))
 360                 goto out;
 361         zero_fd_set(n, fds.res_in);
 362         zero_fd_set(n, fds.res_out);
 363         zero_fd_set(n, fds.res_ex);
 364
 365         ret = do_select(n, &fds, &timeout);
 366
 367         if (tvp && !(current->personality & STICKY_TIMEOUTS)) {
 368                 time_t sec = 0, usec = 0;
 369                 if (timeout) {
 370                         sec = timeout / HZ;
 371                         usec = timeout % HZ;
 372                         usec *= (1000000/HZ);
 373                 }
 374                 put_user(sec, &tvp->tv_sec);
 375                 put_user(usec, &tvp->tv_usec);
 376         }
 377
 378         if (ret < 0)
 379                 goto out;
 380         if (!ret) {
 381                 ret = -ERESTARTNOHAND;
 382                 if (signal_pending(current))
 383                         goto out;
 384                 ret = 0;
 385         }
 386
 387         if (set_fd_set(n, inp, fds.res_in) ||
 388             set_fd_set(n, outp, fds.res_out) ||
 389             set_fd_set(n, exp, fds.res_ex))
 390                 ret = -EFAULT;
 391
 392 out:
 393         select_bits_free(bits, size);
 394 out_nofds:
 395         return ret;
 396 }
 397
 398 struct poll_list {
 399         struct poll_list *next;
 400         int len;
 401         struct pollfd entries[0];
 402 };
 403
 404 #define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))
 405
 406 static void do_pollfd(unsigned int num, struct pollfd * fdpage,
 407         poll_table ** pwait, int *count)
 408 {
 409         int i;
 410
 411         for (i = 0; i < num; i++) {
 412                 int fd;
 413                 unsigned int mask;
 414                 struct pollfd *fdp;
 415
 416                 mask = 0;
 417                 fdp = fdpage+i;
 418                 fd = fdp->fd;
 419                 if (fd >= 0) {
 420                         struct file * file = fget(fd);
 421                         mask = POLLNVAL;
 422                         if (file != NULL) {
 423                                 mask = DEFAULT_POLLMASK;
 424                                 if (file->f_op && file->f_op->poll)
 425                                         mask = file->f_op->poll(file, *pwait);
 426                                 mask &= fdp->events | POLLERR | POLLHUP;
 427                                 fput(file);
 428                         }
 429                         if (mask) {
 430                                 *pwait = NULL;
 431                                 (*count)++;
 432                         }
 433                 }
 434                 fdp->revents = mask;
 435         }
 436 }
 437
 438 static int do_poll(unsigned int nfds,  struct poll_list *list,
 439                         struct poll_wqueues *wait, long timeout)
 440 {
 441         int count = 0;
 442         poll_table* pt = &wait->pt;
 443
 444         if (!timeout)
 445                 pt = NULL;
 446
 447         for (;;) {
 448                 struct poll_list *walk;
 449                 set_current_state(TASK_INTERRUPTIBLE);
 450                 walk = list;
 451                 while(walk != NULL) {
 452                         do_pollfd( walk->len, walk->entries, &pt, &count);
 453                         walk = walk->next;
 454                 }
 455                 pt = NULL;
 456                 if (count || !timeout || signal_pending(current))
 457                         break;
 458                 count = wait->error;
 459                 if (count)
 460                         break;
 461                 timeout = schedule_timeout(timeout);
 462         }
 463         __set_current_state(TASK_RUNNING);
 464         return count;
 465 }
 466
 467 asmlinkage long sys_poll(struct pollfd __user * ufds, unsigned int nfds, long timeout)
 468 {
 469         struct poll_wqueues table;
 470         int fdcount, err;
 471         unsigned int i;
 472         struct poll_list *head;
 473         struct poll_list *walk;
 474         struct fdtable *fdt;
 475         int max_fdset;
 476
 477         /* Do a sanity check on nfds ... */
 478         rcu_read_lock();
 479         fdt = files_fdtable(current->files);
 480         max_fdset = fdt->max_fdset;
 481         rcu_read_unlock();
 482         if (nfds > max_fdset && nfds > OPEN_MAX)
 483                 return -EINVAL;
 484
 485         if (timeout) {
 486                 /* Careful about overflow in the intermediate values */
 487                 if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
 488                         timeout = (unsigned long)(timeout*HZ+999)/1000+1;
 489                 else /* Negative or overflow */
 490                         timeout = MAX_SCHEDULE_TIMEOUT;
 491         }
 492
 493         poll_initwait(&table);
 494
 495         head = NULL;
 496         walk = NULL;
 497         i = nfds;
 498         err = -ENOMEM;
 499         while(i!=0) {
 500                 struct poll_list *pp;
 501                 pp = kmalloc(sizeof(struct poll_list)+
 502                                 sizeof(struct pollfd)*
 503                                 (i>POLLFD_PER_PAGE?POLLFD_PER_PAGE:i),
 504                                         GFP_KERNEL);
 505                 if(pp==NULL)
 506                         goto out_fds;
 507                 pp->next=NULL;
 508                 pp->len = (i>POLLFD_PER_PAGE?POLLFD_PER_PAGE:i);
 509                 if (head == NULL)
 510                         head = pp;
 511                 else
 512                         walk->next = pp;
 513
 514                 walk = pp;
 515                 if (copy_from_user(pp->entries, ufds + nfds-i,
 516                                 sizeof(struct pollfd)*pp->len)) {
 517                         err = -EFAULT;
 518                         goto out_fds;
 519                 }
 520                 i -= pp->len;
 521         }
 522         fdcount = do_poll(nfds, head, &table, timeout);
 523
 524         /* OK, now copy the revents fields back to user space. */
 525         walk = head;
 526         err = -EFAULT;
 527         while(walk != NULL) {
 528                 struct pollfd *fds = walk->entries;
 529                 int j;
 530
 531                 for (j=0; j < walk->len; j++, ufds++) {
 532                         if(__put_user(fds[j].revents, &ufds->revents))
 533                                 goto out_fds;
 534                 }
 535                 walk = walk->next;
 536         }
 537         err = fdcount;
 538         if (!fdcount && signal_pending(current))
 539                 err = -EINTR;
 540 out_fds:
 541         walk = head;
 542         while(walk!=NULL) {
 543                 struct poll_list *pp = walk->next;
 544                 kfree(walk);
 545                 walk = pp;
 546         }
 547         poll_freewait(&table);
 548         return err;
 549 }