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
  13 #include <linux/malloc.h>
  14 #include <linux/smp_lock.h>
  15 #include <linux/poll.h>
  16 #include <linux/file.h>
  17
  18 #include <asm/uaccess.h>
  19
  20 #define ROUND_UP(x,y) (((x)+(y)-1)/(y))
  21 #define DEFAULT_POLLMASK (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)
  22
  23 /*
  24  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
  25  * I have rewritten this, taking some shortcuts: This code may not be easy to
  26  * follow, but it should be free of race-conditions, and it's practical. If you
  27  * understand what I'm doing here, then you understand how the linux
  28  * sleep/wakeup mechanism works.
  29  *
  30  * Two very simple procedures, poll_wait() and free_wait() make all the
  31  * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
  32  * as all select/poll functions have to call it to add an entry to the
  33  * poll table.
  34  */
  35
  36 /*
  37  * I rewrote this again to make the poll_table size variable, take some
  38  * more shortcuts, improve responsiveness, and remove another race that
  39  * Linus noticed.  -- jrs
  40  */
  41
  42 static void free_wait(poll_table * p)
  43 {
  44         struct poll_table_entry * entry;
  45         poll_table *old;
  46
  47         while (p) {
  48                 entry = p->entry + p->nr;
  49                 while (p->nr > 0) {
  50                         p->nr--;
  51                         entry--;
  52                         remove_wait_queue(entry->wait_address,&entry->wait);
  53                         fput(entry->filp);
  54                 }
  55                 old = p;
  56                 p = p->next;
  57                 free_page((unsigned long) old);
  58         }
  59 }
  60
  61 void __pollwait(struct file * filp, struct wait_queue ** wait_address, poll_table *p)
  62 {
  63         for (;;) {
  64                 if (p->nr < __MAX_POLL_TABLE_ENTRIES) {
  65                         struct poll_table_entry * entry;
  66 ok_table:
  67                         entry = p->entry + p->nr;
  68                         entry->filp = filp;
  69                         filp->f_count++;
  70                         entry->wait_address = wait_address;
  71                         entry->wait.task = current;
  72                         entry->wait.next = NULL;
  73                         add_wait_queue(wait_address,&entry->wait);
  74                         p->nr++;
  75                         return;
  76                 }
  77                 if (p->next == NULL) {
  78                         poll_table *tmp = (poll_table *) __get_free_page(GFP_KERNEL);
  79                         if (!tmp)
  80                                 return;
  81                         tmp->nr = 0;
  82                         tmp->entry = (struct poll_table_entry *)(tmp + 1);
  83                         tmp->next = NULL;
  84                         p->next = tmp;
  85                         p = tmp;
  86                         goto ok_table;
  87                 }
  88                 p = p->next;
  89         }
  90 }
  91
  92 #define __IN(fds, n)            (fds->in + n)
  93 #define __OUT(fds, n)           (fds->out + n)
  94 #define __EX(fds, n)            (fds->ex + n)
  95 #define __RES_IN(fds, n)        (fds->res_in + n)
  96 #define __RES_OUT(fds, n)       (fds->res_out + n)
  97 #define __RES_EX(fds, n)        (fds->res_ex + n)
  98
  99 #define BITS(fds, n)            (*__IN(fds, n)|*__OUT(fds, n)|*__EX(fds, n))
 100
 101 static int max_select_fd(unsigned long n, fd_set_bits *fds)
 102 {
 103         unsigned long *open_fds;
 104         unsigned long set;
 105         int max;
 106
 107         /* handle last in-complete long-word first */
 108         set = ~(~0UL << (n & (__NFDBITS-1)));
 109         n /= __NFDBITS;
 110         open_fds = current->files->open_fds.fds_bits+n;
 111         max = 0;
 112         if (set) {
 113                 set &= BITS(fds, n);
 114                 if (set) {
 115                         if (!(set & ~*open_fds))
 116                                 goto get_max;
 117                         return -EBADF;
 118                 }
 119         }
 120         while (n) {
 121                 open_fds--;
 122                 n--;
 123                 set = BITS(fds, n);
 124                 if (!set)
 125                         continue;
 126                 if (set & ~*open_fds)
 127                         return -EBADF;
 128                 if (max)
 129                         continue;
 130 get_max:
 131                 do {
 132                         max++;
 133                         set >>= 1;
 134                 } while (set);
 135                 max += n * __NFDBITS;
 136         }
 137
 138         return max;
 139 }
 140
 141 #define BIT(i)          (1UL << ((i)&(__NFDBITS-1)))
 142 #define MEM(i,m)        ((m)+(unsigned)(i)/__NFDBITS)
 143 #define ISSET(i,m)      (((i)&*(m)) != 0)
 144 #define SET(i,m)        (*(m) |= (i))
 145
 146 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
 147 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
 148 #define POLLEX_SET (POLLPRI)
 149
 150 int do_select(int n, fd_set_bits *fds, long *timeout)
 151 {
 152         poll_table *wait_table, *wait;
 153         int retval, i, off;
 154         long __timeout = *timeout;
 155
 156         wait = wait_table = NULL;
 157         if (__timeout) {
 158                 wait_table = (poll_table *) __get_free_page(GFP_KERNEL);
 159                 if (!wait_table)
 160                         return -ENOMEM;
 161
 162                 wait_table->nr = 0;
 163                 wait_table->entry = (struct poll_table_entry *)(wait_table + 1);
 164                 wait_table->next = NULL;
 165                 wait = wait_table;
 166         }
 167
 168         lock_kernel();
 169
 170         retval = max_select_fd(n, fds);
 171         if (retval < 0)
 172                 goto out;
 173         n = retval;
 174         retval = 0;
 175         for (;;) {
 176                 current->state = TASK_INTERRUPTIBLE;
 177                 for (i = 0 ; i < n; i++) {
 178                         unsigned long bit = BIT(i);
 179                         unsigned long mask;
 180                         struct file *file;
 181
 182                         off = i / __NFDBITS;
 183                         if (!(bit & BITS(fds, off)))
 184                                 continue;
 185                         /*
 186                          * The poll_wait routine will increment f_count if
 187                          * the file is added to the wait table, so we don't
 188                          * need to increment it now.
 189                          */
 190                         file = fcheck(i);
 191                         mask = POLLNVAL;
 192                         if (file) {
 193                                 mask = DEFAULT_POLLMASK;
 194                                 if (file->f_op && file->f_op->poll)
 195                                         mask = file->f_op->poll(file, wait);
 196                         }
 197                         if ((mask & POLLIN_SET) && ISSET(bit, __IN(fds,off))) {
 198                                 SET(bit, __RES_IN(fds,off));
 199                                 retval++;
 200                                 wait = NULL;
 201                         }
 202                         if ((mask & POLLOUT_SET) && ISSET(bit, __OUT(fds,off))) {
 203                                 SET(bit, __RES_OUT(fds,off));
 204                                 retval++;
 205                                 wait = NULL;
 206                         }
 207                         if ((mask & POLLEX_SET) && ISSET(bit, __EX(fds,off))) {
 208                                 SET(bit, __RES_EX(fds,off));
 209                                 retval++;
 210                                 wait = NULL;
 211                         }
 212                 }
 213                 wait = NULL;
 214                 if (retval || !__timeout || signal_pending(current))
 215                         break;
 216                 __timeout = schedule_timeout(__timeout);
 217         }
 218         current->state = TASK_RUNNING;
 219
 220 out:
 221         if (*timeout)
 222                 free_wait(wait_table);
 223
 224         /*
 225          * Up-to-date the caller timeout.
 226          */
 227         *timeout = __timeout;
 228         unlock_kernel();
 229         return retval;
 230 }
 231
 232 /*
 233  * We can actually return ERESTARTSYS instead of EINTR, but I'd
 234  * like to be certain this leads to no problems. So I return
 235  * EINTR just for safety.
 236  *
 237  * Update: ERESTARTSYS breaks at least the xview clock binary, so
 238  * I'm trying ERESTARTNOHAND which restart only when you want to.
 239  */
 240 #define MAX_SELECT_SECONDS \
 241         ((unsigned long) (MAX_SCHEDULE_TIMEOUT / HZ)-1)
 242
 243 asmlinkage int
 244 sys_select(int n, fd_set *inp, fd_set *outp, fd_set *exp, struct timeval *tvp)
 245 {
 246         fd_set_bits fds;
 247         char *bits;
 248         long timeout;
 249         int ret, size;
 250
 251         timeout = MAX_SCHEDULE_TIMEOUT;
 252         if (tvp) {
 253                 time_t sec, usec;
 254
 255                 if ((ret = verify_area(VERIFY_READ, tvp, sizeof(*tvp)))
 256                     || (ret = __get_user(sec, &tvp->tv_sec))
 257                     || (ret = __get_user(usec, &tvp->tv_usec)))
 258                         goto out_nofds;
 259
 260                 ret = -EINVAL;
 261                 if (sec < 0 || usec < 0)
 262                         goto out_nofds;
 263
 264                 if ((unsigned long) sec < MAX_SELECT_SECONDS) {
 265                         timeout = ROUND_UP(usec, 1000000/HZ);
 266                         timeout += sec * (unsigned long) HZ;
 267                 }
 268         }
 269
 270         ret = -EINVAL;
 271         if (n < 0 || n > KFDS_NR)
 272                 goto out_nofds;
 273         /*
 274          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
 275          * since we used fdset we need to allocate memory in units of
 276          * long-words.
 277          */
 278         ret = -ENOMEM;
 279         size = FDS_BYTES(n);
 280         bits = kmalloc(6 * size, GFP_KERNEL);
 281         if (!bits)
 282                 goto out_nofds;
 283         fds.in      = (unsigned long *)  bits;
 284         fds.out     = (unsigned long *) (bits +   size);
 285         fds.ex      = (unsigned long *) (bits + 2*size);
 286         fds.res_in  = (unsigned long *) (bits + 3*size);
 287         fds.res_out = (unsigned long *) (bits + 4*size);
 288         fds.res_ex  = (unsigned long *) (bits + 5*size);
 289
 290         if ((ret = get_fd_set(n, inp, fds.in)) ||
 291             (ret = get_fd_set(n, outp, fds.out)) ||
 292             (ret = get_fd_set(n, exp, fds.ex)))
 293                 goto out;
 294         zero_fd_set(n, fds.res_in);
 295         zero_fd_set(n, fds.res_out);
 296         zero_fd_set(n, fds.res_ex);
 297
 298         ret = do_select(n, &fds, &timeout);
 299
 300         if (tvp && !(current->personality & STICKY_TIMEOUTS)) {
 301                 time_t sec = 0, usec = 0;
 302                 if (timeout) {
 303                         sec = timeout / HZ;
 304                         usec = timeout % HZ;
 305                         usec *= (1000000/HZ);
 306                 }
 307                 put_user(sec, &tvp->tv_sec);
 308                 put_user(usec, &tvp->tv_usec);
 309         }
 310
 311         if (ret < 0)
 312                 goto out;
 313         if (!ret) {
 314                 ret = -ERESTARTNOHAND;
 315                 if (signal_pending(current))
 316                         goto out;
 317                 ret = 0;
 318         }
 319
 320         set_fd_set(n, inp, fds.res_in);
 321         set_fd_set(n, outp, fds.res_out);
 322         set_fd_set(n, exp, fds.res_ex);
 323
 324 out:
 325         kfree(bits);
 326 out_nofds:
 327         return ret;
 328 }
 329
 330 static int do_poll(unsigned int nfds, struct pollfd *fds, poll_table *wait,
 331                    long timeout)
 332 {
 333         int count = 0;
 334
 335         for (;;) {
 336                 unsigned int j;
 337                 struct pollfd * fdpnt;
 338
 339                 current->state = TASK_INTERRUPTIBLE;
 340                 for (fdpnt = fds, j = 0; j < nfds; j++, fdpnt++) {
 341                         int fd;
 342                         unsigned int mask;
 343
 344                         mask = 0;
 345                         fd = fdpnt->fd;
 346                         if (fd >= 0) {
 347                                 /* poll_wait increments f_count if needed */
 348                                 struct file * file = fcheck(fd);
 349                                 mask = POLLNVAL;
 350                                 if (file != NULL) {
 351                                         mask = DEFAULT_POLLMASK;
 352                                         if (file->f_op && file->f_op->poll)
 353                                                 mask = file->f_op->poll(file, wait);
 354                                         mask &= fdpnt->events | POLLERR | POLLHUP;
 355                                 }
 356                                 if (mask) {
 357                                         wait = NULL;
 358                                         count++;
 359                                 }
 360                         }
 361                         fdpnt->revents = mask;
 362                 }
 363
 364                 wait = NULL;
 365                 if (count || !timeout || signal_pending(current))
 366                         break;
 367                 timeout = schedule_timeout(timeout);
 368         }
 369         current->state = TASK_RUNNING;
 370         return count;
 371 }
 372
 373 asmlinkage int sys_poll(struct pollfd * ufds, unsigned int nfds, long timeout)
 374 {
 375         int i, fdcount, err, size;
 376         struct pollfd * fds, *fds1;
 377         poll_table *wait_table = NULL, *wait = NULL;
 378
 379         lock_kernel();
 380         /* Do a sanity check on nfds ... */
 381         err = -EINVAL;
 382         if (nfds > NR_OPEN)
 383                 goto out;
 384
 385         if (timeout) {
 386                 /* Carefula about overflow in the intermediate values */
 387                 if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ)
 388                         timeout = (unsigned long)(timeout*HZ+999)/1000+1;
 389                 else /* Negative or overflow */
 390                         timeout = MAX_SCHEDULE_TIMEOUT;
 391         }
 392
 393         err = -ENOMEM;
 394         if (timeout) {
 395                 wait_table = (poll_table *) __get_free_page(GFP_KERNEL);
 396                 if (!wait_table)
 397                         goto out;
 398                 wait_table->nr = 0;
 399                 wait_table->entry = (struct poll_table_entry *)(wait_table + 1);
 400                 wait_table->next = NULL;
 401                 wait = wait_table;
 402         }
 403
 404         size = nfds * sizeof(struct pollfd);
 405         fds = (struct pollfd *) kmalloc(size, GFP_KERNEL);
 406         if (!fds)
 407                 goto out;
 408
 409         err = -EFAULT;
 410         if (copy_from_user(fds, ufds, size))
 411                 goto out_fds;
 412
 413         fdcount = do_poll(nfds, fds, wait, timeout);
 414
 415         /* OK, now copy the revents fields back to user space. */
 416         fds1 = fds;
 417         for(i=0; i < (int)nfds; i++, ufds++, fds1++) {
 418                 __put_user(fds1->revents, &ufds->revents);
 419         }
 420
 421         err = fdcount;
 422         if (!fdcount && signal_pending(current))
 423                 err = -EINTR;
 424
 425 out_fds:
 426         kfree(fds);
 427 out:
 428         if (wait)
 429                 free_wait(wait_table);
 430         unlock_kernel();
 431         return err;
 432 }