The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/select.c

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    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 }

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