fs/pipe.c

   1 /*
   2  *  linux/fs/pipe.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
   5  */
   6
   7 #include <linux/mm.h>
   8 #include <linux/file.h>
   9 #include <linux/poll.h>
  10 #include <linux/malloc.h>
  11 #include <linux/module.h>
  12 #include <linux/init.h>
  13
  14 #include <asm/uaccess.h>
  15
  16 /*
  17  * We use a start+len construction, which provides full use of the
  18  * allocated memory.
  19  * -- Florian Coosmann (FGC)
  20  *
  21  * Reads with count = 0 should always return 0.
  22  * -- Julian Bradfield 1999-06-07.
  23  */
  24
  25 /* Drop the inode semaphore and wait for a pipe event, atomically */
  26 void pipe_wait(struct inode * inode)
  27 {
  28         DECLARE_WAITQUEUE(wait, current);
  29         current->state = TASK_INTERRUPTIBLE;
  30         add_wait_queue(PIPE_WAIT(*inode), &wait);
  31         up(PIPE_SEM(*inode));
  32         schedule();
  33         remove_wait_queue(PIPE_WAIT(*inode), &wait);
  34         current->state = TASK_RUNNING;
  35         down(PIPE_SEM(*inode));
  36 }
  37
  38 static ssize_t
  39 pipe_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
  40 {
  41         struct inode *inode = filp->f_dentry->d_inode;
  42         ssize_t size, read, ret;
  43
  44         /* Seeks are not allowed on pipes.  */
  45         ret = -ESPIPE;
  46         read = 0;
  47         if (ppos != &filp->f_pos)
  48                 goto out_nolock;
  49
  50         /* Always return 0 on null read.  */
  51         ret = 0;
  52         if (count == 0)
  53                 goto out_nolock;
  54
  55         /* Get the pipe semaphore */
  56         ret = -ERESTARTSYS;
  57         if (down_interruptible(PIPE_SEM(*inode)))
  58                 goto out_nolock;
  59
  60         if (PIPE_EMPTY(*inode)) {
  61 do_more_read:
  62                 ret = 0;
  63                 if (!PIPE_WRITERS(*inode))
  64                         goto out;
  65
  66                 ret = -EAGAIN;
  67                 if (filp->f_flags & O_NONBLOCK)
  68                         goto out;
  69
  70                 for (;;) {
  71                         PIPE_WAITING_READERS(*inode)++;
  72                         pipe_wait(inode);
  73                         PIPE_WAITING_READERS(*inode)--;
  74                         ret = -ERESTARTSYS;
  75                         if (signal_pending(current))
  76                                 goto out;
  77                         ret = 0;
  78                         if (!PIPE_EMPTY(*inode))
  79                                 break;
  80                         if (!PIPE_WRITERS(*inode))
  81                                 goto out;
  82                 }
  83         }
  84
  85         /* Read what data is available.  */
  86         ret = -EFAULT;
  87         while (count > 0 && (size = PIPE_LEN(*inode))) {
  88                 char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode);
  89                 ssize_t chars = PIPE_MAX_RCHUNK(*inode);
  90
  91                 if (chars > count)
  92                         chars = count;
  93                 if (chars > size)
  94                         chars = size;
  95
  96                 if (copy_to_user(buf, pipebuf, chars))
  97                         goto out;
  98
  99                 read += chars;
 100                 PIPE_START(*inode) += chars;
 101                 PIPE_START(*inode) &= (PIPE_SIZE - 1);
 102                 PIPE_LEN(*inode) -= chars;
 103                 count -= chars;
 104                 buf += chars;
 105         }
 106
 107         /* Cache behaviour optimization */
 108         if (!PIPE_LEN(*inode))
 109                 PIPE_START(*inode) = 0;
 110
 111         if (count && PIPE_WAITING_WRITERS(*inode) && !(filp->f_flags & O_NONBLOCK)) {
 112                 /*
 113                  * We know that we are going to sleep: signal
 114                  * writers synchronously that there is more
 115                  * room.
 116                  */
 117                 wake_up_interruptible_sync(PIPE_WAIT(*inode));
 118                 if (!PIPE_EMPTY(*inode))
 119                         BUG();
 120                 goto do_more_read;
 121         }
 122         /* Signal writers asynchronously that there is more room.  */
 123         wake_up_interruptible(PIPE_WAIT(*inode));
 124
 125         ret = read;
 126 out:
 127         up(PIPE_SEM(*inode));
 128 out_nolock:
 129         if (read)
 130                 ret = read;
 131         return ret;
 132 }
 133
 134 static ssize_t
 135 pipe_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
 136 {
 137         struct inode *inode = filp->f_dentry->d_inode;
 138         ssize_t free, written, ret;
 139
 140         /* Seeks are not allowed on pipes.  */
 141         ret = -ESPIPE;
 142         written = 0;
 143         if (ppos != &filp->f_pos)
 144                 goto out_nolock;
 145
 146         /* Null write succeeds.  */
 147         ret = 0;
 148         if (count == 0)
 149                 goto out_nolock;
 150
 151         ret = -ERESTARTSYS;
 152         if (down_interruptible(PIPE_SEM(*inode)))
 153                 goto out_nolock;
 154
 155         /* No readers yields SIGPIPE.  */
 156         if (!PIPE_READERS(*inode))
 157                 goto sigpipe;
 158
 159         /* If count <= PIPE_BUF, we have to make it atomic.  */
 160         free = (count <= PIPE_BUF ? count : 1);
 161
 162         /* Wait, or check for, available space.  */
 163         if (filp->f_flags & O_NONBLOCK) {
 164                 ret = -EAGAIN;
 165                 if (PIPE_FREE(*inode) < free)
 166                         goto out;
 167         } else {
 168                 while (PIPE_FREE(*inode) < free) {
 169                         PIPE_WAITING_WRITERS(*inode)++;
 170                         pipe_wait(inode);
 171                         PIPE_WAITING_WRITERS(*inode)--;
 172                         ret = -ERESTARTSYS;
 173                         if (signal_pending(current))
 174                                 goto out;
 175
 176                         if (!PIPE_READERS(*inode))
 177                                 goto sigpipe;
 178                 }
 179         }
 180
 181         /* Copy into available space.  */
 182         ret = -EFAULT;
 183         while (count > 0) {
 184                 int space;
 185                 char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode);
 186                 ssize_t chars = PIPE_MAX_WCHUNK(*inode);
 187
 188                 if ((space = PIPE_FREE(*inode)) != 0) {
 189                         if (chars > count)
 190                                 chars = count;
 191                         if (chars > space)
 192                                 chars = space;
 193
 194                         if (copy_from_user(pipebuf, buf, chars))
 195                                 goto out;
 196
 197                         written += chars;
 198                         PIPE_LEN(*inode) += chars;
 199                         count -= chars;
 200                         buf += chars;
 201                         space = PIPE_FREE(*inode);
 202                         continue;
 203                 }
 204
 205                 ret = written;
 206                 if (filp->f_flags & O_NONBLOCK)
 207                         break;
 208
 209                 do {
 210                         /*
 211                          * Synchronous wake-up: it knows that this process
 212                          * is going to give up this CPU, so it doesnt have
 213                          * to do idle reschedules.
 214                          */
 215                         wake_up_interruptible_sync(PIPE_WAIT(*inode));
 216                         PIPE_WAITING_WRITERS(*inode)++;
 217                         pipe_wait(inode);
 218                         PIPE_WAITING_WRITERS(*inode)--;
 219                         if (signal_pending(current))
 220                                 goto out;
 221                         if (!PIPE_READERS(*inode))
 222                                 goto sigpipe;
 223                 } while (!PIPE_FREE(*inode));
 224                 ret = -EFAULT;
 225         }
 226
 227         /* Signal readers asynchronously that there is more data.  */
 228         wake_up_interruptible(PIPE_WAIT(*inode));
 229
 230         inode->i_ctime = inode->i_mtime = CURRENT_TIME;
 231         mark_inode_dirty(inode);
 232
 233 out:
 234         up(PIPE_SEM(*inode));
 235 out_nolock:
 236         if (written)
 237                 ret = written;
 238         return ret;
 239
 240 sigpipe:
 241         if (written)
 242                 goto out;
 243         up(PIPE_SEM(*inode));
 244         send_sig(SIGPIPE, current, 0);
 245         return -EPIPE;
 246 }
 247
 248 static loff_t
 249 pipe_lseek(struct file *file, loff_t offset, int orig)
 250 {
 251         return -ESPIPE;
 252 }
 253
 254 static ssize_t
 255 bad_pipe_r(struct file *filp, char *buf, size_t count, loff_t *ppos)
 256 {
 257         return -EBADF;
 258 }
 259
 260 static ssize_t
 261 bad_pipe_w(struct file *filp, const char *buf, size_t count, loff_t *ppos)
 262 {
 263         return -EBADF;
 264 }
 265
 266 static int
 267 pipe_ioctl(struct inode *pino, struct file *filp,
 268            unsigned int cmd, unsigned long arg)
 269 {
 270         switch (cmd) {
 271                 case FIONREAD:
 272                         return put_user(PIPE_LEN(*pino), (int *)arg);
 273                 default:
 274                         return -EINVAL;
 275         }
 276 }
 277
 278 /* No kernel lock held - fine */
 279 static unsigned int
 280 pipe_poll(struct file *filp, poll_table *wait)
 281 {
 282         unsigned int mask;
 283         struct inode *inode = filp->f_dentry->d_inode;
 284
 285         poll_wait(filp, PIPE_WAIT(*inode), wait);
 286
 287         /* Reading only -- no need for aquiring the semaphore.  */
 288         mask = POLLIN | POLLRDNORM;
 289         if (PIPE_EMPTY(*inode))
 290                 mask = POLLOUT | POLLWRNORM;
 291         if (!PIPE_WRITERS(*inode) && filp->f_version != PIPE_WCOUNTER(*inode))
 292                 mask |= POLLHUP;
 293         if (!PIPE_READERS(*inode))
 294                 mask |= POLLERR;
 295
 296         return mask;
 297 }
 298
 299 /* FIXME: most Unices do not set POLLERR for fifos */
 300 #define fifo_poll pipe_poll
 301
 302 static int
 303 pipe_release(struct inode *inode, int decr, int decw)
 304 {
 305         down(PIPE_SEM(*inode));
 306         PIPE_READERS(*inode) -= decr;
 307         PIPE_WRITERS(*inode) -= decw;
 308         if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode)) {
 309                 struct pipe_inode_info *info = inode->i_pipe;
 310                 inode->i_pipe = NULL;
 311                 free_page((unsigned long) info->base);
 312                 kfree(info);
 313         } else {
 314                 wake_up_interruptible(PIPE_WAIT(*inode));
 315         }
 316         up(PIPE_SEM(*inode));
 317
 318         return 0;
 319 }
 320
 321 static int
 322 pipe_read_release(struct inode *inode, struct file *filp)
 323 {
 324         return pipe_release(inode, 1, 0);
 325 }
 326
 327 static int
 328 pipe_write_release(struct inode *inode, struct file *filp)
 329 {
 330         return pipe_release(inode, 0, 1);
 331 }
 332
 333 static int
 334 pipe_rdwr_release(struct inode *inode, struct file *filp)
 335 {
 336         int decr, decw;
 337
 338         decr = (filp->f_mode & FMODE_READ) != 0;
 339         decw = (filp->f_mode & FMODE_WRITE) != 0;
 340         return pipe_release(inode, decr, decw);
 341 }
 342
 343 static int
 344 pipe_read_open(struct inode *inode, struct file *filp)
 345 {
 346         /* We could have perhaps used atomic_t, but this and friends
 347            below are the only places.  So it doesn't seem worthwhile.  */
 348         down(PIPE_SEM(*inode));
 349         PIPE_READERS(*inode)++;
 350         up(PIPE_SEM(*inode));
 351
 352         return 0;
 353 }
 354
 355 static int
 356 pipe_write_open(struct inode *inode, struct file *filp)
 357 {
 358         down(PIPE_SEM(*inode));
 359         PIPE_WRITERS(*inode)++;
 360         up(PIPE_SEM(*inode));
 361
 362         return 0;
 363 }
 364
 365 static int
 366 pipe_rdwr_open(struct inode *inode, struct file *filp)
 367 {
 368         down(PIPE_SEM(*inode));
 369         if (filp->f_mode & FMODE_READ)
 370                 PIPE_READERS(*inode)++;
 371         if (filp->f_mode & FMODE_WRITE)
 372                 PIPE_WRITERS(*inode)++;
 373         up(PIPE_SEM(*inode));
 374
 375         return 0;
 376 }
 377
 378 /*
 379  * The file_operations structs are not static because they
 380  * are also used in linux/fs/fifo.c to do operations on FIFOs.
 381  */
 382 struct file_operations read_fifo_fops = {
 383         llseek:         pipe_lseek,
 384         read:           pipe_read,
 385         write:          bad_pipe_w,
 386         poll:           fifo_poll,
 387         ioctl:          pipe_ioctl,
 388         open:           pipe_read_open,
 389         release:        pipe_read_release,
 390 };
 391
 392 struct file_operations write_fifo_fops = {
 393         llseek:         pipe_lseek,
 394         read:           bad_pipe_r,
 395         write:          pipe_write,
 396         poll:           fifo_poll,
 397         ioctl:          pipe_ioctl,
 398         open:           pipe_write_open,
 399         release:        pipe_write_release,
 400 };
 401
 402 struct file_operations rdwr_fifo_fops = {
 403         llseek:         pipe_lseek,
 404         read:           pipe_read,
 405         write:          pipe_write,
 406         poll:           fifo_poll,
 407         ioctl:          pipe_ioctl,
 408         open:           pipe_rdwr_open,
 409         release:        pipe_rdwr_release,
 410 };
 411
 412 struct file_operations read_pipe_fops = {
 413         llseek:         pipe_lseek,
 414         read:           pipe_read,
 415         write:          bad_pipe_w,
 416         poll:           pipe_poll,
 417         ioctl:          pipe_ioctl,
 418         open:           pipe_read_open,
 419         release:        pipe_read_release,
 420 };
 421
 422 struct file_operations write_pipe_fops = {
 423         llseek:         pipe_lseek,
 424         read:           bad_pipe_r,
 425         write:          pipe_write,
 426         poll:           pipe_poll,
 427         ioctl:          pipe_ioctl,
 428         open:           pipe_write_open,
 429         release:        pipe_write_release,
 430 };
 431
 432 struct file_operations rdwr_pipe_fops = {
 433         llseek:         pipe_lseek,
 434         read:           pipe_read,
 435         write:          pipe_write,
 436         poll:           pipe_poll,
 437         ioctl:          pipe_ioctl,
 438         open:           pipe_rdwr_open,
 439         release:        pipe_rdwr_release,
 440 };
 441
 442 struct inode* pipe_new(struct inode* inode)
 443 {
 444         unsigned long page;
 445
 446         page = __get_free_page(GFP_USER);
 447         if (!page)
 448                 return NULL;
 449
 450         inode->i_pipe = kmalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
 451         if (!inode->i_pipe)
 452                 goto fail_page;
 453
 454         init_waitqueue_head(PIPE_WAIT(*inode));
 455         PIPE_BASE(*inode) = (char*) page;
 456         PIPE_START(*inode) = PIPE_LEN(*inode) = 0;
 457         PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 0;
 458         PIPE_WAITING_READERS(*inode) = PIPE_WAITING_WRITERS(*inode) = 0;
 459         PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;
 460
 461         return inode;
 462 fail_page:
 463         free_page(page);
 464         return NULL;
 465 }
 466
 467 static struct vfsmount *pipe_mnt;
 468 static int pipefs_delete_dentry(struct dentry *dentry)
 469 {
 470         return 1;
 471 }
 472 static struct dentry_operations pipefs_dentry_operations = {
 473         d_delete:       pipefs_delete_dentry,
 474 };
 475
 476 static struct inode * get_pipe_inode(void)
 477 {
 478         struct inode *inode = get_empty_inode();
 479
 480         if (!inode)
 481                 goto fail_inode;
 482
 483         if(!pipe_new(inode))
 484                 goto fail_iput;
 485         PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 1;
 486         inode->i_fop = &rdwr_pipe_fops;
 487         inode->i_sb = pipe_mnt->mnt_sb;
 488
 489         /*
 490          * Mark the inode dirty from the very beginning,
 491          * that way it will never be moved to the dirty
 492          * list because "mark_inode_dirty()" will think
 493          * that it already _is_ on the dirty list.
 494          */
 495         inode->i_state = I_DIRTY;
 496         inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
 497         inode->i_uid = current->fsuid;
 498         inode->i_gid = current->fsgid;
 499         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 500         inode->i_blksize = PAGE_SIZE;
 501         return inode;
 502
 503 fail_iput:
 504         iput(inode);
 505 fail_inode:
 506         return NULL;
 507 }
 508
 509 int do_pipe(int *fd)
 510 {
 511         struct qstr this;
 512         char name[32];
 513         struct dentry *dentry;
 514         struct inode * inode;
 515         struct file *f1, *f2;
 516         int error;
 517         int i,j;
 518
 519         error = -ENFILE;
 520         f1 = get_empty_filp();
 521         if (!f1)
 522                 goto no_files;
 523
 524         f2 = get_empty_filp();
 525         if (!f2)
 526                 goto close_f1;
 527
 528         inode = get_pipe_inode();
 529         if (!inode)
 530                 goto close_f12;
 531
 532         error = get_unused_fd();
 533         if (error < 0)
 534                 goto close_f12_inode;
 535         i = error;
 536
 537         error = get_unused_fd();
 538         if (error < 0)
 539                 goto close_f12_inode_i;
 540         j = error;
 541
 542         error = -ENOMEM;
 543         sprintf(name, "[%lu]", inode->i_ino);
 544         this.name = name;
 545         this.len = strlen(name);
 546         this.hash = inode->i_ino; /* will go */
 547         dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &this);
 548         dentry->d_op = &pipefs_dentry_operations;
 549         if (!dentry)
 550                 goto close_f12_inode_i_j;
 551         d_add(dentry, inode);
 552         f1->f_vfsmnt = f2->f_vfsmnt = mntget(mntget(pipe_mnt));
 553         f1->f_dentry = f2->f_dentry = dget(dentry);
 554
 555         /* read file */
 556         f1->f_pos = f2->f_pos = 0;
 557         f1->f_flags = O_RDONLY;
 558         f1->f_op = &read_pipe_fops;
 559         f1->f_mode = 1;
 560         f1->f_version = 0;
 561
 562         /* write file */
 563         f2->f_flags = O_WRONLY;
 564         f2->f_op = &write_pipe_fops;
 565         f2->f_mode = 2;
 566         f2->f_version = 0;
 567
 568         fd_install(i, f1);
 569         fd_install(j, f2);
 570         fd[0] = i;
 571         fd[1] = j;
 572         return 0;
 573
 574 close_f12_inode_i_j:
 575         put_unused_fd(j);
 576 close_f12_inode_i:
 577         put_unused_fd(i);
 578 close_f12_inode:
 579         free_page((unsigned long) PIPE_BASE(*inode));
 580         kfree(inode->i_pipe);
 581         inode->i_pipe = NULL;
 582         iput(inode);
 583 close_f12:
 584         put_filp(f2);
 585 close_f1:
 586         put_filp(f1);
 587 no_files:
 588         return error;
 589 }
 590
 591 /*
 592  * pipefs should _never_ be mounted by userland - too much of security hassle,
 593  * no real gain from having the whole whorehouse mounted. So we don't need
 594  * any operations on the root directory. However, we need a non-trivial
 595  * d_name - pipe: will go nicely and kill the special-casing in procfs.
 596  */
 597 static int pipefs_statfs(struct super_block *sb, struct statfs *buf)
 598 {
 599         buf->f_type = PIPEFS_MAGIC;
 600         buf->f_bsize = 1024;
 601         buf->f_namelen = 255;
 602         return 0;
 603 }
 604
 605 static struct super_operations pipefs_ops = {
 606         statfs:         pipefs_statfs,
 607 };
 608
 609 static struct super_block * pipefs_read_super(struct super_block *sb, void *data, int silent)
 610 {
 611         struct inode *root = get_empty_inode();
 612         if (!root)
 613                 return NULL;
 614         root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
 615         root->i_uid = root->i_gid = 0;
 616         root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
 617         root->i_sb = sb;
 618         root->i_dev = sb->s_dev;
 619         sb->s_blocksize = 1024;
 620         sb->s_blocksize_bits = 10;
 621         sb->s_magic = PIPEFS_MAGIC;
 622         sb->s_op        = &pipefs_ops;
 623         sb->s_root = d_alloc(NULL, &(const struct qstr) { "pipe:", 5, 0 });
 624         if (!sb->s_root) {
 625                 iput(root);
 626                 return NULL;
 627         }
 628         sb->s_root->d_sb = sb;
 629         sb->s_root->d_parent = sb->s_root;
 630         d_instantiate(sb->s_root, root);
 631         return sb;
 632 }
 633
 634 static DECLARE_FSTYPE(pipe_fs_type, "pipefs", pipefs_read_super,
 635         FS_NOMOUNT|FS_SINGLE);
 636
 637 static int __init init_pipe_fs(void)
 638 {
 639         int err = register_filesystem(&pipe_fs_type);
 640         if (!err) {
 641                 pipe_mnt = kern_mount(&pipe_fs_type);
 642                 err = PTR_ERR(pipe_mnt);
 643                 if (IS_ERR(pipe_mnt))
 644                         unregister_filesystem(&pipe_fs_type);
 645                 else
 646                         err = 0;
 647         }
 648         return err;
 649 }
 650
 651 static void __exit exit_pipe_fs(void)
 652 {
 653         unregister_filesystem(&pipe_fs_type);
 654         kern_umount(pipe_mnt);
 655 }
 656
 657 module_init(init_pipe_fs)
 658 module_exit(exit_pipe_fs)