4 * Copyright (C) 1991, 1992, 1999 Linus Torvalds
8 #include <linux/file.h>
9 #include <linux/poll.h>
10 #include <linux/slab.h>
11 #include <linux/module.h>
12 #include <linux/init.h>
14 #include <linux/mount.h>
15 #include <linux/pipe_fs_i.h>
16 #include <linux/uio.h>
17 #include <linux/highmem.h>
18 #include <linux/pagemap.h>
19 #include <linux/audit.h>
20 #include <linux/syscalls.h>
22 #include <asm/uaccess.h>
23 #include <asm/ioctls.h>
26 * We use a start+len construction, which provides full use of the
28 * -- Florian Coosmann (FGC)
30 * Reads with count = 0 should always return 0.
31 * -- Julian Bradfield 1999-06-07.
33 * FIFOs and Pipes now generate SIGIO for both readers and writers.
34 * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
36 * pipe_read & write cleanup
37 * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
40 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
43 mutex_lock_nested(&pipe->inode->i_mutex, subclass);
46 void pipe_lock(struct pipe_inode_info *pipe)
49 * pipe_lock() nests non-pipe inode locks (for writing to a file)
51 pipe_lock_nested(pipe, I_MUTEX_PARENT);
53 EXPORT_SYMBOL(pipe_lock);
55 void pipe_unlock(struct pipe_inode_info *pipe)
58 mutex_unlock(&pipe->inode->i_mutex);
60 EXPORT_SYMBOL(pipe_unlock);
62 void pipe_double_lock(struct pipe_inode_info *pipe1,
63 struct pipe_inode_info *pipe2)
65 BUG_ON(pipe1 == pipe2);
68 pipe_lock_nested(pipe1, I_MUTEX_PARENT);
69 pipe_lock_nested(pipe2, I_MUTEX_CHILD);
71 pipe_lock_nested(pipe2, I_MUTEX_CHILD);
72 pipe_lock_nested(pipe1, I_MUTEX_PARENT);
76 /* Drop the inode semaphore and wait for a pipe event, atomically */
77 void pipe_wait(struct pipe_inode_info *pipe)
82 * Pipes are system-local resources, so sleeping on them
83 * is considered a noninteractive wait:
85 prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
88 finish_wait(&pipe->wait, &wait);
93 pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
101 copy = min_t(unsigned long, len, iov->iov_len);
104 if (__copy_from_user_inatomic(to, iov->iov_base, copy))
107 if (copy_from_user(to, iov->iov_base, copy))
112 iov->iov_base += copy;
113 iov->iov_len -= copy;
119 pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
125 while (!iov->iov_len)
127 copy = min_t(unsigned long, len, iov->iov_len);
130 if (__copy_to_user_inatomic(iov->iov_base, from, copy))
133 if (copy_to_user(iov->iov_base, from, copy))
138 iov->iov_base += copy;
139 iov->iov_len -= copy;
145 * Attempt to pre-fault in the user memory, so we can use atomic copies.
146 * Returns the number of bytes not faulted in.
148 static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
150 while (!iov->iov_len)
154 unsigned long this_len;
156 this_len = min_t(unsigned long, len, iov->iov_len);
157 if (fault_in_pages_writeable(iov->iov_base, this_len))
168 * Pre-fault in the user memory, so we can use atomic copies.
170 static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
172 while (!iov->iov_len)
176 unsigned long this_len;
178 this_len = min_t(unsigned long, len, iov->iov_len);
179 fault_in_pages_readable(iov->iov_base, this_len);
185 static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
186 struct pipe_buffer *buf)
188 struct page *page = buf->page;
191 * If nobody else uses this page, and we don't already have a
192 * temporary page, let's keep track of it as a one-deep
193 * allocation cache. (Otherwise just release our reference to it)
195 if (page_count(page) == 1 && !pipe->tmp_page)
196 pipe->tmp_page = page;
198 page_cache_release(page);
202 * generic_pipe_buf_map - virtually map a pipe buffer
203 * @pipe: the pipe that the buffer belongs to
204 * @buf: the buffer that should be mapped
205 * @atomic: whether to use an atomic map
208 * This function returns a kernel virtual address mapping for the
209 * pipe_buffer passed in @buf. If @atomic is set, an atomic map is provided
210 * and the caller has to be careful not to fault before calling
211 * the unmap function.
213 * Note that this function occupies KM_USER0 if @atomic != 0.
215 void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
216 struct pipe_buffer *buf, int atomic)
219 buf->flags |= PIPE_BUF_FLAG_ATOMIC;
220 return kmap_atomic(buf->page, KM_USER0);
223 return kmap(buf->page);
227 * generic_pipe_buf_unmap - unmap a previously mapped pipe buffer
228 * @pipe: the pipe that the buffer belongs to
229 * @buf: the buffer that should be unmapped
230 * @map_data: the data that the mapping function returned
233 * This function undoes the mapping that ->map() provided.
235 void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
236 struct pipe_buffer *buf, void *map_data)
238 if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
239 buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
240 kunmap_atomic(map_data, KM_USER0);
246 * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
247 * @pipe: the pipe that the buffer belongs to
248 * @buf: the buffer to attempt to steal
251 * This function attempts to steal the &struct page attached to
252 * @buf. If successful, this function returns 0 and returns with
253 * the page locked. The caller may then reuse the page for whatever
254 * he wishes; the typical use is insertion into a different file
257 int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
258 struct pipe_buffer *buf)
260 struct page *page = buf->page;
263 * A reference of one is golden, that means that the owner of this
264 * page is the only one holding a reference to it. lock the page
267 if (page_count(page) == 1) {
276 * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
277 * @pipe: the pipe that the buffer belongs to
278 * @buf: the buffer to get a reference to
281 * This function grabs an extra reference to @buf. It's used in
282 * in the tee() system call, when we duplicate the buffers in one
285 void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
287 page_cache_get(buf->page);
291 * generic_pipe_buf_confirm - verify contents of the pipe buffer
292 * @info: the pipe that the buffer belongs to
293 * @buf: the buffer to confirm
296 * This function does nothing, because the generic pipe code uses
297 * pages that are always good when inserted into the pipe.
299 int generic_pipe_buf_confirm(struct pipe_inode_info *info,
300 struct pipe_buffer *buf)
306 * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
307 * @pipe: the pipe that the buffer belongs to
308 * @buf: the buffer to put a reference to
311 * This function releases a reference to @buf.
313 void generic_pipe_buf_release(struct pipe_inode_info *pipe,
314 struct pipe_buffer *buf)
316 page_cache_release(buf->page);
319 static const struct pipe_buf_operations anon_pipe_buf_ops = {
321 .map = generic_pipe_buf_map,
322 .unmap = generic_pipe_buf_unmap,
323 .confirm = generic_pipe_buf_confirm,
324 .release = anon_pipe_buf_release,
325 .steal = generic_pipe_buf_steal,
326 .get = generic_pipe_buf_get,
330 pipe_read(struct kiocb *iocb, const struct iovec *_iov,
331 unsigned long nr_segs, loff_t pos)
333 struct file *filp = iocb->ki_filp;
334 struct inode *inode = filp->f_path.dentry->d_inode;
335 struct pipe_inode_info *pipe;
338 struct iovec *iov = (struct iovec *)_iov;
341 total_len = iov_length(iov, nr_segs);
342 /* Null read succeeds. */
343 if (unlikely(total_len == 0))
348 mutex_lock(&inode->i_mutex);
349 pipe = inode->i_pipe;
351 int bufs = pipe->nrbufs;
353 int curbuf = pipe->curbuf;
354 struct pipe_buffer *buf = pipe->bufs + curbuf;
355 const struct pipe_buf_operations *ops = buf->ops;
357 size_t chars = buf->len;
360 if (chars > total_len)
363 error = ops->confirm(pipe, buf);
370 atomic = !iov_fault_in_pages_write(iov, chars);
372 addr = ops->map(pipe, buf, atomic);
373 error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
374 ops->unmap(pipe, buf, addr);
375 if (unlikely(error)) {
377 * Just retry with the slow path if we failed.
388 buf->offset += chars;
392 ops->release(pipe, buf);
393 curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
394 pipe->curbuf = curbuf;
395 pipe->nrbufs = --bufs;
400 break; /* common path: read succeeded */
402 if (bufs) /* More to do? */
406 if (!pipe->waiting_writers) {
407 /* syscall merging: Usually we must not sleep
408 * if O_NONBLOCK is set, or if we got some data.
409 * But if a writer sleeps in kernel space, then
410 * we can wait for that data without violating POSIX.
414 if (filp->f_flags & O_NONBLOCK) {
419 if (signal_pending(current)) {
425 wake_up_interruptible_sync(&pipe->wait);
426 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
430 mutex_unlock(&inode->i_mutex);
432 /* Signal writers asynchronously that there is more room. */
434 wake_up_interruptible_sync(&pipe->wait);
435 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
443 pipe_write(struct kiocb *iocb, const struct iovec *_iov,
444 unsigned long nr_segs, loff_t ppos)
446 struct file *filp = iocb->ki_filp;
447 struct inode *inode = filp->f_path.dentry->d_inode;
448 struct pipe_inode_info *pipe;
451 struct iovec *iov = (struct iovec *)_iov;
455 total_len = iov_length(iov, nr_segs);
456 /* Null write succeeds. */
457 if (unlikely(total_len == 0))
462 mutex_lock(&inode->i_mutex);
463 pipe = inode->i_pipe;
465 if (!pipe->readers) {
466 send_sig(SIGPIPE, current, 0);
471 /* We try to merge small writes */
472 chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
473 if (pipe->nrbufs && chars != 0) {
474 int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
476 struct pipe_buffer *buf = pipe->bufs + lastbuf;
477 const struct pipe_buf_operations *ops = buf->ops;
478 int offset = buf->offset + buf->len;
480 if (ops->can_merge && offset + chars <= PAGE_SIZE) {
481 int error, atomic = 1;
484 error = ops->confirm(pipe, buf);
488 iov_fault_in_pages_read(iov, chars);
490 addr = ops->map(pipe, buf, atomic);
491 error = pipe_iov_copy_from_user(offset + addr, iov,
493 ops->unmap(pipe, buf, addr);
514 if (!pipe->readers) {
515 send_sig(SIGPIPE, current, 0);
521 if (bufs < PIPE_BUFFERS) {
522 int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
523 struct pipe_buffer *buf = pipe->bufs + newbuf;
524 struct page *page = pipe->tmp_page;
526 int error, atomic = 1;
529 page = alloc_page(GFP_HIGHUSER);
530 if (unlikely(!page)) {
531 ret = ret ? : -ENOMEM;
534 pipe->tmp_page = page;
536 /* Always wake up, even if the copy fails. Otherwise
537 * we lock up (O_NONBLOCK-)readers that sleep due to
539 * FIXME! Is this really true?
543 if (chars > total_len)
546 iov_fault_in_pages_read(iov, chars);
549 src = kmap_atomic(page, KM_USER0);
553 error = pipe_iov_copy_from_user(src, iov, chars,
556 kunmap_atomic(src, KM_USER0);
560 if (unlikely(error)) {
571 /* Insert it into the buffer array */
573 buf->ops = &anon_pipe_buf_ops;
576 pipe->nrbufs = ++bufs;
577 pipe->tmp_page = NULL;
583 if (bufs < PIPE_BUFFERS)
585 if (filp->f_flags & O_NONBLOCK) {
590 if (signal_pending(current)) {
596 wake_up_interruptible_sync(&pipe->wait);
597 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
600 pipe->waiting_writers++;
602 pipe->waiting_writers--;
605 mutex_unlock(&inode->i_mutex);
607 wake_up_interruptible_sync(&pipe->wait);
608 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
611 file_update_time(filp);
616 bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
622 bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
628 static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
630 struct inode *inode = filp->f_path.dentry->d_inode;
631 struct pipe_inode_info *pipe;
632 int count, buf, nrbufs;
636 mutex_lock(&inode->i_mutex);
637 pipe = inode->i_pipe;
640 nrbufs = pipe->nrbufs;
641 while (--nrbufs >= 0) {
642 count += pipe->bufs[buf].len;
643 buf = (buf+1) & (PIPE_BUFFERS-1);
645 mutex_unlock(&inode->i_mutex);
647 return put_user(count, (int __user *)arg);
653 /* No kernel lock held - fine */
655 pipe_poll(struct file *filp, poll_table *wait)
658 struct inode *inode = filp->f_path.dentry->d_inode;
659 struct pipe_inode_info *pipe = inode->i_pipe;
662 poll_wait(filp, &pipe->wait, wait);
664 /* Reading only -- no need for acquiring the semaphore. */
665 nrbufs = pipe->nrbufs;
667 if (filp->f_mode & FMODE_READ) {
668 mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;
669 if (!pipe->writers && filp->f_version != pipe->w_counter)
673 if (filp->f_mode & FMODE_WRITE) {
674 mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
676 * Most Unices do not set POLLERR for FIFOs but on Linux they
677 * behave exactly like pipes for poll().
687 pipe_release(struct inode *inode, int decr, int decw)
689 struct pipe_inode_info *pipe;
691 mutex_lock(&inode->i_mutex);
692 pipe = inode->i_pipe;
693 pipe->readers -= decr;
694 pipe->writers -= decw;
696 if (!pipe->readers && !pipe->writers) {
697 free_pipe_info(inode);
699 wake_up_interruptible_sync(&pipe->wait);
700 kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
701 kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
703 mutex_unlock(&inode->i_mutex);
709 pipe_read_fasync(int fd, struct file *filp, int on)
711 struct inode *inode = filp->f_path.dentry->d_inode;
714 mutex_lock(&inode->i_mutex);
715 retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
716 mutex_unlock(&inode->i_mutex);
723 pipe_write_fasync(int fd, struct file *filp, int on)
725 struct inode *inode = filp->f_path.dentry->d_inode;
728 mutex_lock(&inode->i_mutex);
729 retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
730 mutex_unlock(&inode->i_mutex);
737 pipe_rdwr_fasync(int fd, struct file *filp, int on)
739 struct inode *inode = filp->f_path.dentry->d_inode;
740 struct pipe_inode_info *pipe = inode->i_pipe;
743 mutex_lock(&inode->i_mutex);
744 retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
746 retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
747 if (retval < 0) /* this can happen only if on == T */
748 fasync_helper(-1, filp, 0, &pipe->fasync_readers);
750 mutex_unlock(&inode->i_mutex);
756 pipe_read_release(struct inode *inode, struct file *filp)
758 return pipe_release(inode, 1, 0);
762 pipe_write_release(struct inode *inode, struct file *filp)
764 return pipe_release(inode, 0, 1);
768 pipe_rdwr_release(struct inode *inode, struct file *filp)
772 decr = (filp->f_mode & FMODE_READ) != 0;
773 decw = (filp->f_mode & FMODE_WRITE) != 0;
774 return pipe_release(inode, decr, decw);
778 pipe_read_open(struct inode *inode, struct file *filp)
780 /* We could have perhaps used atomic_t, but this and friends
781 below are the only places. So it doesn't seem worthwhile. */
782 mutex_lock(&inode->i_mutex);
783 inode->i_pipe->readers++;
784 mutex_unlock(&inode->i_mutex);
790 pipe_write_open(struct inode *inode, struct file *filp)
792 mutex_lock(&inode->i_mutex);
793 inode->i_pipe->writers++;
794 mutex_unlock(&inode->i_mutex);
800 pipe_rdwr_open(struct inode *inode, struct file *filp)
802 mutex_lock(&inode->i_mutex);
803 if (filp->f_mode & FMODE_READ)
804 inode->i_pipe->readers++;
805 if (filp->f_mode & FMODE_WRITE)
806 inode->i_pipe->writers++;
807 mutex_unlock(&inode->i_mutex);
813 * The file_operations structs are not static because they
814 * are also used in linux/fs/fifo.c to do operations on FIFOs.
816 * Pipes reuse fifos' file_operations structs.
818 const struct file_operations read_pipefifo_fops = {
820 .read = do_sync_read,
821 .aio_read = pipe_read,
824 .unlocked_ioctl = pipe_ioctl,
825 .open = pipe_read_open,
826 .release = pipe_read_release,
827 .fasync = pipe_read_fasync,
830 const struct file_operations write_pipefifo_fops = {
833 .write = do_sync_write,
834 .aio_write = pipe_write,
836 .unlocked_ioctl = pipe_ioctl,
837 .open = pipe_write_open,
838 .release = pipe_write_release,
839 .fasync = pipe_write_fasync,
842 const struct file_operations rdwr_pipefifo_fops = {
844 .read = do_sync_read,
845 .aio_read = pipe_read,
846 .write = do_sync_write,
847 .aio_write = pipe_write,
849 .unlocked_ioctl = pipe_ioctl,
850 .open = pipe_rdwr_open,
851 .release = pipe_rdwr_release,
852 .fasync = pipe_rdwr_fasync,
855 struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
857 struct pipe_inode_info *pipe;
859 pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
861 init_waitqueue_head(&pipe->wait);
862 pipe->r_counter = pipe->w_counter = 1;
869 void __free_pipe_info(struct pipe_inode_info *pipe)
873 for (i = 0; i < PIPE_BUFFERS; i++) {
874 struct pipe_buffer *buf = pipe->bufs + i;
876 buf->ops->release(pipe, buf);
879 __free_page(pipe->tmp_page);
883 void free_pipe_info(struct inode *inode)
885 __free_pipe_info(inode->i_pipe);
886 inode->i_pipe = NULL;
889 static struct vfsmount *pipe_mnt __read_mostly;
890 static int pipefs_delete_dentry(struct dentry *dentry)
893 * At creation time, we pretended this dentry was hashed
894 * (by clearing DCACHE_UNHASHED bit in d_flags)
895 * At delete time, we restore the truth : not hashed.
896 * (so that dput() can proceed correctly)
898 dentry->d_flags |= DCACHE_UNHASHED;
903 * pipefs_dname() is called from d_path().
905 static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
907 return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
908 dentry->d_inode->i_ino);
911 static const struct dentry_operations pipefs_dentry_operations = {
912 .d_delete = pipefs_delete_dentry,
913 .d_dname = pipefs_dname,
916 static struct inode * get_pipe_inode(void)
918 struct inode *inode = new_inode(pipe_mnt->mnt_sb);
919 struct pipe_inode_info *pipe;
924 pipe = alloc_pipe_info(inode);
927 inode->i_pipe = pipe;
929 pipe->readers = pipe->writers = 1;
930 inode->i_fop = &rdwr_pipefifo_fops;
933 * Mark the inode dirty from the very beginning,
934 * that way it will never be moved to the dirty
935 * list because "mark_inode_dirty()" will think
936 * that it already _is_ on the dirty list.
938 inode->i_state = I_DIRTY;
939 inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
940 inode->i_uid = current_fsuid();
941 inode->i_gid = current_fsgid();
942 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
953 struct file *create_write_pipe(int flags)
958 struct dentry *dentry;
959 struct qstr name = { .name = "" };
962 inode = get_pipe_inode();
967 dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);
971 dentry->d_op = &pipefs_dentry_operations;
973 * We dont want to publish this dentry into global dentry hash table.
974 * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
975 * This permits a working /proc/$pid/fd/XXX on pipes
977 dentry->d_flags &= ~DCACHE_UNHASHED;
978 d_instantiate(dentry, inode);
981 f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipefifo_fops);
984 f->f_mapping = inode->i_mapping;
986 f->f_flags = O_WRONLY | (flags & O_NONBLOCK);
992 free_pipe_info(inode);
997 free_pipe_info(inode);
1000 return ERR_PTR(err);
1003 void free_write_pipe(struct file *f)
1005 free_pipe_info(f->f_dentry->d_inode);
1006 path_put(&f->f_path);
1010 struct file *create_read_pipe(struct file *wrf, int flags)
1012 struct file *f = get_empty_filp();
1014 return ERR_PTR(-ENFILE);
1016 /* Grab pipe from the writer */
1017 f->f_path = wrf->f_path;
1018 path_get(&wrf->f_path);
1019 f->f_mapping = wrf->f_path.dentry->d_inode->i_mapping;
1022 f->f_flags = O_RDONLY | (flags & O_NONBLOCK);
1023 f->f_op = &read_pipefifo_fops;
1024 f->f_mode = FMODE_READ;
1030 int do_pipe_flags(int *fd, int flags)
1032 struct file *fw, *fr;
1036 if (flags & ~(O_CLOEXEC | O_NONBLOCK))
1039 fw = create_write_pipe(flags);
1042 fr = create_read_pipe(fw, flags);
1043 error = PTR_ERR(fr);
1045 goto err_write_pipe;
1047 error = get_unused_fd_flags(flags);
1052 error = get_unused_fd_flags(flags);
1057 audit_fd_pair(fdr, fdw);
1058 fd_install(fdr, fr);
1059 fd_install(fdw, fw);
1068 path_put(&fr->f_path);
1071 free_write_pipe(fw);
1076 * sys_pipe() is the normal C calling standard for creating
1077 * a pipe. It's not the way Unix traditionally does this, though.
1079 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
1084 error = do_pipe_flags(fd, flags);
1086 if (copy_to_user(fildes, fd, sizeof(fd))) {
1095 SYSCALL_DEFINE1(pipe, int __user *, fildes)
1097 return sys_pipe2(fildes, 0);
1101 * pipefs should _never_ be mounted by userland - too much of security hassle,
1102 * no real gain from having the whole whorehouse mounted. So we don't need
1103 * any operations on the root directory. However, we need a non-trivial
1104 * d_name - pipe: will go nicely and kill the special-casing in procfs.
1106 static int pipefs_get_sb(struct file_system_type *fs_type,
1107 int flags, const char *dev_name, void *data,
1108 struct vfsmount *mnt)
1110 return get_sb_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC, mnt);
1113 static struct file_system_type pipe_fs_type = {
1115 .get_sb = pipefs_get_sb,
1116 .kill_sb = kill_anon_super,
1119 static int __init init_pipe_fs(void)
1121 int err = register_filesystem(&pipe_fs_type);
1124 pipe_mnt = kern_mount(&pipe_fs_type);
1125 if (IS_ERR(pipe_mnt)) {
1126 err = PTR_ERR(pipe_mnt);
1127 unregister_filesystem(&pipe_fs_type);
1133 static void __exit exit_pipe_fs(void)
1135 unregister_filesystem(&pipe_fs_type);
1139 fs_initcall(init_pipe_fs);
1140 module_exit(exit_pipe_fs);