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663 lines
16 KiB
663 lines
16 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* Watch queue and general notification mechanism, built on pipes |
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* |
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* Copyright (C) 2020 Red Hat, Inc. All Rights Reserved. |
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* Written by David Howells ([email protected]) |
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* |
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* See Documentation/watch_queue.rst |
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*/ |
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|
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#define pr_fmt(fmt) "watchq: " fmt |
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#include <linux/module.h> |
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#include <linux/init.h> |
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#include <linux/sched.h> |
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#include <linux/slab.h> |
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#include <linux/printk.h> |
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#include <linux/miscdevice.h> |
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#include <linux/fs.h> |
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#include <linux/mm.h> |
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#include <linux/pagemap.h> |
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#include <linux/poll.h> |
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#include <linux/uaccess.h> |
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#include <linux/vmalloc.h> |
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#include <linux/file.h> |
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#include <linux/security.h> |
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#include <linux/cred.h> |
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#include <linux/sched/signal.h> |
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#include <linux/watch_queue.h> |
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#include <linux/pipe_fs_i.h> |
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MODULE_DESCRIPTION("Watch queue"); |
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MODULE_AUTHOR("Red Hat, Inc."); |
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MODULE_LICENSE("GPL"); |
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#define WATCH_QUEUE_NOTE_SIZE 128 |
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#define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE) |
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static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, |
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struct pipe_buffer *buf) |
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{ |
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struct watch_queue *wqueue = (struct watch_queue *)buf->private; |
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struct page *page; |
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unsigned int bit; |
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/* We need to work out which note within the page this refers to, but |
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* the note might have been maximum size, so merely ANDing the offset |
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* off doesn't work. OTOH, the note must've been more than zero size. |
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*/ |
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bit = buf->offset + buf->len; |
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if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0) |
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bit -= WATCH_QUEUE_NOTE_SIZE; |
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bit /= WATCH_QUEUE_NOTE_SIZE; |
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page = buf->page; |
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bit += page->index; |
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set_bit(bit, wqueue->notes_bitmap); |
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} |
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// No try_steal function => no stealing |
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#define watch_queue_pipe_buf_try_steal NULL |
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/* New data written to a pipe may be appended to a buffer with this type. */ |
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static const struct pipe_buf_operations watch_queue_pipe_buf_ops = { |
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.release = watch_queue_pipe_buf_release, |
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.try_steal = watch_queue_pipe_buf_try_steal, |
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.get = generic_pipe_buf_get, |
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}; |
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/* |
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* Post a notification to a watch queue. |
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*/ |
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static bool post_one_notification(struct watch_queue *wqueue, |
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struct watch_notification *n) |
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{ |
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void *p; |
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struct pipe_inode_info *pipe = wqueue->pipe; |
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struct pipe_buffer *buf; |
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struct page *page; |
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unsigned int head, tail, mask, note, offset, len; |
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bool done = false; |
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if (!pipe) |
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return false; |
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spin_lock_irq(&pipe->rd_wait.lock); |
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if (wqueue->defunct) |
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goto out; |
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mask = pipe->ring_size - 1; |
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head = pipe->head; |
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tail = pipe->tail; |
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if (pipe_full(head, tail, pipe->ring_size)) |
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goto lost; |
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note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes); |
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if (note >= wqueue->nr_notes) |
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goto lost; |
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page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE]; |
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offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE; |
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get_page(page); |
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len = n->info & WATCH_INFO_LENGTH; |
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p = kmap_atomic(page); |
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memcpy(p + offset, n, len); |
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kunmap_atomic(p); |
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buf = &pipe->bufs[head & mask]; |
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buf->page = page; |
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buf->private = (unsigned long)wqueue; |
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buf->ops = &watch_queue_pipe_buf_ops; |
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buf->offset = offset; |
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buf->len = len; |
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buf->flags = PIPE_BUF_FLAG_WHOLE; |
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pipe->head = head + 1; |
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if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { |
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spin_unlock_irq(&pipe->rd_wait.lock); |
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BUG(); |
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} |
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wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM); |
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done = true; |
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out: |
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spin_unlock_irq(&pipe->rd_wait.lock); |
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if (done) |
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kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); |
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return done; |
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lost: |
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buf = &pipe->bufs[(head - 1) & mask]; |
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buf->flags |= PIPE_BUF_FLAG_LOSS; |
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goto out; |
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} |
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/* |
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* Apply filter rules to a notification. |
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*/ |
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static bool filter_watch_notification(const struct watch_filter *wf, |
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const struct watch_notification *n) |
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{ |
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const struct watch_type_filter *wt; |
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unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8; |
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unsigned int st_index = n->subtype / st_bits; |
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unsigned int st_bit = 1U << (n->subtype % st_bits); |
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int i; |
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if (!test_bit(n->type, wf->type_filter)) |
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return false; |
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for (i = 0; i < wf->nr_filters; i++) { |
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wt = &wf->filters[i]; |
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if (n->type == wt->type && |
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(wt->subtype_filter[st_index] & st_bit) && |
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(n->info & wt->info_mask) == wt->info_filter) |
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return true; |
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} |
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return false; /* If there is a filter, the default is to reject. */ |
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} |
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/** |
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* __post_watch_notification - Post an event notification |
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* @wlist: The watch list to post the event to. |
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* @n: The notification record to post. |
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* @cred: The creds of the process that triggered the notification. |
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* @id: The ID to match on the watch. |
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* |
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* Post a notification of an event into a set of watch queues and let the users |
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* know. |
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* |
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* The size of the notification should be set in n->info & WATCH_INFO_LENGTH and |
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* should be in units of sizeof(*n). |
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*/ |
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void __post_watch_notification(struct watch_list *wlist, |
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struct watch_notification *n, |
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const struct cred *cred, |
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u64 id) |
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{ |
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const struct watch_filter *wf; |
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struct watch_queue *wqueue; |
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struct watch *watch; |
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if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) { |
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WARN_ON(1); |
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return; |
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} |
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rcu_read_lock(); |
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hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) { |
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if (watch->id != id) |
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continue; |
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n->info &= ~WATCH_INFO_ID; |
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n->info |= watch->info_id; |
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wqueue = rcu_dereference(watch->queue); |
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wf = rcu_dereference(wqueue->filter); |
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if (wf && !filter_watch_notification(wf, n)) |
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continue; |
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if (security_post_notification(watch->cred, cred, n) < 0) |
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continue; |
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post_one_notification(wqueue, n); |
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} |
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rcu_read_unlock(); |
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} |
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EXPORT_SYMBOL(__post_watch_notification); |
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/* |
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* Allocate sufficient pages to preallocation for the requested number of |
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* notifications. |
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*/ |
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long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) |
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{ |
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struct watch_queue *wqueue = pipe->watch_queue; |
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struct page **pages; |
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unsigned long *bitmap; |
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unsigned long user_bufs; |
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unsigned int bmsize; |
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int ret, i, nr_pages; |
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if (!wqueue) |
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return -ENODEV; |
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if (wqueue->notes) |
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return -EBUSY; |
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if (nr_notes < 1 || |
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nr_notes > 512) /* TODO: choose a better hard limit */ |
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return -EINVAL; |
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nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1); |
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nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE; |
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user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages); |
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if (nr_pages > pipe->max_usage && |
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(too_many_pipe_buffers_hard(user_bufs) || |
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too_many_pipe_buffers_soft(user_bufs)) && |
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pipe_is_unprivileged_user()) { |
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ret = -EPERM; |
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goto error; |
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} |
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ret = pipe_resize_ring(pipe, nr_notes); |
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if (ret < 0) |
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goto error; |
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pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL); |
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if (!pages) |
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goto error; |
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for (i = 0; i < nr_pages; i++) { |
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pages[i] = alloc_page(GFP_KERNEL); |
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if (!pages[i]) |
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goto error_p; |
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pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE; |
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} |
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bmsize = (nr_notes + BITS_PER_LONG - 1) / BITS_PER_LONG; |
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bmsize *= sizeof(unsigned long); |
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bitmap = kmalloc(bmsize, GFP_KERNEL); |
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if (!bitmap) |
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goto error_p; |
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memset(bitmap, 0xff, bmsize); |
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wqueue->notes = pages; |
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wqueue->notes_bitmap = bitmap; |
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wqueue->nr_pages = nr_pages; |
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wqueue->nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; |
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return 0; |
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error_p: |
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for (i = 0; i < nr_pages; i++) |
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__free_page(pages[i]); |
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kfree(pages); |
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error: |
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(void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted); |
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return ret; |
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} |
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/* |
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* Set the filter on a watch queue. |
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*/ |
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long watch_queue_set_filter(struct pipe_inode_info *pipe, |
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struct watch_notification_filter __user *_filter) |
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{ |
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struct watch_notification_type_filter *tf; |
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struct watch_notification_filter filter; |
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struct watch_type_filter *q; |
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struct watch_filter *wfilter; |
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struct watch_queue *wqueue = pipe->watch_queue; |
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int ret, nr_filter = 0, i; |
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if (!wqueue) |
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return -ENODEV; |
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if (!_filter) { |
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/* Remove the old filter */ |
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wfilter = NULL; |
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goto set; |
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} |
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/* Grab the user's filter specification */ |
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if (copy_from_user(&filter, _filter, sizeof(filter)) != 0) |
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return -EFAULT; |
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if (filter.nr_filters == 0 || |
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filter.nr_filters > 16 || |
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filter.__reserved != 0) |
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return -EINVAL; |
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tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf)); |
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if (IS_ERR(tf)) |
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return PTR_ERR(tf); |
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ret = -EINVAL; |
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for (i = 0; i < filter.nr_filters; i++) { |
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if ((tf[i].info_filter & ~tf[i].info_mask) || |
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tf[i].info_mask & WATCH_INFO_LENGTH) |
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goto err_filter; |
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/* Ignore any unknown types */ |
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if (tf[i].type >= sizeof(wfilter->type_filter) * 8) |
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continue; |
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nr_filter++; |
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} |
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/* Now we need to build the internal filter from only the relevant |
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* user-specified filters. |
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*/ |
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ret = -ENOMEM; |
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wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL); |
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if (!wfilter) |
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goto err_filter; |
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wfilter->nr_filters = nr_filter; |
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q = wfilter->filters; |
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for (i = 0; i < filter.nr_filters; i++) { |
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if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG) |
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continue; |
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q->type = tf[i].type; |
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q->info_filter = tf[i].info_filter; |
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q->info_mask = tf[i].info_mask; |
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q->subtype_filter[0] = tf[i].subtype_filter[0]; |
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__set_bit(q->type, wfilter->type_filter); |
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q++; |
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} |
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kfree(tf); |
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set: |
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pipe_lock(pipe); |
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wfilter = rcu_replace_pointer(wqueue->filter, wfilter, |
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lockdep_is_held(&pipe->mutex)); |
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pipe_unlock(pipe); |
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if (wfilter) |
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kfree_rcu(wfilter, rcu); |
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return 0; |
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err_filter: |
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kfree(tf); |
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return ret; |
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} |
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static void __put_watch_queue(struct kref *kref) |
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{ |
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struct watch_queue *wqueue = |
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container_of(kref, struct watch_queue, usage); |
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struct watch_filter *wfilter; |
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int i; |
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for (i = 0; i < wqueue->nr_pages; i++) |
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__free_page(wqueue->notes[i]); |
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wfilter = rcu_access_pointer(wqueue->filter); |
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if (wfilter) |
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kfree_rcu(wfilter, rcu); |
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kfree_rcu(wqueue, rcu); |
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} |
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/** |
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* put_watch_queue - Dispose of a ref on a watchqueue. |
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* @wqueue: The watch queue to unref. |
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*/ |
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void put_watch_queue(struct watch_queue *wqueue) |
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{ |
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kref_put(&wqueue->usage, __put_watch_queue); |
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} |
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EXPORT_SYMBOL(put_watch_queue); |
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static void free_watch(struct rcu_head *rcu) |
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{ |
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struct watch *watch = container_of(rcu, struct watch, rcu); |
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put_watch_queue(rcu_access_pointer(watch->queue)); |
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atomic_dec(&watch->cred->user->nr_watches); |
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put_cred(watch->cred); |
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} |
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static void __put_watch(struct kref *kref) |
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{ |
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struct watch *watch = container_of(kref, struct watch, usage); |
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|
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call_rcu(&watch->rcu, free_watch); |
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} |
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/* |
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* Discard a watch. |
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*/ |
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static void put_watch(struct watch *watch) |
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{ |
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kref_put(&watch->usage, __put_watch); |
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} |
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/** |
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* init_watch - Initialise a watch |
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* @watch: The watch to initialise. |
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* @wqueue: The queue to assign. |
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* |
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* Initialise a watch and set the watch queue. |
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*/ |
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void init_watch(struct watch *watch, struct watch_queue *wqueue) |
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{ |
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kref_init(&watch->usage); |
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INIT_HLIST_NODE(&watch->list_node); |
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INIT_HLIST_NODE(&watch->queue_node); |
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rcu_assign_pointer(watch->queue, wqueue); |
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} |
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/** |
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* add_watch_to_object - Add a watch on an object to a watch list |
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* @watch: The watch to add |
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* @wlist: The watch list to add to |
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* |
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* @watch->queue must have been set to point to the queue to post notifications |
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* to and the watch list of the object to be watched. @watch->cred must also |
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* have been set to the appropriate credentials and a ref taken on them. |
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* |
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* The caller must pin the queue and the list both and must hold the list |
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* locked against racing watch additions/removals. |
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*/ |
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int add_watch_to_object(struct watch *watch, struct watch_list *wlist) |
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{ |
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struct watch_queue *wqueue = rcu_access_pointer(watch->queue); |
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struct watch *w; |
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hlist_for_each_entry(w, &wlist->watchers, list_node) { |
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struct watch_queue *wq = rcu_access_pointer(w->queue); |
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if (wqueue == wq && watch->id == w->id) |
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return -EBUSY; |
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} |
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watch->cred = get_current_cred(); |
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rcu_assign_pointer(watch->watch_list, wlist); |
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if (atomic_inc_return(&watch->cred->user->nr_watches) > |
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task_rlimit(current, RLIMIT_NOFILE)) { |
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atomic_dec(&watch->cred->user->nr_watches); |
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put_cred(watch->cred); |
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return -EAGAIN; |
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} |
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spin_lock_bh(&wqueue->lock); |
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kref_get(&wqueue->usage); |
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kref_get(&watch->usage); |
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hlist_add_head(&watch->queue_node, &wqueue->watches); |
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spin_unlock_bh(&wqueue->lock); |
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hlist_add_head(&watch->list_node, &wlist->watchers); |
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return 0; |
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} |
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EXPORT_SYMBOL(add_watch_to_object); |
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/** |
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* remove_watch_from_object - Remove a watch or all watches from an object. |
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* @wlist: The watch list to remove from |
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* @wq: The watch queue of interest (ignored if @all is true) |
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* @id: The ID of the watch to remove (ignored if @all is true) |
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* @all: True to remove all objects |
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* |
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* Remove a specific watch or all watches from an object. A notification is |
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* sent to the watcher to tell them that this happened. |
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*/ |
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int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq, |
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u64 id, bool all) |
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{ |
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struct watch_notification_removal n; |
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struct watch_queue *wqueue; |
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struct watch *watch; |
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int ret = -EBADSLT; |
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|
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rcu_read_lock(); |
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again: |
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spin_lock(&wlist->lock); |
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hlist_for_each_entry(watch, &wlist->watchers, list_node) { |
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if (all || |
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(watch->id == id && rcu_access_pointer(watch->queue) == wq)) |
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goto found; |
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} |
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spin_unlock(&wlist->lock); |
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goto out; |
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found: |
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ret = 0; |
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hlist_del_init_rcu(&watch->list_node); |
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rcu_assign_pointer(watch->watch_list, NULL); |
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spin_unlock(&wlist->lock); |
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/* We now own the reference on watch that used to belong to wlist. */ |
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|
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n.watch.type = WATCH_TYPE_META; |
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n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION; |
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n.watch.info = watch->info_id | watch_sizeof(n.watch); |
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n.id = id; |
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if (id != 0) |
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n.watch.info = watch->info_id | watch_sizeof(n); |
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wqueue = rcu_dereference(watch->queue); |
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|
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/* We don't need the watch list lock for the next bit as RCU is |
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* protecting *wqueue from deallocation. |
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*/ |
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if (wqueue) { |
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post_one_notification(wqueue, &n.watch); |
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|
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spin_lock_bh(&wqueue->lock); |
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|
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if (!hlist_unhashed(&watch->queue_node)) { |
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hlist_del_init_rcu(&watch->queue_node); |
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put_watch(watch); |
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} |
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spin_unlock_bh(&wqueue->lock); |
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} |
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|
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if (wlist->release_watch) { |
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void (*release_watch)(struct watch *); |
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release_watch = wlist->release_watch; |
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rcu_read_unlock(); |
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(*release_watch)(watch); |
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rcu_read_lock(); |
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} |
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put_watch(watch); |
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|
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if (all && !hlist_empty(&wlist->watchers)) |
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goto again; |
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out: |
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rcu_read_unlock(); |
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return ret; |
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} |
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EXPORT_SYMBOL(remove_watch_from_object); |
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|
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/* |
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* Remove all the watches that are contributory to a queue. This has the |
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* potential to race with removal of the watches by the destruction of the |
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* objects being watched or with the distribution of notifications. |
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*/ |
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void watch_queue_clear(struct watch_queue *wqueue) |
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{ |
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struct watch_list *wlist; |
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struct watch *watch; |
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bool release; |
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|
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rcu_read_lock(); |
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spin_lock_bh(&wqueue->lock); |
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|
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/* Prevent new additions and prevent notifications from happening */ |
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wqueue->defunct = true; |
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|
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while (!hlist_empty(&wqueue->watches)) { |
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watch = hlist_entry(wqueue->watches.first, struct watch, queue_node); |
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hlist_del_init_rcu(&watch->queue_node); |
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/* We now own a ref on the watch. */ |
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spin_unlock_bh(&wqueue->lock); |
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|
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/* We can't do the next bit under the queue lock as we need to |
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* get the list lock - which would cause a deadlock if someone |
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* was removing from the opposite direction at the same time or |
|
* posting a notification. |
|
*/ |
|
wlist = rcu_dereference(watch->watch_list); |
|
if (wlist) { |
|
void (*release_watch)(struct watch *); |
|
|
|
spin_lock(&wlist->lock); |
|
|
|
release = !hlist_unhashed(&watch->list_node); |
|
if (release) { |
|
hlist_del_init_rcu(&watch->list_node); |
|
rcu_assign_pointer(watch->watch_list, NULL); |
|
|
|
/* We now own a second ref on the watch. */ |
|
} |
|
|
|
release_watch = wlist->release_watch; |
|
spin_unlock(&wlist->lock); |
|
|
|
if (release) { |
|
if (release_watch) { |
|
rcu_read_unlock(); |
|
/* This might need to call dput(), so |
|
* we have to drop all the locks. |
|
*/ |
|
(*release_watch)(watch); |
|
rcu_read_lock(); |
|
} |
|
put_watch(watch); |
|
} |
|
} |
|
|
|
put_watch(watch); |
|
spin_lock_bh(&wqueue->lock); |
|
} |
|
|
|
spin_unlock_bh(&wqueue->lock); |
|
rcu_read_unlock(); |
|
} |
|
|
|
/** |
|
* get_watch_queue - Get a watch queue from its file descriptor. |
|
* @fd: The fd to query. |
|
*/ |
|
struct watch_queue *get_watch_queue(int fd) |
|
{ |
|
struct pipe_inode_info *pipe; |
|
struct watch_queue *wqueue = ERR_PTR(-EINVAL); |
|
struct fd f; |
|
|
|
f = fdget(fd); |
|
if (f.file) { |
|
pipe = get_pipe_info(f.file, false); |
|
if (pipe && pipe->watch_queue) { |
|
wqueue = pipe->watch_queue; |
|
kref_get(&wqueue->usage); |
|
} |
|
fdput(f); |
|
} |
|
|
|
return wqueue; |
|
} |
|
EXPORT_SYMBOL(get_watch_queue); |
|
|
|
/* |
|
* Initialise a watch queue |
|
*/ |
|
int watch_queue_init(struct pipe_inode_info *pipe) |
|
{ |
|
struct watch_queue *wqueue; |
|
|
|
wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL); |
|
if (!wqueue) |
|
return -ENOMEM; |
|
|
|
wqueue->pipe = pipe; |
|
kref_init(&wqueue->usage); |
|
spin_lock_init(&wqueue->lock); |
|
INIT_HLIST_HEAD(&wqueue->watches); |
|
|
|
pipe->watch_queue = wqueue; |
|
return 0; |
|
}
|
|
|