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Serenity Operating System
1/*
2 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
3 *
4 * SPDX-License-Identifier: BSD-2-Clause
5 */
6
7#include <AK/Atomic.h>
8#include <AK/StdLibExtras.h>
9#include <Kernel/FileSystem/FIFO.h>
10#include <Kernel/FileSystem/OpenFileDescription.h>
11#include <Kernel/Locking/Mutex.h>
12#include <Kernel/Process.h>
13#include <Kernel/Thread.h>
14
15namespace Kernel {
16
17static Atomic<int> s_next_fifo_id = 1;
18
19ErrorOr<NonnullRefPtr<FIFO>> FIFO::try_create(UserID uid)
20{
21 auto buffer = TRY(DoubleBuffer::try_create("FIFO: Buffer"sv));
22 return adopt_nonnull_ref_or_enomem(new (nothrow) FIFO(uid, move(buffer)));
23}
24
25ErrorOr<NonnullRefPtr<OpenFileDescription>> FIFO::open_direction(FIFO::Direction direction)
26{
27 auto description = TRY(OpenFileDescription::try_create(*this));
28 attach(direction);
29 description->set_fifo_direction({}, direction);
30 return description;
31}
32
33ErrorOr<NonnullRefPtr<OpenFileDescription>> FIFO::open_direction_blocking(FIFO::Direction direction)
34{
35 MutexLocker locker(m_open_lock);
36
37 auto description = TRY(open_direction(direction));
38
39 if (direction == Direction::Reader) {
40 m_read_open_queue.wake_all();
41
42 if (m_writers == 0) {
43 locker.unlock();
44 m_write_open_queue.wait_forever("FIFO"sv);
45 locker.lock();
46 }
47 }
48
49 if (direction == Direction::Writer) {
50 m_write_open_queue.wake_all();
51
52 if (m_readers == 0) {
53 locker.unlock();
54 m_read_open_queue.wait_forever("FIFO"sv);
55 locker.lock();
56 }
57 }
58
59 return description;
60}
61
62FIFO::FIFO(UserID uid, NonnullOwnPtr<DoubleBuffer> buffer)
63 : m_buffer(move(buffer))
64 , m_uid(uid)
65{
66 m_fifo_id = ++s_next_fifo_id;
67
68 // Use the same block condition for read and write
69 m_buffer->set_unblock_callback([this]() {
70 evaluate_block_conditions();
71 });
72}
73
74FIFO::~FIFO() = default;
75
76void FIFO::attach(Direction direction)
77{
78 if (direction == Direction::Reader) {
79 ++m_readers;
80 } else if (direction == Direction::Writer) {
81 ++m_writers;
82 }
83
84 evaluate_block_conditions();
85}
86
87void FIFO::detach(Direction direction)
88{
89 if (direction == Direction::Reader) {
90 VERIFY(m_readers);
91 --m_readers;
92 } else if (direction == Direction::Writer) {
93 VERIFY(m_writers);
94 --m_writers;
95 }
96
97 evaluate_block_conditions();
98}
99
100bool FIFO::can_read(OpenFileDescription const&, u64) const
101{
102 return !m_buffer->is_empty() || !m_writers;
103}
104
105bool FIFO::can_write(OpenFileDescription const&, u64) const
106{
107 return m_buffer->space_for_writing() || !m_readers;
108}
109
110ErrorOr<size_t> FIFO::read(OpenFileDescription& fd, u64, UserOrKernelBuffer& buffer, size_t size)
111{
112 if (m_buffer->is_empty()) {
113 if (!m_writers)
114 return 0;
115 if (!fd.is_blocking())
116 return EAGAIN;
117 }
118 return m_buffer->read(buffer, size);
119}
120
121ErrorOr<size_t> FIFO::write(OpenFileDescription& fd, u64, UserOrKernelBuffer const& buffer, size_t size)
122{
123 if (!m_readers)
124 return EPIPE;
125 if (!fd.is_blocking() && m_buffer->space_for_writing() == 0)
126 return EAGAIN;
127
128 return m_buffer->write(buffer, size);
129}
130
131ErrorOr<NonnullOwnPtr<KString>> FIFO::pseudo_path(OpenFileDescription const&) const
132{
133 return KString::formatted("fifo:{}", m_fifo_id);
134}
135
136ErrorOr<struct stat> FIFO::stat() const
137{
138 struct stat st = {};
139 st.st_mode = S_IFIFO;
140 return st;
141}
142
143}