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1 | /* |
2 | * linux/fs/fifo.c |
3 | * |
4 | * written by Paul H. Hargrove |
5 | * |
6 | * Fixes: |
7 | * 10-06-1999, AV: fixed OOM handling in fifo_open(), moved |
8 | * initialization there, switched to external |
9 | * allocation of pipe_inode_info. |
10 | */ |
11 | |
12 | #include <linux/mm.h> |
13 | #include <linux/fs.h> |
14 | #include <linux/sched.h> |
15 | #include <linux/pipe_fs_i.h> |
16 | |
17 | static void wait_for_partner(struct inode* inode, unsigned int *cnt) |
18 | { |
19 | int cur = *cnt; |
20 | |
21 | while (cur == *cnt) { |
22 | pipe_wait(inode->i_pipe); |
23 | if (signal_pending(current)) |
24 | break; |
25 | } |
26 | } |
27 | |
28 | static void wake_up_partner(struct inode* inode) |
29 | { |
30 | wake_up_interruptible(&inode->i_pipe->wait); |
31 | } |
32 | |
33 | static int fifo_open(struct inode *inode, struct file *filp) |
34 | { |
35 | struct pipe_inode_info *pipe; |
36 | int ret; |
37 | |
38 | mutex_lock(&inode->i_mutex); |
39 | pipe = inode->i_pipe; |
40 | if (!pipe) { |
41 | ret = -ENOMEM; |
42 | pipe = alloc_pipe_info(inode); |
43 | if (!pipe) |
44 | goto err_nocleanup; |
45 | inode->i_pipe = pipe; |
46 | } |
47 | filp->f_version = 0; |
48 | |
49 | /* We can only do regular read/write on fifos */ |
50 | filp->f_mode &= (FMODE_READ | FMODE_WRITE); |
51 | |
52 | switch (filp->f_mode) { |
53 | case FMODE_READ: |
54 | /* |
55 | * O_RDONLY |
56 | * POSIX.1 says that O_NONBLOCK means return with the FIFO |
57 | * opened, even when there is no process writing the FIFO. |
58 | */ |
59 | filp->f_op = &read_pipefifo_fops; |
60 | pipe->r_counter++; |
61 | if (pipe->readers++ == 0) |
62 | wake_up_partner(inode); |
63 | |
64 | if (!pipe->writers) { |
65 | if ((filp->f_flags & O_NONBLOCK)) { |
66 | /* suppress POLLHUP until we have |
67 | * seen a writer */ |
68 | filp->f_version = pipe->w_counter; |
69 | } else |
70 | { |
71 | wait_for_partner(inode, &pipe->w_counter); |
72 | if(signal_pending(current)) |
73 | goto err_rd; |
74 | } |
75 | } |
76 | break; |
77 | |
78 | case FMODE_WRITE: |
79 | /* |
80 | * O_WRONLY |
81 | * POSIX.1 says that O_NONBLOCK means return -1 with |
82 | * errno=ENXIO when there is no process reading the FIFO. |
83 | */ |
84 | ret = -ENXIO; |
85 | if ((filp->f_flags & O_NONBLOCK) && !pipe->readers) |
86 | goto err; |
87 | |
88 | filp->f_op = &write_pipefifo_fops; |
89 | pipe->w_counter++; |
90 | if (!pipe->writers++) |
91 | wake_up_partner(inode); |
92 | |
93 | if (!pipe->readers) { |
94 | wait_for_partner(inode, &pipe->r_counter); |
95 | if (signal_pending(current)) |
96 | goto err_wr; |
97 | } |
98 | break; |
99 | |
100 | case FMODE_READ | FMODE_WRITE: |
101 | /* |
102 | * O_RDWR |
103 | * POSIX.1 leaves this case "undefined" when O_NONBLOCK is set. |
104 | * This implementation will NEVER block on a O_RDWR open, since |
105 | * the process can at least talk to itself. |
106 | */ |
107 | filp->f_op = &rdwr_pipefifo_fops; |
108 | |
109 | pipe->readers++; |
110 | pipe->writers++; |
111 | pipe->r_counter++; |
112 | pipe->w_counter++; |
113 | if (pipe->readers == 1 || pipe->writers == 1) |
114 | wake_up_partner(inode); |
115 | break; |
116 | |
117 | default: |
118 | ret = -EINVAL; |
119 | goto err; |
120 | } |
121 | |
122 | /* Ok! */ |
123 | mutex_unlock(&inode->i_mutex); |
124 | return 0; |
125 | |
126 | err_rd: |
127 | if (!--pipe->readers) |
128 | wake_up_interruptible(&pipe->wait); |
129 | ret = -ERESTARTSYS; |
130 | goto err; |
131 | |
132 | err_wr: |
133 | if (!--pipe->writers) |
134 | wake_up_interruptible(&pipe->wait); |
135 | ret = -ERESTARTSYS; |
136 | goto err; |
137 | |
138 | err: |
139 | if (!pipe->readers && !pipe->writers) |
140 | free_pipe_info(inode); |
141 | |
142 | err_nocleanup: |
143 | mutex_unlock(&inode->i_mutex); |
144 | return ret; |
145 | } |
146 | |
147 | /* |
148 | * Dummy default file-operations: the only thing this does |
149 | * is contain the open that then fills in the correct operations |
150 | * depending on the access mode of the file... |
151 | */ |
152 | const struct file_operations def_fifo_fops = { |
153 | .open = fifo_open, /* will set read_ or write_pipefifo_fops */ |
154 | }; |
155 |
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