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/slab.h>
14 #include <linux/fs.h>
15 #include <linux/sched.h>
16 #include <linux/pipe_fs_i.h>
17
18 static void wait_for_partner(struct inode* inode, unsigned int *cnt)
19 {
20 int cur = *cnt;
21
22 while (cur == *cnt) {
23 pipe_wait(inode->i_pipe);
24 if (signal_pending(current))
25 break;
26 }
27 }
28
29 static void wake_up_partner(struct inode* inode)
30 {
31 wake_up_interruptible(&inode->i_pipe->wait);
32 }
33
34 static int fifo_open(struct inode *inode, struct file *filp)
35 {
36 struct pipe_inode_info *pipe;
37 int ret;
38
39 mutex_lock(&inode->i_mutex);
40 pipe = inode->i_pipe;
41 if (!pipe) {
42 ret = -ENOMEM;
43 pipe = alloc_pipe_info(inode);
44 if (!pipe)
45 goto err_nocleanup;
46 inode->i_pipe = pipe;
47 }
48 filp->f_version = 0;
49
50 /* We can only do regular read/write on fifos */
51 filp->f_mode &= (FMODE_READ | FMODE_WRITE);
52
53 switch (filp->f_mode) {
54 case FMODE_READ:
55 /*
56 * O_RDONLY
57 * POSIX.1 says that O_NONBLOCK means return with the FIFO
58 * opened, even when there is no process writing the FIFO.
59 */
60 filp->f_op = &read_pipefifo_fops;
61 pipe->r_counter++;
62 if (pipe->readers++ == 0)
63 wake_up_partner(inode);
64
65 if (!pipe->writers) {
66 if ((filp->f_flags & O_NONBLOCK)) {
67 /* suppress POLLHUP until we have
68 * seen a writer */
69 filp->f_version = pipe->w_counter;
70 } else
71 {
72 wait_for_partner(inode, &pipe->w_counter);
73 if(signal_pending(current))
74 goto err_rd;
75 }
76 }
77 break;
78
79 case FMODE_WRITE:
80 /*
81 * O_WRONLY
82 * POSIX.1 says that O_NONBLOCK means return -1 with
83 * errno=ENXIO when there is no process reading the FIFO.
84 */
85 ret = -ENXIO;
86 if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
87 goto err;
88
89 filp->f_op = &write_pipefifo_fops;
90 pipe->w_counter++;
91 if (!pipe->writers++)
92 wake_up_partner(inode);
93
94 if (!pipe->readers) {
95 wait_for_partner(inode, &pipe->r_counter);
96 if (signal_pending(current))
97 goto err_wr;
98 }
99 break;
100
101 case FMODE_READ | FMODE_WRITE:
102 /*
103 * O_RDWR
104 * POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
105 * This implementation will NEVER block on a O_RDWR open, since
106 * the process can at least talk to itself.
107 */
108 filp->f_op = &rdwr_pipefifo_fops;
109
110 pipe->readers++;
111 pipe->writers++;
112 pipe->r_counter++;
113 pipe->w_counter++;
114 if (pipe->readers == 1 || pipe->writers == 1)
115 wake_up_partner(inode);
116 break;
117
118 default:
119 ret = -EINVAL;
120 goto err;
121 }
122
123 /* Ok! */
124 mutex_unlock(&inode->i_mutex);
125 return 0;
126
127 err_rd:
128 if (!--pipe->readers)
129 wake_up_interruptible(&pipe->wait);
130 ret = -ERESTARTSYS;
131 goto err;
132
133 err_wr:
134 if (!--pipe->writers)
135 wake_up_interruptible(&pipe->wait);
136 ret = -ERESTARTSYS;
137 goto err;
138
139 err:
140 if (!pipe->readers && !pipe->writers)
141 free_pipe_info(inode);
142
143 err_nocleanup:
144 mutex_unlock(&inode->i_mutex);
145 return ret;
146 }
147
148 /*
149 * Dummy default file-operations: the only thing this does
150 * is contain the open that then fills in the correct operations
151 * depending on the access mode of the file...
152 */
153 const struct file_operations def_fifo_fops = {
154 .open = fifo_open, /* will set read_ or write_pipefifo_fops */
155 };
156
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