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
wait_for_partner(struct inode * inode,unsigned int * cnt)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
wake_up_partner(struct inode * inode)28 static void wake_up_partner(struct inode* inode)
29 {
30 wake_up_interruptible(&inode->i_pipe->wait);
31 }
32
fifo_open(struct inode * inode,struct file * filp)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 wait_for_partner(inode, &pipe->w_counter);
71 if(signal_pending(current))
72 goto err_rd;
73 }
74 }
75 break;
76
77 case FMODE_WRITE:
78 /*
79 * O_WRONLY
80 * POSIX.1 says that O_NONBLOCK means return -1 with
81 * errno=ENXIO when there is no process reading the FIFO.
82 */
83 ret = -ENXIO;
84 if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
85 goto err;
86
87 filp->f_op = &write_pipefifo_fops;
88 pipe->w_counter++;
89 if (!pipe->writers++)
90 wake_up_partner(inode);
91
92 if (!pipe->readers) {
93 wait_for_partner(inode, &pipe->r_counter);
94 if (signal_pending(current))
95 goto err_wr;
96 }
97 break;
98
99 case FMODE_READ | FMODE_WRITE:
100 /*
101 * O_RDWR
102 * POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
103 * This implementation will NEVER block on a O_RDWR open, since
104 * the process can at least talk to itself.
105 */
106 filp->f_op = &rdwr_pipefifo_fops;
107
108 pipe->readers++;
109 pipe->writers++;
110 pipe->r_counter++;
111 pipe->w_counter++;
112 if (pipe->readers == 1 || pipe->writers == 1)
113 wake_up_partner(inode);
114 break;
115
116 default:
117 ret = -EINVAL;
118 goto err;
119 }
120
121 /* Ok! */
122 mutex_unlock(&inode->i_mutex);
123 return 0;
124
125 err_rd:
126 if (!--pipe->readers)
127 wake_up_interruptible(&pipe->wait);
128 ret = -ERESTARTSYS;
129 goto err;
130
131 err_wr:
132 if (!--pipe->writers)
133 wake_up_interruptible(&pipe->wait);
134 ret = -ERESTARTSYS;
135 goto err;
136
137 err:
138 if (!pipe->readers && !pipe->writers)
139 free_pipe_info(inode);
140
141 err_nocleanup:
142 mutex_unlock(&inode->i_mutex);
143 return ret;
144 }
145
146 /*
147 * Dummy default file-operations: the only thing this does
148 * is contain the open that then fills in the correct operations
149 * depending on the access mode of the file...
150 */
151 const struct file_operations def_fifo_fops = {
152 .open = fifo_open, /* will set read_ or write_pipefifo_fops */
153 .llseek = noop_llseek,
154 };
155