Root/fs/fifo.c

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
17static 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
28static void wake_up_partner(struct inode* inode)
29{
30    wake_up_interruptible(&inode->i_pipe->wait);
31}
32
33static 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
125err_rd:
126    if (!--pipe->readers)
127        wake_up_interruptible(&pipe->wait);
128    ret = -ERESTARTSYS;
129    goto err;
130
131err_wr:
132    if (!--pipe->writers)
133        wake_up_interruptible(&pipe->wait);
134    ret = -ERESTARTSYS;
135    goto err;
136
137err:
138    if (!pipe->readers && !pipe->writers)
139        free_pipe_info(inode);
140
141err_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 */
151const struct file_operations def_fifo_fops = {
152    .open = fifo_open, /* will set read_ or write_pipefifo_fops */
153    .llseek = noop_llseek,
154};
155

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