1 .. SPDX-License-Identifier: GPL-2.0
2
3 .. _GPIO_V2_LINEINFO_CHANGED_READ:
4
5 *****************************
6 GPIO_V2_LINEINFO_CHANGED_READ
7 *****************************
8
9 Name
10 ====
11
12 GPIO_V2_LINEINFO_CHANGED_READ - Read line info
13 lines from the chip.
14
15 Synopsis
16 ========
17
18 ``int read(int chip_fd, void *buf, size_t coun
19
20 Arguments
21 =========
22
23 ``chip_fd``
24 The file descriptor of the GPIO character
25
26 ``buf``
27 The buffer to contain the :c:type:`events<
28
29 ``count``
30 The number of bytes available in ``buf``,
31 of a :c:type:`gpio_v2_line_info_changed` e
32
33 Description
34 ===========
35
36 Read line info changed events for watched line
37
38 .. note::
39 Monitoring line info changes is not genera
40 only be performed by a system monitoring c
41
42 These events relate to changes in a line's
43 not its value. Use gpio-v2-line-event-read
44 line changes value.
45
46 A line must be watched using gpio-v2-get-linei
47 info changed events. Subsequently, a request,
48 of the line will generate an info changed even
49
50 The kernel timestamps events when they occur a
51 from where they can be read by userspace at it
52
53 The size of the kernel event buffer is fixed a
54
55 The buffer may overflow if bursts of events oc
56 by userspace. If an overflow occurs then the m
57 Overflow cannot be detected from userspace.
58
59 Events read from the buffer are always in the
60 detected by the kernel, including when multipl
61 the one ``chip_fd``.
62
63 To minimize the number of calls required to co
64 userspace, `read()` supports copying multiple
65 copied is the lower of the number available in
66 number that will fit in the userspace buffer (
67
68 A `read()` will block if no event is available
69 been set **O_NONBLOCK**.
70
71 The presence of an event can be tested for by
72 readable using `poll()` or an equivalent.
73
74 Return Value
75 ============
76
77 On success the number of bytes read, which wil
78 of a :c:type:`gpio_v2_line_info_changed` event
79
80 On error -1 and the ``errno`` variable is set
81 Common error codes are described in error-code
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