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== Article purpose == | == Article purpose == | ||
This article provides some information about the sysfs pseudo filesystem usage from the user space. | This article provides some information about the sysfs pseudo filesystem usage from the user space. | ||
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* open a file descriptor of the sysfs entry file | * open a file descriptor of the sysfs entry file | ||
<syntaxhighlight lang="c" line start="10"> | |||
len=snprintf(buf, sizeof(buf), "/sys/class/pwm/pwmchip0/pwm%d/duty_cycle", pwm_channel); | len=snprintf(buf, sizeof(buf), "/sys/class/pwm/pwmchip0/pwm%d/duty_cycle", pwm_channel); | ||
fd = open(buf, O_RDWR); | fd = open(buf, O_RDWR); | ||
</ | </syntaxhighlight> | ||
*if fd is correctly opened, write/read value in the file: pay attention to the "text" format | *if fd is correctly opened, write/read value in the file: pay attention to the "text" format | ||
< | <syntaxhighlight lang="c" line start="12"> | ||
if (fd < 0) | if (fd < 0) | ||
{ | { | ||
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return fd; | return fd; | ||
} | } | ||
</ | </syntaxhighlight> | ||
:*read: store data to buffer | :*read: store data to buffer | ||
< | <syntaxhighlight lang="c" line start="18"> | ||
read(fd, buf, sizeof(buf)); | read(fd, buf, sizeof(buf)); | ||
</ | </syntaxhighlight> | ||
:*write: write data from buffer | :*write: write data from buffer | ||
< | <syntaxhighlight lang="c" line start="20"> | ||
len = snprintf(buf, sizeof(buf), "%d", 900000); | len = snprintf(buf, sizeof(buf), "%d", 900000); | ||
write(fd, buf, len); | write(fd, buf, len); | ||
</ | </syntaxhighlight> | ||
* close file descriptor | * close file descriptor | ||
< | <syntaxhighlight lang="c" line start="30"> | ||
close(fd); | close(fd); | ||
</ | </syntaxhighlight> | ||
=== Example for shell command / bash script === | === Example for shell command / bash script === | ||
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== References == | == References == | ||
<references /> | <references /> | ||
<noinclude> | |||
[[Category:How to trace and debug]] | |||
[[Category:OpenSTLinux filesystem]] | |||
{{PublicationRequestId | 10265 | 2019-01-16 |BrunoB}} | |||
</noinclude> | |||
Latest revision as of 11:31, 24 January 2020
1. Article purpose[edit source]
This article provides some information about the sysfs pseudo filesystem usage from the user space.
2. Sysfs (/sys) pseudo filesystem[edit source]
Sysfs provides a mean to export kernel data structures, their attributes, and the linkages between them to the user space.
Please refer to sysfs part of pseudo filesystem page.
3. Sysfs usage[edit source]
Linux kernel provides a documentation[1] about the rules for sysfs usage.
Some examples are also described below with two different approaches for using sysfs entries from the user space:
- Linux application in C language
- bash script.
3.1. Example from Linux application[edit source]
The below example is a typical sequence for using sysfs entry (here a PWM component):
- open a file descriptor of the sysfs entry file
len=snprintf(buf, sizeof(buf), "/sys/class/pwm/pwmchip0/pwm%d/duty_cycle", pwm_channel);
fd = open(buf, O_RDWR);
- if fd is correctly opened, write/read value in the file: pay attention to the "text" format
if (fd < 0)
{
perror("pwm/duty_cycle");
return fd;
}
- read: store data to buffer
read(fd, buf, sizeof(buf));
- write: write data from buffer
len = snprintf(buf, sizeof(buf), "%d", 900000);
write(fd, buf, len);
- close file descriptor
close(fd);
3.2. Example for shell command / bash script[edit source]
Operations on sysfs entries can be done by using command lines (i.e. echo for writing, cat for reading).
In this way, it is possible to use a bash script to execute a configuration sequence, similarly to what a user would do by typing multiple shell commands.
An example is provided in How_to_use_PWM_with_sysfs_interface.
4. References[edit source]