如何在sysfs中访问信息
目录
Article purpose
This article provides some information about the sysfs pseudo filesystem usage from the user space.
Sysfs (/sys) pseudo filesystem
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 伪文件系统 page.
Sysfs usage
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.
Example from Linux application
The below example is a typical sequence for using sysfs entry (here a PWM component):
- open a file descriptor of the sysfs entry file
10 len=snprintf(buf, sizeof(buf), "/sys/class/pwm/pwmchip0/pwm%d/duty_cycle", pwm_channel);
11 fd = open(buf, O_RDWR);
- if fd is correctly opened, write/read value in the file: pay attention to the "text" format
12 if (fd < 0)
13 {
14 perror("pwm/duty_cycle");
15 return fd;
16 }
- read: store data to buffer
18 read(fd, buf, sizeof(buf));
- write: write data from buffer
20 len = snprintf(buf, sizeof(buf), "%d", 900000);
21 write(fd, buf, len);
- close file descriptor
30 close(fd);
Example for shell command / bash script
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.
References
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