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Linux driver | procfs interface creation

Release： 2023-08-01 15:26:10

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The previous article introduced the creation of the sysfs interface in the Linux driver. Today we will introduce the creation of the procfs interface.

procfs: Can implement operations similar tocat /proc/cpuinfo

procfs interface creation

Achievement effect:

For example, create a clk node under/procand passcat /proc/clkViewable content:

Linux driver | procfs interface creation

Code implementation:

Add the following code in the driver:

#include  #include  #include  #include  #include  struct proc_dir_entry *my_proc_entry; static int proc_clk_show(struct seq_file *m, void *v) { //cat显示的内容 seq_printf(m, "pll0: %u Mhz\n" "pll1: %u Mhz\n" "pll2: %u Mhz\n", 100, 200, 300); return 0; } static int clk_info_open(struct inode *inode, struct file *filp) { return single_open(filp, proc_clk_show, NULL); } static struct file_operations myops = { .owner = THIS_MODULE, .open = clk_info_open, .read = seq_read, .llseek = seq_lseek, .release = seq_release, }; static int __init my_module_init(void) { //注册proc接口 my_proc_entry = proc_create("clk", 0644, NULL, &myops); return 0; } static void __exit my_module_exit(void) { //注销proc接口 proc_remove(my_proc_entry); } module_init(my_module_init); module_exit(my_module_exit); MODULE_LICENSE("GPL");

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The creation of the procfs interface mainly implements thestruct file_operationsstructure, and then proceeds through theproc_createfunction Register and unregister through theproc_removefunction.

procfs is usually used to obtain various information such as CPU, memory, process, etc., such ascat /proc/cpuinfo,cat /proc/meminfo, so we only Need to implement the .open member function. When using thecatcommand to view the information under/proc, the corresponding implementation function of.openwill be called.

Here we use theseq_fileinterface. What needs to be remembered is thatprocfs is usually usedtogether with the seq_file interface. seq_file is a sequence file interface.When the proc data content we create is composed of a series of data sequences or it is a relatively large proc file system, it is recommended to use the seq_file interface, such ascat / proc/meminfowill display a lot of content.

The seq_file interface mainly solves the problems existing in proc interface programming.It is recommended to use the seq_file interfacewhen programming the proc interface. In addition, the .read, .llseek, and .release member functions can also be used directlyseq_read,seq_lseekandseq_release.

proc new interface

Note that in newer versions of the kernel,procfsThe function interface has changed.

##System Kernel version Linux 4.9.88

System	Kernel version
Linux	5.10.111

在驱动中添加以下代码：

#include  #include  #include  #include  #include  struct proc_dir_entry *my_proc_entry; static int proc_clk_show(struct seq_file *m, void *v) { seq_printf(m, "pll0: %lu Mhz\n" "pll1: %lu Mhz\n" "pll2: %lu Mhz\n", 100, 200, 300); return 0; } static int clk_info_open(struct inode *inode, struct file *filp) { return single_open(filp, proc_clk_show, NULL); } static const struct proc_ops clk_stat_proc_fops = { .proc_open = clk_info_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_release = seq_release, }; static int __init my_module_init(void) { my_proc_entry = proc_create("clk", 0, NULL, &clk_stat_proc_fops); return 0; } static void __exit my_module_exit(void) { proc_remove(my_proc_entry); } module_init(my_module_init); module_exit(my_module_exit); MODULE_LICENSE("GPL");

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新的proc接口中，将原来的struct file_operations换成了struct proc_ops，其中成员函数也添加了对应的前缀proc，但本质还是一样的，只是换了名字，更加规范了一些。

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