mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
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85 lines
2.1 KiB
C
85 lines
2.1 KiB
C
/*
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Adapted from: https://github.com/t3rm1n4l/kern-dev-tutorial/blob/1f036ef40fc4378f5c8d2842e55bcea7c6f8894a/05-sysfs/sysfs.c
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Vs procfs:
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- https://unix.stackexchange.com/questions/4884/what-is-the-difference-between-procfs-and-sysfs
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- https://stackoverflow.com/questions/37237835/how-to-attach-file-operations-to-sysfs-attribute-in-platform-driver
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This example shows how sysfs is more restricted, as it does not take a file_operations.
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So you basically can only do open, close, read, write, and lseek on sysfs files.
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It is kind of similar to a seq_file file_operations, except that write is also implemented.
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TODO: what are those kobject structs? Make a more complex example that shows what they can do.
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- https://www.kernel.org/doc/Documentation/kobject.txt
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- https://www.quora.com/What-are-kernel-objects-Kobj
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- http://www.makelinux.net/ldd3/chp-14-sect-1
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- https://www.win.tue.nl/~aeb/linux/lk/lk-13.html
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*/
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#include <linux/init.h>
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#include <linux/kobject.h>
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#include <linux/module.h>
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#include <linux/stat.h>
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#include <linux/string.h>
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#include <linux/sysfs.h>
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#include <uapi/linux/stat.h> /* S_IRUSR, S_IWUSR */
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enum { FOO_SIZE_MAX = 4 };
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static int foo_size;
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static char foo_tmp[FOO_SIZE_MAX];
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static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
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char *buff)
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{
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strncpy(buff, foo_tmp, foo_size);
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return foo_size;
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}
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static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
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const char *buff, size_t count)
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{
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foo_size = min(count, (size_t)FOO_SIZE_MAX);
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strncpy(foo_tmp, buff, foo_size);
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return count;
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}
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static struct kobj_attribute foo_attribute =
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__ATTR(foo, S_IRUGO | S_IWUSR, foo_show, foo_store);
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static struct attribute *attrs[] = {
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&foo_attribute.attr,
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NULL,
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};
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static struct attribute_group attr_group = {
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.attrs = attrs,
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};
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static struct kobject *kobj;
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static int myinit(void)
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{
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int ret;
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kobj = kobject_create_and_add("lkmc_sysfs", kernel_kobj);
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if (!kobj)
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return -ENOMEM;
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ret = sysfs_create_group(kobj, &attr_group);
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if (ret)
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kobject_put(kobj);
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return ret;
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}
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static void myexit(void)
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{
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kobject_put(kobj);
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}
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module_init(myinit);
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module_exit(myexit);
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MODULE_LICENSE("GPL");
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