如何建立一個產生連續0x01
字元流的檔案?就像/dev/zero
,除了產生我選擇的角色:
/dev/zero – 接受並丟棄寫入其中的所有輸入;讀取時產生連續的空字元(零值位元組)流作為輸出。
它必須可由 讀取cat
。我考慮過在命名管道中運行循環,但這需要一個活動進程。
答案1
……但這需要一個正面的過程。
原件/dev/zero
也由主動“過程”, 但在核心中。如果您不想在用戶空間層級處理它,那麼您的其他選擇非常有限 - 那麼它應該是一些核心驅動程式。
答案2
好吧,你總是可以通過管道 /dev/zerotr
或其他東西
# cat /dev/zero | tr '\000' '\001' | hexdump -C
00000000 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 |................|
*
如果你想跳過cat並使用進程替換。
# hexdump -C <( tr '\000' '\001' </dev/zero )
00000000 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 |................|
相對。
# cat /dev/zero | hexdump -C
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
答案3
無恥地改編自Linux 核心模組程式設計指南
#include <linux/cdev.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/poll.h>
/* Prototypes - this would normally go in a .h file */
static int device_open(struct inode *, struct file *);
static int device_release(struct inode *, struct file *);
static ssize_t device_read(struct file *, char __user *, size_t, loff_t *);
static ssize_t device_write(struct file *, const char __user *, size_t,
loff_t *);
#define SUCCESS 0
#define DEVICE_NAME "one" /* Dev name as it appears in /proc/devices */
/* Global variables are declared as static, so are global within the file. */
static int major; /* major number assigned to our device driver */
static struct class *cls;
static struct file_operations chardev_fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release = device_release,
};
static int __init chardev_init(void)
{
major = register_chrdev(0, DEVICE_NAME, &chardev_fops);
if (major < 0) {
pr_alert("Registering char device failed with %d\n", major);
return major;
}
pr_info("I was assigned major number %d.\n", major);
cls = class_create(THIS_MODULE, DEVICE_NAME);
device_create(cls, NULL, MKDEV(major, 0), NULL, DEVICE_NAME);
pr_info("Device created on /dev/%s\n", DEVICE_NAME);
return SUCCESS;
}
static void __exit chardev_exit(void)
{
device_destroy(cls, MKDEV(major, 0));
class_destroy(cls);
/* Unregister the device */
unregister_chrdev(major, DEVICE_NAME);
}
/* Methods */
/* Called when a process tries to open the device file, like
* "sudo cat /dev/chardev"
*/
static int device_open(struct inode *inode, struct file *file)
{
try_module_get(THIS_MODULE);
return SUCCESS;
}
/* Called when a process closes the device file. */
static int device_release(struct inode *inode, struct file *file)
{
/* Decrement the usage count, or else once you opened the file, you will
* never get rid of the module.
*/
module_put(THIS_MODULE);
return SUCCESS;
}
/* Called when a process, which already opened the dev file, attempts to
* read from it.
*/
static ssize_t device_read(struct file *filp, /* see include/linux/fs.h */
char __user *buffer, /* buffer to fill with data */
size_t length, /* length of the buffer */
loff_t *offset)
{
int i;
for (i = 0; i < length; i++) {
put_user('1', buffer + i);
}
/* Most read functions return the number of bytes put into the buffer. */
return length;
}
/* Called when a process writes to dev file: echo "hi" > /dev/hello */
static ssize_t device_write(struct file *filp, const char __user *buff,
size_t len, loff_t *off)
{
pr_alert("Sorry, this operation is not supported.\n");
return -EINVAL;
}
module_init(chardev_init);
module_exit(chardev_exit);
MODULE_LICENSE("GPL");
產生檔案
obj-m += onedev.o
PWD := $(CURDIR)
ifeq ($(CONFIG_STATUS_CHECK_GCC),y)
CC=$(STATUS_CHECK_GCC)
ccflags-y += -fanalyzer
endif
all:
$(MAKE) -C /lib/modules/$(shell uname -r)/build CC=$(CC) M=$(PWD) modules
clean:
$(MAKE) -C /lib/modules/$(shell uname -r)/build CC=$(CC) M=$(PWD) clean
$(RM) other/cat_noblock *.plist
indent:
clang-format -i *[.ch]
clang-format -i other/*[.ch]