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como criar/dev/one como/dev/zero?

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como criar/dev/one como/dev/zero?

Como posso criar um arquivo que produza um fluxo contínuo de 0x01caracteres? Assim como /dev/zero, exceto produzindo personagem de minha escolha:

/dev/zero – aceita e descarta todas as entradas escritas nele; produz um fluxo contínuo de caracteres nulos (bytes de valor zero) como saída quando lido.

Deve ser legível por cat. Considerei executar um loop em um pipe nomeado, mas isso requer um processo ativo.

Responder1

… mas isso requer um processo ativo.

Original /dev/zerotambém manuseado por"processo" ativo, masno núcleo. Se você não quiser lidar com isso no nível do espaço do usuário, suas outras opções são bastante limitadas - então deve ser algum driver de kernel.

Responder2

Bem, você sempre pode canalizar /dev/zero trou algo mais

# 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  |................|
*

Se você quiser pular o gato e usar a substituição do processo.

# hexdump -C <( tr '\000' '\001' </dev/zero ) 
00000000  01 01 01 01 01 01 01 01  01 01 01 01 01 01 01 01  |................|

contra.

# cat /dev/zero | hexdump -C
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*

Responder3

Adaptado descaradamente deO Guia de Programação do Módulo Kernel Linux

#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");

Makefile

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]

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