From: Andreas Hartmann <andihartmann@01019freenet.de>
Subject: f_op->read seems to be always NULL since Linux 4.1
Date: Sat, 27 Jun 2015 19:32:39 +0200
Organization: privat
Message-ID: <mmmmkc$5dp$1@327.eternal-september.org>
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Hello!

Given is a module like the following snippet running fine w/ Linux 4.0
and ext4 fs - but doesn't work w/ Linux 4.1 because f->f_op->read is not
defined any more (= NULL). Is this the intended behavior now?

vfs_read(f, buf, 128, &f->f_pos) works fine.


module.c
--------------------------------------------------------------------
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

int init_module(void)
{
    struct file *f;
    char buf[128];
    mm_segment_t fs;
    int i;
    int len=128;

    for(i=0;i<len;i++)
        buf[i] = 0;

    printk(KERN_INFO "My module is loaded\n");

    f = filp_open("/etc/fedora-release", O_RDONLY, 0);
    if(f == NULL)
        printk(KERN_ALERT "filp_open error!!.\n");
    else{
        fs = get_fs();
        set_fs(get_ds());

        if (f->f_op->read) {
            f->f_op->read(f, buf, len, &f->f_pos);
            printk(KERN_INFO "buf:%s\n",buf);
            }
        else {
            printk(KERN_INFO "No read method\n");
            }

        set_fs(fs);

    }
    filp_close(f,NULL);
    return 0;
}

void cleanup_module(void)
{
    printk(KERN_INFO "My module is unloaded\n");
}
-----------------------------------------------------------

Makefile:
-----------------------------------------------------------
obj-m += module.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
------------------------------------------------------------


Regards,
Andreas
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