CODEWITHSUNDEEP
clinuxlinux-kernelkernel-module
user2743
user2743

Reputation: 1513

Trying to write a struct to a proc file from kernel space

I'm trying to write a structure to a proc file (I know I'm not suppose to). I'm able to successfully write out the struct members using the seq_print method but I want to try writing the struct so I don't have to parse it in user space. I'm not sure how to write to it using the seq_file implementation. Below is the code I'm trying. The seq_show function is part of my .read, file_operation struct callback mechanism (file_operations, seq_file, .start, .next, .stop, .show) when the /proc/info is opened from user space.

typedef struct tmp_t{
    int number;
    uint_32 info;
    char name[10];
} tmp_t;


static int seq_show(struct seq_file *s, void *v)
{
ssize_t proc_write;
mm_segment_t old_fs;
struct file *file;
loff_t offset = 0;

old_fs = get_fs();
set_fs(get_ds());
file = filp_open("/proc/info", O_WRONLY, 0777);
if(file){
      //tmp is a global pointer to the struct I want to write
      proc_write = vfs_write(file, tmp, sizeof(tmp_t), &offset);
      // I've also tried this using the v parameter
      //proc_write = vfs_write(file, tmp, sizeof(tmp_t), v);
      fput(file);
      printk(KERN_ALERT "proc_write: %zd.\n");
}
filp_close(file, NULL);
set_fs(old_fs);

return 0;
}

static void *info_start(struct seq_file *s, loff_t *pos)
{

}

static void *info_next(struct seq_file *s, void *v, loff_t *pos)
{

}

static void info_stop(struct seq_file *s, void *v)
{

}

static int open_info(struct inode *inode, struct file *file)
{
    return seq_open(file, &seq_ops_info);
}

static struct seq_operations seq_ops_info = {
    .start  = info_start,
    .next   = info_next,
    .stop   = info_stop,
    .show   = info_show,
};

static const struct file_operations fops_info = {
    .owner          = THIS_MODULE,
    .open           = open_info,
    .read           = seq_read,
    .llseek         = seq_lseek,
    .release        = seq_release,
 };

static int __init app_init(void)
{
info_file = proc_create("info", 0777, NULL, &fops_info);
}

The printk statement gives proc_write: -5. I have those structs stored in a link list so each iteration through the seq_file stuff I'd like to write the struct to the /proc/info. I'm trying to work off of this example that I found in the kernel source tree. Any help is appreciated.

Upvotes: 0

Views: 1628

Answers (1)

Oleksii Shmalko
Oleksii Shmalko

Reputation: 3768

As far, as I know, you can't create and write file in /proc that easily. Most likely, call to filp_open() has failed and you don't check it's return value properly. You have to check return value with IS_ERR() function.

But I should mention again that this idea seems wrong for me. If you want create an entry in /proc directory, consider using standard way.

Upvotes: 1

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