How do you get the size of a file in the linux kernel?

Question

I found this link (http://www.spinics.net/lists/newbies/msg41016.html) and have been looking into doing just that. So I wrote code in a kernel module:

#include &         


        

Answer 1

vfs_stat is an option to do it.

Below is an example:

#include 
#include 
#include 
#include 

static char *load_file(char* filename, int *input_size)
{
        struct kstat *stat;
        struct file *fp;
        mm_segment_t fs;
        loff_t pos = 0;
        char *buf;

        fp = filp_open(filename, O_RDWR, 0644);
                if (IS_ERR(fp)) {
                        printk("Open file error!\n");
                        return ERR_PTR(-ENOENT);
        }

        fs = get_fs();
        set_fs(KERNEL_DS);
        
        stat =(struct kstat *) kmalloc(sizeof(struct kstat), GFP_KERNEL);
        if (!stat)
                return ERR_PTR(-ENOMEM);

        vfs_stat(filename, stat);
        *input_size = stat->size;

        buf = kmalloc(*input_size, GFP_KERNEL);
                if (!buf) {
                        kfree(stat);
                        printk("malloc input buf error!\n");
                        return ERR_PTR(-ENOMEM);
                }
        kernel_read(fp, buf, *input_size, &pos);

        filp_close(fp, NULL);
        set_fs(fs);
        kfree(stat);
        return buf;
}

Since the size is not known, so we need to kmalloc inside the function, thus the buf need to kfree later when not use any longer.