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Subjectscan directory content in kernel-level code
I'm trying to scan the content of the /dev directory in a init_module function.
I've not found example in the kernel source. So I try to reproduce the work of the system call.
I open the directory, check if the readdir pointer is not null in the f_op structure and then use it with my filldir function.
Because I don't need to stock names, I use filename directly in the filldir callback.
So in the filldir function, I check if the name match a simple regexp and if yes, I open the file and store the filp pointer.

First I don't understand why I need to call several times readdir in order to scan the directory (I imagine each times I obtain the content of one buffer). I check the number of callback call to stop calling readdir. It works but it seems strange.

Second problem, Sometimes the modprobe dead-locks in my filldir function. And I've found that it never arrives if i do a "ls /dev" before modprobe. Moreover if I don't take the directory inode semaphore, the problem never arrives.
What's wrong ?

Christophe ...


struct my_dentry {
char fullname[5];
char name[MAX_DEVNAME_SIZE+1];
int count;
};

int my_filldir(void * __buf, const char * name, int namlen, off_t offset, ino_t ino, unsigned unused)
{
struct my_dentry * buf = (struct my_dentry *)__buf;

if (namlen>MAX_DEVNAME_SIZE) namlen=MAX_DEVNAME_SIZE;

memcpy((char *)buf->name, name, namlen);
buf->name[namlen]='\0';
check_device(buf->fullname); // here I open the file if the string match criteria
buf->count++;
return 0;
}

void scan_device_directory(void)
{
struct file * filp;
struct inode * d_inode;
struct my_dentry dir_entry={"/dev/",};
int rc;

filp = filp_open("/dev", O_RDONLY|O_SYNC, 0600);
if ((rc=IS_ERR(filp))>0) {
printk("bad filp : %d\n", rc);
return;
}

d_inode = filp->f_dentry->d_inode;
if (!d_inode) {
printk("NULL inode\n");
goto out_close_dir;
}

if (! S_ISDIR(d_inode->i_mode)) {
printk("/dev is not a directory (?)\n");
goto out_close_dir;
}

if (filp->f_op->readdir == NULL) {
printk("can't find readidir f_ops\n");
goto out_close_dir;
}

v_printk("/dev : inode=%ld\n", d_inode->i_ino);

down(&d_inode->i_sem);

do {
dir_entry.count=0;
rc=filp->f_op->readdir(filp, (void *)&dir_entry, my_filldir);
} while (dir_entry.count>0);

up(&d_inode->i_sem);

out_close_dir:
fput(filp);
}

--
Christophe Barbé
Software Engineer
Lineo High Availability Group
42-46, rue Médéric
92110 Clichy - France
phone (33).1.41.40.02.12
fax (33).1.41.40.02.01
www.lineo.com
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