Re: [PATCH 06/20] sysfs: Use dentry_ops instead of directly playing with the dcache

Eric W. Biederman
2009-05-21T07:37:43Z

Tejun Heo <tj@kernel.org> writes:

>> +static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
>> +{
>> + struct sysfs_dirent *sd = dentry->d_fsdata;
>> + int is_dir;
>> +
>> + mutex_lock(&sysfs_mutex);
>> +
>> + /* The sysfs dirent has been deleted */
>> + if (sd->s_flags & SYSFS_FLAG_REMOVED)
>> + goto out_bad;
>> +
>> + mutex_unlock(&sysfs_mutex);
>> +out_valid:
>> + return 1;
>> +out_bad:
>> + /* Remove the dentry from the dcache hashes.
>> + * If this is a deleted dentry we use d_drop instead of d_delete
>> + * so sysfs doesn't need to cope with negative dentries.
>> + */
>> + is_dir = (sysfs_type(sd) == SYSFS_DIR);
>> + mutex_unlock(&sysfs_mutex);
>> + if (is_dir) {
>> + /* If we have submounts we must allow the vfs caches
>> + * to lie about the state of the filesystem to prevent
>> + * leaks and other nasty things.
>> + */
>> + if (have_submounts(dentry))
>> + goto out_valid;
>> + shrink_dcache_parent(dentry);
>> + }
>> + d_drop(dentry);
>> + return 0;
>> +}
>
> Ummm... what happens if sysfs recreates those identical nodes again
> while the old dentries are lingering? The dead ones will linger till
> the submounts are gone and then look ups after that will show the new
> ones, right?

Yep. On the vfs level. The sysfs dirent tree will reflect what is
going on with the hardware.

This is a vfs misfeature, that I hope someday we will get fixed.
But for now it is better not to leak mount points. Especially
since no one actually mounts things on sysfs.

Eric