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From: J. R. Okajima on 22 Jun 2010 02:00

Ian Kent:
> +static vfsmount *autofs4_find_vfsmount(struct path *parent, struct dentry *root)
> +{
> + struct vfsmount *mnt = NULL;
> + struct dentry *child;
> +
> + spin_lock(&dcache_lock);
> + list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) {

dentry->d_subdirs?
parent->dentry->...?

Or how about iterate_mounts() instead of loop over dentries?
For example (just a example),

struct args {
/* input */
struct dentry *root;

/* output */
struct vfsmount *mnt;
};

static int compare_mnt(struct vfsmount *mnt, void *arg)
{
struct args *a = arg;

if (mnt->mnt_root != a->root)
return 0;
a->mnt = mntget(mnt);
return 1;
}

struct vfsmount *autofs4_find_vfsmount(struct dentry *root)
{
int err;
struct args args = {
.root = root
};

err = iterate_mounts(compare_mnt, &args, current->nsproxy->mnt_ns);
}


J. R. Okajima
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From: J. R. Okajima on 22 Jun 2010 22:20

Ian Kent:
> I may be missing something about this, but why is it safe to use
> iterate_mounts(), since it doesn't take the vfsmount_lock when
> traversing the list of mounts?

The sample code was not correct.
We need to acquire vfsmount_lock or down_read(namespace_sem).

Or it may be better to extract the body of iterate_mounts() and create a
new function __iterate_mounts() such like that.

__iterate_mounts()
{
/* equiv to the current iterate_mounts */
}

iterate_mount()
{
down_read(namespace_sem);
or spin_lock(&vfsmount_lock);

__iterate_mount();

spin_unlock(&vfsmount_lock);
or up_read(namespace_sem);
}


J. R. Okajima
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