From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCH v3 2/4] of: overlay: global sysfs enable attribute Date: Fri, 24 Apr 2015 22:29:22 +0200 Message-ID: <20150424202922.GA14970@kroah.com> References: <1429868744-19863-1-git-send-email-pantelis.antoniou@konsulko.com> <1429868744-19863-3-git-send-email-pantelis.antoniou@konsulko.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1429868744-19863-3-git-send-email-pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pantelis Antoniou Cc: Rob Herring , Grant Likely , Andrew Morton , Matt Porter , Koen Kooi , Guenter Roeck , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Pantelis Antoniou List-Id: linux-api@vger.kernel.org On Fri, Apr 24, 2015 at 12:45:42PM +0300, Pantelis Antoniou wrote: > A throw once master enable switch to protect against any > further overlay applications if the administrator desires so. > > Signed-off-by: Pantelis Antoniou > --- > drivers/of/overlay.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 44 insertions(+), 1 deletion(-) > > diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c > index f17f5ef..c335809 100644 > --- a/drivers/of/overlay.c > +++ b/drivers/of/overlay.c > @@ -21,6 +21,7 @@ > #include > #include > #include > +#include > > #include "of_private.h" > > @@ -55,8 +56,12 @@ struct of_overlay { > struct kobject kobj; > }; > > +/* master enable switch; once set to 0 can't be re-enabled */ > +static atomic_t ov_enable = ATOMIC_INIT(1); > + > static int of_overlay_apply_one(struct of_overlay *ov, > struct device_node *target, const struct device_node *overlay); > +static int overlay_removal_is_ok(struct of_overlay *ov); > > static int of_overlay_apply_single_property(struct of_overlay *ov, > struct device_node *target, struct property *prop) > @@ -339,6 +344,37 @@ void of_overlay_release(struct kobject *kobj) > kfree(ov); > } > > +static ssize_t enable_show(struct kobject *kobj, > + struct kobj_attribute *attr, char *buf) > +{ > + return snprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&ov_enable)); > +} > + > +static ssize_t enable_store(struct kobject *kobj, > + struct kobj_attribute *attr, const char *buf, size_t count) > +{ > + int ret; > + long new_enable; > + > + ret = kstrtol(buf, 10, &new_enable); > + if (ret != 0) > + return ret; > + if ((unsigned long)new_enable > 1) > + return -EINVAL; > + /* if we've disabled it, no going back */ > + if (atomic_read(&ov_enable) == 0) > + return -EPERM; > + atomic_set(&ov_enable, (int)new_enable); > + return count; > +} > + > +static struct kobj_attribute enable_attr = __ATTR_RW(enable); > + > +static const struct attribute *overlay_global_attrs[] = { > + &enable_attr.attr, > + NULL > +}; Why not make this an attribute group and then attach it to the kobj_type to create the files in a race-free manner? > + > static struct kobj_type of_overlay_ktype = { > .release = of_overlay_release, > }; > @@ -360,6 +396,10 @@ int of_overlay_create(struct device_node *tree) > struct of_overlay *ov; > int err, id; > > + /* administratively disabled */ > + if (!atomic_read(&ov_enable)) > + return -EPERM; > + > /* allocate the overlay structure */ > ov = kzalloc(sizeof(*ov), GFP_KERNEL); > if (ov == NULL) > @@ -596,5 +636,8 @@ int of_overlay_init(void) > if (!ov_kset) > return -ENOMEM; > > - return 0; > + rc = sysfs_create_files(&ov_kset->kobj, overlay_global_attrs); > + WARN(rc, "%s: error adding global attributes\n", __func__); What can a user do with this warning message? If nothing, then don't print it out, right? You are creating sysfs files _after_ the kobject has been announced to userspace, causing nasty race conditions. Please don't do that. thanks, greg k-h