Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965047AbbD0SOG (ORCPT ); Mon, 27 Apr 2015 14:14:06 -0400 Received: from mail-wg0-f49.google.com ([74.125.82.49]:33430 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965029AbbD0SOD convert rfc822-to-8bit (ORCPT ); Mon, 27 Apr 2015 14:14:03 -0400 Subject: Re: [PATCH v3 2/4] of: overlay: global sysfs enable attribute Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: text/plain; charset=utf-8 From: Pantelis Antoniou In-Reply-To: <20150424202922.GA14970@kroah.com> Date: Mon, 27 Apr 2015 21:13:56 +0300 Cc: Rob Herring , Grant Likely , Andrew Morton , Matt Porter , Koen Kooi , Guenter Roeck , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <355B6AF0-7F58-4BE4-BEE6-A77246D40652@konsulko.com> References: <1429868744-19863-1-git-send-email-pantelis.antoniou@konsulko.com> <1429868744-19863-3-git-send-email-pantelis.antoniou@konsulko.com> <20150424202922.GA14970@kroah.com> To: Greg KH X-Mailer: Apple Mail (2.2098) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3980 Lines: 128 Hi Greg, > On Apr 24, 2015, at 23:29 , Greg KH wrote: > > 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? > Err, these are the global attributes. They are attached to the parent of the overlay objects which is a kset object itself. There’s no way which I can attach the attribute to it as far as I can tell. >> + >> 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. > This is at overlay_init() time, which is way way before userspace ever has a chance to start. If there’s a different way to attach a attribute group to a kset object I’d like to find out how :) > thanks, > > greg k-h Regards — Pantelis-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/