Re: [PATCH v6 2/3] sysfs: Add a attr_is_visible function to attribute_group

[Greg KH]

On Fri, Sep 01, 2023 at 11:00:59PM +0200, Greg KH wrote:
> On Thu, Aug 31, 2023 at 04:36:13PM +0200, Greg KH wrote:
> > On Thu, Aug 31, 2023 at 10:31:07AM +0200, Greg KH wrote:
> > > On Mon, Aug 28, 2023 at 03:05:41PM +1000, Alistair Francis wrote:
> > > > On Wed, Aug 23, 2023 at 5:02 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > > >
> > > > > On Tue, Aug 22, 2023 at 04:20:06PM -0400, Alistair Francis wrote:
> > > > > > On Sat, Aug 19, 2023 at 6:57 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Thu, Aug 17, 2023 at 07:58:09PM -0400, Alistair Francis wrote:
> > > > > > > > The documentation for sysfs_merge_group() specifically says
> > > > > > > >
> > > > > > > >     This function returns an error if the group doesn't exist or any of the
> > > > > > > >     files already exist in that group, in which case none of the new files
> > > > > > > >     are created.
> > > > > > > >
> > > > > > > > So just not adding the group if it's empty doesn't work, at least not
> > > > > > > > with the code we currently have. The code can be changed to support
> > > > > > > > this, but it is difficult to determine how this will affect existing use
> > > > > > > > cases.
> > > > > > >
> > > > > > > Did you try?  I'd really really really prefer we do it this way as it's
> > > > > > > much simpler overall to have the sysfs core "do the right thing
> > > > > > > automatically" than to force each and every bus/subsystem to have to
> > > > > > > manually add this type of attribute.
> > > > > > >
> > > > > > > Also, on a personal level, I want this function to work as it will allow
> > > > > > > us to remove some code in some busses that don't really need to be there
> > > > > > > (dynamic creation of some device attributes), which will then also allow
> > > > > > > me to remove some apis in the driver core that should not be used at all
> > > > > > > anymore (but keep creeping back in as there is still a few users.)
> > > > > > >
> > > > > > > So I'll be selfish here and say "please try to get my proposed change to
> > > > > > > work, it's really the correct thing to do here."
> > > > > >
> > > > > > I did try!
> > > > > >
> > > > > > This is an attempt:
> > > > > > https://github.com/alistair23/linux/commit/56b55756a2d7a66f7b6eb8a5692b1b5e2f81a9a9
> > > > > >
> > > > > > It is based on your original patch with a bunch of:
> > > > > >
> > > > > > if (!parent) {
> > > > > >     parent = kernfs_create_dir_ns(kobj->sd, grp->name,
> > > > > >                   S_IRWXU | S_IRUGO | S_IXUGO,
> > > > > >                   uid, gid, kobj, NULL);
> > > > > >     ...
> > > > > >     }
> > > > > >
> > > > > >
> > > > > > added throughout the code base.
> > > > > >
> > > > > > Very basic testing shows that it does what I need it to do and I don't
> > > > > > see any kernel oops on boot.
> > > > >
> > > > > Nice!
> > > > >
> > > > > Mind if I take it and clean it up a bit and test with it here?  Again, I
> > > > > need this functionality for other stuff as well, so getting it merged
> > > > > for your feature is fine with me.
> > > > 
> > > > Sure! Go ahead. Sorry I was travelling last week.
> > > > 
> > > > >
> > > > > > I prefer the approach I have in this mailing list patch. But if you
> > > > > > like the commit mentioned above I can tidy and clean it up and then
> > > > > > use that instead
> > > > >
> > > > > I would rather do it this way.  I can work on this on Friday if you want
> > > > > me to.
> > > > 
> > > > Yeah, that's fine with me. If you aren't able to let me know and I can
> > > > finish up the patch and send it with this series
> > > 
> > > Great, and for the email record, as github links are not stable, here's
> > > the patch that you have above attached below.  I'll test this out and
> > > clean it up a bit more and see how it goes...
> > > 
> > > thanks,
> > > 
> > > greg k-h
> > > 
> > > 
> > > From 2929d17b58d02dcf52d0345fa966c616e09a5afa Mon Sep 17 00:00:00 2001
> > > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Date: Wed, 24 Aug 2022 15:45:36 +0200
> > > Subject: [PATCH] sysfs: do not create empty directories if no attributes are
> > >  present
> > > 
> > > When creating an attribute group, if it is named a subdirectory is
> > > created and the sysfs files are placed into that subdirectory.  If no
> > > files are created, normally the directory would still be present, but it
> > > would be empty.  Clean this up by removing the directory if no files
> > > were successfully created in the group at all.
> > > 
> > > Co-developed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Co-developed-by: Alistair Francis <alistair.francis@xxxxxxx>
> > > Signed-off-by: Alistair Francis <alistair.francis@xxxxxxx>
> > > ---
> > >  fs/sysfs/file.c  | 14 ++++++++++--
> > >  fs/sysfs/group.c | 56 ++++++++++++++++++++++++++++++++++++------------
> > >  2 files changed, 54 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> > > index a12ac0356c69..7aab6c09662c 100644
> > > --- a/fs/sysfs/file.c
> > > +++ b/fs/sysfs/file.c
> > > @@ -391,8 +391,18 @@ int sysfs_add_file_to_group(struct kobject *kobj,
> > >  		kernfs_get(parent);
> > >  	}
> > >  
> > > -	if (!parent)
> > > -		return -ENOENT;
> > > +	if (!parent) {
> > > +		parent = kernfs_create_dir_ns(kobj->sd, group,
> > > +					  S_IRWXU | S_IRUGO | S_IXUGO,
> > > +					  uid, gid, kobj, NULL);
> > > +		if (IS_ERR(parent)) {
> > > +			if (PTR_ERR(parent) == -EEXIST)
> > > +				sysfs_warn_dup(kobj->sd, group);
> > > +			return PTR_ERR(parent);
> > > +		}
> > > +
> > > +		kernfs_get(parent);
> > > +	}
> > >  
> > >  	kobject_get_ownership(kobj, &uid, &gid);
> > >  	error = sysfs_add_file_mode_ns(parent, attr, attr->mode, uid, gid,
> > > diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> > > index 138676463336..013fa333cd3c 100644
> > > --- a/fs/sysfs/group.c
> > > +++ b/fs/sysfs/group.c
> > > @@ -31,12 +31,14 @@ static void remove_files(struct kernfs_node *parent,
> > >  			kernfs_remove_by_name(parent, (*bin_attr)->attr.name);
> > >  }
> > >  
> > > +/* returns -ERROR if error, or >= 0 for number of files actually created */
> > >  static int create_files(struct kernfs_node *parent, struct kobject *kobj,
> > >  			kuid_t uid, kgid_t gid,
> > >  			const struct attribute_group *grp, int update)
> > >  {
> > >  	struct attribute *const *attr;
> > >  	struct bin_attribute *const *bin_attr;
> > > +	int files_created = 0;
> > >  	int error = 0, i;
> > >  
> > >  	if (grp->attrs) {
> > > @@ -65,6 +67,8 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
> > >  						       gid, NULL);
> > >  			if (unlikely(error))
> > >  				break;
> > > +
> > > +			files_created++;
> > >  		}
> > >  		if (error) {
> > >  			remove_files(parent, grp);
> > > @@ -95,12 +99,15 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
> > >  							   NULL);
> > >  			if (error)
> > >  				break;
> > > +			files_created++;
> > >  		}
> > >  		if (error)
> > >  			remove_files(parent, grp);
> > >  	}
> > >  exit:
> > > -	return error;
> > > +	if (error)
> > > +		return error;
> > > +	return files_created;
> > >  }
> > >  
> > >  
> > > @@ -130,9 +137,14 @@ static int internal_create_group(struct kobject *kobj, int update,
> > >  		if (update) {
> > >  			kn = kernfs_find_and_get(kobj->sd, grp->name);
> > >  			if (!kn) {
> > > -				pr_warn("Can't update unknown attr grp name: %s/%s\n",
> > > -					kobj->name, grp->name);
> > > -				return -EINVAL;
> > > +				kn = kernfs_create_dir_ns(kobj->sd, grp->name,
> > > +							  S_IRWXU | S_IRUGO | S_IXUGO,
> > > +							  uid, gid, kobj, NULL);
> > > +				if (IS_ERR(kn)) {
> > > +					if (PTR_ERR(kn) == -EEXIST)
> > > +						sysfs_warn_dup(kobj->sd, grp->name);
> > > +					return PTR_ERR(kn);
> > > +				}
> > >  			}
> > >  		} else {
> > >  			kn = kernfs_create_dir_ns(kobj->sd, grp->name,
> > > @@ -150,11 +162,18 @@ static int internal_create_group(struct kobject *kobj, int update,
> > >  
> > >  	kernfs_get(kn);
> > >  	error = create_files(kn, kobj, uid, gid, grp, update);
> > > -	if (error) {
> > > +	if (error <= 0) {
> > > +		/*
> > > +		 * If an error happened _OR_ if no files were created in the
> > > +		 * attribute group, and we have a name for this group, delete
> > > +		 * the name so there's not an empty directory.
> > > +		 */
> > >  		if (grp->name)
> > >  			kernfs_remove(kn);
> > > +	} else {
> > > +		error = 0;
> > > +		kernfs_put(kn);
> > >  	}
> > > -	kernfs_put(kn);
> > >  
> > >  	if (grp->name && update)
> > >  		kernfs_put(kn);
> > > @@ -318,13 +337,12 @@ void sysfs_remove_groups(struct kobject *kobj,
> > >  EXPORT_SYMBOL_GPL(sysfs_remove_groups);
> > >  
> > >  /**
> > > - * sysfs_merge_group - merge files into a pre-existing attribute group.
> > > + * sysfs_merge_group - merge files into a attribute group.
> > >   * @kobj:	The kobject containing the group.
> > >   * @grp:	The files to create and the attribute group they belong to.
> > >   *
> > > - * This function returns an error if the group doesn't exist or any of the
> > > - * files already exist in that group, in which case none of the new files
> > > - * are created.
> > > + * This function returns an error if any of the files already exist in
> > > + * that group, in which case none of the new files are created.
> > >   */
> > >  int sysfs_merge_group(struct kobject *kobj,
> > >  		       const struct attribute_group *grp)
> > > @@ -336,12 +354,22 @@ int sysfs_merge_group(struct kobject *kobj,
> > >  	struct attribute *const *attr;
> > >  	int i;
> > >  
> > > -	parent = kernfs_find_and_get(kobj->sd, grp->name);
> > > -	if (!parent)
> > > -		return -ENOENT;
> > > -
> > >  	kobject_get_ownership(kobj, &uid, &gid);
> > >  
> > > +	parent = kernfs_find_and_get(kobj->sd, grp->name);
> > > +	if (!parent) {
> > > +		parent = kernfs_create_dir_ns(kobj->sd, grp->name,
> > > +					  S_IRWXU | S_IRUGO | S_IXUGO,
> > > +					  uid, gid, kobj, NULL);
> > > +		if (IS_ERR(parent)) {
> > > +			if (PTR_ERR(parent) == -EEXIST)
> > > +				sysfs_warn_dup(kobj->sd, grp->name);
> > > +			return PTR_ERR(parent);
> > > +		}
> > > +
> > > +		kernfs_get(parent);
> > > +	}
> > > +
> > >  	for ((i = 0, attr = grp->attrs); *attr && !error; (++i, ++attr))
> > >  		error = sysfs_add_file_mode_ns(parent, *attr, (*attr)->mode,
> > >  					       uid, gid, NULL);
> > > -- 
> > > 2.42.0
> > > 
> > 
> > And as the 0-day bot just showed, this patch isn't going to work
> > properly, the uid/gid stuff isn't all hooked up properly, I'll work on
> > fixing that up when I get some cycles...
> 
> Oops, nope, that was my fault in applying this to my tree, sorry for the
> noise...

And I just got around to testing this, and it does not boot at all.
Below is the patch I am using, are you sure you got this to boot for
you?

thanks,

greg k-h