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

[Greg KH <gregkh@linuxfoundation.org>]

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@linuxfoundation.org> 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@linuxfoundation.org> 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@linuxfoundation.org>
> 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@linuxfoundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Co-developed-by: Alistair Francis <alistair.francis@wdc.com>
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  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...

thanks,

greg k-h