Re: [PATCH v6 2/3] sysfs: Add a attr_is_visible function to attribute_group
From: Greg KH
Date: Thu Aug 31 2023 - 10:36:20 EST
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...
thanks,
greg k-h