On 05.10.2021 20:54, Cyrill Gorcunov wrote:
> From: Angelo Ruocco <angeloruocc...@gmail.com>
>
> This commit enables a cftype to have a symlink (of any name) that
> points to the file associated with the cftype.
>
> Signed-off-by: Angelo Ruocco <angeloruocc...@gmail.com>
> Signed-off-by: Paolo Valente <paolo.vale...@linaro.org>
> Signed-off-by: Jens Axboe <ax...@kernel.dk>
>
> https://jira.sw.ru/browse/PSBM-101019
> (cherry-picked from 54b7b868e826b294687c439b68ec55fe20cafe5b)
> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
> Signed-off-by: Cyrill Gorcunov <gorcu...@virtuozzo.com>
> ---
> include/linux/cgroup-defs.h | 3 +++
> kernel/cgroup/cgroup.c | 33 +++++++++++++++++++++++++++++----
> 2 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
> index 583ce2bce98c..0b2222b884ce 100644
> --- a/include/linux/cgroup-defs.h
> +++ b/include/linux/cgroup-defs.h
> @@ -125,6 +125,8 @@ enum {
> */
> CFTYPE_VE_WRITABLE = (1 << 15),
>
> + CFTYPE_SYMLINKED = (1 << 6), /* pointed to by symlink too */
We already have:
CFTYPE_PRESSURE = (1 << 6), /* only if pressure feature is
enabled */
> +
> /* internal flags, do not use outside cgroup core proper */
> __CFTYPE_ONLY_ON_DFL = (1 << 16), /* only on default hierarchy */
> __CFTYPE_NOT_ON_DFL = (1 << 17), /* not on default hierarchy */
> @@ -552,6 +554,7 @@ struct cftype {
> * end of cftype array.
> */
> char name[MAX_CFTYPE_NAME];
> + char link_name[MAX_CFTYPE_NAME];
> unsigned long private;
>
> /*
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 08b7cff7a1c3..74d0b503e696 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -1471,8 +1471,8 @@ struct cgroup *task_cgroup_from_root(struct task_struct
> *task,
>
> static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
>
> -static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
> - char *buf)
> +static char *cgroup_fill_name(struct cgroup *cgrp, const struct cftype *cft,
> + char *buf, bool write_link_name)
> {
> struct cgroup_subsys *ss = cft->ss;
>
> @@ -1482,13 +1482,26 @@ static char *cgroup_file_name(struct cgroup *cgrp,
> const struct cftype *cft,
>
> snprintf(buf, CGROUP_FILE_NAME_MAX, "%s%s.%s",
> dbg, cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
> - cft->name);
> + write_link_name ? cft->link_name : cft->name);
> } else {
> - strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
> + strscpy(buf, write_link_name ? cft->link_name : cft->name,
> + CGROUP_FILE_NAME_MAX);
> }
> return buf;
> }
>
> +static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
> + char *buf)
> +{
> + return cgroup_fill_name(cgrp, cft, buf, false);
> +}
> +
> +static char *cgroup_link_name(struct cgroup *cgrp, const struct cftype *cft,
> + char *buf)
> +{
> + return cgroup_fill_name(cgrp, cft, buf, true);
> +}
> +
> /**
> * cgroup_file_mode - deduce file mode of a control file
> * @cft: the control file in question
> @@ -1647,6 +1660,9 @@ static void cgroup_rm_file(struct cgroup *cgrp, const
> struct cftype *cft)
> }
>
> kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
> + if (cft->flags & CFTYPE_SYMLINKED)
> + kernfs_remove_by_name(cgrp->kn,
> + cgroup_link_name(cgrp, cft, name));
> }
>
> /**
> @@ -4012,6 +4028,7 @@ static int cgroup_add_file(struct cgroup_subsys_state
> *css, struct cgroup *cgrp,
> {
> char name[CGROUP_FILE_NAME_MAX];
> struct kernfs_node *kn;
> + struct kernfs_node *kn_link;
> struct lock_class_key *key = NULL;
> int ret;
>
> @@ -4042,6 +4059,14 @@ static int cgroup_add_file(struct cgroup_subsys_state
> *css, struct cgroup *cgrp,
> spin_unlock_irq(&cgroup_file_kn_lock);
> }
>
> + if (cft->flags & CFTYPE_SYMLINKED) {
> + kn_link = kernfs_create_link(cgrp->kn,
> + cgroup_link_name(cgrp, cft, name),
> + kn);
> + if (IS_ERR(kn_link))
> + return PTR_ERR(kn_link);
> + }
> +
> return 0;
> }
>
>
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