Re: [PATCH 1/2] cgroup: revise how we re-populate root directory

[Sha <handai.szj@gmail.com>]

Hi Zefan,

On Mon, Jan 16, 2012 at 4:06 PM, Li Zefan <lizf@cn.fujitsu.com> wrote:
> When remounting cgroupfs with some subsystems added to it and some
> removed, cgroup will remove all the files in root directory and then
> re-popluate it.
>
> What I'm doing here is, only remove files which belong to subsystems that
> are to be unbound, and only create files for newly-added subsystems.
> The purpose is to have all other files untouched.
>
> This is a preparation for cgroup xattr support.
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
>  include/linux/cgroup.h |   11 +++---
>  kernel/cgroup.c        |   92 +++++++++++++++++++++++++++++++----------------
>  2 files changed, 67 insertions(+), 36 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index e9b6021..13db9e8 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -327,6 +327,9 @@ struct cftype {
>         */
>        size_t max_write_len;
>
> +       /* The subsystem this cgroup file belongs to */
> +       struct cgroup_subsys *subsys;
> +
>        int (*open)(struct inode *inode, struct file *file);
>        ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
>                        struct file *file,
> @@ -419,16 +422,14 @@ struct cgroup_scanner {
>  * called by subsystems from within a populate() method
>  */
>  int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
> -                      const struct cftype *cft);
> +                   struct cftype *cft);
>
>  /*
>  * Add a set of new files to the given cgroup directory. Should
>  * only be called by subsystems from within a populate() method
>  */
> -int cgroup_add_files(struct cgroup *cgrp,
> -                       struct cgroup_subsys *subsys,
> -                       const struct cftype cft[],
> -                       int count);
> +int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
> +                    struct cftype cft[], int count);
>
>  int cgroup_is_removed(const struct cgroup *cgrp);
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index a5d3b53..c4ed6fe 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -781,6 +781,8 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode);
>  static struct dentry *cgroup_lookup(struct inode *, struct dentry *, struct nameidata *);
>  static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
>  static int cgroup_populate_dir(struct cgroup *cgrp);
> +static int cgroup_repopulate_dir(struct cgroup *cgrp, unsigned long added_bits,
> +                                unsigned long removed_bits);
>  static const struct inode_operations cgroup_dir_inode_operations;
>  static const struct file_operations proc_cgroupstats_operations;
>
> @@ -882,34 +884,44 @@ static void remove_dir(struct dentry *d)
>        dput(parent);
>  }
>
> -static void cgroup_clear_directory(struct dentry *dentry)
> +static void cgroup_clear_directory(struct dentry *dentry, bool remove_all,
> +                                  unsigned long removed_bits)
>  {
> -       struct list_head *node;
> +       LIST_HEAD(head);
> +       struct dentry *d, *node;
>
>        BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
> +
>        spin_lock(&dentry->d_lock);
> -       node = dentry->d_subdirs.next;
> -       while (node != &dentry->d_subdirs) {
> -               struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
> +       list_for_each_entry_safe(d, node, &dentry->d_subdirs, d_u.d_child) {
> +               struct cftype *cft = d->d_fsdata;
> +
> +               if (!remove_all && cft->subsys &&
> +                   !test_bit(cft->subsys->subsys_id, &removed_bits))
> +                       continue;
>
>                spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
> -               list_del_init(node);
> +               list_move(&d->d_u.d_child, &head);
>                if (d->d_inode) {
>                        /* This should never be called on a cgroup
>                         * directory with child cgroups */
>                        BUG_ON(d->d_inode->i_mode & S_IFDIR);
>                        dget_dlock(d);
> -                       spin_unlock(&d->d_lock);
> -                       spin_unlock(&dentry->d_lock);
> +               }
> +               spin_unlock(&d->d_lock);
> +       }
> +       spin_unlock(&dentry->d_lock);
> +
> +       list_for_each_entry_safe(d, node, &head, d_u.d_child) {
> +               spin_lock(&d->d_lock);
> +               list_del_init(&d->d_u.d_child);
> +               spin_unlock(&d->d_lock);
> +               if (d->d_inode) {
>                        d_delete(d);
>                        simple_unlink(dentry->d_inode, d);
>                        dput(d);
> -                       spin_lock(&dentry->d_lock);
> -               } else
> -                       spin_unlock(&d->d_lock);
> -               node = dentry->d_subdirs.next;
> +               }
>        }
> -       spin_unlock(&dentry->d_lock);
>  }
>
>  /*
> @@ -919,7 +931,7 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
>  {
>        struct dentry *parent;
>
> -       cgroup_clear_directory(dentry);
> +       cgroup_clear_directory(dentry, true, 0);
>
>        parent = dentry->d_parent;
>        spin_lock(&parent->d_lock);
> @@ -1284,6 +1296,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
>        struct cgroupfs_root *root = sb->s_fs_info;
>        struct cgroup *cgrp = &root->top_cgroup;
>        struct cgroup_sb_opts opts;
> +       unsigned long added_bits, removed_bits;
>
>        mutex_lock(&cgrp->dentry->d_inode->i_mutex);
>        mutex_lock(&cgroup_mutex);
> @@ -1294,6 +1307,9 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
>        if (ret)
>                goto out_unlock;
>
> +       added_bits = opts.subsys_bits & ~root->subsys_bits;
> +       removed_bits = root->subsys_bits & ~opts.subsys_bits;
> +

Should it be the following？：
          added_bits = opts.subsys_bits & ~root->actual_subsys_bits;
          removed_bits = root->actual_subsys_bits & ~opts.subsys_bits;

Thanks,
Sha

>        /* Don't allow flags or name to change at remount */
>        if (opts.flags != root->flags ||
>            (opts.name && strcmp(opts.name, root->name))) {
> @@ -1308,8 +1324,8 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
>                goto out_unlock;
>        }
>
> -       /* (re)populate subsystem files */
> -       cgroup_populate_dir(cgrp);
> +       /* re-populate subsystem files */
> +       cgroup_repopulate_dir(cgrp, added_bits, removed_bits);
>
>        if (opts.release_agent)
>                strcpy(root->release_agent_path, opts.release_agent);
> @@ -2710,16 +2726,17 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
>        return mode;
>  }
>
> -int cgroup_add_file(struct cgroup *cgrp,
> -                      struct cgroup_subsys *subsys,
> -                      const struct cftype *cft)
> +int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
> +                   struct cftype *cft)
>  {
>        struct dentry *dir = cgrp->dentry;
>        struct dentry *dentry;
>        int error;
>        umode_t mode;
> -
>        char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
> +
> +       cft->subsys = subsys;
> +
>        if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
>                strcpy(name, subsys->name);
>                strcat(name, ".");
> @@ -2740,10 +2757,8 @@ int cgroup_add_file(struct cgroup *cgrp,
>  }
>  EXPORT_SYMBOL_GPL(cgroup_add_file);
>
> -int cgroup_add_files(struct cgroup *cgrp,
> -                       struct cgroup_subsys *subsys,
> -                       const struct cftype cft[],
> -                       int count)
> +int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
> +                    struct cftype cft[], int count)
>  {
>        int i, err;
>        for (i = 0; i < count; i++) {
> @@ -3703,26 +3718,27 @@ static struct cftype cft_release_agent = {
>        .max_write_len = PATH_MAX,
>  };
>
> -static int cgroup_populate_dir(struct cgroup *cgrp)
> +static int __cgroup_populate_dir(struct cgroup *cgrp, unsigned long added_bits)
>  {
>        int err;
>        struct cgroup_subsys *ss;
>
> -       /* First clear out any existing files */
> -       cgroup_clear_directory(cgrp->dentry);
> -
>        err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
>        if (err < 0)
>                return err;
>
>        if (cgrp == cgrp->top_cgroup) {
> -               if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
> +               err = cgroup_add_file(cgrp, NULL, &cft_release_agent);
> +               if (err < 0)
>                        return err;
>        }
>
>        for_each_subsys(cgrp->root, ss) {
> -               if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
> -                       return err;
> +               if (test_bit(ss->subsys_id, &added_bits) && ss->populate) {
> +                       err = ss->populate(ss, cgrp);
> +                       if (err < 0)
> +                               return err;
> +               }
>        }
>        /* This cgroup is ready now */
>        for_each_subsys(cgrp->root, ss) {
> @@ -3739,6 +3755,20 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
>        return 0;
>  }
>
> +static int cgroup_populate_dir(struct cgroup *cgrp)
> +{
> +       return __cgroup_populate_dir(cgrp, cgrp->root->subsys_bits);
> +}
> +
> +static int cgroup_repopulate_dir(struct cgroup *cgrp, unsigned long added_bits,
> +                                unsigned long removed_bits)
> +{
> +       /* First clear out files */
> +       cgroup_clear_directory(cgrp->dentry, false, removed_bits);
> +
> +       return __cgroup_populate_dir(cgrp, added_bits);
> +}
> +
>  static void init_cgroup_css(struct cgroup_subsys_state *css,
>                               struct cgroup_subsys *ss,
>                               struct cgroup *cgrp)
> --
> 1.7.3.1
> --
> To unsubscribe from this list: send the line "unsubscribe cgroups" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html