Paul Menage wrote:
> Support named cgroups hierarchies
>
> To simplify referring to cgroup hierarchies in mount statements, and
> to allow disambiguation in the presence of empty hierarchies and
> multiply-bindable subsystems this patch adds support for naming a new
> cgroup hierarchy via the "name=" mount option
>
> A pre-existing hierarchy may be specified by either name or by
> subsystems; a hierarchy's name cannot be changed by a remount
> operation.
>
> Example usage:
>
> # To create a hierarchy called "foo" containing the "cpu" subsystem
> mount -t cgroup -oname=foo,cpu cgroup /mnt/cgroup1
>
> # To mount the "foo" hierarchy on a second location
> mount -t cgroup -oname=foo cgroup /mnt/cgroup2
>
>
> Signed-off-by: Paul Menage <men...@google.com>
>
Looks good to me.
Reviewed-by: Li Zefan <l...@cn.fujitsu.com>
Except a few comments below:
> ---
>
> Documentation/cgroups/cgroups.txt | 19 ++++
> kernel/cgroup.c | 186
> +++++++++++++++++++++++++++----------
> 2 files changed, 157 insertions(+), 48 deletions(-)
>
> diff --git a/Documentation/cgroups/cgroups.txt
> b/Documentation/cgroups/cgroups.txt
> index 6eb1a97..1f7cf9f 100644
> --- a/Documentation/cgroups/cgroups.txt
> +++ b/Documentation/cgroups/cgroups.txt
> @@ -408,6 +408,25 @@ You can attach the current shell task by echoing 0:
>
> # echo 0 > tasks
>
> +2.3 Mounting hierarchies by name
> +--------------------------------
> +
> +Passing the name=<x> option when mounting a cgroups hierarchy
> +associates the given name with the hierarchy. This can be used when
> +mounting a pre-existing hierarchy, in order to refer to it by name
> +rather than by its set of active subsystems.
> +
> +The name should match [\w.-]+
> +
"[\w._-]+" ?
But I double we need to check this.
> +When passing a name=<x> option for a new hierarchy, you need to
> +specify subsystems manually; the legacy behaviour of mounting all
> +subsystems when none are explicitly specified is not supported when
> +you give a subsystem a name.
> +
Mention that a hierarchy either has no name or should have a uniq name?
> +The name of the subsystem appears as part of the hierarchy description
> +in /proc/mounts and /proc/<pid>/cgroups.
...
> static int cgroup_set_super(struct super_block *sb, void *data)
> {
> int ret;
> - struct cgroupfs_root *root = data;
> + struct cgroup_sb_opts *opts = data;
> +
> + /* If we don't have a new root, we can't set up a new sb */
> + if (!opts->new_root)
> + return -EINVAL;
> +
I think this should be BUG_ON(). If set_super() is called,
we are allocating a new root, so opts->new_root won't be NULL.
> + BUG_ON(!opts->subsys_bits);
>
> ret = set_anon_super(sb, NULL);
> if (ret)
> return ret;
>
> - sb->s_fs_info = root;
> - root->sb = sb;
> + sb->s_fs_info = opts->new_root;
> + opts->new_root->sb = sb;
>
> sb->s_blocksize = PAGE_CACHE_SIZE;
> sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
> @@ -1039,48 +1106,44 @@ static int cgroup_get_sb(struct file_system_type
> *fs_type,
> void *data, struct vfsmount *mnt)
> {
> struct cgroup_sb_opts opts;
> + struct cgroupfs_root *root;
> int ret = 0;
> struct super_block *sb;
> - struct cgroupfs_root *root;
> - struct list_head tmp_cg_links;
>
> /* First find the desired set of subsystems */
> ret = parse_cgroupfs_options(data, &opts);
> - if (ret) {
> - kfree(opts.release_agent);
> - return ret;
> - }
> -
> - root = kzalloc(sizeof(*root), GFP_KERNEL);
> - if (!root) {
> - kfree(opts.release_agent);
> - return -ENOMEM;
> - }
> + if (ret)
> + goto out_err;
>
> - init_cgroup_root(root);
> - root->subsys_bits = opts.subsys_bits;
> - root->flags = opts.flags;
> - if (opts.release_agent) {
> - strcpy(root->release_agent_path, opts.release_agent);
> - kfree(opts.release_agent);
> + /*
> + * Allocate a new cgroup root. We may not need it if we're
> + * reusing an existing hierarchy.
> + */
> + {
I don't think this is a normal coding style.
> + struct cgroupfs_root *new_root = cgroup_root_from_opts(&opts);
Why not just declare new_root in the beginning of cgroup_get_sb()?
> + if (IS_ERR(new_root)) {
> + ret = PTR_ERR(new_root);
> + goto out_err;
> + }
> + opts.new_root = new_root;
> }
>
> - sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
> -
> + /* Locate an existing or new sb for this hierarchy */
> + sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
> if (IS_ERR(sb)) {
> - kfree(root);
> - return PTR_ERR(sb);
> + ret = PTR_ERR(sb);
> + kfree(opts.new_root);
> + goto out_err;
> }
>
> - if (sb->s_fs_info != root) {
> - /* Reusing an existing superblock */
> - BUG_ON(sb->s_root == NULL);
> - kfree(root);
> - root = NULL;
> - } else {
> - /* New superblock */
> + root = sb->s_fs_info;
> + BUG_ON(!root);
> + if (root == opts.new_root) {
> + /* We used the new root structure, so this is a new hierarchy */
> + struct list_head tmp_cg_links;
> struct cgroup *root_cgrp = &root->top_cgroup;
> struct inode *inode;
> + struct cgroupfs_root *existing_root;
> int i;
>
> BUG_ON(sb->s_root != NULL);
> @@ -1093,6 +1156,18 @@ static int cgroup_get_sb(struct file_system_type
> *fs_type,
> mutex_lock(&inode->i_mutex);
> mutex_lock(&cgroup_mutex);
>
> + if (strlen(root->name)) {
> + /* Check for name clashes with existing mounts */
> + for_each_active_root(existing_root) {
> + if (!strcmp(existing_root->name, root->name)) {
> + ret = -EBUSY;
> + mutex_unlock(&cgroup_mutex);
> + mutex_unlock(&inode->i_mutex);
> + goto drop_new_super;
> + }
> + }
> + }
> +
> /*
> * We're accessing css_set_count without locking
> * css_set_lock here, but that's OK - it can only be
> @@ -1111,7 +1186,8 @@ static int cgroup_get_sb(struct file_system_type
> *fs_type,
> if (ret == -EBUSY) {
> mutex_unlock(&cgroup_mutex);
> mutex_unlock(&inode->i_mutex);
> - goto free_cg_links;
> + free_cg_links(&tmp_cg_links);
> + goto drop_new_super;
> }
>
> /* EBUSY should be the only error here */
> @@ -1145,15 +1221,26 @@ static int cgroup_get_sb(struct file_system_type
> *fs_type,
> cgroup_populate_dir(root_cgrp);
> mutex_unlock(&inode->i_mutex);
> mutex_unlock(&cgroup_mutex);
> + } else {
> + /*
> + * We re-used an existing hierarchy - the new root (if
> + * any) is not needed
> + */
> + kfree(opts.new_root);
> }
>
> simple_set_mnt(mnt, sb);
> + kfree(opts.release_agent);
> + kfree(opts.name);
> return 0;
>
> - free_cg_links:
> - free_cg_links(&tmp_cg_links);
> drop_new_super:
> deactivate_locked_super(sb);
> +
> + out_err:
> + kfree(opts.release_agent);
> + kfree(opts.name);
> +
> return ret;
> }
>
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