[Devel] Re: [PATCH 1/7] [RFC] Support named cgroups hierarchies
Li Zefan
lizf at cn.fujitsu.com
Mon Mar 16 23:44:12 PDT 2009
Paul Menage wrote:
> [RFC] 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 (see later patches in series) 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
>
> Open issues:
>
> - should the specification be via a name= option as in this patch, or
> should we simply use the "device name" as passed to the mount()
> system call? Using the device name is more conceptually clean and
> consistent with the filesystem API; however, given that the device
> name is currently ignored by cgroups, this would lead to a
> user-visible behaviour change.
>
If we use "device name" and don't allow it to be changed on remount,
this seems a change that may break/suprise existing users?
And another issue is, using "device name" won't allow us to use NULL
name, which is also user-visible in /proc/pid/cgroups/.
Some comments below.
> Signed-off-by: Paul Menage <menage at google.com>
>
> ---
>
> kernel/cgroup.c | 126 ++++++++++++++++++++++++++++++++++++-------------------
> 1 files changed, 82 insertions(+), 44 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 5995477..aa5edc8 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -92,6 +92,9 @@ struct cgroupfs_root {
>
> /* The path to use for release notifications. */
> char release_agent_path[PATH_MAX];
> +
> + /* The name for this hierarchy - may be empty */
> + char name[PATH_MAX];
I think 32 or 64 is sufficient. How about reuse MAX_CGROUP_TYPE_NAMELEN
which is the length limit of cgroup_subsys.name?
> };
>
> /*
> @@ -826,6 +829,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
> seq_puts(seq, ",noprefix");
> if (strlen(root->release_agent_path))
> seq_printf(seq, ",release_agent=%s", root->release_agent_path);
> + if (strlen(root->name))
> + seq_printf(seq, ",name=%s", root->name);
> mutex_unlock(&cgroup_mutex);
> return 0;
> }
> @@ -834,18 +839,22 @@ struct cgroup_sb_opts {
> unsigned long subsys_bits;
> unsigned long flags;
> char *release_agent;
> + char *name;
> + /* A flag indicating that a root was created from this options block */
> + bool created_root;
> };
>
> /* Convert a hierarchy specifier into a bitmask of subsystems and
> * flags. */
> static int parse_cgroupfs_options(char *data,
> - struct cgroup_sb_opts *opts)
> + struct cgroup_sb_opts *opts)
> {
> char *token, *o = data ?: "all";
>
> opts->subsys_bits = 0;
> opts->flags = 0;
> opts->release_agent = NULL;
> + opts->name = NULL;
>
memset() can save us some bytes.
> while ((token = strsep(&o, ",")) != NULL) {
> if (!*token)
> @@ -870,6 +879,15 @@ static int parse_cgroupfs_options(char *data,
> return -ENOMEM;
> strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
> opts->release_agent[PATH_MAX - 1] = 0;
> + } else if (!strncmp(token, "name=", 5)) {
> + /* Specifying two names is forbidden */
> + if (opts->name)
> + return -EINVAL;
> + opts->name = kzalloc(PATH_MAX, GFP_KERNEL);
> + if (!opts->name)
> + return -ENOMEM;
> + strncpy(opts->name, token + 5, PATH_MAX - 1);
> + opts->name[PATH_MAX - 1] = 0;
kstrndup()
> } else {
> struct cgroup_subsys *ss;
> int i;
> @@ -887,7 +905,7 @@ static int parse_cgroupfs_options(char *data,
> }
>
> /* We can't have an empty hierarchy */
> - if (!opts->subsys_bits)
> + if (!opts->subsys_bits && !opts->name)
> return -EINVAL;
>
> return 0;
> @@ -914,6 +932,12 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
> goto out_unlock;
> }
>
> + /* Don't allow name to change at remount */
> + if (opts.name && strcmp(opts.name, root->name)) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> ret = rebind_subsystems(root, opts.subsys_bits);
> if (ret)
> goto out_unlock;
> @@ -925,6 +949,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
> strcpy(root->release_agent_path, opts.release_agent);
> out_unlock:
> kfree(opts.release_agent);
> + kfree(opts.name);
> mutex_unlock(&cgroup_mutex);
> mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
> return ret;
> @@ -958,28 +983,56 @@ static void init_cgroup_root(struct cgroupfs_root *root)
>
> static int cgroup_test_super(struct super_block *sb, void *data)
> {
> - struct cgroupfs_root *new = data;
> + struct cgroup_sb_opts *new = data;
> struct cgroupfs_root *root = sb->s_fs_info;
>
> - /* First check subsystems */
> - if (new->subsys_bits != root->subsys_bits)
> - return 0;
> + /* If we asked for a name then it must match */
> + if (new->name && strcmp(new->name, root->name))
> + return 0;
>
> - /* Next check flags */
> - if (new->flags != root->flags)
Is this change intended or unintended? With this change we allow:
# mount -t cgroup -o cpu xxx /mnt1
# mount -t cgroup -o cpu,noprefix xxx /mnt2
But files in /mnt2 still prefix with 'cpu.'
> + /* If we asked for subsystems then they must match */
> + if (new->subsys_bits && new->subsys_bits != root->subsys_bits)
> return 0;
This has already been checked.
>
> return 1;
> }
>
> +static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
> +{
> + struct cgroupfs_root *root;
> +
> + if (!opts->subsys_bits)
> + return ERR_PTR(-EINVAL);
> +
> + root = kzalloc(sizeof(*root), GFP_KERNEL);
> + if (!root)
> + return ERR_PTR(-ENOMEM);
> +
> + 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);
> + if (opts->name)
> + strcpy(root->name, opts->name);
> + opts->created_root = true;
> + return root;
> +}
> +
> static int cgroup_set_super(struct super_block *sb, void *data)
> {
> int ret;
> - struct cgroupfs_root *root = data;
> + struct cgroup_sb_opts *opts = data;
> + struct cgroupfs_root *root;
>
> + root = cgroup_root_from_opts(opts);
> + if (IS_ERR(root))
> + return PTR_ERR(root);
> ret = set_anon_super(sb, NULL);
> - if (ret)
> + if (ret) {
> + kfree(root);
> return ret;
> + }
>
> sb->s_fs_info = root;
> root->sb = sb;
> @@ -1018,47 +1071,26 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
> int flags, const char *unused_dev_name,
> void *data, struct vfsmount *mnt)
> {
> - struct cgroup_sb_opts opts;
> + struct cgroup_sb_opts opts = { 0 };
with the memset() in parse_cgroupfs_options(), this init is unneeded.
> 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;
> - }
> -
> - 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);
> - }
leaking opts.release_agent and opts.name with every successful mount.
> + if (ret)
> + goto out_err;
>
> - sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
> + 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);
> + goto out_err;
> }
>
> - if (sb->s_fs_info != root) {
> - /* Reusing an existing superblock */
> - BUG_ON(sb->s_root == NULL);
> - kfree(root);
> - root = NULL;
> - } else {
> + if (opts.created_root) {
> /* New superblock */
> + struct cgroupfs_root *root = sb->s_fs_info;
> + struct list_head tmp_cg_links;
> struct cgroup *root_cgrp = &root->top_cgroup;
> struct inode *inode;
> int i;
> @@ -1091,7 +1123,8 @@ 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 */
> @@ -1130,11 +1163,14 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
> simple_set_mnt(mnt, sb);
> return 0;
>
> - free_cg_links:
> - free_cg_links(&tmp_cg_links);
> drop_new_super:
> up_write(&sb->s_umount);
> deactivate_super(sb);
> +
> + out_err:
> + kfree(opts.release_agent);
> + kfree(opts.name);
> +
> return ret;
> }
>
> @@ -2906,6 +2942,9 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
> seq_printf(m, "%lu:", root->subsys_bits);
> for_each_subsys(root, ss)
> seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
> + if (strlen(root->name))
> + seq_printf(m, "%sname=%s",
> + count++ ? "," : "", root->name);
s/count++/count
> seq_putc(m, ':');
> get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
> cgrp = task_cgroup(tsk, subsys_id);
> @@ -3606,4 +3645,3 @@ css_get_next(struct cgroup_subsys *ss, int id,
> }
> return ret;
> }
> -
>
>
>
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