[Devel] Re: [PATCH 1/4] Support named cgroups hierarchies
Dhaval Giani
dhaval at linux.vnet.ibm.com
Wed Jul 29 03:43:33 PDT 2009
On Tue, Jul 28, 2009 at 04:26:21PM -0700, 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 <menage at google.com>
> Reviewed-by: Li Zefan <lizf at cn.fujitsu.com>
>
> ---
>
> Documentation/cgroups/cgroups.txt | 20 ++++
> kernel/cgroup.c | 185 +++++++++++++++++++++++++++----------
> 2 files changed, 157 insertions(+), 48 deletions(-)
>
> diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
> index 6eb1a97..4bccfc1 100644
> --- a/Documentation/cgroups/cgroups.txt
> +++ b/Documentation/cgroups/cgroups.txt
> @@ -408,6 +408,26 @@ 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. Each hierarchy is either
> +nameless, or has a unique name.
> +
> +The name should match [\w.-]+
> +
> +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.
> +
> +The name of the subsystem appears as part of the hierarchy description
> +in /proc/mounts and /proc/<pid>/cgroups.
> +
> +
> 3. Kernel API
> =============
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 18acba7..85573e8 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -23,6 +23,7 @@
> */
>
> #include <linux/cgroup.h>
> +#include <linux/ctype.h>
> #include <linux/errno.h>
> #include <linux/fs.h>
> #include <linux/kernel.h>
> @@ -60,6 +61,8 @@ static struct cgroup_subsys *subsys[] = {
> #include <linux/cgroup_subsys.h>
> };
>
> +#define MAX_CGROUP_ROOT_NAMELEN 64
> +
> /*
> * A cgroupfs_root represents the root of a cgroup hierarchy,
> * and may be associated with a superblock to form an active
> @@ -94,6 +97,9 @@ 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[MAX_CGROUP_ROOT_NAMELEN];
> };
>
> /*
> @@ -829,6 +835,8 @@ 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;
> }
> @@ -837,6 +845,9 @@ struct cgroup_sb_opts {
> unsigned long subsys_bits;
> unsigned long flags;
> char *release_agent;
> + char *name;
> +
> + struct cgroupfs_root *new_root;
> };
>
> /* Convert a hierarchy specifier into a bitmask of subsystems and
> @@ -851,9 +862,7 @@ static int parse_cgroupfs_options(char *data,
> mask = ~(1UL << cpuset_subsys_id);
> #endif
>
> - opts->subsys_bits = 0;
> - opts->flags = 0;
> - opts->release_agent = NULL;
> + memset(opts, 0, sizeof(*opts));
>
> while ((token = strsep(&o, ",")) != NULL) {
> if (!*token)
> @@ -873,11 +882,33 @@ static int parse_cgroupfs_options(char *data,
> /* Specifying two release agents is forbidden */
> if (opts->release_agent)
> return -EINVAL;
> - opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
> + opts->release_agent =
> + kstrndup(token + 14, PATH_MAX, GFP_KERNEL);
I am not sure how it can be acheived, but can we avoid using 14 here (it
took me a moment before I realized it was strlen("release_agent")
> if (!opts->release_agent)
> return -ENOMEM;
> - strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
> - opts->release_agent[PATH_MAX - 1] = 0;
> + } else if (!strncmp(token, "name=", 5)) {
> + int i;
> + const char *name = token + 5;
similarly here as well
> + /* Can't specify an empty name */
> + if (!strlen(name))
> + return -EINVAL;
> + /* Must match [\w.-]+ */
> + for (i = 0; i < strlen(name); i++) {
> + char c = name[i];
> + if (isalnum(c))
> + continue;
> + if ((c == '.') || (c == '-') || (c == '_'))
> + continue;
> + return -EINVAL;
> + }
> + /* Specifying two names is forbidden */
> + if (opts->name)
> + return -EINVAL;
> + opts->name = kstrndup(name,
> + MAX_CGROUP_ROOT_NAMELEN,
> + GFP_KERNEL);
> + if (!opts->name)
> + return -ENOMEM;
> } else {
> struct cgroup_subsys *ss;
> int i;
> @@ -904,7 +935,7 @@ static int parse_cgroupfs_options(char *data,
> return -EINVAL;
>
> /* We can't have an empty hierarchy */
> - if (!opts->subsys_bits)
> + if (!opts->subsys_bits && !opts->name)
> return -EINVAL;
>
> return 0;
> @@ -932,6 +963,12 @@ 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;
> @@ -943,6 +980,7 @@ 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);
> unlock_kernel();
> @@ -965,6 +1003,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
> INIT_LIST_HEAD(&cgrp->pids_list);
> init_rwsem(&cgrp->pids_mutex);
> }
> +
> static void init_cgroup_root(struct cgroupfs_root *root)
> {
> struct cgroup *cgrp = &root->top_cgroup;
> @@ -978,31 +1017,59 @@ 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 *opts = 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 (opts->name && strcmp(opts->name, root->name))
> + return 0;
>
> - /* Next check flags */
> - if (new->flags != root->flags)
> + /* If we asked for subsystems then they must match */
> + if (opts->subsys_bits && (opts->subsys_bits != root->subsys_bits))
> return 0;
>
> return 1;
> }
>
> +static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
> +{
> + struct cgroupfs_root *root;
> +
> + /* Empty hierarchies aren't supported */
> + if (!opts->subsys_bits)
> + return NULL;
> +
> + 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);
> + 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;
> +
> + /* If we don't have a new root, we can't set up a new sb */
> + if (!opts->new_root)
> + return -EINVAL;
> +
> + 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 +1106,43 @@ 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;
> + struct cgroupfs_root *new_root;
>
> /* 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.
> + */
> + new_root = cgroup_root_from_opts(&opts);
> + 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 +1155,18 @@ 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 +1185,8 @@ 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 +1220,26 @@ 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;
> }
>
> @@ -2971,6 +3057,9 @@ 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);
> seq_putc(m, ':');
> get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
> cgrp = task_cgroup(tsk, subsys_id);
>
--
regards,
Dhaval
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