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    Subject[RFC][PATCH 2/3] memcg:: seq_ops support for cgroup
    Does anyone have a better idea ?
    ==

    Currently, cgroup's seq_file interface just supports single_open.
    This patch allows arbitrary seq_ops if passed.

    For example, "status per cpu, status per node" can be very big
    in general and they tend to use its own start/next/stop ops.

    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


    ---
    include/linux/cgroup.h | 9 +++++++++
    kernel/cgroup.c | 32 +++++++++++++++++++++++++++++---
    2 files changed, 38 insertions(+), 3 deletions(-)

    Index: mm-2.6.26-rc2-mm1/include/linux/cgroup.h
    ===================================================================
    --- mm-2.6.26-rc2-mm1.orig/include/linux/cgroup.h
    +++ mm-2.6.26-rc2-mm1/include/linux/cgroup.h
    @@ -232,6 +232,11 @@ struct cftype {
    */
    int (*read_seq_string) (struct cgroup *cont, struct cftype *cft,
    struct seq_file *m);
    + /*
    + * If this is not NULL, read ops will use this instead of
    + * single_open(). Useful for showing very large data.
    + */
    + struct seq_operations *seq_ops;

    ssize_t (*write) (struct cgroup *cgrp, struct cftype *cft,
    struct file *file,
    @@ -285,6 +290,10 @@ int cgroup_path(const struct cgroup *cgr

    int cgroup_task_count(const struct cgroup *cgrp);

    +
    +struct cgroup *cgroup_of_seqfile(struct seq_file *m);
    +struct cftype *cftype_of_seqfile(struct seq_file *m);
    +
    /* Return true if the cgroup is a descendant of the current cgroup */
    int cgroup_is_descendant(const struct cgroup *cgrp);

    Index: mm-2.6.26-rc2-mm1/kernel/cgroup.c
    ===================================================================
    --- mm-2.6.26-rc2-mm1.orig/kernel/cgroup.c
    +++ mm-2.6.26-rc2-mm1/kernel/cgroup.c
    @@ -1540,6 +1540,16 @@ struct cgroup_seqfile_state {
    struct cgroup *cgroup;
    };

    +struct cgroup *cgroup_of_seqfile(struct seq_file *m)
    +{
    + return ((struct cgroup_seqfile_state *)m->private)->cgroup;
    +}
    +
    +struct cftype *cftype_of_seqfile(struct seq_file *m)
    +{
    + return ((struct cgroup_seqfile_state *)m->private)->cft;
    +}
    +
    static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
    {
    struct seq_file *sf = cb->state;
    @@ -1563,8 +1573,14 @@ static int cgroup_seqfile_show(struct se
    static int cgroup_seqfile_release(struct inode *inode, struct file *file)
    {
    struct seq_file *seq = file->private_data;
    + struct cgroup_seqfile_state *state = seq->private;
    + struct cftype *cft = state->cft;
    +
    kfree(seq->private);
    - return single_release(inode, file);
    + if (!cft->seq_ops)
    + return single_release(inode, file);
    + else
    + return seq_release(inode, file);
    }

    static struct file_operations cgroup_seqfile_operations = {
    @@ -1585,7 +1601,7 @@ static int cgroup_file_open(struct inode
    cft = __d_cft(file->f_dentry);
    if (!cft)
    return -ENODEV;
    - if (cft->read_map || cft->read_seq_string) {
    + if (cft->read_map || cft->read_seq_string || cft->seq_ops) {
    struct cgroup_seqfile_state *state =
    kzalloc(sizeof(*state), GFP_USER);
    if (!state)
    @@ -1593,7 +1609,17 @@ static int cgroup_file_open(struct inode
    state->cft = cft;
    state->cgroup = __d_cgrp(file->f_dentry->d_parent);
    file->f_op = &cgroup_seqfile_operations;
    - err = single_open(file, cgroup_seqfile_show, state);
    +
    + if (!cft->seq_ops)
    + err = single_open(file, cgroup_seqfile_show, state);
    + else {
    + err = seq_open(file, cft->seq_ops);
    + if (!err) {
    + struct seq_file *sf;
    + sf = ((struct seq_file *)file->private_data);
    + sf->private = state;
    + }
    + }
    if (err < 0)
    kfree(state);
    } else if (cft->open)


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