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    SubjectRe: [PATCH 1/2] cgroup allow subsys to set default mode of its own file
    KAMEZAWA Hiroyuki wrote:
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > cgroup's subsys has "readonly" files, but default permission is always
    > rw-r--r--. This allows to create r--r--r-- file to subsys.
    > (The user can do chmod on this read-only file. But this behavior is not
    > different from current pseudo file systems as /proc.)
    >
    > Reason:
    > When I wrote tools for maintain cgroup, I can't find which file is
    > writable intarfece or not via cgroup file systems. (finally, I did
    > dirty approach.)
    > IMHO, showing "this file is read-only" in explicit way is useful
    > for user-land (tools). In other story, a file whose name sounds read-only
    > may have "trigger" operation and support reseting. In this case,
    > "writable" is informative.
    >

    I once planed to do so. I think there's one trial issue, that some files are
    read-only in top-cgroup, but read-write in sub-dirs, like cpuset.cpus and
    cpuset.mems. But for those files, they must have a write function, so I think
    it's still valid to mask them as read-write even they are in top-cgroup.

    Unless Paul has different option towards this:

    Acked-by: Li Zefan <lizf@cn.fujitsu.cn>

    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    > include/linux/cgroup.h | 2 ++
    > kernel/cgroup.c | 5 ++++-
    > 2 files changed, 6 insertions(+), 1 deletion(-)
    >
    > Index: mmotm-2.6.29-Feb24/include/linux/cgroup.h
    > ===================================================================
    > --- mmotm-2.6.29-Feb24.orig/include/linux/cgroup.h
    > +++ mmotm-2.6.29-Feb24/include/linux/cgroup.h
    > @@ -258,6 +258,8 @@ struct cftype {
    > */
    > char name[MAX_CFTYPE_NAME];
    > int private;
    > + /* if not 0, mode is set to mode, otherwise 0644 */
    > + int mode;
    >
    > /*
    > * If non-zero, defines the maximum length of string that can
    > Index: mmotm-2.6.29-Feb24/kernel/cgroup.c
    > ===================================================================
    > --- mmotm-2.6.29-Feb24.orig/kernel/cgroup.c
    > +++ mmotm-2.6.29-Feb24/kernel/cgroup.c
    > @@ -1767,7 +1767,10 @@ int cgroup_add_file(struct cgroup *cgrp,
    > BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
    > dentry = lookup_one_len(name, dir, strlen(name));
    > if (!IS_ERR(dentry)) {
    > - error = cgroup_create_file(dentry, 0644 | S_IFREG,
    > + int mode = 0644;
    > + if (cft->mode)
    > + mode = cft->mode;
    > + error = cgroup_create_file(dentry, mode | S_IFREG,
    > cgrp->root->sb);
    > if (!error)
    > dentry->d_fsdata = (void *)cft;
    >


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