Re: [PATCH 0/4] cgroups: show correct file mode

[Li Zefan <lizf@cn.fujitsu.com>]

Paul Menage wrote:
> On Sun, Mar 1, 2009 at 6:13 PM, Li Zefan <lizf@cn.fujitsu.com> wrote:
>> Now a cgroup subsystem can set default file mode of its control files,
>> so here is a patchset to correct file mode of each subsystem's files.
> 
> I really think that we should be defaulting this based on whether the
> control file has read or write handlers.
> 
> Sure, there are special cases like "tasks" that we'd need to set a
> manual value for, but most of these patches would be unnecessary.
> 

Those patches are small and trivial, but it's ok for me to do this
automatically. How about below patch.

Note cpuset.memory_pressure is read-only though it has read handler.
Since if the read handler is removed, it'll return EINVAL instead of
the current EACCESS, I think it's better to leave as it is.

=====================

cgroups: show correct file mode

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 include/linux/cgroup.h |    5 +++++
 kernel/cgroup.c        |   30 ++++++++++++++++++++++++++++++
 kernel/cpuset.c        |    1 +
 3 files changed, 36 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 6ad1989..af3c10f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -258,6 +258,11 @@ struct cftype {
 	 */
 	char name[MAX_CFTYPE_NAME];
 	int private;
+	/*
+	 * If not 0, file mode is set to this value, otherwise it will
+	 * be figured out automatically
+	 */
+	int mode;
 
 	/*
 	 * If non-zero, defines the maximum length of string that can
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 379baa3..0b19204 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1750,6 +1750,33 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
 	return error;
 }
 
+/**
+ * cgroup_file_mode - deduce file mode of a control file
+ * @cft: the control file in question
+ *
+ * returns cftype->mode if ->mode is not 0
+ * returns 0644 if it has both a read and a write handler
+ * returns 0444 if it has only a read handler
+ * returns 0200 if it has only a write hander
+ */
+static int cgroup_file_mode(const struct cftype *cft)
+{
+	int mode = 0;
+
+	if (cft->mode)
+		return cft->mode;
+
+	if (cft->read || cft->read_u64 || cft->read_s64 ||
+	    cft->read_map || cft->read_seq_string)
+		mode += 0444;
+
+	if (cft->write || cft->write_u64 || cft->write_s64 ||
+	    cft->write_string || cft->trigger)
+		mode += 0200;
+
+	return mode;
+}
+
 int cgroup_add_file(struct cgroup *cgrp,
 		       struct cgroup_subsys *subsys,
 		       const struct cftype *cft)
@@ -1757,6 +1784,7 @@ int cgroup_add_file(struct cgroup *cgrp,
 	struct dentry *dir = cgrp->dentry;
 	struct dentry *dentry;
 	int error;
+	int mode;
 
 	char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
 	if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
@@ -1767,6 +1795,7 @@ 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)) {
+		mode = cgroup_file_mode(cft);
 		error = cgroup_create_file(dentry, 0644 | S_IFREG,
 						cgrp->root->sb);
 		if (!error)
@@ -2349,6 +2378,7 @@ static struct cftype files[] = {
 		.write_u64 = cgroup_tasks_write,
 		.release = cgroup_tasks_release,
 		.private = FILE_TASKLIST,
+		.mode = 0644,
 	},
 
 	{
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index a46d693..31e28b3 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1678,6 +1678,7 @@ static struct cftype files[] = {
 		.read_u64 = cpuset_read_u64,
 		.write_u64 = cpuset_write_u64,
 		.private = FILE_MEMORY_PRESSURE,
+		.mode = 0444,
 	},
 
 	{