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Commit 5f469907 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: update the meaning of cftype->max_write_len 



cftype->max_write_len is used to extend the maximum size of writes.
It's interpreted in such a way that the actual maximum size is one
less than the specified value.  The default size is defined by
CGROUP_LOCAL_BUFFER_SIZE.  Its interpretation is quite confusing - its
value is decremented by 1 and then compared for equality with max
size, which means that the actual default size is
CGROUP_LOCAL_BUFFER_SIZE - 2, which is 62 chars.

There's no point in having a limit that low.  Update its definition so
that it means the actual string length sans termination and anything
below PAGE_SIZE-1 is treated as PAGE_SIZE-1.

.max_write_len for "release_agent" is updated to PATH_MAX-1 and
cgroup_release_agent_write() is updated so that the redundant strlen()
check is removed and it uses strlcpy() instead of strcpy().
.max_write_len initializations in blk-throttle.c and cfq-iosched.c are
no longer necessary and removed.  The one in cpuset is kept unchanged
as it's an approximated value to begin with.

This will also make transition to kernfs smoother.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent de00ffa5

block/blk-throttle.c

+0 −4
Original line number Diff line number Diff line
@@ -1425,28 +1425,24 @@ static struct cftype throtl_files[] = { 
		.private = offsetof(struct throtl_grp, bps[READ]),

		.seq_show = tg_print_conf_u64,

		.write_string = tg_set_conf_u64,

		.max_write_len = 256,

	},

	{

		.name = "throttle.write_bps_device",

		.private = offsetof(struct throtl_grp, bps[WRITE]),

		.seq_show = tg_print_conf_u64,

		.write_string = tg_set_conf_u64,

		.max_write_len = 256,

	},

	{

		.name = "throttle.read_iops_device",

		.private = offsetof(struct throtl_grp, iops[READ]),

		.seq_show = tg_print_conf_uint,

		.write_string = tg_set_conf_uint,

		.max_write_len = 256,

	},

	{

		.name = "throttle.write_iops_device",

		.private = offsetof(struct throtl_grp, iops[WRITE]),

		.seq_show = tg_print_conf_uint,

		.write_string = tg_set_conf_uint,

		.max_write_len = 256,

	},

	{

		.name = "throttle.io_service_bytes",

block/cfq-iosched.c

+0 −3
Original line number Diff line number Diff line
@@ -1838,7 +1838,6 @@ static struct cftype cfq_blkcg_files[] = { 
		.flags = CFTYPE_ONLY_ON_ROOT,

		.seq_show = cfqg_print_leaf_weight_device,

		.write_string = cfqg_set_leaf_weight_device,

		.max_write_len = 256,

	},

	{

		.name = "weight",
@@ -1853,7 +1852,6 @@ static struct cftype cfq_blkcg_files[] = { 
		.flags = CFTYPE_NOT_ON_ROOT,

		.seq_show = cfqg_print_weight_device,

		.write_string = cfqg_set_weight_device,

		.max_write_len = 256,

	},

	{

		.name = "weight",
@@ -1866,7 +1864,6 @@ static struct cftype cfq_blkcg_files[] = { 
		.name = "leaf_weight_device",

		.seq_show = cfqg_print_leaf_weight_device,

		.write_string = cfqg_set_leaf_weight_device,

		.max_write_len = 256,

	},

	{

		.name = "leaf_weight",

include/linux/cgroup.h

+3 −2
Original line number Diff line number Diff line
@@ -400,8 +400,9 @@ struct cftype { 
	umode_t mode;



	/*

	 * If non-zero, defines the maximum length of string that can

	 * be passed to write_string; defaults to 64

	 * The maximum length of string, excluding trailing nul, that can

	 * be passed to write_string.  If < PAGE_SIZE-1, PAGE_SIZE-1 is

	 * assumed.

	 */

	size_t max_write_len;

kernel/cgroup.c

+8 −10
Original line number Diff line number Diff line
@@ -2213,13 +2213,14 @@ static int cgroup_procs_write(struct cgroup_subsys_state *css, 
static int cgroup_release_agent_write(struct cgroup_subsys_state *css,

				      struct cftype *cft, const char *buffer)

{

	BUILD_BUG_ON(sizeof(css->cgroup->root->release_agent_path) < PATH_MAX);

	if (strlen(buffer) >= PATH_MAX)

		return -EINVAL;

	struct cgroupfs_root *root = css->cgroup->root;



	BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);

	if (!cgroup_lock_live_group(css->cgroup))

		return -ENODEV;

	spin_lock(&release_agent_path_lock);

	strcpy(css->cgroup->root->release_agent_path, buffer);

	strlcpy(root->release_agent_path, buffer,

		sizeof(root->release_agent_path));

	spin_unlock(&release_agent_path_lock);

	mutex_unlock(&cgroup_mutex);

	return 0;
@@ -2245,20 +2246,17 @@ static int cgroup_sane_behavior_show(struct seq_file *seq, void *v) 
	return 0;

}



/* A buffer size big enough for numbers or short strings */

#define CGROUP_LOCAL_BUFFER_SIZE 64



static ssize_t cgroup_file_write(struct file *file, const char __user *userbuf,

				 size_t nbytes, loff_t *ppos)

{

	struct cfent *cfe = __d_cfe(file->f_dentry);

	struct cftype *cft = __d_cft(file->f_dentry);

	struct cgroup_subsys_state *css = cfe->css;

	size_t max_bytes = cft->max_write_len ?: CGROUP_LOCAL_BUFFER_SIZE - 1;

	size_t max_bytes = max(cft->max_write_len, PAGE_SIZE);

	char *buf;

	int ret;



	if (nbytes >= max_bytes)

	if (nbytes > max_bytes)

		return -E2BIG;



	buf = kmalloc(nbytes + 1, GFP_KERNEL);
@@ -3919,7 +3917,7 @@ static struct cftype cgroup_base_files[] = { 
		.flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT,

		.seq_show = cgroup_release_agent_show,

		.write_string = cgroup_release_agent_write,

		.max_write_len = PATH_MAX,

		.max_write_len = PATH_MAX - 1,

	},

	{ }	/* terminate */

};