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: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

2 files changed, 0 insertions, 7 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1474c3ab7e72..861c363e4129 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -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",
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 744833b630c6..461187943392 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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",