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>

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 1474c3ab7e72cb85698ffe8bb3687df66729281b..861c363e412914f4d4a9b53655089adaa7d91ee0 100644 (file)
--- 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 744833b630c69c5b56c98c81e76c21b774be29ad..461187943392e96d5db9a50327fad3e9239eed31 100644 (file)
--- 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",

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c4350a82320b37ebc4853f4c686e4b8ea026632d..63feaed83bc62c3263c6554e07bd9c4e854ad14b 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -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;
 

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index eb002c622cd6798e886d1f1e415ca401f85c2b6e..fde3633ef38993f45652ecc1eaee8d17a7992882 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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 */
 };