cpuset: convert away from cftype->read()

In preparation of conversion to kernfs, cgroup file handling is being
consolidated so that it can be easily mapped to the seq_file based
interface of kernfs.

All users of cftype->read() can be easily served, usually better, by
seq_file and other methods.  Rename cpuset_common_file_read() to
cpuset_common_read_seq_string() and convert it to use
read_seq_string() interface instead.  This not only simplifies the
code but also makes it more versatile.  Before, the file couldn't
output if the result is longer than PAGE_SIZE.  After the conversion,
seq_file automatically grows the buffer until the output can fit.

This patch doesn't make any visible behavior changes except for being
able to handle output larger than PAGE_SIZE.

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

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 4772034..032929f 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1731,66 +1731,43 @@ out_unlock:
  * used, list of ranges of sequential numbers, is variable length,
  * and since these maps can change value dynamically, one could read
  * gibberish by doing partial reads while a list was changing.
- * A single large read to a buffer that crosses a page boundary is
- * ok, because the result being copied to user land is not recomputed
- * across a page fault.
  */
-
-static size_t cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
-{
-       size_t count;
-
-       mutex_lock(&callback_mutex);
-       count = cpulist_scnprintf(page, PAGE_SIZE, cs->cpus_allowed);
-       mutex_unlock(&callback_mutex);
-
-       return count;
-}
-
-static size_t cpuset_sprintf_memlist(char *page, struct cpuset *cs)
-{
-       size_t count;
-
-       mutex_lock(&callback_mutex);
-       count = nodelist_scnprintf(page, PAGE_SIZE, cs->mems_allowed);
-       mutex_unlock(&callback_mutex);
-
-       return count;
-}
-
-static ssize_t cpuset_common_file_read(struct cgroup_subsys_state *css,
-                                      struct cftype *cft, struct file *file,
-                                      char __user *buf, size_t nbytes,
-                                      loff_t *ppos)
+static int cpuset_common_read_seq_string(struct cgroup_subsys_state *css,
+                                        struct cftype *cft,
+                                        struct seq_file *sf)
 {
        struct cpuset *cs = css_cs(css);
        cpuset_filetype_t type = cft->private;
-       char *page;
-       ssize_t retval = 0;
-       char *s;
+       ssize_t count;
+       char *buf, *s;
+       int ret = 0;
 
-       if (!(page = (char *)__get_free_page(GFP_TEMPORARY)))
-               return -ENOMEM;
+       count = seq_get_buf(sf, &buf);
+       s = buf;
 
-       s = page;
+       mutex_lock(&callback_mutex);
 
        switch (type) {
        case FILE_CPULIST:
-               s += cpuset_sprintf_cpulist(s, cs);
+               s += cpulist_scnprintf(s, count, cs->cpus_allowed);
                break;
        case FILE_MEMLIST:
-               s += cpuset_sprintf_memlist(s, cs);
+               s += nodelist_scnprintf(s, count, cs->mems_allowed);
                break;
        default:
-               retval = -EINVAL;
-               goto out;
+               ret = -EINVAL;
+               goto out_unlock;
        }
-       *s++ = '\n';
 
-       retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
-out:
-       free_page((unsigned long)page);
-       return retval;
+       if (s < buf + count - 1) {
+               *s++ = '\n';
+               seq_commit(sf, s - buf);
+       } else {
+               seq_commit(sf, -1);
+       }
+out_unlock:
+       mutex_unlock(&callback_mutex);
+       return ret;
 }
 
 static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
@@ -1847,7 +1824,7 @@ static s64 cpuset_read_s64(struct cgroup_subsys_state *css, struct cftype *cft)
 static struct cftype files[] = {
        {
                .name = "cpus",
-               .read = cpuset_common_file_read,
+               .read_seq_string = cpuset_common_read_seq_string,
                .write_string = cpuset_write_resmask,
                .max_write_len = (100U + 6 * NR_CPUS),
                .private = FILE_CPULIST,
@@ -1855,7 +1832,7 @@ static struct cftype files[] = {
 
        {
                .name = "mems",
-               .read = cpuset_common_file_read,
+               .read_seq_string = cpuset_common_read_seq_string,
                .write_string = cpuset_write_resmask,
                .max_write_len = (100U + 6 * MAX_NUMNODES),
                .private = FILE_MEMLIST,