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
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1731,66 +1731,43 @@
* 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 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 @@
{
.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,