The counter file is automatically added to all sample_kernfs
directories (including the root directory). This demonstrates how to tie an
internal datastructure -- sample_kernfs_directory in this case -- to kernfs
nodes via kernfs_node->priv. Also demonstrates how to read and write simple
integer values to/from kernfs files.
Signed-off-by: David Reaver <me@xxxxxxxxxxxxxxx>
---
samples/kernfs/sample_kernfs.c | 110 ++++++++++++++++++++++++++++++++-
1 file changed, 108 insertions(+), 2 deletions(-)
diff --git a/samples/kernfs/sample_kernfs.c b/samples/kernfs/sample_kernfs.c
index 3ea8411a72ae..b6d44fc3b935 100644
--- a/samples/kernfs/sample_kernfs.c
+++ b/samples/kernfs/sample_kernfs.c
@@ -14,6 +14,93 @@
#define SAMPLE_KERNFS_MAGIC 0x8d000ff0
+/**
+ * struct sample_kernfs_directory - Represents a directory in the pseudo-filesystem
+ * @count: Holds the current count in the counter file.
+ */
+struct sample_kernfs_directory {
+ atomic64_t count;
+};
+
+static struct sample_kernfs_directory *sample_kernfs_create_dir(void)
+{
+ struct sample_kernfs_directory *dir;
+
+ dir = kzalloc(sizeof(struct sample_kernfs_directory), GFP_KERNEL);
+ if (!dir)
+ return NULL;
+
+ return dir;
+}
+
+static struct sample_kernfs_directory *kernfs_of_to_dir(struct kernfs_open_file *of)
+{
+ struct kernfs_node *dir_kn = kernfs_get_parent(of->kn);
+ struct sample_kernfs_directory *dir = dir_kn->priv;
+
+ /* kernfs_get_parent adds a reference; drop it with kernfs_put */
+ kernfs_put(dir_kn);
+
+ return dir;
+}
+
+static int sample_kernfs_counter_seq_show(struct seq_file *sf, void *v)
+{
+ struct kernfs_open_file *of = sf->private;
+ struct sample_kernfs_directory *counter_dir = kernfs_of_to_dir(of);
+ u64 count = atomic64_inc_return(&counter_dir->count);
+
+ seq_printf(sf, "%llu\n", count);
+
+ return 0;
+}
+
+static ssize_t sample_kernfs_counter_write(struct kernfs_open_file *of, char *buf,
+ size_t nbytes, loff_t off)
+{
+ struct sample_kernfs_directory *counter_dir = kernfs_of_to_dir(of);
+ int ret;
+ u64 new_value;
+
+ ret = kstrtou64(strstrip(buf), 10, &new_value);
+ if (ret)
+ return ret;
+
+ atomic64_set(&counter_dir->count, new_value);
+
+ return nbytes;
+}
+
+static struct kernfs_ops counter_kf_ops = {
+ .seq_show = sample_kernfs_counter_seq_show,
+ .write = sample_kernfs_counter_write,
+};
+
+static int sample_kernfs_add_file(struct kernfs_node *dir_kn, const char *name,
+ struct kernfs_ops *ops)
+{
+ struct kernfs_node *kn;
+
+ kn = __kernfs_create_file(dir_kn, name, 0666, current_fsuid(),
+ current_fsgid(), 0, ops, NULL, NULL, NULL);
+
+ if (IS_ERR(kn))
+ return PTR_ERR(kn);
+
+ return 0;
+}
+
+static int sample_kernfs_populate_dir(struct kernfs_node *dir_kn)
+{
+ int err;
+
+ err = sample_kernfs_add_file(dir_kn, "counter", &counter_kf_ops);
+ if (err)
+ return err;
+
+ return 0;
+}
+
static void sample_kernfs_fs_context_free(struct fs_context *fc)
{
struct kernfs_fs_context *kfc = fc->fs_private;
@@ -30,6 +117,7 @@ static const struct fs_context_operations sample_kernfs_fs_context_ops = {
static int sample_kernfs_init_fs_context(struct fs_context *fc)
{
struct kernfs_fs_context *kfc;
+ struct sample_kernfs_directory *root_dir;
struct kernfs_root *root;
int err;
@@ -37,10 +125,17 @@ static int sample_kernfs_init_fs_context(struct fs_context *fc)
if (!kfc)
return -ENOMEM;
- root = kernfs_create_root(NULL, 0, NULL);
+ root_dir = sample_kernfs_create_dir();
+ if (!root_dir) {
+ err = -ENOMEM;
+ goto err_free_kfc;
+ }
+
+ /* dir gets stored in root->priv so we can access it later. */
+ root = kernfs_create_root(NULL, 0, root_dir);
if (IS_ERR(root)) {
err = PTR_ERR(root);
- goto err_free_kfc;
+ goto err_free_dir;
}
kfc->root = root;
@@ -49,8 +144,16 @@ static int sample_kernfs_init_fs_context(struct fs_context *fc)
fc->ops = &sample_kernfs_fs_context_ops;
fc->global = true;
+ err = sample_kernfs_populate_dir(kernfs_root_to_node(root));
+ if (err)
+ goto err_free_root;
+
return 0;
+err_free_root:
+ kernfs_destroy_root(root);
+err_free_dir:
+ kfree(root_dir);
err_free_kfc:
kfree(kfc);
return err;
@@ -59,9 +162,12 @@ static int sample_kernfs_init_fs_context(struct fs_context *fc)
static void sample_kernfs_kill_sb(struct super_block *sb)
{
struct kernfs_root *root = kernfs_root_from_sb(sb);
+ struct kernfs_node *root_kn = kernfs_root_to_node(root);
+ struct sample_kernfs_directory *root_dir = root_kn->priv;
kernfs_kill_sb(sb);
kernfs_destroy_root(root);
+ kfree(root_dir);
}
static struct file_system_type sample_kernfs_fs_type = {
