hypfs_dbfs.c

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/*
 * Hypervisor filesystem for Linux on s390 - debugfs interface
 *
 * Copyright IBM Corp. 2010
 * Author(s): Michael Holzheu <[email protected]>
 */

#include <linux/slab.h>
#include "hypfs.h"

static struct dentry *dbfs_dir;

static struct hypfs_dbfs_data *hypfs_dbfs_data_alloc(struct hypfs_dbfs_file *f)
{
    struct hypfs_dbfs_data *data;

    data = kmalloc(sizeof(*data), GFP_KERNEL);
    if (!data)
        return NULL;
    kref_init(&data->kref);
    data->dbfs_file = f;
    return data;
}

static void hypfs_dbfs_data_free(struct kref *kref)
{
    struct hypfs_dbfs_data *data;

    data = container_of(kref, struct hypfs_dbfs_data, kref);
    data->dbfs_file->data_free(data->buf_free_ptr);
    kfree(data);
}

static void data_free_delayed(struct work_struct *work)
{
    struct hypfs_dbfs_data *data;
    struct hypfs_dbfs_file *df;

    df = container_of(work, struct hypfs_dbfs_file, data_free_work.work);
    mutex_lock(&df->lock);
    data = df->data;
    df->data = NULL;
    mutex_unlock(&df->lock);
    kref_put(&data->kref, hypfs_dbfs_data_free);
}

static ssize_t dbfs_read(struct file *file, char __user *buf,
             size_t size, loff_t *ppos)
{
    struct hypfs_dbfs_data *data;
    struct hypfs_dbfs_file *df;
    ssize_t rc;

    if (*ppos != 0)
        return 0;

    df = file->f_path.dentry->d_inode->i_private;
    mutex_lock(&df->lock);
    if (!df->data) {
        data = hypfs_dbfs_data_alloc(df);
        if (!data) {
            mutex_unlock(&df->lock);
            return -ENOMEM;
        }
        rc = df->data_create(&data->buf, &data->buf_free_ptr,
                     &data->size);
        if (rc) {
            mutex_unlock(&df->lock);
            kfree(data);
            return rc;
        }
        df->data = data;
        schedule_delayed_work(&df->data_free_work, HZ);
    }
    data = df->data;
    kref_get(&data->kref);
    mutex_unlock(&df->lock);

    rc = simple_read_from_buffer(buf, size, ppos, data->buf, data->size);
    kref_put(&data->kref, hypfs_dbfs_data_free);
    return rc;
}

static const struct file_operations dbfs_ops = {
    .read       = dbfs_read,
    .llseek     = no_llseek,
};

int hypfs_dbfs_create_file(struct hypfs_dbfs_file *df)
{
    df->dentry = debugfs_create_file(df->name, 0400, dbfs_dir, df,
                     &dbfs_ops);
    if (IS_ERR(df->dentry))
        return PTR_ERR(df->dentry);
    mutex_init(&df->lock);
    INIT_DELAYED_WORK(&df->data_free_work, data_free_delayed);
    return 0;
}

void hypfs_dbfs_remove_file(struct hypfs_dbfs_file *df)
{
    debugfs_remove(df->dentry);
}

int hypfs_dbfs_init(void)
{
    dbfs_dir = debugfs_create_dir("s390_hypfs", NULL);
    if (IS_ERR(dbfs_dir))
        return PTR_ERR(dbfs_dir);
    return 0;
}

void hypfs_dbfs_exit(void)
{
    debugfs_remove(dbfs_dir);
}