/*
 * Copyright(c) 2017 Intel Corporation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */
#include <linux/pagemap.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/magic.h>
#include <linux/genhd.h>
#include <linux/cdev.h>
#include <linux/hash.h>
#include <linux/slab.h>
#include <linux/dax.h>
#include <linux/fs.h>
#include <linux/idr.h>
#include <linux/backing-dev.h>
#include "stringhash.h"

static dev_t dax_devt;
DEFINE_STATIC_SRCU(dax_srcu);
static struct vfsmount *dax_mnt;
static DEFINE_IDA(dax_minor_ida);
static struct kmem_cache *dax_cache __read_mostly;
static struct super_block *dax_superblock __read_mostly;

#define DAX_HASH_SIZE (PAGE_SIZE / sizeof(struct hlist_head))
static struct hlist_head dax_host_list[DAX_HASH_SIZE];
static DEFINE_SPINLOCK(dax_host_lock);

int dax_read_lock(void)
{
        return srcu_read_lock(&dax_srcu);
}
EXPORT_SYMBOL_GPL(dax_read_lock);

void dax_read_unlock(int id)
{
        srcu_read_unlock(&dax_srcu, id);
}
EXPORT_SYMBOL_GPL(dax_read_unlock);

#ifdef CONFIG_BLOCK
int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
                pgoff_t *pgoff)
{
        phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;

        if (pgoff)
                *pgoff = PHYS_PFN(phys_off);
        if (phys_off % PAGE_SIZE || size % PAGE_SIZE)
                return -EINVAL;
        return 0;
}
EXPORT_SYMBOL(bdev_dax_pgoff);

/**
 * __bdev_dax_supported() - Check if the device supports dax for filesystem
 * @sb: The superblock of the device
 * @blocksize: The block size of the device
 *
 * This is a library function for filesystems to check if the block device
 * can be mounted with dax option.
 *
 * Return: negative errno if unsupported, 0 if supported.
 */
int __bdev_dax_supported(struct super_block *sb, int blocksize)
{
        struct block_device *bdev = sb->s_bdev;
        struct dax_device *dax_dev;
        pgoff_t pgoff;
        int err, id;
        void *kaddr;
        pfn_t pfn;
        long len;

        if (blocksize != PAGE_SIZE) {
                pr_err("VFS (%s): error: unsupported blocksize for dax\n",
                                sb->s_id);
                return -EINVAL;
        }

        err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
        if (err) {
                pr_err("VFS (%s): error: unaligned partition for dax\n",
                                sb->s_id);
                return err;
        }

        dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
        if (!dax_dev) {
                pr_err("VFS (%s): error: device does not support dax\n",
                                sb->s_id);
                return -EOPNOTSUPP;
        }

        id = dax_read_lock();
        len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
        dax_read_unlock(id);

        put_dax(dax_dev);

        if (len < 1) {
                pr_err("VFS (%s): error: dax access failed (%ld)",
                                sb->s_id, len);
                return len < 0 ? len : -EIO;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(__bdev_dax_supported);
#endif

enum dax_device_flags {
        /* !alive + rcu grace period == no new operations / mappings */
        DAXDEV_ALIVE,
};

/**
 * struct dax_device - anchor object for dax services
 * @inode: core vfs
 * @cdev: optional character interface for "device dax"
 * @host: optional name for lookups where the device path is not available
 * @private: dax driver private data
 * @flags: state and boolean properties
 */
struct dax_device {
        struct hlist_node list;
        struct inode inode;
        struct cdev cdev;
        const char *host;
        void *private;
        unsigned long flags;
        const struct dax_operations *ops;
};

/**
 * dax_direct_access() - translate a device pgoff to an absolute pfn
 * @dax_dev: a dax_device instance representing the logical memory range
 * @pgoff: offset in pages from the start of the device to translate
 * @nr_pages: number of consecutive pages caller can handle relative to @pfn
 * @kaddr: output parameter that returns a virtual address mapping of pfn
 * @pfn: output parameter that returns an absolute pfn translation of @pgoff
 *
 * Return: negative errno if an error occurs, otherwise the number of
 * pages accessible at the device relative @pgoff.
 */
long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
                void **kaddr, pfn_t *pfn)
{
        long avail;

        /*
         * The device driver is allowed to sleep, in order to make the
         * memory directly accessible.
         */
        might_sleep();

        if (!dax_dev)
                return -EOPNOTSUPP;

        if (!dax_alive(dax_dev))
                return -ENXIO;

        if (nr_pages < 0)
                return nr_pages;

        avail = dax_dev->ops->direct_access(dax_dev, pgoff, nr_pages,
                        kaddr, pfn);
        if (!avail)
                return -ERANGE;
        return min(avail, nr_pages);
}
EXPORT_SYMBOL_GPL(dax_direct_access);

bool dax_alive(struct dax_device *dax_dev)
{
        lockdep_assert_held(&dax_srcu);
        return test_bit(DAXDEV_ALIVE, &dax_dev->flags);
}
EXPORT_SYMBOL_GPL(dax_alive);

static int dax_host_hash(const char *host)
{
        return hashlen_hash(hashlen_string("DAX", host)) % DAX_HASH_SIZE;
}

/*
 * Note, rcu is not protecting the liveness of dax_dev, rcu is ensuring
 * that any fault handlers or operations that might have seen
 * dax_alive(), have completed.  Any operations that start after
 * synchronize_srcu() has run will abort upon seeing !dax_alive().
 */
void kill_dax(struct dax_device *dax_dev)
{
        if (!dax_dev)
                return;

        clear_bit(DAXDEV_ALIVE, &dax_dev->flags);

        synchronize_srcu(&dax_srcu);

        spin_lock(&dax_host_lock);
        hlist_del_init(&dax_dev->list);
        spin_unlock(&dax_host_lock);

        dax_dev->private = NULL;
}
EXPORT_SYMBOL_GPL(kill_dax);

static struct inode *dax_alloc_inode(struct super_block *sb)
{
        struct dax_device *dax_dev;
        struct inode *inode;

        dax_dev = kmem_cache_alloc(dax_cache, GFP_KERNEL);
        inode = &dax_dev->inode;
        inode->i_rdev = 0;
        return inode;
}

static struct dax_device *to_dax_dev(struct inode *inode)
{
        return container_of(inode, struct dax_device, inode);
}

static void dax_i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        struct dax_device *dax_dev = to_dax_dev(inode);

        kfree(dax_dev->host);
        dax_dev->host = NULL;
        if (inode->i_rdev)
                ida_simple_remove(&dax_minor_ida, MINOR(inode->i_rdev));
        kmem_cache_free(dax_cache, dax_dev);
}

static void dax_destroy_inode(struct inode *inode)
{
        struct dax_device *dax_dev = to_dax_dev(inode);

        WARN_ONCE(test_bit(DAXDEV_ALIVE, &dax_dev->flags),
                        "kill_dax() must be called before final iput()\n");
        call_rcu(&inode->i_rcu, dax_i_callback);
}

static const struct super_operations dax_sops = {
        .statfs = simple_statfs,
        .alloc_inode = dax_alloc_inode,
        .destroy_inode = dax_destroy_inode,
        .drop_inode = generic_delete_inode,
};

static struct dentry *dax_mount(struct file_system_type *fs_type,
                int flags, const char *dev_name, void *data)
{
        return mount_pseudo(fs_type, "dax:", &dax_sops, NULL, DAXFS_MAGIC);
}

static struct file_system_type dax_fs_type = {
        .name = "dax",
        .mount = dax_mount,
        .kill_sb = kill_anon_super,
};

static int dax_test(struct inode *inode, void *data)
{
        dev_t devt = *(dev_t *) data;

        return inode->i_rdev == devt;
}

static int dax_set(struct inode *inode, void *data)
{
        dev_t devt = *(dev_t *) data;

        inode->i_rdev = devt;
        return 0;
}

static struct dax_device *dax_dev_get(dev_t devt)
{
        struct dax_device *dax_dev;
        struct inode *inode;

        inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
                        dax_test, dax_set, &devt);

        if (!inode)
                return NULL;

        dax_dev = to_dax_dev(inode);
        if (inode->i_state & I_NEW) {
                set_bit(DAXDEV_ALIVE, &dax_dev->flags);
                inode->i_cdev = &dax_dev->cdev;
                inode->i_mode = S_IFCHR;
                inode->i_flags = S_DAX;
                inode->i_mapping->backing_dev_info = &noop_backing_dev_info;
                mapping_set_gfp_mask(&inode->i_data, GFP_USER);
                unlock_new_inode(inode);
        }

        return dax_dev;
}

static void dax_add_host(struct dax_device *dax_dev, const char *host)
{
        int hash;

        /*
         * Unconditionally init dax_dev since it's coming from a
         * non-zeroed slab cache
         */
        INIT_HLIST_NODE(&dax_dev->list);
        dax_dev->host = host;
        if (!host)
                return;

        hash = dax_host_hash(host);
        spin_lock(&dax_host_lock);
        hlist_add_head(&dax_dev->list, &dax_host_list[hash]);
        spin_unlock(&dax_host_lock);
}

struct dax_device *alloc_dax(void *private, const char *__host,
                const struct dax_operations *ops)
{
        struct dax_device *dax_dev;
        const char *host;
        dev_t devt;
        int minor;

        host = kstrdup(__host, GFP_KERNEL);
        if (__host && !host)
                return NULL;

        minor = ida_simple_get(&dax_minor_ida, 0, MINORMASK+1, GFP_KERNEL);
        if (minor < 0)
                goto err_minor;

        devt = MKDEV(MAJOR(dax_devt), minor);
        dax_dev = dax_dev_get(devt);
        if (!dax_dev)
                goto err_dev;

        dax_add_host(dax_dev, host);
        dax_dev->ops = ops;
        dax_dev->private = private;
        return dax_dev;

 err_dev:
        ida_simple_remove(&dax_minor_ida, minor);
 err_minor:
        kfree(host);
        return NULL;
}
EXPORT_SYMBOL_GPL(alloc_dax);

void put_dax(struct dax_device *dax_dev)
{
        if (!dax_dev)
                return;
        iput(&dax_dev->inode);
}
EXPORT_SYMBOL_GPL(put_dax);

/**
 * dax_get_by_host() - temporary lookup mechanism for filesystem-dax
 * @host: alternate name for the device registered by a dax driver
 */
struct dax_device *dax_get_by_host(const char *host)
{
        struct dax_device *dax_dev, *found = NULL;
        int hash, id;

        if (!host)
                return NULL;

        hash = dax_host_hash(host);

        id = dax_read_lock();
        spin_lock(&dax_host_lock);
        hlist_for_each_entry(dax_dev, &dax_host_list[hash], list) {
                if (!dax_alive(dax_dev)
                                || strcmp(host, dax_dev->host) != 0)
                        continue;

                if (igrab(&dax_dev->inode))
                        found = dax_dev;
                break;
        }
        spin_unlock(&dax_host_lock);
        dax_read_unlock(id);

        return found;
}
EXPORT_SYMBOL_GPL(dax_get_by_host);

/**
 * inode_dax: convert a public inode into its dax_dev
 * @inode: An inode with i_cdev pointing to a dax_dev
 *
 * Note this is not equivalent to to_dax_dev() which is for private
 * internal use where we know the inode filesystem type == dax_fs_type.
 */
struct dax_device *inode_dax(struct inode *inode)
{
        struct cdev *cdev = inode->i_cdev;

        return container_of(cdev, struct dax_device, cdev);
}
EXPORT_SYMBOL_GPL(inode_dax);

struct inode *dax_inode(struct dax_device *dax_dev)
{
        return &dax_dev->inode;
}
EXPORT_SYMBOL_GPL(dax_inode);

void *dax_get_private(struct dax_device *dax_dev)
{
        return dax_dev->private;
}
EXPORT_SYMBOL_GPL(dax_get_private);

static void init_once(void *_dax_dev)
{
        struct dax_device *dax_dev = _dax_dev;
        struct inode *inode = &dax_dev->inode;

        memset(dax_dev, 0, sizeof(*dax_dev));
        inode_init_once(inode);
}

static int __dax_fs_init(void)
{
        int rc;

        dax_cache = kmem_cache_create("dax_cache", sizeof(struct dax_device), 0,
                        (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
                         SLAB_MEM_SPREAD),
                        init_once);
        if (!dax_cache)
                return -ENOMEM;

        rc = register_filesystem(&dax_fs_type);
        if (rc)
                goto err_register_fs;

        dax_mnt = kern_mount(&dax_fs_type);
        if (IS_ERR(dax_mnt)) {
                rc = PTR_ERR(dax_mnt);
                goto err_mount;
        }
        dax_superblock = dax_mnt->mnt_sb;

        return 0;

 err_mount:
        unregister_filesystem(&dax_fs_type);
 err_register_fs:
        kmem_cache_destroy(dax_cache);

        return rc;
}

static void __dax_fs_exit(void)
{
        kern_unmount(dax_mnt);
        unregister_filesystem(&dax_fs_type);
        kmem_cache_destroy(dax_cache);
}

static int __init dax_fs_init(void)
{
        int rc;

        rc = __dax_fs_init();
        if (rc)
                return rc;

        rc = alloc_chrdev_region(&dax_devt, 0, MINORMASK+1, "dax");
        if (rc)
                __dax_fs_exit();
        return rc;
}

static void __exit dax_fs_exit(void)
{
        unregister_chrdev_region(dax_devt, MINORMASK+1);
        ida_destroy(&dax_minor_ida);
        __dax_fs_exit();
}

MODULE_AUTHOR("Intel Corporation");
MODULE_LICENSE("GPL v2");
subsys_initcall(dax_fs_init);
module_exit(dax_fs_exit);