// SPDX-License-Identifier: GPL-2.0-only
/*
 * Ram backed block device driver.
 *
 * Copyright (C) 2007 Nick Piggin
 * Copyright (C) 2007 Novell Inc.
 *
 * Parts derived from drivers/block/rd.c, and drivers/block/loop.c, copyright
 * of their respective owners.
 */

#include <linux/init.h>
#include <linux/initrd.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/highmem.h>
#include <linux/mutex.h>
#include <linux/pagemap.h>
#include <linux/xarray.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/debugfs.h>

#include <linux/uaccess.h>

/*
 * Each block ramdisk device has a xarray brd_pages of pages that stores
 * the pages containing the block device's contents.
 */
struct brd_device {
        int                     brd_number;
        struct gendisk          *brd_disk;
        struct list_head        brd_list;

        /*
         * Backing store of pages. This is the contents of the block device.
         */
        struct xarray           brd_pages;
        u64                     brd_nr_pages;
};

/*
 * Look up and return a brd's page with reference grabbed for a given sector.
 */
static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
{
        struct page *page;
        XA_STATE(xas, &brd->brd_pages, sector >> PAGE_SECTORS_SHIFT);

        rcu_read_lock();
repeat:
        page = xas_load(&xas);
        if (xas_retry(&xas, page)) {
                xas_reset(&xas);
                goto repeat;
        }

        if (!page)
                goto out;

        if (!get_page_unless_zero(page)) {
                xas_reset(&xas);
                goto repeat;
        }

        if (unlikely(page != xas_reload(&xas))) {
                put_page(page);
                xas_reset(&xas);
                goto repeat;
        }
out:
        rcu_read_unlock();

        return page;
}

/*
 * Insert a new page for a given sector, if one does not already exist.
 * The returned page will grab reference.
 */
static struct page *brd_insert_page(struct brd_device *brd, sector_t sector,
                blk_opf_t opf)
{
        gfp_t gfp = (opf & REQ_NOWAIT) ? GFP_NOWAIT : GFP_NOIO;
        struct page *page, *ret;

        page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
        if (!page)
                return ERR_PTR(-ENOMEM);

        xa_lock(&brd->brd_pages);
        ret = __xa_cmpxchg(&brd->brd_pages, sector >> PAGE_SECTORS_SHIFT, NULL,
                        page, gfp);
        if (!ret) {
                brd->brd_nr_pages++;
                get_page(page);
                xa_unlock(&brd->brd_pages);
                return page;
        }

        if (!xa_is_err(ret)) {
                get_page(ret);
                xa_unlock(&brd->brd_pages);
                put_page(page);
                return ret;
        }

        xa_unlock(&brd->brd_pages);
        put_page(page);
        return ERR_PTR(xa_err(ret));
}

/*
 * Free all backing store pages and xarray. This must only be called when
 * there are no other users of the device.
 */
static void brd_free_pages(struct brd_device *brd)
{
        struct page *page;
        pgoff_t idx;

        xa_for_each(&brd->brd_pages, idx, page) {
                put_page(page);
                cond_resched();
        }

        xa_destroy(&brd->brd_pages);
}

/*
 * Process a single segment.  The segment is capped to not cross page boundaries
 * in both the bio and the brd backing memory.
 */
static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
{
        struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter);
        sector_t sector = bio->bi_iter.bi_sector;
        u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;
        blk_opf_t opf = bio->bi_opf;
        struct page *page;
        void *kaddr;

        bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);

        page = brd_lookup_page(brd, sector);
        if (!page && op_is_write(opf)) {
                page = brd_insert_page(brd, sector, opf);
                if (IS_ERR(page))
                        goto out_error;
        }

        kaddr = bvec_kmap_local(&bv);
        if (op_is_write(opf)) {
                memcpy_to_page(page, offset, kaddr, bv.bv_len);
        } else {
                if (page)
                        memcpy_from_page(kaddr, page, offset, bv.bv_len);
                else
                        memset(kaddr, 0, bv.bv_len);
        }
        kunmap_local(kaddr);

        bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len);
        if (page)
                put_page(page);
        return true;

out_error:
        if (PTR_ERR(page) == -ENOMEM && (opf & REQ_NOWAIT))
                bio_wouldblock_error(bio);
        else
                bio_io_error(bio);
        return false;
}

static void brd_do_discard(struct brd_device *brd, sector_t sector, u32 size)
{
        sector_t aligned_sector = round_up(sector, PAGE_SECTORS);
        sector_t aligned_end = round_down(
                        sector + (size >> SECTOR_SHIFT), PAGE_SECTORS);
        struct page *page;

        if (aligned_end <= aligned_sector)
                return;

        xa_lock(&brd->brd_pages);
        while (aligned_sector < aligned_end && aligned_sector < rd_size * 2) {
                page = __xa_erase(&brd->brd_pages, aligned_sector >> PAGE_SECTORS_SHIFT);
                if (page) {
                        put_page(page);
                        brd->brd_nr_pages--;
                }
                aligned_sector += PAGE_SECTORS;
        }
        xa_unlock(&brd->brd_pages);
}

static void brd_submit_bio(struct bio *bio)
{
        struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;

        if (unlikely(op_is_discard(bio->bi_opf))) {
                brd_do_discard(brd, bio->bi_iter.bi_sector,
                                bio->bi_iter.bi_size);
                bio_endio(bio);
                return;
        }

        do {
                if (!brd_rw_bvec(brd, bio))
                        return;
        } while (bio->bi_iter.bi_size);

        bio_endio(bio);
}

static const struct block_device_operations brd_fops = {
        .owner =                THIS_MODULE,
        .submit_bio =           brd_submit_bio,
};

/*
 * And now the modules code and kernel interface.
 */
static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
module_param(rd_nr, int, 0444);
MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");

unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
module_param(rd_size, ulong, 0444);
MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");

static int max_part = 1;
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");

MODULE_DESCRIPTION("Ram backed block device driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
MODULE_ALIAS("rd");

#ifndef MODULE
/* Legacy boot options - nonmodular */
static int __init ramdisk_size(char *str)
{
        return kstrtoul(str, 0, &rd_size) == 0;
}
__setup("ramdisk_size=", ramdisk_size);
#endif

/*
 * The device scheme is derived from loop.c. Keep them in synch where possible
 * (should share code eventually).
 */
static LIST_HEAD(brd_devices);
static DEFINE_MUTEX(brd_devices_mutex);
static struct dentry *brd_debugfs_dir;

static struct brd_device *brd_find_or_alloc_device(int i)
{
        struct brd_device *brd;

        mutex_lock(&brd_devices_mutex);
        list_for_each_entry(brd, &brd_devices, brd_list) {
                if (brd->brd_number == i) {
                        mutex_unlock(&brd_devices_mutex);
                        return ERR_PTR(-EEXIST);
                }
        }

        brd = kzalloc_obj(*brd);
        if (!brd) {
                mutex_unlock(&brd_devices_mutex);
                return ERR_PTR(-ENOMEM);
        }
        brd->brd_number = i;
        list_add_tail(&brd->brd_list, &brd_devices);
        mutex_unlock(&brd_devices_mutex);
        return brd;
}

static void brd_free_device(struct brd_device *brd)
{
        mutex_lock(&brd_devices_mutex);
        list_del(&brd->brd_list);
        mutex_unlock(&brd_devices_mutex);
        kfree(brd);
}

static int brd_alloc(int i)
{
        struct brd_device *brd;
        struct gendisk *disk;
        char buf[DISK_NAME_LEN];
        int err = -ENOMEM;
        struct queue_limits lim = {
                /*
                 * This is so fdisk will align partitions on 4k, because of
                 * direct_access API needing 4k alignment, returning a PFN
                 * (This is only a problem on very small devices <= 4M,
                 *  otherwise fdisk will align on 1M. Regardless this call
                 *  is harmless)
                 */
                .physical_block_size    = PAGE_SIZE,
                .max_hw_discard_sectors = UINT_MAX,
                .max_discard_segments   = 1,
                .discard_granularity    = PAGE_SIZE,
                .features               = BLK_FEAT_SYNCHRONOUS |
                                          BLK_FEAT_NOWAIT,
        };

        brd = brd_find_or_alloc_device(i);
        if (IS_ERR(brd))
                return PTR_ERR(brd);

        xa_init(&brd->brd_pages);

        snprintf(buf, DISK_NAME_LEN, "ram%d", i);
        if (!IS_ERR_OR_NULL(brd_debugfs_dir))
                debugfs_create_u64(buf, 0444, brd_debugfs_dir,
                                &brd->brd_nr_pages);

        disk = brd->brd_disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
        if (IS_ERR(disk)) {
                err = PTR_ERR(disk);
                goto out_free_dev;
        }
        disk->major             = RAMDISK_MAJOR;
        disk->first_minor       = i * max_part;
        disk->minors            = max_part;
        disk->fops              = &brd_fops;
        disk->private_data      = brd;
        strscpy(disk->disk_name, buf, DISK_NAME_LEN);
        set_capacity(disk, rd_size * 2);
        
        err = add_disk(disk);
        if (err)
                goto out_cleanup_disk;

        return 0;

out_cleanup_disk:
        put_disk(disk);
out_free_dev:
        brd_free_device(brd);
        return err;
}

static void brd_probe(dev_t dev)
{
        brd_alloc(MINOR(dev) / max_part);
}

static void brd_cleanup(void)
{
        struct brd_device *brd, *next;

        debugfs_remove_recursive(brd_debugfs_dir);

        list_for_each_entry_safe(brd, next, &brd_devices, brd_list) {
                del_gendisk(brd->brd_disk);
                put_disk(brd->brd_disk);
                brd_free_pages(brd);
                brd_free_device(brd);
        }
}

static inline void brd_check_and_reset_par(void)
{
        if (unlikely(!max_part))
                max_part = 1;

        /*
         * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
         * otherwise, it is possiable to get same dev_t when adding partitions.
         */
        if ((1U << MINORBITS) % max_part != 0)
                max_part = 1UL << fls(max_part);

        if (max_part > DISK_MAX_PARTS) {
                pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
                        DISK_MAX_PARTS, DISK_MAX_PARTS);
                max_part = DISK_MAX_PARTS;
        }
}

static int __init brd_init(void)
{
        int err, i;

        /*
         * brd module now has a feature to instantiate underlying device
         * structure on-demand, provided that there is an access dev node.
         *
         * (1) if rd_nr is specified, create that many upfront. else
         *     it defaults to CONFIG_BLK_DEV_RAM_COUNT
         * (2) User can further extend brd devices by create dev node themselves
         *     and have kernel automatically instantiate actual device
         *     on-demand. Example:
         *              mknod /path/devnod_name b 1 X   # 1 is the rd major
         *              fdisk -l /path/devnod_name
         *      If (X / max_part) was not already created it will be created
         *      dynamically.
         */

        brd_check_and_reset_par();

        brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL);

        if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe)) {
                err = -EIO;
                goto out_free;
        }

        for (i = 0; i < rd_nr; i++)
                brd_alloc(i);

        pr_info("brd: module loaded\n");
        return 0;

out_free:
        brd_cleanup();

        pr_info("brd: module NOT loaded !!!\n");
        return err;
}

static void __exit brd_exit(void)
{

        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
        brd_cleanup();

        pr_info("brd: module unloaded\n");
}

module_init(brd_init);
module_exit(brd_exit);