// 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/radix-tree.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/debugfs.h>

#include <linux/uaccess.h>

#define PAGE_SECTORS_SHIFT      (PAGE_SHIFT - SECTOR_SHIFT)
#define PAGE_SECTORS            (1 << PAGE_SECTORS_SHIFT)

/*
 * Each block ramdisk device has a radix_tree brd_pages of pages that stores
 * the pages containing the block device's contents. A brd page's ->index is
 * its offset in PAGE_SIZE units. This is similar to, but in no way connected
 * with, the kernel's pagecache or buffer cache (which sit above our block
 * device).
 */
struct brd_device {
        int                     brd_number;
        struct gendisk          *brd_disk;
        struct list_head        brd_list;

        /*
         * Backing store of pages and lock to protect it. This is the contents
         * of the block device.
         */
        spinlock_t              brd_lock;
        struct radix_tree_root  brd_pages;
        u64                     brd_nr_pages;
};

/*
 * Look up and return a brd's page for a given sector.
 */
static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
{
        pgoff_t idx;
        struct page *page;

        /*
         * The page lifetime is protected by the fact that we have opened the
         * device node -- brd pages will never be deleted under us, so we
         * don't need any further locking or refcounting.
         *
         * This is strictly true for the radix-tree nodes as well (ie. we
         * don't actually need the rcu_read_lock()), however that is not a
         * documented feature of the radix-tree API so it is better to be
         * safe here (we don't have total exclusion from radix tree updates
         * here, only deletes).
         */
        rcu_read_lock();
        idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
        page = radix_tree_lookup(&brd->brd_pages, idx);
        rcu_read_unlock();

        BUG_ON(page && page->index != idx);

        return page;
}

/*
 * Look up and return a brd's page for a given sector.
 * If one does not exist, allocate an empty page, and insert that. Then
 * return it.
 */
static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
{
        pgoff_t idx;
        struct page *page;
        gfp_t gfp_flags;

        page = brd_lookup_page(brd, sector);
        if (page)
                return page;

        /*
         * Must use NOIO because we don't want to recurse back into the
         * block or filesystem layers from page reclaim.
         */
        gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM;
        page = alloc_page(gfp_flags);
        if (!page)
                return NULL;

        if (radix_tree_preload(GFP_NOIO)) {
                __free_page(page);
                return NULL;
        }

        spin_lock(&brd->brd_lock);
        idx = sector >> PAGE_SECTORS_SHIFT;
        page->index = idx;
        if (radix_tree_insert(&brd->brd_pages, idx, page)) {
                __free_page(page);
                page = radix_tree_lookup(&brd->brd_pages, idx);
                BUG_ON(!page);
                BUG_ON(page->index != idx);
        } else {
                brd->brd_nr_pages++;
        }
        spin_unlock(&brd->brd_lock);

        radix_tree_preload_end();

        return page;
}

/*
 * Free all backing store pages and radix tree. This must only be called when
 * there are no other users of the device.
 */
#define FREE_BATCH 16
static void brd_free_pages(struct brd_device *brd)
{
        unsigned long pos = 0;
        struct page *pages[FREE_BATCH];
        int nr_pages;

        do {
                int i;

                nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
                                (void **)pages, pos, FREE_BATCH);

                for (i = 0; i < nr_pages; i++) {
                        void *ret;

                        BUG_ON(pages[i]->index < pos);
                        pos = pages[i]->index;
                        ret = radix_tree_delete(&brd->brd_pages, pos);
                        BUG_ON(!ret || ret != pages[i]);
                        __free_page(pages[i]);
                }

                pos++;

                /*
                 * It takes 3.4 seconds to remove 80GiB ramdisk.
                 * So, we need cond_resched to avoid stalling the CPU.
                 */
                cond_resched();

                /*
                 * This assumes radix_tree_gang_lookup always returns as
                 * many pages as possible. If the radix-tree code changes,
                 * so will this have to.
                 */
        } while (nr_pages == FREE_BATCH);
}

/*
 * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
 */
static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
{
        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
        size_t copy;

        copy = min_t(size_t, n, PAGE_SIZE - offset);
        if (!brd_insert_page(brd, sector))
                return -ENOSPC;
        if (copy < n) {
                sector += copy >> SECTOR_SHIFT;
                if (!brd_insert_page(brd, sector))
                        return -ENOSPC;
        }
        return 0;
}

/*
 * Copy n bytes from src to the brd starting at sector. Does not sleep.
 */
static void copy_to_brd(struct brd_device *brd, const void *src,
                        sector_t sector, size_t n)
{
        struct page *page;
        void *dst;
        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
        size_t copy;

        copy = min_t(size_t, n, PAGE_SIZE - offset);
        page = brd_lookup_page(brd, sector);
        BUG_ON(!page);

        dst = kmap_atomic(page);
        memcpy(dst + offset, src, copy);
        kunmap_atomic(dst);

        if (copy < n) {
                src += copy;
                sector += copy >> SECTOR_SHIFT;
                copy = n - copy;
                page = brd_lookup_page(brd, sector);
                BUG_ON(!page);

                dst = kmap_atomic(page);
                memcpy(dst, src, copy);
                kunmap_atomic(dst);
        }
}

/*
 * Copy n bytes to dst from the brd starting at sector. Does not sleep.
 */
static void copy_from_brd(void *dst, struct brd_device *brd,
                        sector_t sector, size_t n)
{
        struct page *page;
        void *src;
        unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
        size_t copy;

        copy = min_t(size_t, n, PAGE_SIZE - offset);
        page = brd_lookup_page(brd, sector);
        if (page) {
                src = kmap_atomic(page);
                memcpy(dst, src + offset, copy);
                kunmap_atomic(src);
        } else
                memset(dst, 0, copy);

        if (copy < n) {
                dst += copy;
                sector += copy >> SECTOR_SHIFT;
                copy = n - copy;
                page = brd_lookup_page(brd, sector);
                if (page) {
                        src = kmap_atomic(page);
                        memcpy(dst, src, copy);
                        kunmap_atomic(src);
                } else
                        memset(dst, 0, copy);
        }
}

/*
 * Process a single bvec of a bio.
 */
static int brd_do_bvec(struct brd_device *brd, struct page *page,
                        unsigned int len, unsigned int off, unsigned int op,
                        sector_t sector)
{
        void *mem;
        int err = 0;

        if (op_is_write(op)) {
                err = copy_to_brd_setup(brd, sector, len);
                if (err)
                        goto out;
        }

        mem = kmap_atomic(page);
        if (!op_is_write(op)) {
                copy_from_brd(mem + off, brd, sector, len);
                flush_dcache_page(page);
        } else {
                flush_dcache_page(page);
                copy_to_brd(brd, mem + off, sector, len);
        }
        kunmap_atomic(mem);

out:
        return err;
}

static blk_qc_t brd_submit_bio(struct bio *bio)
{
        struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;
        sector_t sector = bio->bi_iter.bi_sector;
        struct bio_vec bvec;
        struct bvec_iter iter;

        bio_for_each_segment(bvec, bio, iter) {
                unsigned int len = bvec.bv_len;
                int err;

                /* Don't support un-aligned buffer */
                WARN_ON_ONCE((bvec.bv_offset & (SECTOR_SIZE - 1)) ||
                                (len & (SECTOR_SIZE - 1)));

                err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
                                  bio_op(bio), sector);
                if (err)
                        goto io_error;
                sector += len >> SECTOR_SHIFT;
        }

        bio_endio(bio);
        return BLK_QC_T_NONE;
io_error:
        bio_io_error(bio);
        return BLK_QC_T_NONE;
}

static int brd_rw_page(struct block_device *bdev, sector_t sector,
                       struct page *page, unsigned int op)
{
        struct brd_device *brd = bdev->bd_disk->private_data;
        int err;

        if (PageTransHuge(page))
                return -ENOTSUPP;
        err = brd_do_bvec(brd, page, PAGE_SIZE, 0, op, sector);
        page_endio(page, op_is_write(op), err);
        return err;
}

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

/*
 * 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_LICENSE("GPL");
MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
MODULE_ALIAS("rd");

#ifndef MODULE
/* Legacy boot options - nonmodular */
static int __init ramdisk_size(char *str)
{
        rd_size = simple_strtol(str, NULL, 0);
        return 1;
}
__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 int brd_alloc(int i)
{
        struct brd_device *brd;
        struct gendisk *disk;
        char buf[DISK_NAME_LEN];

        brd = kzalloc(sizeof(*brd), GFP_KERNEL);
        if (!brd)
                return -ENOMEM;
        brd->brd_number         = i;
        spin_lock_init(&brd->brd_lock);
        INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);

        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(NUMA_NO_NODE);
        if (!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;
        disk->flags             = GENHD_FL_EXT_DEVT;
        strlcpy(disk->disk_name, buf, DISK_NAME_LEN);
        set_capacity(disk, rd_size * 2);
        
        /*
         * 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)
         */
        blk_queue_physical_block_size(disk->queue, PAGE_SIZE);

        /* Tell the block layer that this is not a rotational device */
        blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
        blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, disk->queue);
        add_disk(disk);
        list_add_tail(&brd->brd_list, &brd_devices);

        return 0;

out_free_dev:
        kfree(brd);
        return -ENOMEM;
}

static void brd_probe(dev_t dev)
{
        int i = MINOR(dev) / max_part;
        struct brd_device *brd;

        mutex_lock(&brd_devices_mutex);
        list_for_each_entry(brd, &brd_devices, brd_list) {
                if (brd->brd_number == i)
                        goto out_unlock;
        }

        brd_alloc(i);
out_unlock:
        mutex_unlock(&brd_devices_mutex);
}

static void brd_del_one(struct brd_device *brd)
{
        list_del(&brd->brd_list);
        del_gendisk(brd->brd_disk);
        blk_cleanup_disk(brd->brd_disk);
        brd_free_pages(brd);
        kfree(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)
{
        struct brd_device *brd, *next;
        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.
         */

        if (__register_blkdev(RAMDISK_MAJOR, "ramdisk", brd_probe))
                return -EIO;

        brd_check_and_reset_par();

        brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL);

        mutex_lock(&brd_devices_mutex);
        for (i = 0; i < rd_nr; i++) {
                err = brd_alloc(i);
                if (err)
                        goto out_free;
        }

        mutex_unlock(&brd_devices_mutex);

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

out_free:
        debugfs_remove_recursive(brd_debugfs_dir);

        list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
                brd_del_one(brd);
        mutex_unlock(&brd_devices_mutex);
        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

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

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

        debugfs_remove_recursive(brd_debugfs_dir);

        list_for_each_entry_safe(brd, next, &brd_devices, brd_list)
                brd_del_one(brd);

        unregister_blkdev(RAMDISK_MAJOR, "ramdisk");

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

module_init(brd_init);
module_exit(brd_exit);