1 files changed, 443 insertions, 0 deletions
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
new file mode 100644
index 000000000..00cc81220
--- /dev/null
+++ b/drivers/block/brd.c
@@ -0,0 +1,443 @@
+// 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);
+