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brd: remove dax support
DAX support in brd is awkward because its backing page frames are distinct from the ones provided by pmem, dcssblk, or axonram. We need pfn_t_devmap() entries to fully support DAX, and the limited DAX support for pfn_t_special() page frames is not interesting for brd when pmem is already a superset of brd. Lastly, brd is the only dax capable driver that may sleep in its ->direct_access() implementation. So it causes a global burden with no net gain of kernel functionality. For all these reasons, remove DAX support. Cc: Jens Axboe <axboe@kernel.dk> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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‎drivers/block/Kconfig

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Original file line numberDiff line numberDiff line change
@@ -297,7 +297,6 @@ config BLK_DEV_SX8
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config BLK_DEV_RAM
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tristate "RAM block device support"
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select DAX if BLK_DEV_RAM_DAX
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---help---
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Saying Y here will allow you to use a portion of your RAM memory as
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a block device, so that you can make file systems on it, read and
@@ -333,17 +332,6 @@ config BLK_DEV_RAM_SIZE
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The default value is 4096 kilobytes. Only change this if you know
334333
what you are doing.
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config BLK_DEV_RAM_DAX
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bool "Support Direct Access (DAX) to RAM block devices"
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depends on BLK_DEV_RAM && FS_DAX
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default n
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help
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Support filesystems using DAX to access RAM block devices. This
342-
avoids double-buffering data in the page cache before copying it
343-
to the block device. Answering Y will slightly enlarge the kernel,
344-
and will prevent RAM block device backing store memory from being
345-
allocated from highmem (only a problem for highmem systems).
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347335
config CDROM_PKTCDVD
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tristate "Packet writing on CD/DVD media (DEPRECATED)"
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depends on !UML

‎drivers/block/brd.c

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Original file line numberDiff line numberDiff line change
@@ -20,11 +20,6 @@
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#include <linux/radix-tree.h>
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#include <linux/fs.h>
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#include <linux/slab.h>
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#ifdef CONFIG_BLK_DEV_RAM_DAX
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#include <linux/pfn_t.h>
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#include <linux/dax.h>
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#include <linux/uio.h>
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#endif
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#include <linux/uaccess.h>
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@@ -44,9 +39,6 @@ struct brd_device {
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4540
struct request_queue *brd_queue;
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struct gendisk *brd_disk;
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#ifdef CONFIG_BLK_DEV_RAM_DAX
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struct dax_device *dax_dev;
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#endif
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struct list_head brd_list;
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/*
@@ -112,9 +104,6 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
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* restriction might be able to be lifted.
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*/
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gfp_flags = GFP_NOIO | __GFP_ZERO;
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#ifndef CONFIG_BLK_DEV_RAM_DAX
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gfp_flags |= __GFP_HIGHMEM;
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#endif
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page = alloc_page(gfp_flags);
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if (!page)
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return NULL;
@@ -334,43 +323,6 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector,
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return err;
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}
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#ifdef CONFIG_BLK_DEV_RAM_DAX
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static long __brd_direct_access(struct brd_device *brd, pgoff_t pgoff,
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long nr_pages, void **kaddr, pfn_t *pfn)
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{
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struct page *page;
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if (!brd)
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return -ENODEV;
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page = brd_insert_page(brd, (sector_t)pgoff << PAGE_SECTORS_SHIFT);
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if (!page)
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return -ENOSPC;
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*kaddr = page_address(page);
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*pfn = page_to_pfn_t(page);
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return 1;
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}
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static long brd_dax_direct_access(struct dax_device *dax_dev,
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pgoff_t pgoff, long nr_pages, void **kaddr, pfn_t *pfn)
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{
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struct brd_device *brd = dax_get_private(dax_dev);
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return __brd_direct_access(brd, pgoff, nr_pages, kaddr, pfn);
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}
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static size_t brd_dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
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void *addr, size_t bytes, struct iov_iter *i)
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{
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return copy_from_iter(addr, bytes, i);
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}
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static const struct dax_operations brd_dax_ops = {
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.direct_access = brd_dax_direct_access,
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.copy_from_iter = brd_dax_copy_from_iter,
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};
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#endif
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static const struct block_device_operations brd_fops = {
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.owner = THIS_MODULE,
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.rw_page = brd_rw_page,
@@ -450,21 +402,8 @@ static struct brd_device *brd_alloc(int i)
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sprintf(disk->disk_name, "ram%d", i);
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set_capacity(disk, rd_size * 2);
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453-
#ifdef CONFIG_BLK_DEV_RAM_DAX
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queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);
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brd->dax_dev = alloc_dax(brd, disk->disk_name, &brd_dax_ops);
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if (!brd->dax_dev)
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goto out_free_inode;
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#endif
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460-
461405
return brd;
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463-
#ifdef CONFIG_BLK_DEV_RAM_DAX
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out_free_inode:
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kill_dax(brd->dax_dev);
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put_dax(brd->dax_dev);
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#endif
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out_free_queue:
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blk_cleanup_queue(brd->brd_queue);
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out_free_dev:
@@ -504,10 +443,6 @@ static struct brd_device *brd_init_one(int i, bool *new)
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static void brd_del_one(struct brd_device *brd)
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{
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list_del(&brd->brd_list);
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#ifdef CONFIG_BLK_DEV_RAM_DAX
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kill_dax(brd->dax_dev);
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put_dax(brd->dax_dev);
510-
#endif
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del_gendisk(brd->brd_disk);
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brd_free(brd);
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}

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