From 055d3ecec1d9c449a8586860f570433a110f0125 Mon Sep 17 00:00:00 2001
From: David Teigland <teigland@redhat.com>
Date: Fri, 6 Sep 2019 16:20:00 -0500
Subject: io-manager: use from lvm

---
 include/Makefile.in            |   2 +-
 lib/cache/lvmcache.c           |   3 +-
 lib/device/dev-io.c            | 125 ++-----
 lib/device/dev-luks.c          |   2 +-
 lib/device/dev-md.c            |   2 +-
 lib/device/dev-swap.c          |   2 +-
 lib/device/dev-type.c          |   3 +-
 lib/device/device.h            |  10 +-
 lib/device/io-manager.c        |  27 +-
 lib/filters/filter-signature.c |   2 +-
 lib/format_text/format-text.c  |  16 +-
 lib/label/hints.c              |   1 -
 lib/label/label.c              | 754 ++++++++++++++---------------------------
 lib/label/label.h              |  12 +-
 lib/metadata/mirror.c          |   4 -
 tools/pvck.c                   |   6 +-
 16 files changed, 329 insertions(+), 642 deletions(-)

diff --git a/include/Makefile.in b/include/Makefile.in
index d6c30d15b..b82dc1667 100644
--- a/include/Makefile.in
+++ b/include/Makefile.in
@@ -24,7 +24,7 @@ CLEAN_TARGETS += \
  .symlinks_created \
  activate.h \
  archiver.h \
- bcache.h \
+ io-manager.h \
  btree.h \
  clvm.h \
  config-util.h \
diff --git a/lib/cache/lvmcache.c b/lib/cache/lvmcache.c
index 29d6446a6..e0a7b0764 100644
--- a/lib/cache/lvmcache.c
+++ b/lib/cache/lvmcache.c
@@ -913,7 +913,8 @@ int lvmcache_label_scan(struct cmd_context *cmd)
 	 * an info struct already exists in lvmcache for
 	 * the device.
 	 */
-	label_scan(cmd);
+	if (!label_scan(cmd))
+		return_0;
 
 	/*
 	 * _choose_duplicates() returns:
diff --git a/lib/device/dev-io.c b/lib/device/dev-io.c
index dd65c3d2e..6c6600672 100644
--- a/lib/device/dev-io.c
+++ b/lib/device/dev-io.c
@@ -58,13 +58,6 @@ static int _dev_get_size_file(struct device *dev, uint64_t *size)
 	const char *name = dev_name(dev);
 	struct stat info;
 
-	if (dev->size_seqno == _dev_size_seqno) {
-		log_very_verbose("%s: using cached size %" PRIu64 " sectors",
-				 name, dev->size);
-		*size = dev->size;
-		return 1;
-	}
-
 	if (stat(name, &info)) {
 		log_sys_error("stat", name);
 		return 0;
@@ -73,52 +66,12 @@ static int _dev_get_size_file(struct device *dev, uint64_t *size)
 	*size = info.st_size;
 	*size >>= SECTOR_SHIFT;	/* Convert to sectors */
 	dev->size = *size;
-	dev->size_seqno = _dev_size_seqno;
 
 	log_very_verbose("%s: size is %" PRIu64 " sectors", name, *size);
 
 	return 1;
 }
 
-static int _dev_get_size_dev(struct device *dev, uint64_t *size)
-{
-	const char *name = dev_name(dev);
-	int fd = dev->bcache_fd;
-	int do_close = 0;
-
-	if (dev->size_seqno == _dev_size_seqno) {
-		log_very_verbose("%s: using cached size %" PRIu64 " sectors",
-				 name, dev->size);
-		*size = dev->size;
-		return 1;
-	}
-
-	if (fd <= 0) {
-		if (!dev_open_readonly(dev))
-			return_0;
-		fd = dev_fd(dev);
-		do_close = 1;
-	}
-
-	if (ioctl(fd, BLKGETSIZE64, size) < 0) {
-		log_sys_error("ioctl BLKGETSIZE64", name);
-		if (do_close && !dev_close_immediate(dev))
-			log_sys_error("close", name);
-		return 0;
-	}
-
-	*size >>= BLKSIZE_SHIFT;	/* Convert to sectors */
-	dev->size = *size;
-	dev->size_seqno = _dev_size_seqno;
-
-	log_very_verbose("%s: size is %" PRIu64 " sectors", name, *size);
-
-	if (do_close && !dev_close_immediate(dev))
-		log_sys_error("close", name);
-
-	return 1;
-}
-
 static int _dev_read_ahead_dev(struct device *dev, uint32_t *read_ahead)
 {
 	long read_ahead_long;
@@ -182,55 +135,24 @@ static int _dev_discard_blocks(struct device *dev, uint64_t offset_bytes, uint64
 int dev_get_direct_block_sizes(struct device *dev, unsigned int *physical_block_size,
 				unsigned int *logical_block_size)
 {
-	int fd = dev->bcache_fd;
-	int do_close = 0;
-	unsigned int pbs = 0;
-	unsigned int lbs = 0;
-
-	if (dev->physical_block_size || dev->logical_block_size) {
-		*physical_block_size = dev->physical_block_size;
-		*logical_block_size = dev->logical_block_size;
-		return 1;
-	}
+	int put = !dev->iodev;
+	int ret = 1;
 
-	if (fd <= 0) {
-		if (!dev_open_readonly(dev))
-			return 0;
-		fd = dev_fd(dev);
-		do_close = 1;
-	}
+	if (!dev->iodev)
+		dev->iodev = io_get_dev(lvm_iom, dev_name(dev), EF_READ_ONLY);
 
-#ifdef BLKPBSZGET /* not defined before kernel version 2.6.32 (e.g. rhel5) */
-	/*
-	 * BLKPBSZGET from kernel comment for blk_queue_physical_block_size:
-	 * "the lowest possible sector size that the hardware can operate on
-	 * without reverting to read-modify-write operations"
-	 */
-	if (ioctl(fd, BLKPBSZGET, &pbs)) {
-		stack;
-		pbs = 0;
-	}
-#endif
-
-	/*
-	 * BLKSSZGET from kernel comment for blk_queue_logical_block_size:
-	 * "the lowest possible block size that the storage device can address."
-	 */
-	if (ioctl(fd, BLKSSZGET, &lbs)) {
-		stack;
-		lbs = 0;
-	}
-
-	dev->physical_block_size = pbs;
-	dev->logical_block_size = lbs;
+	if (!dev->iodev)
+		return 1;
 
-	*physical_block_size = pbs;
-	*logical_block_size = lbs;
+	if (!io_dev_block_sizes(dev->iodev, physical_block_size, logical_block_size))
+		ret = 0;
 
-	if (do_close && !dev_close_immediate(dev))
-		stack;
+	if (put) {
+		io_put_dev(dev->iodev);
+		dev->iodev = NULL;
+	}
 
-	return 1;
+	return ret;
 }
 
 /*-----------------------------------------------------------------
@@ -243,13 +165,32 @@ void dev_size_seqno_inc(void)
 
 int dev_get_size(struct device *dev, uint64_t *size)
 {
+	int put = !dev->iodev;
+	int ret = 1;
+
 	if (!dev)
 		return 0;
 
 	if ((dev->flags & DEV_REGULAR))
 		return _dev_get_size_file(dev, size);
 
-	return _dev_get_size_dev(dev, size);
+	if (!dev->iodev)
+		dev->iodev = io_get_dev(lvm_iom, dev_name(dev), EF_READ_ONLY);
+
+	if (!dev->iodev)
+		return 0;
+
+	if (!io_dev_size(dev->iodev, size))
+		ret = 0;
+	else
+		dev->size = *size;
+
+	if (put) {
+		io_put_dev(dev->iodev);
+		dev->iodev = NULL;
+	}
+
+	return ret;
 }
 
 int dev_get_read_ahead(struct device *dev, uint32_t *read_ahead)
diff --git a/lib/device/dev-luks.c b/lib/device/dev-luks.c
index 344a55432..30b6745a2 100644
--- a/lib/device/dev-luks.c
+++ b/lib/device/dev-luks.c
@@ -23,7 +23,7 @@ int dev_is_luks(struct device *dev, uint64_t *offset_found, int full)
 	char buf[LUKS_SIGNATURE_SIZE];
 	int ret = -1;
 
-	if (!scan_bcache)
+	if (!io_data_ready)
 		return -EAGAIN;
 
 	if (offset_found)
diff --git a/lib/device/dev-md.c b/lib/device/dev-md.c
index 9d0a36363..9b47746a4 100644
--- a/lib/device/dev-md.c
+++ b/lib/device/dev-md.c
@@ -134,7 +134,7 @@ static int _native_dev_is_md_component(struct device *dev, uint64_t *offset_foun
 	uint64_t size, sb_offset;
 	int ret;
 
-	if (!scan_bcache)
+	if (!io_data_ready)
 		return -EAGAIN;
 
 	if (!dev_get_size(dev, &size)) {
diff --git a/lib/device/dev-swap.c b/lib/device/dev-swap.c
index 564bb58ec..c6a500f4a 100644
--- a/lib/device/dev-swap.c
+++ b/lib/device/dev-swap.c
@@ -42,7 +42,7 @@ int dev_is_swap(struct device *dev, uint64_t *offset_found, int full)
 	unsigned page;
 	int ret = 0;
 
-	if (!scan_bcache)
+	if (!io_data_ready)
 		return -EAGAIN;
 
 	if (!dev_get_size(dev, &size)) {
diff --git a/lib/device/dev-type.c b/lib/device/dev-type.c
index ebe0f99df..d352e3340 100644
--- a/lib/device/dev-type.c
+++ b/lib/device/dev-type.c
@@ -19,7 +19,6 @@
 #include "lib/mm/xlate.h"
 #include "lib/config/config.h"
 #include "lib/metadata/metadata.h"
-#include "lib/device/bcache.h"
 #include "lib/label/label.h"
 
 #ifdef BLKID_WIPING_SUPPORT
@@ -512,7 +511,7 @@ static int _native_dev_is_partitioned(struct dev_types *dt, struct device *dev)
 {
 	int r;
 
-	if (!scan_bcache)
+	if (!io_data_ready)
 		return -EAGAIN;
 
 	if (!_is_partitionable(dt, dev))
diff --git a/lib/device/device.h b/lib/device/device.h
index bd3b35557..ab59a58e4 100644
--- a/lib/device/device.h
+++ b/lib/device/device.h
@@ -30,11 +30,8 @@
 #define DEV_USED_FOR_LV		0x00000100	/* Is device used for an LV */
 #define DEV_ASSUMED_FOR_LV	0x00000200	/* Is device assumed for an LV */
 #define DEV_NOT_O_NOATIME	0x00000400	/* Don't use O_NOATIME */
-#define DEV_IN_BCACHE		0x00000800      /* dev fd is open and used in bcache */
-#define DEV_BCACHE_EXCL		0x00001000      /* bcache_fd should be open EXCL */
 #define DEV_FILTER_AFTER_SCAN	0x00002000	/* apply filter after bcache has data */
 #define DEV_FILTER_OUT_SCAN	0x00004000	/* filtered out during label scan */
-#define DEV_BCACHE_WRITE	0x00008000      /* bcache_fd is open with RDWR */
 #define DEV_SCAN_FOUND_LABEL	0x00010000      /* label scan read dev and found label */
 #define DEV_IS_MD_COMPONENT	0x00020000	/* device is an md component */
 #define DEV_UDEV_INFO_MISSING   0x00040000	/* we have no udev info for this device */
@@ -64,15 +61,14 @@ struct device {
 	struct dm_list aliases;	/* struct dm_str_list */
 	dev_t dev;
 
+	struct io_dev *iodev; /* from io_get_dev() */
+	unsigned iom_flags;   /* last used in io_get_dev() */
+
 	/* private */
 	int fd;
 	int open_count;
-	int physical_block_size; /* From BLKPBSZGET: lowest possible sector size that the hardware can operate on without reverting to read-modify-write operations */
-	int logical_block_size;  /* From BLKSSZGET: lowest possible block size that the storage device can address */
 	int read_ahead;
-	int bcache_fd;
 	uint32_t flags;
-	unsigned size_seqno;
 	uint64_t size;
 	uint64_t end;
 	struct dev_ext ext;
diff --git a/lib/device/io-manager.c b/lib/device/io-manager.c
index e903b224d..1fd6372de 100644
--- a/lib/device/io-manager.c
+++ b/lib/device/io-manager.c
@@ -246,6 +246,18 @@ static bool _fallback_issue(struct async_engine *ae, enum dir d, int fd,
 		return false;
 	}
 
+#if 1
+        if (d == DIR_READ) {
+                log_debug("io R off %llu bytes %llu",
+                          (unsigned long long)where,
+                          (unsigned long long)len);
+        } else {
+                log_debug("io W off %llu bytes %llu",
+                          (unsigned long long)where,
+                          (unsigned long long)len);
+        }
+#endif
+
 	while (len) {
 		do {
 			if (d == DIR_READ)
@@ -256,7 +268,8 @@ static bool _fallback_issue(struct async_engine *ae, enum dir d, int fd,
 		} while ((r < 0) && ((r == EINTR) || (r == EAGAIN)));
 
 		if (r < 0) {
-			log_warn("io failed %d", r);
+			log_warn("%s failed fd %d %d errno %d",
+				 (d == DIR_READ) ? "read" : "write", fd, r, errno);
 			return false;
 		}
 
@@ -296,6 +309,18 @@ static bool _async_issue_(struct async_engine *e, enum dir d, int fd,
 	cb->cb.u.c.nbytes = (se - sb) << SECTOR_SHIFT;
 	cb->cb.aio_lio_opcode = (d == DIR_READ) ? IO_CMD_PREAD : IO_CMD_PWRITE;
 
+#if 1
+        if (d == DIR_READ) {
+                log_debug("io RA off %llu bytes %llu",
+                          (unsigned long long)cb->cb.u.c.offset,
+                          (unsigned long long)cb->cb.u.c.nbytes);
+        } else {
+                log_debug("io WA off %llu bytes %llu",
+                          (unsigned long long)cb->cb.u.c.offset,
+                          (unsigned long long)cb->cb.u.c.nbytes);
+        }
+#endif
+
 	cb_array[0] = &cb->cb;
 	do {
 		r = io_submit(e->aio_context, 1, cb_array);
diff --git a/lib/filters/filter-signature.c b/lib/filters/filter-signature.c
index 6a81203a9..bc9c70eba 100644
--- a/lib/filters/filter-signature.c
+++ b/lib/filters/filter-signature.c
@@ -27,7 +27,7 @@ static int _ignore_signature(struct cmd_context *cmd, struct dev_filter *f __att
 	char buf[BUFSIZE];
 	int ret = 0;
 
-	if (!scan_bcache) {
+	if (!io_data_ready) {
 		/* let pass, call again after scan */
 		log_debug_devs("filter signature deferred %s", dev_name(dev));
 		dev->flags |= DEV_FILTER_AFTER_SCAN;
diff --git a/lib/format_text/format-text.c b/lib/format_text/format-text.c
index 2a5c8ece1..9ace66a52 100644
--- a/lib/format_text/format-text.c
+++ b/lib/format_text/format-text.c
@@ -247,14 +247,10 @@ static int _raw_write_mda_header(const struct format_type *fmt,
 					     MDA_HEADER_SIZE -
 					     sizeof(mdah->checksum_xl)));
 
-	dev_set_last_byte(dev, start_byte + MDA_HEADER_SIZE);
-
 	if (!dev_write_bytes(dev, start_byte, MDA_HEADER_SIZE, mdah)) {
-		dev_unset_last_byte(dev);
-		log_error("Failed to write mda header to %s fd %d", dev_name(dev), dev->bcache_fd);
+		log_error("Failed to write mda header to %s", dev_name(dev));
 		return 0;
 	}
-	dev_unset_last_byte(dev);
 
 	return 1;
 }
@@ -950,8 +946,6 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 		goto out;
 	}
 
-	dev_set_last_byte(mdac->area.dev, mda_start + mdah->size);
-
 	log_debug_metadata("VG %s %u metadata write at %llu size %llu (wrap %llu)", 
 			   vg->name, vg->seqno,
 			   (unsigned long long)write1_start,
@@ -959,8 +953,7 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 			   (unsigned long long)write2_size);
 
 	if (!dev_write_bytes(mdac->area.dev, write1_start, (size_t)write1_size, write_buf)) {
-		log_error("Failed to write metadata to %s fd %d", devname, mdac->area.dev->bcache_fd);
-		dev_unset_last_byte(mdac->area.dev);
+		log_error("Failed to write metadata to %s", devname);
 		goto out;
 	}
 
@@ -972,14 +965,11 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 
 		if (!dev_write_bytes(mdac->area.dev, write2_start, write2_size,
 				     write_buf + new_size - new_wrap)) {
-			log_error("Failed to write metadata wrap to %s fd %d", devname, mdac->area.dev->bcache_fd);
-			dev_unset_last_byte(mdac->area.dev);
+			log_error("Failed to write metadata wrap to %s", devname);
 			goto out;
 		}
 	}
 
-	dev_unset_last_byte(mdac->area.dev);
-
 	rlocn_new->checksum = calc_crc(INITIAL_CRC,
 				       (uint8_t *)write_buf,
 				       (uint32_t)(new_size - new_wrap));
diff --git a/lib/label/hints.c b/lib/label/hints.c
index 6510fcf74..b87ab317c 100644
--- a/lib/label/hints.c
+++ b/lib/label/hints.c
@@ -141,7 +141,6 @@
 #include "lib/misc/crc.h"
 #include "lib/mm/xlate.h"
 #include "lib/cache/lvmcache.h"
-#include "lib/device/bcache.h"
 #include "lib/commands/toolcontext.h"
 #include "lib/activate/activate.h"
 #include "lib/label/hints.h"
diff --git a/lib/label/label.c b/lib/label/label.c
index fe59394b0..7673d0347 100644
--- a/lib/label/label.c
+++ b/lib/label/label.c
@@ -19,7 +19,7 @@
 #include "lib/misc/crc.h"
 #include "lib/mm/xlate.h"
 #include "lib/cache/lvmcache.h"
-#include "lib/device/bcache.h"
+#include "lib/device/io-manager.h"
 #include "lib/commands/toolcontext.h"
 #include "lib/activate/activate.h"
 #include "lib/label/hints.h"
@@ -31,9 +31,73 @@
 #include <sys/types.h>
 #include <sys/resource.h>
 
-/* FIXME Allow for larger labels?  Restricted to single sector currently */
+int io_data_ready;
 
-static uint64_t _current_bcache_size_bytes;
+static uint64_t _current_io_size_bytes;
+
+static int _get_dev(struct device *dev, unsigned flags)
+{
+	if (dev->iodev) {
+		if (flags == dev->iom_flags)
+			return 1;
+
+		/* currently writable, want to read */
+		if ((flags & EF_READ_ONLY) && !dev->iom_flags)
+			return 1;
+
+		/* currently excl, want to read */
+		if ((flags & EF_READ_ONLY) && (dev->iom_flags & EF_EXCL))
+			return 1;
+
+		/* currently excl, want to write */
+		if (!flags && (dev->iom_flags & EF_EXCL))
+			return 1;
+
+		/* currently readonly, want to write */
+		if (!flags && (dev->iom_flags & EF_READ_ONLY)) {
+			log_print("dev reopen for writing %s", dev_name(dev));
+			io_put_dev(dev->iodev);
+			dev->iom_flags = 0;
+			goto get;
+		}
+
+		/* currently non-excl, want excl */
+		if ((flags & EF_EXCL) && !(dev->iom_flags & EF_EXCL)) {
+			log_print("dev reopen excl %s", dev_name(dev));
+			io_put_dev(dev->iodev);
+			dev->iom_flags = 0;
+			goto get;
+		}
+
+		/* Can this happen? */
+		log_print("dev reopen flags %x iom_flags %x %s", flags, dev->iom_flags, dev_name(dev));
+		io_put_dev(dev->iodev);
+		dev->iom_flags = 0;
+	}
+get:
+	dev->iodev = io_get_dev(lvm_iom, dev_name(dev), flags);
+
+	if (!dev->iodev) {
+		log_error("No io device available %s", dev_name(dev));
+		return 0;
+	}
+
+	dev->iom_flags = flags;
+
+	return 1;
+}
+
+static void _put_dev(struct device *dev)
+{
+	if (!dev->iodev) {
+		log_error("put_dev no iodev %s", dev_name(dev));
+		return;
+	}
+
+	io_put_dev(dev->iodev);
+	dev->iodev = NULL;
+	dev->iom_flags = 0;
+}
 
 /*
  * Internal labeller struct.
@@ -119,7 +183,7 @@ int label_remove(struct device *dev)
 
 	log_very_verbose("Scanning for labels to wipe from %s", dev_name(dev));
 
-	if (!label_scan_open_excl(dev)) {
+	if (!_get_dev(dev, EF_EXCL)) {
 		log_error("Failed to open device %s", dev_name(dev));
 		return 0;
 	}
@@ -169,6 +233,7 @@ int label_remove(struct device *dev)
 		}
 	}
 
+	_put_dev(dev);
 	return r;
 }
 
@@ -207,22 +272,19 @@ int label_write(struct device *dev, struct label *label)
 			 PRIu32 ".", dev_name(dev), label->sector,
 			 xlate32(lh->offset_xl));
 
-	if (!label_scan_open(dev)) {
+	if (!_get_dev(dev, 0)) {
 		log_error("Failed to open device %s", dev_name(dev));
 		return 0;
 	}
 
 	offset = label->sector << SECTOR_SHIFT;
 
-	dev_set_last_byte(dev, offset + LABEL_SIZE);
-
 	if (!dev_write_bytes(dev, offset, LABEL_SIZE, buf)) {
 		log_debug_devs("Failed to write label to %s", dev_name(dev));
 		r = 0;
 	}
 
-	dev_unset_last_byte(dev);
-
+	_put_dev(dev);
 	return r;
 }
 
@@ -249,17 +311,10 @@ struct label *label_create(struct labeller *labeller)
 }
 
 
-/* global variable for accessing the bcache populated by label scan */
-struct bcache *scan_bcache;
+/* global variable for accessing the io-manager populated by label scan */
+struct io_manager *lvm_iom;
 
-#define BCACHE_BLOCK_SIZE_IN_SECTORS 256 /* 256*512 = 128K */
-
-static bool _in_bcache(struct device *dev)
-{
-	if (!dev)
-		return NULL;
-	return (dev->flags & DEV_IN_BCACHE) ? true : false;
-}
+#define IOM_BLOCK_SIZE_IN_SECTORS 64 /* 64*512 = 32K */
 
 static struct labeller *_find_lvm_header(struct device *dev,
 				   char *scan_buf,
@@ -284,8 +339,8 @@ static struct labeller *_find_lvm_header(struct device *dev,
 	     sector += LABEL_SIZE >> SECTOR_SHIFT) {
 
 		/*
-		 * The scan_buf passed in is a bcache block, which is
-		 * BCACHE_BLOCK_SIZE_IN_SECTORS large.  So if start_sector is
+		 * The scan_buf passed in is a iom block, which is
+		 * IOM_BLOCK_SIZE_IN_SECTORS large.  So if start_sector is
 		 * one of the last couple sectors in that buffer, we need to
 		 * break early.
 		 */
@@ -367,8 +422,8 @@ static int _process_block(struct cmd_context *cmd, struct dev_filter *f,
 
 	/*
 	 * The device may have signatures that exclude it from being processed.
-	 * If filters were applied before bcache data was available, some
-	 * filters may have deferred their check until the point where bcache
+	 * If filters were applied before iom data was available, some
+	 * filters may have deferred their check until the point where iom
 	 * data had been read (here).  They set this flag to indicate that the
 	 * filters should be retested now that data from the device is ready.
 	 */
@@ -401,7 +456,7 @@ static int _process_block(struct cmd_context *cmd, struct dev_filter *f,
 	 * FIXME: we don't need to copy one sector from bb->data into label_buf,
 	 * we can just point label_buf at one sector in ld->buf.
 	 */
-	if (!(labeller = _find_lvm_header(dev, bb->data, BCACHE_BLOCK_SIZE_IN_SECTORS, label_buf, &sector, block_sector, start_sector))) {
+	if (!(labeller = _find_lvm_header(dev, bb->data, IOM_BLOCK_SIZE_IN_SECTORS, label_buf, &sector, block_sector, start_sector))) {
 
 		/*
 		 * Non-PVs exit here
@@ -461,165 +516,6 @@ static int _process_block(struct cmd_context *cmd, struct dev_filter *f,
 	return ret;
 }
 
-static int _scan_dev_open(struct device *dev)
-{
-	struct dm_list *name_list;
-	struct dm_str_list *name_sl;
-	const char *name;
-	struct stat sbuf;
-	int retried = 0;
-	int flags = 0;
-	int fd;
-
-	if (!dev)
-		return 0;
-
-	if (dev->flags & DEV_IN_BCACHE) {
-		/* Shouldn't happen */
-		log_error("Device open %s has DEV_IN_BCACHE already set", dev_name(dev));
-		dev->flags &= ~DEV_IN_BCACHE;
-	}
-
-	if (dev->bcache_fd > 0) {
-		/* Shouldn't happen */
-		log_error("Device open %s already open with fd %d",
-			  dev_name(dev), dev->bcache_fd);
-		return 0;
-	}
-
-	/*
-	 * All the names for this device (major:minor) are kept on
-	 * dev->aliases, the first one is the primary/preferred name.
-	 */
-	if (!(name_list = dm_list_first(&dev->aliases))) {
-		/* Shouldn't happen */
-		log_error("Device open %s %d:%d has no path names.",
-			  dev_name(dev), (int)MAJOR(dev->dev), (int)MINOR(dev->dev));
-		return 0;
-	}
-	name_sl = dm_list_item(name_list, struct dm_str_list);
-	name = name_sl->str;
-
-	flags |= O_DIRECT;
-	flags |= O_NOATIME;
-
-	/*
-	 * FIXME: udev is a train wreck when we open RDWR and close, so we
-	 * need to only use RDWR when we actually need to write, and use
-	 * RDONLY otherwise.  Fix, disable or scrap udev nonsense so we can
-	 * just open with RDWR by default.
-	 */
-
-	if (dev->flags & DEV_BCACHE_EXCL) {
-		flags |= O_EXCL;
-		flags |= O_RDWR;
-	} else if (dev->flags & DEV_BCACHE_WRITE) {
-		flags |= O_RDWR;
-	} else {
-		flags |= O_RDONLY;
-	}
-
-retry_open:
-
-	fd = open(name, flags, 0777);
-
-	if (fd < 0) {
-		if ((errno == EBUSY) && (flags & O_EXCL)) {
-			log_error("Can't open %s exclusively.  Mounted filesystem?",
-				  dev_name(dev));
-		} else {
-			int major, minor;
-
-			/*
-			 * Shouldn't happen, if it does, print stat info to help figure
-			 * out what's wrong.
-			 */
-
-			major = (int)MAJOR(dev->dev);
-			minor = (int)MINOR(dev->dev);
-
-			log_error("Device open %s %d:%d failed errno %d", name, major, minor, errno);
-
-			if (stat(name, &sbuf)) {
-				log_debug_devs("Device open %s %d:%d stat failed errno %d",
-					       name, major, minor, errno);
-			} else if (sbuf.st_rdev != dev->dev) {
-				log_debug_devs("Device open %s %d:%d stat %d:%d does not match.",
-					       name, major, minor,
-					       (int)MAJOR(sbuf.st_rdev), (int)MINOR(sbuf.st_rdev));
-			}
-
-			if (!retried) {
-				/*
-				 * FIXME: remove this, the theory for this retry is that
-				 * there may be a udev race that we can sometimes mask by
-				 * retrying.  This is here until we can figure out if it's
-				 * needed and if so fix the real problem.
-				 */
-				usleep(5000);
-				log_debug_devs("Device open %s retry", dev_name(dev));
-				retried = 1;
-				goto retry_open;
-			}
-		}
-		return 0;
-	}
-
-	dev->flags |= DEV_IN_BCACHE;
-	dev->bcache_fd = fd;
-	return 1;
-}
-
-static int _scan_dev_close(struct device *dev)
-{
-	if (!(dev->flags & DEV_IN_BCACHE))
-		log_error("scan_dev_close %s no DEV_IN_BCACHE set", dev_name(dev));
-
-	dev->flags &= ~DEV_IN_BCACHE;
-	dev->flags &= ~DEV_BCACHE_EXCL;
-
-	if (dev->bcache_fd < 0) {
-		log_error("scan_dev_close %s already closed", dev_name(dev));
-		return 0;
-	}
-
-	if (close(dev->bcache_fd))
-		log_warn("close %s errno %d", dev_name(dev), errno);
-	dev->bcache_fd = -1;
-	return 1;
-}
-
-static void _drop_bad_aliases(struct device *dev)
-{
-	struct dm_str_list *strl, *strl2;
-	const char *name;
-	struct stat sbuf;
-	int major = (int)MAJOR(dev->dev);
-	int minor = (int)MINOR(dev->dev);
-	int bad;
-
-	dm_list_iterate_items_safe(strl, strl2, &dev->aliases) {
-		name = strl->str;
-		bad = 0;
-
-		if (stat(name, &sbuf)) {
-			bad = 1;
-			log_debug_devs("Device path check %d:%d %s stat failed errno %d",
-					major, minor, name, errno);
-		} else if (sbuf.st_rdev != dev->dev) {
-			bad = 1;
-			log_debug_devs("Device path check %d:%d %s stat %d:%d does not match.",
-				       major, minor, name,
-				       (int)MAJOR(sbuf.st_rdev), (int)MINOR(sbuf.st_rdev));
-		}
-
-		if (bad) {
-			log_debug_devs("Device path check %d:%d dropping path %s.", major, minor, name);
-			dev_cache_failed_path(dev, name);
-		}
-	}
-}
-
 /*
  * Read or reread label/metadata from selected devs.
  *
@@ -639,7 +535,6 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 	struct dm_list reopen_devs;
 	struct device_list *devl, *devl2;
 	struct block *bb;
-	int retried_open = 0;
 	int scan_read_errors = 0;
 	int scan_process_errors = 0;
 	int scan_failed_count = 0;
@@ -657,7 +552,7 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 	log_debug_devs("Scanning %d devices for VG info", dm_list_size(devs));
 
  scan_more:
-	rem_prefetches = bcache_max_prefetches(scan_bcache);
+	rem_prefetches = io_max_prefetches(lvm_iom);
 	submit_count = 0;
 
 	dm_list_iterate_items_safe(devl, devl2, devs) {
@@ -672,16 +567,17 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 		if (!rem_prefetches)
 			break;
 
-		if (!_in_bcache(devl->dev)) {
-			if (!_scan_dev_open(devl->dev)) {
-				log_debug_devs("Scan failed to open %s.", dev_name(devl->dev));
-				dm_list_del(&devl->list);
-				dm_list_add(&reopen_devs, &devl->list);
-				continue;
-			}
-		}
+		if (!_get_dev(devl->dev, EF_READ_ONLY))
+			break;
 
-		bcache_prefetch(scan_bcache, devl->dev->bcache_fd, 0);
+		/*
+		 * Prefetch the first block of the disk which holds the label
+		 * and pv header, the mda header, and some the metadata text
+		 * (if current metadata text is further into the metadata area,
+		 * it will not be in this block and will require reading another
+		 * block or more later.)
+		 */
+		io_prefetch_block(lvm_iom, devl->dev->iodev, 0);
 
 		rem_prefetches--;
 		submit_count++;
@@ -698,18 +594,18 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 		scan_failed = 0;
 		is_lvm_device = 0;
 
-		if (!bcache_get(scan_bcache, devl->dev->bcache_fd, 0, 0, &bb)) {
+		if (!io_get_block(lvm_iom, devl->dev->iodev, 0, 0, &bb)) {
 			log_debug_devs("Scan failed to read %s error %d.", dev_name(devl->dev), error);
 			scan_failed = 1;
 			scan_read_errors++;
 			scan_failed_count++;
 			lvmcache_del_dev(devl->dev);
 		} else {
-			log_debug_devs("Processing data from device %s %d:%d fd %d block %p",
+			log_debug_devs("Processing data from device %s %d:%d block %p",
 				       dev_name(devl->dev),
 				       (int)MAJOR(devl->dev->dev),
 				       (int)MINOR(devl->dev->dev),
-				       devl->dev->bcache_fd, bb);
+				       bb);
 
 			ret = _process_block(cmd, f, devl->dev, bb, 0, 0, &is_lvm_device);
 
@@ -722,18 +618,27 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 		}
 
 		if (bb)
-			bcache_put(bb);
+			io_put_block(bb);
 
 		/*
-		 * Keep the bcache block of lvm devices we have processed so
-		 * that the vg_read phase can reuse it.  If bcache failed to
-		 * read the block, or the device does not belong to lvm, then
-		 * drop it from bcache.
+		 * If iom failed to read the block, or the device does not
+		 * belong to lvm, then drop it from iom.
 		 */
-		if (scan_failed || !is_lvm_device) {
-			bcache_invalidate_fd(scan_bcache, devl->dev->bcache_fd);
-			_scan_dev_close(devl->dev);
-		}
+		if (scan_failed || !is_lvm_device)
+			io_invalidate_dev(lvm_iom, devl->dev->iodev);
+
+		/*
+		 * Allow io manager to drop this dev (close the fd and
+		 * invalidate the cached block) if needed due to a full cache.
+		 * If the common case, the cache should not be full and fds do
+		 * not reach the max, so the dev will remain open in iomanager
+		 * and the block we've read will remain cached, and when
+		 * vg_read() comes to reading the metadata again, no new open
+		 * or read will be needed.  In the uncommon case, vg_read()
+		 * will trigger a new open() and rereading the data from disk.
+		 */
+		io_put_dev(devl->dev->iodev);
+		devl->dev->iodev = NULL;
 
 		dm_list_del(&devl->list);
 		dm_list_add(&done_devs, &devl->list);
@@ -742,51 +647,6 @@ static int _scan_list(struct cmd_context *cmd, struct dev_filter *f,
 	if (!dm_list_empty(devs))
 		goto scan_more;
 
-	/*
-	 * We're done scanning all the devs.  If we failed to open any of them
-	 * the first time through, refresh device paths and retry.  We failed
-	 * to open the devs on the reopen_devs list.
-	 *
-	 * FIXME: it's not clear if or why this helps.
-	 */
-	if (!dm_list_empty(&reopen_devs)) {
-		if (retried_open) {
-			/* Don't try again. */
-			scan_failed_count += dm_list_size(&reopen_devs);
-			dm_list_splice(&done_devs, &reopen_devs);
-			goto out;
-		}
-		retried_open = 1;
-
-		dm_list_iterate_items_safe(devl, devl2, &reopen_devs) {
-			_drop_bad_aliases(devl->dev);
-
-			if (dm_list_empty(&devl->dev->aliases)) {
-				log_warn("WARNING: Scan ignoring device %d:%d with no paths.",
-					 (int)MAJOR(devl->dev->dev),
-					 (int)MINOR(devl->dev->dev));
-					 
-				dm_list_del(&devl->list);
-				lvmcache_del_dev(devl->dev);
-				scan_failed_count++;
-			}
-		}
-
-		/*
-		 * This will search the system's /dev for new path names and
-		 * could help us reopen the device if it finds a new preferred
-		 * path name for this dev's major:minor.  It does that by
-		 * inserting a new preferred path name on dev->aliases.  open
-		 * uses the first name from that list.
-		 */
-		log_debug_devs("Scanning refreshing device paths.");
-		dev_cache_scan();
-
-		/* Put devs that failed to open back on the original list to retry. */
-		dm_list_splice(devs, &reopen_devs);
-		goto scan_more;
-	}
-out:
 	log_debug_devs("Scanned devices: read errors %d process errors %d failed %d",
 			scan_read_errors, scan_process_errors, scan_failed_count);
 
@@ -800,50 +660,52 @@ out:
 
 /*
  * We don't know ahead of time if we will find some VG metadata 
- * that is larger than the total size of the bcache, which would
+ * that is larger than the total size of the iom, which would
  * prevent us from reading/writing the VG since we do not dynamically
- * increase the bcache size when we find it's too small.  In these
+ * increase the iom size when we find it's too small.  In these
  * cases the user would need to set io_memory_size to be larger
  * than the max VG metadata size (lvm does not impose any limit on
  * the metadata size.)
  */
 
-#define MIN_BCACHE_BLOCKS 32    /* 4MB (32 * 128KB) */
-#define MAX_BCACHE_BLOCKS 4096  /* 512MB (4096 * 128KB) */
+#define MIN_IOM_BLOCKS 32    /* 4MB (128 * 32KB) */
+#define MAX_IOM_BLOCKS 16384 /* 512MB (16384 * 32KB) */
 
-static int _setup_bcache(void)
+#define IOM_MAX_DEVS 4096
+
+static int _setup_io_manager(void)
 {
-	struct io_engine_ *ioe = NULL;
+	struct io_engine *ioe = NULL;
 	int iomem_kb = io_memory_size();
-	int block_size_kb = (BCACHE_BLOCK_SIZE_IN_SECTORS * 512) / 1024;
+	int block_size_kb = (IOM_BLOCK_SIZE_IN_SECTORS * 512) / 1024;
 	int cache_blocks;
 
 	cache_blocks = iomem_kb / block_size_kb;
 
-	if (cache_blocks < MIN_BCACHE_BLOCKS)
-		cache_blocks = MIN_BCACHE_BLOCKS;
+	if (cache_blocks < MIN_IOM_BLOCKS)
+		cache_blocks = MIN_IOM_BLOCKS;
 
-	if (cache_blocks > MAX_BCACHE_BLOCKS)
-		cache_blocks = MAX_BCACHE_BLOCKS;
+	if (cache_blocks > MAX_IOM_BLOCKS)
+		cache_blocks = MAX_IOM_BLOCKS;
 
-	_current_bcache_size_bytes = cache_blocks * BCACHE_BLOCK_SIZE_IN_SECTORS * 512;
+	_current_io_size_bytes = cache_blocks * IOM_BLOCK_SIZE_IN_SECTORS * 512;
 
 	if (use_aio()) {
-		if (!(ioe = create_async_io_engine_())) {
+		if (!(ioe = create_async_io_engine(true))) {
 			log_warn("Failed to set up async io, using sync io.");
 			init_use_aio(0);
 		}
 	}
 
 	if (!ioe) {
-		if (!(ioe = create_sync_io_engine_())) {
+		if (!(ioe = create_sync_io_engine(true))) {
 			log_error("Failed to set up sync io.");
 			return 0;
 		}
 	}
 
-	if (!(scan_bcache = bcache_create(BCACHE_BLOCK_SIZE_IN_SECTORS, cache_blocks, ioe))) {
-		log_error("Failed to create bcache with %d cache blocks.", cache_blocks);
+	if (!(lvm_iom = io_manager_create(IOM_BLOCK_SIZE_IN_SECTORS, cache_blocks, IOM_MAX_DEVS, ioe))) {
+		log_error("Failed to create io-manager with %d cache blocks.", cache_blocks);
 		return 0;
 	}
 
@@ -939,6 +801,14 @@ int label_scan(struct cmd_context *cmd)
 	dm_list_init(&scan_devs);
 	dm_list_init(&hints_list);
 
+	if (lvm_iom)
+		io_invalidate_all(lvm_iom);
+
+	if (!lvm_iom) {
+		if (!_setup_io_manager())
+			return 0;
+	}
+
 	/*
 	 * dev_cache_scan() creates a list of devices on the system
 	 * (saved in in dev-cache) which we can iterate through to
@@ -990,23 +860,9 @@ int label_scan(struct cmd_context *cmd)
 			continue;
 		devl->dev = dev;
 		dm_list_add(&all_devs, &devl->list);
-
-		/*
-		 * label_scan should not generally be called a second time,
-		 * so this will usually not be true.
-		 */
-		if (_in_bcache(dev)) {
-			bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-			_scan_dev_close(dev);
-		}
 	};
 	dev_iter_destroy(iter);
 
-	if (!scan_bcache) {
-		if (!_setup_bcache())
-			return 0;
-	}
-
 	/*
 	 * In some common cases we can avoid scanning all devices
 	 * by using hints which tell us which devices are PVs, which
@@ -1039,35 +895,37 @@ int label_scan(struct cmd_context *cmd)
 	 */
 	_prepare_open_file_limit(cmd, dm_list_size(&scan_devs));
 
+	io_data_ready = 1;
+
 	/*
 	 * Do the main scan.
 	 */
 	_scan_list(cmd, cmd->filter, &scan_devs, NULL);
 
 	/*
-	 * Metadata could be larger than total size of bcache, and bcache
+	 * Metadata could be larger than total size of iom, and iom 
 	 * cannot currently be resized during the command.  If this is the
 	 * case (or within reach), warn that io_memory_size needs to be
 	 * set larger.
 	 *
-	 * Even if bcache out of space did not cause a failure during scan, it
+	 * Even if iom out of space did not cause a failure during scan, it
 	 * may cause a failure during the next vg_read phase or during vg_write.
 	 *
-	 * If there was an error during scan, we could recreate bcache here
+	 * If there was an error during scan, we could recreate iom here
 	 * with a larger size and then restart label_scan.  But, this does not
-	 * address the problem of writing new metadata that excedes the bcache
+	 * address the problem of writing new metadata that excedes the iom
 	 * size and failing, which would often be hit first, i.e. we'll fail
 	 * to write new metadata exceding the max size before we have a chance
 	 * to read any metadata with that size, unless we find an existing vg
 	 * that has been previously created with the larger size.
 	 *
-	 * If the largest metadata is within 1MB of the bcache size, then start
+	 * If the largest metadata is within 1MB of the iom size, then start
 	 * warning.
 	 */
 	max_metadata_size_bytes = lvmcache_max_metadata_size();
 
-	if (max_metadata_size_bytes + (1024 * 1024) > _current_bcache_size_bytes) {
-		/* we want bcache to be 1MB larger than the max metadata seen */
+	if (max_metadata_size_bytes + (1024 * 1024) > _current_io_size_bytes) {
+		/* we want io-manager to be 1MB larger than the max metadata seen */
 		uint64_t want_size_kb = (max_metadata_size_bytes / 1024) + 1024;
 		uint64_t remainder;
 		if ((remainder = (want_size_kb % 1024)))
@@ -1154,7 +1012,7 @@ int label_scan(struct cmd_context *cmd)
  * Scan and cache lvm data from the listed devices.  If a device is already
  * scanned and cached, this replaces the previously cached lvm data for the
  * device.  This is called when vg_read() wants to guarantee that it is using
- * the latest data from the devices in the VG (since the scan populated bcache
+ * the latest data from the devices in the VG (since the scan populated iom
  * without a lock.)
  */
 
@@ -1162,16 +1020,16 @@ int label_scan_devs(struct cmd_context *cmd, struct dev_filter *f, struct dm_lis
 {
 	struct device_list *devl;
 
-	if (!scan_bcache) {
-		if (!_setup_bcache())
+	if (!lvm_iom) {
+		if (!_setup_io_manager())
 			return 0;
 	}
 
 	dm_list_iterate_items(devl, devs) {
-		if (_in_bcache(devl->dev)) {
-			bcache_invalidate_fd(scan_bcache, devl->dev->bcache_fd);
-			_scan_dev_close(devl->dev);
-		}
+		if (!_get_dev(devl->dev, EF_READ_ONLY))
+			continue;
+
+		io_invalidate_dev(lvm_iom, devl->dev->iodev);
 	}
 
 	_scan_list(cmd, f, devs, NULL);
@@ -1189,21 +1047,16 @@ int label_scan_devs_rw(struct cmd_context *cmd, struct dev_filter *f, struct dm_
 {
 	struct device_list *devl;
 
-	if (!scan_bcache) {
-		if (!_setup_bcache())
+	if (!lvm_iom) {
+		if (!_setup_io_manager())
 			return 0;
 	}
 
 	dm_list_iterate_items(devl, devs) {
-		if (_in_bcache(devl->dev)) {
-			bcache_invalidate_fd(scan_bcache, devl->dev->bcache_fd);
-			_scan_dev_close(devl->dev);
-		}
-		/*
-		 * With this flag set, _scan_dev_open() done by
-		 * _scan_list() will do open RW
-		 */
-		devl->dev->flags |= DEV_BCACHE_WRITE;
+		if (!_get_dev(devl->dev, 0))
+			continue;
+
+		io_invalidate_dev(lvm_iom, devl->dev->iodev);
 	}
 
 	_scan_list(cmd, f, devs, NULL);
@@ -1217,15 +1070,10 @@ int label_scan_devs_excl(struct dm_list *devs)
 	int failed = 0;
 
 	dm_list_iterate_items(devl, devs) {
-		if (_in_bcache(devl->dev)) {
-			bcache_invalidate_fd(scan_bcache, devl->dev->bcache_fd);
-			_scan_dev_close(devl->dev);
-		}
-		/*
-		 * With this flag set, _scan_dev_open() done by
-		 * _scan_list() will do open EXCL
-		 */
-		devl->dev->flags |= DEV_BCACHE_EXCL;
+		if (!_get_dev(devl->dev, EF_EXCL))
+			continue;
+
+		io_invalidate_dev(lvm_iom, devl->dev->iodev);
 	}
 
 	_scan_list(NULL, NULL, devs, &failed);
@@ -1237,15 +1085,15 @@ int label_scan_devs_excl(struct dm_list *devs)
 
 void label_scan_invalidate(struct device *dev)
 {
-	if (_in_bcache(dev)) {
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-	}
+	if (!_get_dev(dev, EF_READ_ONLY))
+		return;
+	io_invalidate_dev(lvm_iom, dev->iodev);
+	_put_dev(dev);
 }
 
 /*
  * If a PV is stacked on an LV, then the LV is kept open
- * in bcache, and needs to be closed so the open fd doesn't
+ * in iom, and needs to be closed so the open fd doesn't
  * interfere with processing the LV.
  */
 
@@ -1264,44 +1112,34 @@ void label_scan_invalidate_lv(struct cmd_context *cmd, struct logical_volume *lv
 }
 
 /*
- * Empty the bcache of all blocks and close all open fds,
- * but keep the bcache set up.
+ * Empty the iom of all blocks and close all open fds,
+ * but keep the iom set up.
  */
 
 void label_scan_drop(struct cmd_context *cmd)
 {
-	struct dev_iter *iter;
-	struct device *dev;
-
-	if (!(iter = dev_iter_create(NULL, 0)))
-		return;
-
-	while ((dev = dev_iter_get(cmd, iter))) {
-		if (_in_bcache(dev))
-			_scan_dev_close(dev);
-	}
-	dev_iter_destroy(iter);
+	if (lvm_iom)
+		io_invalidate_all(lvm_iom);
 }
 
 /*
- * Close devices that are open because bcache is holding blocks for them.
- * Destroy the bcache.
+ * Close devices that are open because iom is holding blocks for them.
+ * Destroy the iom.
  */
 
 void label_scan_destroy(struct cmd_context *cmd)
 {
-	if (!scan_bcache)
+	if (!lvm_iom)
 		return;
 
-	label_scan_drop(cmd);
-
-	bcache_destroy(scan_bcache);
-	scan_bcache = NULL;
+	io_invalidate_all(lvm_iom);
+	io_manager_destroy(lvm_iom);
+	lvm_iom = NULL;
 }
 
 /*
  * Read (or re-read) and process (or re-process) the data for a device.  This
- * will reset (clear and repopulate) the bcache and lvmcache info for this
+ * will reset (clear and repopulate) the iom and lvmcache info for this
  * device.  There are only a couple odd places that want to reread a specific
  * device, this is not a commonly used function.
  */
@@ -1319,11 +1157,13 @@ int label_read(struct device *dev)
 	dm_list_init(&one_dev);
 	dm_list_add(&one_dev, &devl->list);
 
-	if (_in_bcache(dev)) {
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
+	if (!_get_dev(dev, EF_READ_ONLY)) {
+		log_error("No io device available for %s", dev_name(devl->dev));
+		return 0;
 	}
 
+	io_invalidate_dev(lvm_iom, dev->iodev);
+
 	_scan_list(NULL, NULL, &one_dev, &failed);
 
 	free(devl);
@@ -1333,264 +1173,166 @@ int label_read(struct device *dev)
 	return 1;
 }
 
-int label_scan_setup_bcache(void)
+int label_scan_setup_io_manager(void)
 {
-	if (!scan_bcache) {
-		if (!_setup_bcache())
+	if (!lvm_iom) {
+		if (!_setup_io_manager())
 			return 0;
 	}
 
 	return 1;
 }
 
-/*
- * This is needed to write to a new non-lvm device.
- * Scanning that dev would not keep it open or in
- * bcache, but to use bcache_write we need the dev
- * to be open so we can use dev->bcache_fd to write.
- */
-
+/* FIXME: probably not needed, read will do it */
 int label_scan_open(struct device *dev)
 {
-	if (!_in_bcache(dev))
-		return _scan_dev_open(dev);
-	return 1;
+	return _get_dev(dev, EF_READ_ONLY);
 }
 
 int label_scan_open_excl(struct device *dev)
 {
-	if (_in_bcache(dev) && !(dev->flags & DEV_BCACHE_EXCL)) {
-		/* FIXME: avoid tossing out bcache blocks just to replace fd. */
-		log_debug("Close and reopen excl %s", dev_name(dev));
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-	}
-	dev->flags |= DEV_BCACHE_EXCL;
-	dev->flags |= DEV_BCACHE_WRITE;
-	return label_scan_open(dev);
+	return _get_dev(dev, EF_EXCL);
 }
 
+/* FIXME: probably not needed, write will do it */
 int label_scan_open_rw(struct device *dev)
 {
-	if (_in_bcache(dev) && !(dev->flags & DEV_BCACHE_WRITE)) {
-		/* FIXME: avoid tossing out bcache blocks just to replace fd. */
-		log_debug("Close and reopen rw %s", dev_name(dev));
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-	}
-	dev->flags |= DEV_BCACHE_WRITE;
-	return label_scan_open(dev);
+	return _get_dev(dev, 0);
 }
 
 bool dev_read_bytes(struct device *dev, uint64_t start, size_t len, void *data)
 {
-	if (!scan_bcache) {
+	int put = !dev->iodev;
+
+	if (!lvm_iom) {
 		/* Should not happen */
-		log_error("dev_read bcache not set up %s", dev_name(dev));
+		log_error("dev_read io manager not set up %s", dev_name(dev));
 		return false;
 	}
 
-	if (dev->bcache_fd <= 0) {
-		/* This is not often needed. */
-		if (!label_scan_open(dev)) {
-			log_error("Error opening device %s for reading at %llu length %u.",
-				  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-			return false;
-		}
-	}
+	if (!_get_dev(dev, EF_READ_ONLY))
+		return false;
 
-	if (!bcache_read_bytes(scan_bcache, dev->bcache_fd, start, len, data)) {
+	if (!io_read_bytes(lvm_iom, dev->iodev, start, len, data)) {
 		log_error("Error reading device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
+
+	if (put)
+		_put_dev(dev);
 	return true;
 
 }
 
 bool dev_write_bytes(struct device *dev, uint64_t start, size_t len, void *data)
 {
+	int put = !dev->iodev;
+
 	if (test_mode())
 		return true;
 
-	if (!scan_bcache) {
+	if (!lvm_iom) {
 		/* Should not happen */
-		log_error("dev_write bcache not set up %s", dev_name(dev));
+		log_error("dev_write io manager not set up %s", dev_name(dev));
 		return false;
 	}
 
-	if (_in_bcache(dev) && !(dev->flags & DEV_BCACHE_WRITE)) {
-		/* FIXME: avoid tossing out bcache blocks just to replace fd. */
-		log_debug("Close and reopen to write %s", dev_name(dev));
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-
-		dev->flags |= DEV_BCACHE_WRITE;
-		label_scan_open(dev);
-	}
-
-	if (dev->bcache_fd <= 0) {
-		/* This is not often needed. */
-		dev->flags |= DEV_BCACHE_WRITE;
-		if (!label_scan_open(dev)) {
-			log_error("Error opening device %s for writing at %llu length %u.",
-				  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-			return false;
-		}
-	}
+	if (!_get_dev(dev, 0))
+		return false;
 
-	if (!bcache_write_bytes(scan_bcache, dev->bcache_fd, start, len, data)) {
+	if (!io_write_bytes(lvm_iom, dev->iodev, start, len, data)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
 
-	if (!bcache_flush(scan_bcache)) {
+	if (!io_flush(lvm_iom)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
+
+	if (put)
+		_put_dev(dev);
 	return true;
 }
 
 bool dev_write_zeros(struct device *dev, uint64_t start, size_t len)
 {
+	int put = !dev->iodev;
+
 	if (test_mode())
 		return true;
 
-	if (!scan_bcache) {
-		log_error("dev_write_zeros bcache not set up %s", dev_name(dev));
+	if (!lvm_iom) {
+		log_error("dev_write_zeros io manager not set up %s", dev_name(dev));
 		return false;
 	}
 
-	if (_in_bcache(dev) && !(dev->flags & DEV_BCACHE_WRITE)) {
-		/* FIXME: avoid tossing out bcache blocks just to replace fd. */
-		log_debug("Close and reopen to write %s", dev_name(dev));
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-
-		dev->flags |= DEV_BCACHE_WRITE;
-		label_scan_open(dev);
-	}
-
-	if (dev->bcache_fd <= 0) {
-		/* This is not often needed. */
-		dev->flags |= DEV_BCACHE_WRITE;
-		if (!label_scan_open(dev)) {
-			log_error("Error opening device %s for writing at %llu length %u.",
-				  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-			return false;
-		}
-	}
-
-	dev_set_last_byte(dev, start + len);
+	if (!_get_dev(dev, 0))
+		return false;
 
-	if (!bcache_zero_bytes(scan_bcache, dev->bcache_fd, start, len)) {
+	if (!io_zero_bytes(lvm_iom, dev->iodev, start, len)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		dev_unset_last_byte(dev);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
 
-	if (!bcache_flush(scan_bcache)) {
+	if (!io_flush(lvm_iom)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		dev_unset_last_byte(dev);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
-	dev_unset_last_byte(dev);
+
+	if (put)
+		_put_dev(dev);
 	return true;
 }
 
 bool dev_set_bytes(struct device *dev, uint64_t start, size_t len, uint8_t val)
 {
+	int put = !dev->iodev;
+
 	if (test_mode())
 		return true;
 
-	if (!scan_bcache) {
-		log_error("dev_set_bytes bcache not set up %s", dev_name(dev));
+	if (!lvm_iom) {
+		log_error("dev_set_bytes io manager not set up %s", dev_name(dev));
 		return false;
 	}
 
-	if (_in_bcache(dev) && !(dev->flags & DEV_BCACHE_WRITE)) {
-		/* FIXME: avoid tossing out bcache blocks just to replace fd. */
-		log_debug("Close and reopen to write %s", dev_name(dev));
-		bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
-		_scan_dev_close(dev);
-		/* goes to label_scan_open() since bcache_fd < 0 */
-	}
-
-	if (dev->bcache_fd <= 0) {
-		/* This is not often needed. */
-		dev->flags |= DEV_BCACHE_WRITE;
-		if (!label_scan_open(dev)) {
-			log_error("Error opening device %s for writing at %llu length %u.",
-				  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-			return false;
-		}
-	}
-
-	dev_set_last_byte(dev, start + len);
+	if (!_get_dev(dev, 0))
+		return false;
 
-	if (!bcache_set_bytes(scan_bcache, dev->bcache_fd, start, len, val)) {
+	if (!io_set_bytes(lvm_iom, dev->iodev, start, len, val)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		dev_unset_last_byte(dev);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
 
-	if (!bcache_flush(scan_bcache)) {
+	if (!io_flush(lvm_iom)) {
 		log_error("Error writing device %s at %llu length %u.",
 			  dev_name(dev), (unsigned long long)start, (uint32_t)len);
-		dev_unset_last_byte(dev);
-		label_scan_invalidate(dev);
+		if (put)
+			_put_dev(dev);
 		return false;
 	}
 
-	dev_unset_last_byte(dev);
+	if (put)
+		_put_dev(dev);
 	return true;
 }
 
-void dev_set_last_byte(struct device *dev, uint64_t offset)
-{
-	unsigned int physical_block_size = 0;
-	unsigned int logical_block_size = 0;
-	unsigned int bs;
-
-	if (!dev_get_direct_block_sizes(dev, &physical_block_size, &logical_block_size)) {
-		stack;
-		return; /* FIXME: error path ? */
-	}
-
-	if ((physical_block_size == 512) && (logical_block_size == 512))
-		bs = 512;
-	else if ((physical_block_size == 4096) && (logical_block_size == 4096))
-		bs = 4096;
-	else if ((physical_block_size == 512) || (logical_block_size == 512)) {
-		log_debug("Set last byte mixed block sizes physical %u logical %u using 512",
-			  physical_block_size, logical_block_size);
-		bs = 512;
-	} else if ((physical_block_size == 4096) || (logical_block_size == 4096)) {
-		log_debug("Set last byte mixed block sizes physical %u logical %u using 4096",
-			  physical_block_size, logical_block_size);
-		bs = 4096;
-	} else {
-		log_debug("Set last byte mixed block sizes physical %u logical %u using 512",
-			  physical_block_size, logical_block_size);
-		bs = 512;
-	}
-
-	bcache_set_last_byte(scan_bcache, dev->bcache_fd, offset, bs);
-}
-
-void dev_unset_last_byte(struct device *dev)
-{
-	bcache_unset_last_byte(scan_bcache, dev->bcache_fd);
-}
-
diff --git a/lib/label/label.h b/lib/label/label.h
index f06b7df63..b60f9b5e1 100644
--- a/lib/label/label.h
+++ b/lib/label/label.h
@@ -18,7 +18,7 @@
 
 #include "lib/uuid/uuid.h"
 #include "lib/device/device.h"
-#include "lib/device/bcache.h"
+#include "lib/device/io-manager.h"
 
 #define LABEL_ID "LABELONE"
 #define LABEL_SIZE SECTOR_SIZE	/* Think very carefully before changing this */
@@ -100,7 +100,8 @@ int label_write(struct device *dev, struct label *label);
 struct label *label_create(struct labeller *labeller);
 void label_destroy(struct label *label);
 
-extern struct bcache *scan_bcache;
+extern struct io_manager *lvm_iom;
+extern int io_data_ready; /* set once io manager is populated with device blocks */
 
 int label_scan(struct cmd_context *cmd);
 int label_scan_devs(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
@@ -113,20 +114,17 @@ void label_scan_destroy(struct cmd_context *cmd);
 int label_read(struct device *dev);
 int label_read_sector(struct device *dev, uint64_t scan_sector);
 void label_scan_confirm(struct device *dev);
-int label_scan_setup_bcache(void);
+int label_scan_setup_io_manager(void);
 int label_scan_open(struct device *dev);
 int label_scan_open_excl(struct device *dev);
 int label_scan_open_rw(struct device *dev);
 
 /*
- * Wrappers around bcache equivalents.
- * (these make it easier to disable bcache and revert to direct rw if needed)
+ * Wrappers around io-manager equivalents.
  */
 bool dev_read_bytes(struct device *dev, uint64_t start, size_t len, void *data);
 bool dev_write_bytes(struct device *dev, uint64_t start, size_t len, void *data);
 bool dev_write_zeros(struct device *dev, uint64_t start, size_t len);
 bool dev_set_bytes(struct device *dev, uint64_t start, size_t len, uint8_t val);
-void dev_set_last_byte(struct device *dev, uint64_t offset);
-void dev_unset_last_byte(struct device *dev);
 
 #endif
diff --git a/lib/metadata/mirror.c b/lib/metadata/mirror.c
index 845945728..73489a91e 100644
--- a/lib/metadata/mirror.c
+++ b/lib/metadata/mirror.c
@@ -302,14 +302,10 @@ static int _write_log_header(struct cmd_context *cmd, struct logical_volume *lv)
 		return 0;
 	}
 
-	dev_set_last_byte(dev, sizeof(log_header));
-
 	if (!dev_write_bytes(dev, UINT64_C(0), sizeof(log_header), &log_header)) {
-		dev_unset_last_byte(dev);
 		log_error("Failed to write log header to %s.", name);
 		return 0;
 	}
-	dev_unset_last_byte(dev);
 
 	label_scan_invalidate(dev);
 
diff --git a/tools/pvck.c b/tools/pvck.c
index af2dd8e8a..a59240938 100644
--- a/tools/pvck.c
+++ b/tools/pvck.c
@@ -1126,7 +1126,7 @@ static int _dump_headers(struct cmd_context *cmd,
 		return ECMD_FAILED;
 	}
 
-	label_scan_setup_bcache();
+	label_scan_setup_io_manager();
 
 	if (!_dump_label_and_pv_header(cmd, 1, dev, NULL,
 			&mda1_offset, &mda1_size, &mda2_offset, &mda2_size))
@@ -1199,7 +1199,7 @@ static int _dump_metadata(struct cmd_context *cmd,
 		return ECMD_FAILED;
 	}
 
-	label_scan_setup_bcache();
+	label_scan_setup_io_manager();
 
 	if (!_dump_label_and_pv_header(cmd, 0, dev, NULL,
 			&mda1_offset, &mda1_size, &mda2_offset, &mda2_size))
@@ -1324,7 +1324,7 @@ int pvck(struct cmd_context *cmd, int argc, char **argv)
 	if (arg_is_set(cmd, labelsector_ARG))
 		labelsector = arg_uint64_value(cmd, labelsector_ARG, UINT64_C(0));
 
-	label_scan_setup_bcache();
+	label_scan_setup_io_manager();
 
 	for (i = 0; i < argc; i++) {
 		pv_name = argv[i];
-- 
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