Merge branch 'for-linus' of git://git.kernel.dk/linux-2.6-block

		I/O statistics of partition <part>. The format is the

		same as the above-written /sys/block/<disk>/stat

		format.

What:		/sys/block/<disk>/integrity/format

Date:		June 2008

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Metadata format for integrity capable block device.

		E.g. T10-DIF-TYPE1-CRC.

What:		/sys/block/<disk>/integrity/read_verify

Date:		June 2008

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Indicates whether the block layer should verify the

		integrity of read requests serviced by devices that

		support sending integrity metadata.

What:		/sys/block/<disk>/integrity/tag_size

Date:		June 2008

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Number of bytes of integrity tag space available per

		512 bytes of data.

What:		/sys/block/<disk>/integrity/write_generate

Date:		June 2008

Contact:	Martin K. Petersen <martin.petersen@oracle.com>

Description:

		Indicates whether the block layer should automatically

		generate checksums for write requests bound for

		devices that support receiving integrity metadata.

----------------------------------------------------------------------

1. INTRODUCTION

Modern filesystems feature checksumming of data and metadata to

protect against data corruption.  However, the detection of the

corruption is done at read time which could potentially be months

after the data was written.  At that point the original data that the

application tried to write is most likely lost.

The solution is to ensure that the disk is actually storing what the

application meant it to.  Recent additions to both the SCSI family

protocols (SBC Data Integrity Field, SCC protection proposal) as well

as SATA/T13 (External Path Protection) try to remedy this by adding

support for appending integrity metadata to an I/O.  The integrity

metadata (or protection information in SCSI terminology) includes a

checksum for each sector as well as an incrementing counter that

ensures the individual sectors are written in the right order.  And

for some protection schemes also that the I/O is written to the right

place on disk.

Current storage controllers and devices implement various protective

measures, for instance checksumming and scrubbing.  But these

technologies are working in their own isolated domains or at best

between adjacent nodes in the I/O path.  The interesting thing about

DIF and the other integrity extensions is that the protection format

is well defined and every node in the I/O path can verify the

integrity of the I/O and reject it if corruption is detected.  This

allows not only corruption prevention but also isolation of the point

of failure.

----------------------------------------------------------------------

2. THE DATA INTEGRITY EXTENSIONS

As written, the protocol extensions only protect the path between

controller and storage device.  However, many controllers actually

allow the operating system to interact with the integrity metadata

(IMD).  We have been working with several FC/SAS HBA vendors to enable

the protection information to be transferred to and from their

controllers.

The SCSI Data Integrity Field works by appending 8 bytes of protection

information to each sector.  The data + integrity metadata is stored

in 520 byte sectors on disk.  Data + IMD are interleaved when

transferred between the controller and target.  The T13 proposal is

similar.

Because it is highly inconvenient for operating systems to deal with

520 (and 4104) byte sectors, we approached several HBA vendors and

encouraged them to allow separation of the data and integrity metadata

scatter-gather lists.

The controller will interleave the buffers on write and split them on

read.  This means that the Linux can DMA the data buffers to and from

host memory without changes to the page cache.

Also, the 16-bit CRC checksum mandated by both the SCSI and SATA specs

is somewhat heavy to compute in software.  Benchmarks found that

calculating this checksum had a significant impact on system

performance for a number of workloads.  Some controllers allow a

lighter-weight checksum to be used when interfacing with the operating

system.  Emulex, for instance, supports the TCP/IP checksum instead.

The IP checksum received from the OS is converted to the 16-bit CRC

when writing and vice versa.  This allows the integrity metadata to be

generated by Linux or the application at very low cost (comparable to

software RAID5).

The IP checksum is weaker than the CRC in terms of detecting bit

errors.  However, the strength is really in the separation of the data

buffers and the integrity metadata.  These two distinct buffers much

match up for an I/O to complete.

The separation of the data and integrity metadata buffers as well as

the choice in checksums is referred to as the Data Integrity

Extensions.  As these extensions are outside the scope of the protocol

bodies (T10, T13), Oracle and its partners are trying to standardize

them within the Storage Networking Industry Association.

----------------------------------------------------------------------

3. KERNEL CHANGES

The data integrity framework in Linux enables protection information

to be pinned to I/Os and sent to/received from controllers that

support it.

The advantage to the integrity extensions in SCSI and SATA is that

they enable us to protect the entire path from application to storage

device.  However, at the same time this is also the biggest

disadvantage. It means that the protection information must be in a

format that can be understood by the disk.

Generally Linux/POSIX applications are agnostic to the intricacies of

the storage devices they are accessing.  The virtual filesystem switch

and the block layer make things like hardware sector size and

transport protocols completely transparent to the application.

However, this level of detail is required when preparing the

protection information to send to a disk.  Consequently, the very

concept of an end-to-end protection scheme is a layering violation.

It is completely unreasonable for an application to be aware whether

it is accessing a SCSI or SATA disk.

The data integrity support implemented in Linux attempts to hide this

from the application.  As far as the application (and to some extent

the kernel) is concerned, the integrity metadata is opaque information

that's attached to the I/O.

The current implementation allows the block layer to automatically

generate the protection information for any I/O.  Eventually the

intent is to move the integrity metadata calculation to userspace for

user data.  Metadata and other I/O that originates within the kernel

will still use the automatic generation interface.

Some storage devices allow each hardware sector to be tagged with a

16-bit value.  The owner of this tag space is the owner of the block

device.  I.e. the filesystem in most cases.  The filesystem can use

this extra space to tag sectors as they see fit.  Because the tag

space is limited, the block interface allows tagging bigger chunks by

way of interleaving.  This way, 8*16 bits of information can be

attached to a typical 4KB filesystem block.

This also means that applications such as fsck and mkfs will need

access to manipulate the tags from user space.  A passthrough

interface for this is being worked on.

----------------------------------------------------------------------

4. BLOCK LAYER IMPLEMENTATION DETAILS

4.1 BIO

The data integrity patches add a new field to struct bio when

CONFIG_BLK_DEV_INTEGRITY is enabled.  bio->bi_integrity is a pointer

to a struct bip which contains the bio integrity payload.  Essentially

a bip is a trimmed down struct bio which holds a bio_vec containing

the integrity metadata and the required housekeeping information (bvec

pool, vector count, etc.)

A kernel subsystem can enable data integrity protection on a bio by

calling bio_integrity_alloc(bio).  This will allocate and attach the

bip to the bio.

Individual pages containing integrity metadata can subsequently be

attached using bio_integrity_add_page().

bio_free() will automatically free the bip.

4.2 BLOCK DEVICE

Because the format of the protection data is tied to the physical

disk, each block device has been extended with a block integrity

profile (struct blk_integrity).  This optional profile is registered

with the block layer using blk_integrity_register().

The profile contains callback functions for generating and verifying

the protection data, as well as getting and setting application tags.

The profile also contains a few constants to aid in completing,

merging and splitting the integrity metadata.

Layered block devices will need to pick a profile that's appropriate

for all subdevices.  blk_integrity_compare() can help with that.  DM

and MD linear, RAID0 and RAID1 are currently supported.  RAID4/5/6

will require extra work due to the application tag.

----------------------------------------------------------------------

5.0 BLOCK LAYER INTEGRITY API

5.1 NORMAL FILESYSTEM

    The normal filesystem is unaware that the underlying block device

    is capable of sending/receiving integrity metadata.  The IMD will

    be automatically generated by the block layer at submit_bio() time

    in case of a WRITE.  A READ request will cause the I/O integrity

    to be verified upon completion.

    IMD generation and verification can be toggled using the

      /sys/block/<bdev>/integrity/write_generate

    and

      /sys/block/<bdev>/integrity/read_verify

    flags.

5.2 INTEGRITY-AWARE FILESYSTEM

    A filesystem that is integrity-aware can prepare I/Os with IMD

    attached.  It can also use the application tag space if this is

    supported by the block device.

    int bdev_integrity_enabled(block_device, int rw);

      bdev_integrity_enabled() will return 1 if the block device

      supports integrity metadata transfer for the data direction

      specified in 'rw'.

      bdev_integrity_enabled() honors the write_generate and

      read_verify flags in sysfs and will respond accordingly.

    int bio_integrity_prep(bio);

      To generate IMD for WRITE and to set up buffers for READ, the

      filesystem must call bio_integrity_prep(bio).

      Prior to calling this function, the bio data direction and start

      sector must be set, and the bio should have all data pages

      added.  It is up to the caller to ensure that the bio does not

      change while I/O is in progress.

      bio_integrity_prep() should only be called if

      bio_integrity_enabled() returned 1.

    int bio_integrity_tag_size(bio);

      If the filesystem wants to use the application tag space it will

      first have to find out how much storage space is available.

      Because tag space is generally limited (usually 2 bytes per

      sector regardless of sector size), the integrity framework

      supports interleaving the information between the sectors in an

      I/O.

      Filesystems can call bio_integrity_tag_size(bio) to find out how

      many bytes of storage are available for that particular bio.

      Another option is bdev_get_tag_size(block_device) which will

      return the number of available bytes per hardware sector.

    int bio_integrity_set_tag(bio, void *tag_buf, len);

      After a successful return from bio_integrity_prep(),

      bio_integrity_set_tag() can be used to attach an opaque tag

      buffer to a bio.  Obviously this only makes sense if the I/O is

      a WRITE.

    int bio_integrity_get_tag(bio, void *tag_buf, len);

      Similarly, at READ I/O completion time the filesystem can

      retrieve the tag buffer using bio_integrity_get_tag().

6.3 PASSING EXISTING INTEGRITY METADATA

    Filesystems that either generate their own integrity metadata or

    are capable of transferring IMD from user space can use the

    following calls:

    struct bip * bio_integrity_alloc(bio, gfp_mask, nr_pages);

      Allocates the bio integrity payload and hangs it off of the bio.

      nr_pages indicate how many pages of protection data need to be

      stored in the integrity bio_vec list (similar to bio_alloc()).

      The integrity payload will be freed at bio_free() time.

    int bio_integrity_add_page(bio, page, len, offset);

      Attaches a page containing integrity metadata to an existing

      bio.  The bio must have an existing bip,

      i.e. bio_integrity_alloc() must have been called.  For a WRITE,

      the integrity metadata in the pages must be in a format

      understood by the target device with the notable exception that

      the sector numbers will be remapped as the request traverses the

      I/O stack.  This implies that the pages added using this call

      will be modified during I/O!  The first reference tag in the

      integrity metadata must have a value of bip->bip_sector.

      Pages can be added using bio_integrity_add_page() as long as

      there is room in the bip bio_vec array (nr_pages).

      Upon completion of a READ operation, the attached pages will

      contain the integrity metadata received from the storage device.

      It is up to the receiver to process them and verify data

      integrity upon completion.

6.4 REGISTERING A BLOCK DEVICE AS CAPABLE OF EXCHANGING INTEGRITY

    METADATA

    To enable integrity exchange on a block device the gendisk must be

    registered as capable:

    int blk_integrity_register(gendisk, blk_integrity);

      The blk_integrity struct is a template and should contain the

      following:

        static struct blk_integrity my_profile = {

            .name                   = "STANDARDSBODY-TYPE-VARIANT-CSUM",

            .generate_fn            = my_generate_fn,

       	    .verify_fn              = my_verify_fn,

       	    .get_tag_fn             = my_get_tag_fn,

       	    .set_tag_fn             = my_set_tag_fn,

	    .tuple_size             = sizeof(struct my_tuple_size),

	    .tag_size               = <tag bytes per hw sector>,

        };

      'name' is a text string which will be visible in sysfs.  This is

      part of the userland API so chose it carefully and never change

      it.  The format is standards body-type-variant.

      E.g. T10-DIF-TYPE1-IP or T13-EPP-0-CRC.

      'generate_fn' generates appropriate integrity metadata (for WRITE).

      'verify_fn' verifies that the data buffer matches the integrity

      metadata.

      'tuple_size' must be set to match the size of the integrity

      metadata per sector.  I.e. 8 for DIF and EPP.

      'tag_size' must be set to identify how many bytes of tag space

      are available per hardware sector.  For DIF this is either 2 or

      0 depending on the value of the Control Mode Page ATO bit.

      See 6.2 for a description of get_tag_fn and set_tag_fn.

----------------------------------------------------------------------

2007-12-24 Martin K. Petersen <martin.petersen@oracle.com>

	  If unsure, say N.

config BLK_DEV_INTEGRITY

	bool "Block layer data integrity support"

	---help---

	Some storage devices allow extra information to be

	stored/retrieved to help protect the data.  The block layer

	data integrity option provides hooks which can be used by

	filesystems to ensure better data integrity.

	Say yes here if you have a storage device that provides the

	T10/SCSI Data Integrity Field or the T13/ATA External Path

	Protection.  If in doubt, say N.

endif # BLOCK

config BLOCK_COMPAT

obj-$(CONFIG_BLOCK) := elevator.o blk-core.o blk-tag.o blk-sysfs.o \

			blk-barrier.o blk-settings.o blk-ioc.o blk-map.o \

			blk-exec.o blk-merge.o ioctl.o genhd.o scsi_ioctl.o

			blk-exec.o blk-merge.o ioctl.o genhd.o scsi_ioctl.o \

			cmd-filter.o

obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o

obj-$(CONFIG_IOSCHED_NOOP)	+= noop-iosched.o

obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o

obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o

obj-$(CONFIG_BLK_DEV_INTEGRITY)	+= blk-integrity.o

static DEFINE_PER_CPU(unsigned long, ioc_count);

static struct completion *ioc_gone;

static DEFINE_SPINLOCK(ioc_gone_lock);

static void as_move_to_dispatch(struct as_data *ad, struct request *rq);

static void as_antic_stop(struct as_data *ad);

{

	kfree(aic);

	elv_ioc_count_dec(ioc_count);

	if (ioc_gone && !elv_ioc_count_read(ioc_count))

	if (ioc_gone) {

		/*

		 * AS scheduler is exiting, grab exit lock and check

		 * the pending io context count. If it hits zero,

		 * complete ioc_gone and set it back to NULL.

		 */

		spin_lock(&ioc_gone_lock);

		if (ioc_gone && !elv_ioc_count_read(ioc_count)) {

			complete(ioc_gone);

			ioc_gone = NULL;

		}

		spin_unlock(&ioc_gone_lock);

	}

}

static void as_trim(struct io_context *ioc)

	/* ioc_gone's update must be visible before reading ioc_count */

	smp_wmb();

	if (elv_ioc_count_read(ioc_count))

		wait_for_completion(ioc_gone);

		wait_for_completion(&all_gone);

	synchronize_rcu();

}