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mirror_zfs/include/sys/zio_impl.h
Brian Atkinson a10e552b99
Adding Direct IO Support 
Adding O_DIRECT support to ZFS to bypass the ARC for writes/reads.

O_DIRECT support in ZFS will always ensure there is coherency between
buffered and O_DIRECT IO requests. This ensures that all IO requests,
whether buffered or direct, will see the same file contents at all
times. Just as in other FS's , O_DIRECT does not imply O_SYNC. While
data is written directly to VDEV disks, metadata will not be synced
until the associated  TXG is synced.
For both O_DIRECT read and write request the offset and request sizes,
at a minimum, must be PAGE_SIZE aligned. In the event they are not,
then EINVAL is returned unless the direct property is set to always (see
below).

For O_DIRECT writes:
The request also must be block aligned (recordsize) or the write
request will take the normal (buffered) write path. In the event that
request is block aligned and a cached copy of the buffer in the ARC,
then it will be discarded from the ARC forcing all further reads to
retrieve the data from disk.

For O_DIRECT reads:
The only alignment restrictions are PAGE_SIZE alignment. In the event
that the requested data is in buffered (in the ARC) it will just be
copied from the ARC into the user buffer.

For both O_DIRECT writes and reads the O_DIRECT flag will be ignored in
the event that file contents are mmap'ed. In this case, all requests
that are at least PAGE_SIZE aligned will just fall back to the buffered
paths. If the request however is not PAGE_SIZE aligned, EINVAL will
be returned as always regardless if the file's contents are mmap'ed.

Since O_DIRECT writes go through the normal ZIO pipeline, the
following operations are supported just as with normal buffered writes:
Checksum
Compression
Encryption
Erasure Coding
There is one caveat for the data integrity of O_DIRECT writes that is
distinct for each of the OS's supported by ZFS.
FreeBSD - FreeBSD is able to place user pages under write protection so
          any data in the user buffers and written directly down to the
	  VDEV disks is guaranteed to not change. There is no concern
	  with data integrity and O_DIRECT writes.
Linux - Linux is not able to place anonymous user pages under write
        protection. Because of this, if the user decides to manipulate
	the page contents while the write operation is occurring, data
	integrity can not be guaranteed. However, there is a module
	parameter `zfs_vdev_direct_write_verify` that controls the
	if a O_DIRECT writes that can occur to a top-level VDEV before
	a checksum verify is run before the contents of the I/O buffer
        are committed to disk. In the event of a checksum verification
	failure the write will return EIO. The number of O_DIRECT write
	checksum verification errors can be observed by doing
	`zpool status -d`, which will list all verification errors that
	have occurred on a top-level VDEV. Along with `zpool status`, a
	ZED event will be issues as `dio_verify` when a checksum
	verification error occurs.

ZVOLs and dedup is not currently supported with Direct I/O.

A new dataset property `direct` has been added with the following 3
allowable values:
disabled - Accepts O_DIRECT flag, but silently ignores it and treats
	   the request as a buffered IO request.
standard - Follows the alignment restrictions  outlined above for
	   write/read IO requests when the O_DIRECT flag is used.
always   - Treats every write/read IO request as though it passed
           O_DIRECT and will do O_DIRECT if the alignment restrictions
	   are met otherwise will redirect through the ARC. This
	   property will not allow a request to fail.

There is also a module parameter zfs_dio_enabled that can be used to
force all reads and writes through the ARC. By setting this module
parameter to 0, it mimics as if the  direct dataset property is set to
disabled.

Reviewed-by: Brian Behlendorf <behlendorf@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Co-authored-by: Mark Maybee <mark.maybee@delphix.com>
Co-authored-by: Matt Macy <mmacy@FreeBSD.org>
Co-authored-by: Brian Behlendorf <behlendorf@llnl.gov>
Closes #10018
2024-09-14 13:47:59 -07:00

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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or https://opensource.org/licenses/CDDL-1.0.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/*
* Copyright (c) 2012, 2015 by Delphix. All rights reserved.
* Copyright (c) 2024, Klara Inc.
*/
#ifndef _ZIO_IMPL_H
#define _ZIO_IMPL_H
#ifdef __cplusplus
extern "C" {
#endif
/*
* XXX -- Describe ZFS I/O pipeline here. Fill in as needed.
*
* The ZFS I/O pipeline is comprised of various stages which are defined
* in the zio_stage enum below. The individual stages are used to construct
* these basic I/O operations: Read, Write, Free, Claim, Flush and Trim.
*
* I/O operations: (XXX - provide detail for each of the operations)
*
* Read:
* Write:
* Free:
* Claim:
* Flush:
* Trim:
*
* Although the most common pipeline are used by the basic I/O operations
* above, there are some helper pipelines (one could consider them
* sub-pipelines) which are used internally by the ZIO module and are
* explained below:
*
* Interlock Pipeline:
* The interlock pipeline is the most basic pipeline and is used by all
* of the I/O operations. The interlock pipeline does not perform any I/O
* and is used to coordinate the dependencies between I/Os that are being
* issued (i.e. the parent/child relationship).
*
* Vdev child Pipeline:
* The vdev child pipeline is responsible for performing the physical I/O.
* It is in this pipeline where the I/O are queued and possibly cached.
*
* In addition to performing I/O, the pipeline is also responsible for
* data transformations. The transformations performed are based on the
* specific properties that user may have selected and modify the
* behavior of the pipeline. Examples of supported transformations are
* compression, dedup, and nop writes. Transformations will either modify
* the data or the pipeline. This list below further describes each of
* the supported transformations:
*
* Compression:
* ZFS supports five different flavors of compression -- gzip, lzjb, lz4, zle,
* and zstd. Compression occurs as part of the write pipeline and is
* performed in the ZIO_STAGE_WRITE_BP_INIT stage.
*
* Block cloning:
* The block cloning functionality introduces ZIO_STAGE_BRT_FREE stage which
* is called during a free pipeline. If the block is referenced in the
* Block Cloning Table (BRT) we will just decrease its reference counter
* instead of actually freeing the block.
*
* Dedup:
* Dedup reads are handled by the ZIO_STAGE_DDT_READ_START and
* ZIO_STAGE_DDT_READ_DONE stages. These stages are added to an existing
* read pipeline if the dedup bit is set on the block pointer.
* Writing a dedup block is performed by the ZIO_STAGE_DDT_WRITE stage
* and added to a write pipeline if a user has enabled dedup on that
* particular dataset.
*
* NOP Write:
* The NOP write feature is performed by the ZIO_STAGE_NOP_WRITE stage
* and is added to an existing write pipeline if a cryptographically
* secure checksum (i.e. SHA256) is enabled and compression is turned on.
* The NOP write stage will compare the checksums of the current data
* on-disk (level-0 blocks only) and the data that is currently being written.
* If the checksum values are identical then the pipeline is converted to
* an interlock pipeline skipping block allocation and bypassing the
* physical I/O. The nop write feature can handle writes in either
* syncing or open context (i.e. zil writes) and as a result is mutually
* exclusive with dedup.
*
* Encryption:
* Encryption and authentication is handled by the ZIO_STAGE_ENCRYPT stage.
* This stage determines how the encryption metadata is stored in the bp.
* Decryption and MAC verification is performed during zio_decrypt() as a
* transform callback. Encryption is mutually exclusive with nopwrite, because
* blocks with the same plaintext will be encrypted with different salts and
* IV's (if dedup is off), and therefore have different ciphertexts. For dedup
* blocks we deterministically generate the IV and salt by performing an HMAC
* of the plaintext, which is computationally expensive, but allows us to keep
* support for encrypted dedup. See the block comment in zio_crypt.c for
* details.
*/
/*
* zio pipeline stage definitions
*
* NOTE: PLEASE UPDATE THE BITFIELD STRINGS IN zfs_valstr.c IF YOU ADD ANOTHER
* FLAG.
*/
enum zio_stage {
ZIO_STAGE_OPEN = 1 << 0, /* RWFCXT */
ZIO_STAGE_READ_BP_INIT = 1 << 1, /* R----- */
ZIO_STAGE_WRITE_BP_INIT = 1 << 2, /* -W---- */
ZIO_STAGE_FREE_BP_INIT = 1 << 3, /* --F--- */
ZIO_STAGE_ISSUE_ASYNC = 1 << 4, /* -WF--T */
ZIO_STAGE_WRITE_COMPRESS = 1 << 5, /* -W---- */
ZIO_STAGE_ENCRYPT = 1 << 6, /* -W---- */
ZIO_STAGE_CHECKSUM_GENERATE = 1 << 7, /* -W---- */
ZIO_STAGE_NOP_WRITE = 1 << 8, /* -W---- */
ZIO_STAGE_BRT_FREE = 1 << 9, /* --F--- */
ZIO_STAGE_DDT_READ_START = 1 << 10, /* R----- */
ZIO_STAGE_DDT_READ_DONE = 1 << 11, /* R----- */
ZIO_STAGE_DDT_WRITE = 1 << 12, /* -W---- */
ZIO_STAGE_DDT_FREE = 1 << 13, /* --F--- */
ZIO_STAGE_GANG_ASSEMBLE = 1 << 14, /* RWFC-- */
ZIO_STAGE_GANG_ISSUE = 1 << 15, /* RWFC-- */
ZIO_STAGE_DVA_THROTTLE = 1 << 16, /* -W---- */
ZIO_STAGE_DVA_ALLOCATE = 1 << 17, /* -W---- */
ZIO_STAGE_DVA_FREE = 1 << 18, /* --F--- */
ZIO_STAGE_DVA_CLAIM = 1 << 19, /* ---C-- */
ZIO_STAGE_READY = 1 << 20, /* RWFCXT */
ZIO_STAGE_VDEV_IO_START = 1 << 21, /* RW--XT */
ZIO_STAGE_VDEV_IO_DONE = 1 << 22, /* RW--XT */
ZIO_STAGE_VDEV_IO_ASSESS = 1 << 23, /* RW--XT */
ZIO_STAGE_CHECKSUM_VERIFY = 1 << 24, /* R----- */
ZIO_STAGE_DIO_CHECKSUM_VERIFY = 1 << 25, /* -W---- */
ZIO_STAGE_DONE = 1 << 26 /* RWFCXT */
};
#define ZIO_ROOT_PIPELINE \
ZIO_STAGE_DONE
#define ZIO_INTERLOCK_STAGES \
(ZIO_STAGE_READY | \
ZIO_STAGE_DONE)
#define ZIO_INTERLOCK_PIPELINE \
ZIO_INTERLOCK_STAGES
#define ZIO_VDEV_IO_STAGES \
(ZIO_STAGE_VDEV_IO_START | \
ZIO_STAGE_VDEV_IO_DONE | \
ZIO_STAGE_VDEV_IO_ASSESS)
#define ZIO_VDEV_CHILD_PIPELINE \
(ZIO_VDEV_IO_STAGES | \
ZIO_STAGE_DONE)
#define ZIO_READ_COMMON_STAGES \
(ZIO_INTERLOCK_STAGES | \
ZIO_VDEV_IO_STAGES | \
ZIO_STAGE_CHECKSUM_VERIFY)
#define ZIO_READ_PHYS_PIPELINE \
ZIO_READ_COMMON_STAGES
#define ZIO_READ_PIPELINE \
(ZIO_READ_COMMON_STAGES | \
ZIO_STAGE_READ_BP_INIT)
#define ZIO_DDT_CHILD_READ_PIPELINE \
ZIO_READ_COMMON_STAGES
#define ZIO_DDT_READ_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_READ_BP_INIT | \
ZIO_STAGE_DDT_READ_START | \
ZIO_STAGE_DDT_READ_DONE)
#define ZIO_WRITE_COMMON_STAGES \
(ZIO_INTERLOCK_STAGES | \
ZIO_VDEV_IO_STAGES | \
ZIO_STAGE_ISSUE_ASYNC | \
ZIO_STAGE_CHECKSUM_GENERATE)
#define ZIO_WRITE_PHYS_PIPELINE \
ZIO_WRITE_COMMON_STAGES
#define ZIO_REWRITE_PIPELINE \
(ZIO_WRITE_COMMON_STAGES | \
ZIO_STAGE_WRITE_COMPRESS | \
ZIO_STAGE_ENCRYPT | \
ZIO_STAGE_WRITE_BP_INIT)
#define ZIO_WRITE_PIPELINE \
(ZIO_WRITE_COMMON_STAGES | \
ZIO_STAGE_WRITE_BP_INIT | \
ZIO_STAGE_WRITE_COMPRESS | \
ZIO_STAGE_ENCRYPT | \
ZIO_STAGE_DVA_THROTTLE | \
ZIO_STAGE_DVA_ALLOCATE)
#define ZIO_DIRECT_WRITE_PIPELINE \
ZIO_WRITE_PIPELINE & \
(~ZIO_STAGE_ISSUE_ASYNC)
#define ZIO_DDT_CHILD_WRITE_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_VDEV_IO_STAGES | \
ZIO_STAGE_DVA_THROTTLE | \
ZIO_STAGE_DVA_ALLOCATE)
#define ZIO_DDT_WRITE_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_WRITE_BP_INIT | \
ZIO_STAGE_ISSUE_ASYNC | \
ZIO_STAGE_WRITE_COMPRESS | \
ZIO_STAGE_ENCRYPT | \
ZIO_STAGE_CHECKSUM_GENERATE | \
ZIO_STAGE_DDT_WRITE)
#define ZIO_GANG_STAGES \
(ZIO_STAGE_GANG_ASSEMBLE | \
ZIO_STAGE_GANG_ISSUE)
#define ZIO_FREE_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_FREE_BP_INIT | \
ZIO_STAGE_BRT_FREE | \
ZIO_STAGE_DVA_FREE)
#define ZIO_DDT_FREE_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_FREE_BP_INIT | \
ZIO_STAGE_ISSUE_ASYNC | \
ZIO_STAGE_DDT_FREE)
#define ZIO_CLAIM_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_DVA_CLAIM)
#define ZIO_FLUSH_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_VDEV_IO_STAGES)
#define ZIO_TRIM_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_ISSUE_ASYNC | \
ZIO_VDEV_IO_STAGES)
#define ZIO_BLOCKING_STAGES \
(ZIO_STAGE_DVA_ALLOCATE | \
ZIO_STAGE_DVA_CLAIM | \
ZIO_STAGE_VDEV_IO_START)
extern void zio_inject_init(void);
extern void zio_inject_fini(void);
#ifdef __cplusplus
}
#endif
#endif /* _ZIO_IMPL_H */
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