*/
/*
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
*/
#ifndef _ZIO_IMPL_H
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, and Ioctl.
+ *
+ * I/O operations: (XXX - provide detail for each of the operations)
+ *
+ * Read:
+ * Write:
+ * Free:
+ * Claim:
+ * Ioctl:
+ *
+ * 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 three different flavors of compression -- gzip, lzjb, and
+ * zle. Compression occurs as part of the write pipeline and is performed
+ * in the ZIO_STAGE_WRITE_BP_INIT stage.
+ *
+ * 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 crypographically
+ * 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.
+ */
+
/*
* zio pipeline stage definitions
*/
ZIO_STAGE_CHECKSUM_GENERATE = 1 << 5, /* -W--- */
- ZIO_STAGE_DDT_READ_START = 1 << 6, /* R---- */
- ZIO_STAGE_DDT_READ_DONE = 1 << 7, /* R---- */
- ZIO_STAGE_DDT_WRITE = 1 << 8, /* -W--- */
- ZIO_STAGE_DDT_FREE = 1 << 9, /* --F-- */
+ ZIO_STAGE_NOP_WRITE = 1 << 6, /* -W--- */
+
+ ZIO_STAGE_DDT_READ_START = 1 << 7, /* R---- */
+ ZIO_STAGE_DDT_READ_DONE = 1 << 8, /* R---- */
+ ZIO_STAGE_DDT_WRITE = 1 << 9, /* -W--- */
+ ZIO_STAGE_DDT_FREE = 1 << 10, /* --F-- */
- ZIO_STAGE_GANG_ASSEMBLE = 1 << 10, /* RWFC- */
- ZIO_STAGE_GANG_ISSUE = 1 << 11, /* RWFC- */
+ ZIO_STAGE_GANG_ASSEMBLE = 1 << 11, /* RWFC- */
+ ZIO_STAGE_GANG_ISSUE = 1 << 12, /* RWFC- */
- ZIO_STAGE_DVA_ALLOCATE = 1 << 12, /* -W--- */
- ZIO_STAGE_DVA_FREE = 1 << 13, /* --F-- */
- ZIO_STAGE_DVA_CLAIM = 1 << 14, /* ---C- */
+ ZIO_STAGE_DVA_ALLOCATE = 1 << 13, /* -W--- */
+ ZIO_STAGE_DVA_FREE = 1 << 14, /* --F-- */
+ ZIO_STAGE_DVA_CLAIM = 1 << 15, /* ---C- */
- ZIO_STAGE_READY = 1 << 15, /* RWFCI */
+ ZIO_STAGE_READY = 1 << 16, /* RWFCI */
- ZIO_STAGE_VDEV_IO_START = 1 << 16, /* RW--I */
- ZIO_STAGE_VDEV_IO_DONE = 1 << 17, /* RW--I */
- ZIO_STAGE_VDEV_IO_ASSESS = 1 << 18, /* RW--I */
+ ZIO_STAGE_VDEV_IO_START = 1 << 17, /* RW--I */
+ ZIO_STAGE_VDEV_IO_DONE = 1 << 18, /* RW--I */
+ ZIO_STAGE_VDEV_IO_ASSESS = 1 << 19, /* RW--I */
- ZIO_STAGE_CHECKSUM_VERIFY = 1 << 19, /* R---- */
+ ZIO_STAGE_CHECKSUM_VERIFY = 1 << 20, /* R---- */
- ZIO_STAGE_DONE = 1 << 20 /* RWFCI */
+ ZIO_STAGE_DONE = 1 << 21 /* RWFCI */
};
#define ZIO_INTERLOCK_STAGES \
#define ZIO_FREE_PIPELINE \
(ZIO_INTERLOCK_STAGES | \
ZIO_STAGE_FREE_BP_INIT | \
- ZIO_STAGE_ISSUE_ASYNC | \
ZIO_STAGE_DVA_FREE)
#define ZIO_DDT_FREE_PIPELINE \
projects / mirror_zfs-debian.git / blobdiff