diff --git a/module/os/linux/zfs/vdev_disk.c b/module/os/linux/zfs/vdev_disk.c index e1c19a085b0e..62c7aa14fd1f 100644 --- a/module/os/linux/zfs/vdev_disk.c +++ b/module/os/linux/zfs/vdev_disk.c @@ -1,1610 +1,1611 @@ /* * 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 (C) 2008-2010 Lawrence Livermore National Security, LLC. * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER). * Rewritten for Linux by Brian Behlendorf . * LLNL-CODE-403049. * Copyright (c) 2012, 2019 by Delphix. All rights reserved. * Copyright (c) 2023, 2024, Klara Inc. */ #include #include #include #include #include #include #include #include #include #include #include #ifdef HAVE_LINUX_BLK_CGROUP_HEADER #include #endif /* * Linux 6.8.x uses a bdev_handle as an instance/refcount for an underlying * block_device. Since it carries the block_device inside, its convenient to * just use the handle as a proxy. For pre-6.8, we just emulate this with * a cast, since we don't need any of the other fields inside the handle. */ #ifdef HAVE_BDEV_OPEN_BY_PATH typedef struct bdev_handle zfs_bdev_handle_t; #define BDH_BDEV(bdh) ((bdh)->bdev) #define BDH_IS_ERR(bdh) (IS_ERR(bdh)) #define BDH_PTR_ERR(bdh) (PTR_ERR(bdh)) #define BDH_ERR_PTR(err) (ERR_PTR(err)) #else typedef void zfs_bdev_handle_t; #define BDH_BDEV(bdh) ((struct block_device *)bdh) #define BDH_IS_ERR(bdh) (IS_ERR(BDH_BDEV(bdh))) #define BDH_PTR_ERR(bdh) (PTR_ERR(BDH_BDEV(bdh))) #define BDH_ERR_PTR(err) (ERR_PTR(err)) #endif typedef struct vdev_disk { zfs_bdev_handle_t *vd_bdh; krwlock_t vd_lock; } vdev_disk_t; /* * Maximum number of segments to add to a bio (min 4). If this is higher than * the maximum allowed by the device queue or the kernel itself, it will be * clamped. Setting it to zero will cause the kernel's ideal size to be used. */ uint_t zfs_vdev_disk_max_segs = 0; /* * Unique identifier for the exclusive vdev holder. */ static void *zfs_vdev_holder = VDEV_HOLDER; /* * Wait up to zfs_vdev_open_timeout_ms milliseconds before determining the * device is missing. The missing path may be transient since the links * can be briefly removed and recreated in response to udev events. */ static uint_t zfs_vdev_open_timeout_ms = 1000; /* * Size of the "reserved" partition, in blocks. */ #define EFI_MIN_RESV_SIZE (16 * 1024) /* * BIO request failfast mask. */ static unsigned int zfs_vdev_failfast_mask = 1; #ifdef HAVE_BLK_MODE_T static blk_mode_t #else static fmode_t #endif vdev_bdev_mode(spa_mode_t spa_mode, boolean_t exclusive) { #ifdef HAVE_BLK_MODE_T blk_mode_t mode = 0; if (spa_mode & SPA_MODE_READ) mode |= BLK_OPEN_READ; if (spa_mode & SPA_MODE_WRITE) mode |= BLK_OPEN_WRITE; if (exclusive) mode |= BLK_OPEN_EXCL; #else fmode_t mode = 0; if (spa_mode & SPA_MODE_READ) mode |= FMODE_READ; if (spa_mode & SPA_MODE_WRITE) mode |= FMODE_WRITE; if (exclusive) mode |= FMODE_EXCL; #endif return (mode); } /* * Returns the usable capacity (in bytes) for the partition or disk. */ static uint64_t bdev_capacity(struct block_device *bdev) { return (i_size_read(bdev->bd_inode)); } #if !defined(HAVE_BDEV_WHOLE) static inline struct block_device * bdev_whole(struct block_device *bdev) { return (bdev->bd_contains); } #endif #if defined(HAVE_BDEVNAME) #define vdev_bdevname(bdev, name) bdevname(bdev, name) #else static inline void vdev_bdevname(struct block_device *bdev, char *name) { snprintf(name, BDEVNAME_SIZE, "%pg", bdev); } #endif /* * Returns the maximum expansion capacity of the block device (in bytes). * * It is possible to expand a vdev when it has been created as a wholedisk * and the containing block device has increased in capacity. Or when the * partition containing the pool has been manually increased in size. * * This function is only responsible for calculating the potential expansion * size so it can be reported by 'zpool list'. The efi_use_whole_disk() is * responsible for verifying the expected partition layout in the wholedisk * case, and updating the partition table if appropriate. Once the partition * size has been increased the additional capacity will be visible using * bdev_capacity(). * * The returned maximum expansion capacity is always expected to be larger, or * at the very least equal, to its usable capacity to prevent overestimating * the pool expandsize. */ static uint64_t bdev_max_capacity(struct block_device *bdev, uint64_t wholedisk) { uint64_t psize; int64_t available; if (wholedisk && bdev != bdev_whole(bdev)) { /* * When reporting maximum expansion capacity for a wholedisk * deduct any capacity which is expected to be lost due to * alignment restrictions. Over reporting this value isn't * harmful and would only result in slightly less capacity * than expected post expansion. * The estimated available space may be slightly smaller than * bdev_capacity() for devices where the number of sectors is * not a multiple of the alignment size and the partition layout * is keeping less than PARTITION_END_ALIGNMENT bytes after the * "reserved" EFI partition: in such cases return the device * usable capacity. */ available = i_size_read(bdev_whole(bdev)->bd_inode) - ((EFI_MIN_RESV_SIZE + NEW_START_BLOCK + PARTITION_END_ALIGNMENT) << SECTOR_BITS); psize = MAX(available, bdev_capacity(bdev)); } else { psize = bdev_capacity(bdev); } return (psize); } static void vdev_disk_error(zio_t *zio) { /* * This function can be called in interrupt context, for instance while * handling IRQs coming from a misbehaving disk device; use printk() * which is safe from any context. */ printk(KERN_WARNING "zio pool=%s vdev=%s error=%d type=%d " "offset=%llu size=%llu flags=%llu\n", spa_name(zio->io_spa), zio->io_vd->vdev_path, zio->io_error, zio->io_type, (u_longlong_t)zio->io_offset, (u_longlong_t)zio->io_size, zio->io_flags); } static void vdev_disk_kobj_evt_post(vdev_t *v) { vdev_disk_t *vd = v->vdev_tsd; if (vd && vd->vd_bdh) { spl_signal_kobj_evt(BDH_BDEV(vd->vd_bdh)); } else { vdev_dbgmsg(v, "vdev_disk_t is NULL for VDEV:%s\n", v->vdev_path); } } static zfs_bdev_handle_t * vdev_blkdev_get_by_path(const char *path, spa_mode_t mode, void *holder) { #if defined(HAVE_BDEV_OPEN_BY_PATH) return (bdev_open_by_path(path, vdev_bdev_mode(mode, B_TRUE), holder, NULL)); #elif defined(HAVE_BLKDEV_GET_BY_PATH_4ARG) return (blkdev_get_by_path(path, vdev_bdev_mode(mode, B_TRUE), holder, NULL)); #else return (blkdev_get_by_path(path, vdev_bdev_mode(mode, B_TRUE), holder)); #endif } static void vdev_blkdev_put(zfs_bdev_handle_t *bdh, spa_mode_t mode, void *holder) { #if defined(HAVE_BDEV_RELEASE) return (bdev_release(bdh)); #elif defined(HAVE_BLKDEV_PUT_HOLDER) return (blkdev_put(BDH_BDEV(bdh), holder)); #else return (blkdev_put(BDH_BDEV(bdh), vdev_bdev_mode(mode, B_TRUE))); #endif } static int vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize, uint64_t *logical_ashift, uint64_t *physical_ashift) { zfs_bdev_handle_t *bdh; #ifdef HAVE_BLK_MODE_T blk_mode_t mode = vdev_bdev_mode(spa_mode(v->vdev_spa), B_FALSE); #else fmode_t mode = vdev_bdev_mode(spa_mode(v->vdev_spa), B_FALSE); #endif hrtime_t timeout = MSEC2NSEC(zfs_vdev_open_timeout_ms); vdev_disk_t *vd; /* Must have a pathname and it must be absolute. */ if (v->vdev_path == NULL || v->vdev_path[0] != '/') { v->vdev_stat.vs_aux = VDEV_AUX_BAD_LABEL; vdev_dbgmsg(v, "invalid vdev_path"); return (SET_ERROR(EINVAL)); } /* * Reopen the device if it is currently open. When expanding a * partition force re-scanning the partition table if userland * did not take care of this already. We need to do this while closed * in order to get an accurate updated block device size. Then * since udev may need to recreate the device links increase the * open retry timeout before reporting the device as unavailable. */ vd = v->vdev_tsd; if (vd) { char disk_name[BDEVNAME_SIZE + 6] = "/dev/"; boolean_t reread_part = B_FALSE; rw_enter(&vd->vd_lock, RW_WRITER); bdh = vd->vd_bdh; vd->vd_bdh = NULL; if (bdh) { struct block_device *bdev = BDH_BDEV(bdh); if (v->vdev_expanding && bdev != bdev_whole(bdev)) { vdev_bdevname(bdev_whole(bdev), disk_name + 5); /* * If userland has BLKPG_RESIZE_PARTITION, * then it should have updated the partition * table already. We can detect this by * comparing our current physical size * with that of the device. If they are * the same, then we must not have * BLKPG_RESIZE_PARTITION or it failed to * update the partition table online. We * fallback to rescanning the partition * table from the kernel below. However, * if the capacity already reflects the * updated partition, then we skip * rescanning the partition table here. */ if (v->vdev_psize == bdev_capacity(bdev)) reread_part = B_TRUE; } vdev_blkdev_put(bdh, mode, zfs_vdev_holder); } if (reread_part) { bdh = vdev_blkdev_get_by_path(disk_name, mode, zfs_vdev_holder); if (!BDH_IS_ERR(bdh)) { int error = vdev_bdev_reread_part(BDH_BDEV(bdh)); vdev_blkdev_put(bdh, mode, zfs_vdev_holder); if (error == 0) { timeout = MSEC2NSEC( zfs_vdev_open_timeout_ms * 2); } } } } else { vd = kmem_zalloc(sizeof (vdev_disk_t), KM_SLEEP); rw_init(&vd->vd_lock, NULL, RW_DEFAULT, NULL); rw_enter(&vd->vd_lock, RW_WRITER); } /* * Devices are always opened by the path provided at configuration * time. This means that if the provided path is a udev by-id path * then drives may be re-cabled without an issue. If the provided * path is a udev by-path path, then the physical location information * will be preserved. This can be critical for more complicated * configurations where drives are located in specific physical * locations to maximize the systems tolerance to component failure. * * Alternatively, you can provide your own udev rule to flexibly map * the drives as you see fit. It is not advised that you use the * /dev/[hd]d devices which may be reordered due to probing order. * Devices in the wrong locations will be detected by the higher * level vdev validation. * * The specified paths may be briefly removed and recreated in * response to udev events. This should be exceptionally unlikely * because the zpool command makes every effort to verify these paths * have already settled prior to reaching this point. Therefore, * a ENOENT failure at this point is highly likely to be transient * and it is reasonable to sleep and retry before giving up. In * practice delays have been observed to be on the order of 100ms. * * When ERESTARTSYS is returned it indicates the block device is * a zvol which could not be opened due to the deadlock detection * logic in zvol_open(). Extend the timeout and retry the open * subsequent attempts are expected to eventually succeed. */ hrtime_t start = gethrtime(); bdh = BDH_ERR_PTR(-ENXIO); while (BDH_IS_ERR(bdh) && ((gethrtime() - start) < timeout)) { bdh = vdev_blkdev_get_by_path(v->vdev_path, mode, zfs_vdev_holder); if (unlikely(BDH_PTR_ERR(bdh) == -ENOENT)) { /* * There is no point of waiting since device is removed * explicitly */ if (v->vdev_removed) break; schedule_timeout(MSEC_TO_TICK(10)); } else if (unlikely(BDH_PTR_ERR(bdh) == -ERESTARTSYS)) { timeout = MSEC2NSEC(zfs_vdev_open_timeout_ms * 10); continue; } else if (BDH_IS_ERR(bdh)) { break; } } if (BDH_IS_ERR(bdh)) { int error = -BDH_PTR_ERR(bdh); vdev_dbgmsg(v, "open error=%d timeout=%llu/%llu", error, (u_longlong_t)(gethrtime() - start), (u_longlong_t)timeout); vd->vd_bdh = NULL; v->vdev_tsd = vd; rw_exit(&vd->vd_lock); return (SET_ERROR(error)); } else { vd->vd_bdh = bdh; v->vdev_tsd = vd; rw_exit(&vd->vd_lock); } struct block_device *bdev = BDH_BDEV(vd->vd_bdh); /* Determine the physical block size */ int physical_block_size = bdev_physical_block_size(bdev); /* Determine the logical block size */ int logical_block_size = bdev_logical_block_size(bdev); /* Clear the nowritecache bit, causes vdev_reopen() to try again. */ v->vdev_nowritecache = B_FALSE; /* Set when device reports it supports TRIM. */ v->vdev_has_trim = bdev_discard_supported(bdev); /* Set when device reports it supports secure TRIM. */ v->vdev_has_securetrim = bdev_secure_discard_supported(bdev); /* Inform the ZIO pipeline that we are non-rotational */ v->vdev_nonrot = blk_queue_nonrot(bdev_get_queue(bdev)); /* Physical volume size in bytes for the partition */ *psize = bdev_capacity(bdev); /* Physical volume size in bytes including possible expansion space */ *max_psize = bdev_max_capacity(bdev, v->vdev_wholedisk); /* Based on the minimum sector size set the block size */ *physical_ashift = highbit64(MAX(physical_block_size, SPA_MINBLOCKSIZE)) - 1; *logical_ashift = highbit64(MAX(logical_block_size, SPA_MINBLOCKSIZE)) - 1; return (0); } static void vdev_disk_close(vdev_t *v) { vdev_disk_t *vd = v->vdev_tsd; if (v->vdev_reopening || vd == NULL) return; if (vd->vd_bdh != NULL) vdev_blkdev_put(vd->vd_bdh, spa_mode(v->vdev_spa), zfs_vdev_holder); rw_destroy(&vd->vd_lock); kmem_free(vd, sizeof (vdev_disk_t)); v->vdev_tsd = NULL; } static inline void vdev_submit_bio_impl(struct bio *bio) { #ifdef HAVE_1ARG_SUBMIT_BIO (void) submit_bio(bio); #else (void) submit_bio(bio_data_dir(bio), bio); #endif } /* * preempt_schedule_notrace is GPL-only which breaks the ZFS build, so * replace it with preempt_schedule under the following condition: */ #if defined(CONFIG_ARM64) && \ defined(CONFIG_PREEMPTION) && \ defined(CONFIG_BLK_CGROUP) #define preempt_schedule_notrace(x) preempt_schedule(x) #endif /* * As for the Linux 5.18 kernel bio_alloc() expects a block_device struct * as an argument removing the need to set it with bio_set_dev(). This * removes the need for all of the following compatibility code. */ #if !defined(HAVE_BIO_ALLOC_4ARG) #ifdef HAVE_BIO_SET_DEV #if defined(CONFIG_BLK_CGROUP) && defined(HAVE_BIO_SET_DEV_GPL_ONLY) /* * The Linux 5.5 kernel updated percpu_ref_tryget() which is inlined by * blkg_tryget() to use rcu_read_lock() instead of rcu_read_lock_sched(). * As a side effect the function was converted to GPL-only. Define our * own version when needed which uses rcu_read_lock_sched(). * * The Linux 5.17 kernel split linux/blk-cgroup.h into a private and a public * part, moving blkg_tryget into the private one. Define our own version. */ #if defined(HAVE_BLKG_TRYGET_GPL_ONLY) || !defined(HAVE_BLKG_TRYGET) static inline bool vdev_blkg_tryget(struct blkcg_gq *blkg) { struct percpu_ref *ref = &blkg->refcnt; unsigned long __percpu *count; bool rc; rcu_read_lock_sched(); if (__ref_is_percpu(ref, &count)) { this_cpu_inc(*count); rc = true; } else { #ifdef ZFS_PERCPU_REF_COUNT_IN_DATA rc = atomic_long_inc_not_zero(&ref->data->count); #else rc = atomic_long_inc_not_zero(&ref->count); #endif } rcu_read_unlock_sched(); return (rc); } #else #define vdev_blkg_tryget(bg) blkg_tryget(bg) #endif #ifdef HAVE_BIO_SET_DEV_MACRO /* * The Linux 5.0 kernel updated the bio_set_dev() macro so it calls the * GPL-only bio_associate_blkg() symbol thus inadvertently converting * the entire macro. Provide a minimal version which always assigns the * request queue's root_blkg to the bio. */ static inline void vdev_bio_associate_blkg(struct bio *bio) { #if defined(HAVE_BIO_BDEV_DISK) struct request_queue *q = bio->bi_bdev->bd_disk->queue; #else struct request_queue *q = bio->bi_disk->queue; #endif ASSERT3P(q, !=, NULL); ASSERT3P(bio->bi_blkg, ==, NULL); if (q->root_blkg && vdev_blkg_tryget(q->root_blkg)) bio->bi_blkg = q->root_blkg; } #define bio_associate_blkg vdev_bio_associate_blkg #else static inline void vdev_bio_set_dev(struct bio *bio, struct block_device *bdev) { #if defined(HAVE_BIO_BDEV_DISK) struct request_queue *q = bdev->bd_disk->queue; #else struct request_queue *q = bio->bi_disk->queue; #endif bio_clear_flag(bio, BIO_REMAPPED); if (bio->bi_bdev != bdev) bio_clear_flag(bio, BIO_THROTTLED); bio->bi_bdev = bdev; ASSERT3P(q, !=, NULL); ASSERT3P(bio->bi_blkg, ==, NULL); if (q->root_blkg && vdev_blkg_tryget(q->root_blkg)) bio->bi_blkg = q->root_blkg; } #define bio_set_dev vdev_bio_set_dev #endif #endif #else /* * Provide a bio_set_dev() helper macro for pre-Linux 4.14 kernels. */ static inline void bio_set_dev(struct bio *bio, struct block_device *bdev) { bio->bi_bdev = bdev; } #endif /* HAVE_BIO_SET_DEV */ #endif /* !HAVE_BIO_ALLOC_4ARG */ static inline void vdev_submit_bio(struct bio *bio) { struct bio_list *bio_list = current->bio_list; current->bio_list = NULL; vdev_submit_bio_impl(bio); current->bio_list = bio_list; } static inline struct bio * vdev_bio_alloc(struct block_device *bdev, gfp_t gfp_mask, unsigned short nr_vecs) { struct bio *bio; #ifdef HAVE_BIO_ALLOC_4ARG bio = bio_alloc(bdev, nr_vecs, 0, gfp_mask); #else bio = bio_alloc(gfp_mask, nr_vecs); if (likely(bio != NULL)) bio_set_dev(bio, bdev); #endif return (bio); } static inline uint_t vdev_bio_max_segs(struct block_device *bdev) { /* * Smallest of the device max segs and the tuneable max segs. Minimum * 4, so there's room to finish split pages if they come up. */ const uint_t dev_max_segs = queue_max_segments(bdev_get_queue(bdev)); const uint_t tune_max_segs = (zfs_vdev_disk_max_segs > 0) ? MAX(4, zfs_vdev_disk_max_segs) : dev_max_segs; const uint_t max_segs = MIN(tune_max_segs, dev_max_segs); #ifdef HAVE_BIO_MAX_SEGS return (bio_max_segs(max_segs)); #else return (MIN(max_segs, BIO_MAX_PAGES)); #endif } static inline uint_t vdev_bio_max_bytes(struct block_device *bdev) { return (queue_max_sectors(bdev_get_queue(bdev)) << 9); } /* * Virtual block IO object (VBIO) * * Linux block IO (BIO) objects have a limit on how many data segments (pages) * they can hold. Depending on how they're allocated and structured, a large * ZIO can require more than one BIO to be submitted to the kernel, which then * all have to complete before we can return the completed ZIO back to ZFS. * * A VBIO is a wrapper around multiple BIOs, carrying everything needed to * translate a ZIO down into the kernel block layer and back again. * * Note that these are only used for data ZIOs (read/write). Meta-operations * (flush/trim) don't need multiple BIOs and so can just make the call * directly. */ typedef struct { zio_t *vbio_zio; /* parent zio */ struct block_device *vbio_bdev; /* blockdev to submit bios to */ abd_t *vbio_abd; /* abd carrying borrowed linear buf */ uint_t vbio_max_segs; /* max segs per bio */ uint_t vbio_max_bytes; /* max bytes per bio */ uint_t vbio_lbs_mask; /* logical block size mask */ uint64_t vbio_offset; /* start offset of next bio */ struct bio *vbio_bio; /* pointer to the current bio */ int vbio_flags; /* bio flags */ } vbio_t; static vbio_t * vbio_alloc(zio_t *zio, struct block_device *bdev, int flags) { vbio_t *vbio = kmem_zalloc(sizeof (vbio_t), KM_SLEEP); vbio->vbio_zio = zio; vbio->vbio_bdev = bdev; vbio->vbio_abd = NULL; vbio->vbio_max_segs = vdev_bio_max_segs(bdev); vbio->vbio_max_bytes = vdev_bio_max_bytes(bdev); vbio->vbio_lbs_mask = ~(bdev_logical_block_size(bdev)-1); vbio->vbio_offset = zio->io_offset; vbio->vbio_bio = NULL; vbio->vbio_flags = flags; return (vbio); } BIO_END_IO_PROTO(vbio_completion, bio, error); static int vbio_add_page(vbio_t *vbio, struct page *page, uint_t size, uint_t offset) { struct bio *bio = vbio->vbio_bio; uint_t ssize; while (size > 0) { if (bio == NULL) { /* New BIO, allocate and set up */ bio = vdev_bio_alloc(vbio->vbio_bdev, GFP_NOIO, vbio->vbio_max_segs); VERIFY(bio); BIO_BI_SECTOR(bio) = vbio->vbio_offset >> 9; bio_set_op_attrs(bio, vbio->vbio_zio->io_type == ZIO_TYPE_WRITE ? WRITE : READ, vbio->vbio_flags); if (vbio->vbio_bio) { bio_chain(vbio->vbio_bio, bio); vdev_submit_bio(vbio->vbio_bio); } vbio->vbio_bio = bio; } /* * Only load as much of the current page data as will fit in * the space left in the BIO, respecting lbs alignment. Older * kernels will error if we try to overfill the BIO, while * newer ones will accept it and split the BIO. This ensures * everything works on older kernels, and avoids an additional * overhead on the new. */ ssize = MIN(size, (vbio->vbio_max_bytes - BIO_BI_SIZE(bio)) & vbio->vbio_lbs_mask); if (ssize > 0 && bio_add_page(bio, page, ssize, offset) == ssize) { /* Accepted, adjust and load any remaining. */ size -= ssize; offset += ssize; continue; } /* No room, set up for a new BIO and loop */ vbio->vbio_offset += BIO_BI_SIZE(bio); /* Signal new BIO allocation wanted */ bio = NULL; } return (0); } /* Iterator callback to submit ABD pages to the vbio. */ static int vbio_fill_cb(struct page *page, size_t off, size_t len, void *priv) { vbio_t *vbio = priv; return (vbio_add_page(vbio, page, len, off)); } /* Create some BIOs, fill them with data and submit them */ static void vbio_submit(vbio_t *vbio, abd_t *abd, uint64_t size) { - ASSERT(vbio->vbio_bdev); - /* * We plug so we can submit the BIOs as we go and only unplug them when * they are fully created and submitted. This is important; if we don't * plug, then the kernel may start executing earlier BIOs while we're * still creating and executing later ones, and if the device goes * away while that's happening, older kernels can get confused and * trample memory. */ struct blk_plug plug; blk_start_plug(&plug); (void) abd_iterate_page_func(abd, 0, size, vbio_fill_cb, vbio); ASSERT(vbio->vbio_bio); vbio->vbio_bio->bi_end_io = vbio_completion; vbio->vbio_bio->bi_private = vbio; + /* + * Once submitted, vbio_bio now owns vbio (through bi_private) and we + * can't touch it again. The bio may complete and vbio_completion() be + * called and free the vbio before this task is run again, so we must + * consider it invalid from this point. + */ vdev_submit_bio(vbio->vbio_bio); blk_finish_plug(&plug); - - vbio->vbio_bio = NULL; - vbio->vbio_bdev = NULL; } /* IO completion callback */ BIO_END_IO_PROTO(vbio_completion, bio, error) { vbio_t *vbio = bio->bi_private; zio_t *zio = vbio->vbio_zio; ASSERT(zio); /* Capture and log any errors */ #ifdef HAVE_1ARG_BIO_END_IO_T zio->io_error = BIO_END_IO_ERROR(bio); #else zio->io_error = 0; if (error) zio->io_error = -(error); else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) zio->io_error = EIO; #endif ASSERT3U(zio->io_error, >=, 0); if (zio->io_error) vdev_disk_error(zio); /* Return the BIO to the kernel */ bio_put(bio); /* * If we copied the ABD before issuing it, clean up and return the copy * to the ADB, with changes if appropriate. */ if (vbio->vbio_abd != NULL) { void *buf = abd_to_buf(vbio->vbio_abd); abd_free(vbio->vbio_abd); vbio->vbio_abd = NULL; if (zio->io_type == ZIO_TYPE_READ) abd_return_buf_copy(zio->io_abd, buf, zio->io_size); else abd_return_buf(zio->io_abd, buf, zio->io_size); } /* Final cleanup */ kmem_free(vbio, sizeof (vbio_t)); /* All done, submit for processing */ zio_delay_interrupt(zio); } /* * Iterator callback to count ABD pages and check their size & alignment. * * On Linux, each BIO segment can take a page pointer, and an offset+length of * the data within that page. A page can be arbitrarily large ("compound" * pages) but we still have to ensure the data portion is correctly sized and * aligned to the logical block size, to ensure that if the kernel wants to * split the BIO, the two halves will still be properly aligned. */ typedef struct { uint_t bmask; uint_t npages; uint_t end; } vdev_disk_check_pages_t; static int vdev_disk_check_pages_cb(struct page *page, size_t off, size_t len, void *priv) { vdev_disk_check_pages_t *s = priv; /* * If we didn't finish on a block size boundary last time, then there * would be a gap if we tried to use this ABD as-is, so abort. */ if (s->end != 0) return (1); /* * Note if we're taking less than a full block, so we can check it * above on the next call. */ s->end = len & s->bmask; /* All blocks after the first must start on a block size boundary. */ if (s->npages != 0 && (off & s->bmask) != 0) return (1); s->npages++; return (0); } /* * Check if we can submit the pages in this ABD to the kernel as-is. Returns * the number of pages, or 0 if it can't be submitted like this. */ static boolean_t vdev_disk_check_pages(abd_t *abd, uint64_t size, struct block_device *bdev) { vdev_disk_check_pages_t s = { .bmask = bdev_logical_block_size(bdev)-1, .npages = 0, .end = 0, }; if (abd_iterate_page_func(abd, 0, size, vdev_disk_check_pages_cb, &s)) return (B_FALSE); return (B_TRUE); } static int vdev_disk_io_rw(zio_t *zio) { vdev_t *v = zio->io_vd; vdev_disk_t *vd = v->vdev_tsd; struct block_device *bdev = BDH_BDEV(vd->vd_bdh); int flags = 0; /* * Accessing outside the block device is never allowed. */ if (zio->io_offset + zio->io_size > bdev->bd_inode->i_size) { vdev_dbgmsg(zio->io_vd, "Illegal access %llu size %llu, device size %llu", (u_longlong_t)zio->io_offset, (u_longlong_t)zio->io_size, (u_longlong_t)i_size_read(bdev->bd_inode)); return (SET_ERROR(EIO)); } if (!(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)) && v->vdev_failfast == B_TRUE) { bio_set_flags_failfast(bdev, &flags, zfs_vdev_failfast_mask & 1, zfs_vdev_failfast_mask & 2, zfs_vdev_failfast_mask & 4); } /* * Check alignment of the incoming ABD. If any part of it would require * submitting a page that is not aligned to the logical block size, * then we take a copy into a linear buffer and submit that instead. * This should be impossible on a 512b LBS, and fairly rare on 4K, * usually requiring abnormally-small data blocks (eg gang blocks) * mixed into the same ABD as larger ones (eg aggregated). */ abd_t *abd = zio->io_abd; if (!vdev_disk_check_pages(abd, zio->io_size, bdev)) { void *buf; if (zio->io_type == ZIO_TYPE_READ) buf = abd_borrow_buf(zio->io_abd, zio->io_size); else buf = abd_borrow_buf_copy(zio->io_abd, zio->io_size); /* * Wrap the copy in an abd_t, so we can use the same iterators * to count and fill the vbio later. */ abd = abd_get_from_buf(buf, zio->io_size); /* * False here would mean the borrowed copy has an invalid * alignment too, which would mean we've somehow been passed a * linear ABD with an interior page that has a non-zero offset * or a size not a multiple of PAGE_SIZE. This is not possible. * It would mean either zio_buf_alloc() or its underlying * allocators have done something extremely strange, or our * math in vdev_disk_check_pages() is wrong. In either case, * something in seriously wrong and its not safe to continue. */ VERIFY(vdev_disk_check_pages(abd, zio->io_size, bdev)); } /* Allocate vbio, with a pointer to the borrowed ABD if necessary */ vbio_t *vbio = vbio_alloc(zio, bdev, flags); if (abd != zio->io_abd) vbio->vbio_abd = abd; /* Fill it with data pages and submit it to the kernel */ vbio_submit(vbio, abd, zio->io_size); return (0); } /* ========== */ /* * This is the classic, battle-tested BIO submission code. Until we're totally * sure that the new code is safe and correct in all cases, this will remain * available. * * It is enabled by setting zfs_vdev_disk_classic=1 at module load time. It is * enabled (=1) by default since 2.2.4, and disabled by default (=0) on master. * * These functions have been renamed to vdev_classic_* to make it clear what * they belong to, but their implementations are unchanged. */ /* * Virtual device vector for disks. */ typedef struct dio_request { zio_t *dr_zio; /* Parent ZIO */ atomic_t dr_ref; /* References */ int dr_error; /* Bio error */ int dr_bio_count; /* Count of bio's */ struct bio *dr_bio[]; /* Attached bio's */ } dio_request_t; static dio_request_t * vdev_classic_dio_alloc(int bio_count) { dio_request_t *dr = kmem_zalloc(sizeof (dio_request_t) + sizeof (struct bio *) * bio_count, KM_SLEEP); atomic_set(&dr->dr_ref, 0); dr->dr_bio_count = bio_count; dr->dr_error = 0; for (int i = 0; i < dr->dr_bio_count; i++) dr->dr_bio[i] = NULL; return (dr); } static void vdev_classic_dio_free(dio_request_t *dr) { int i; for (i = 0; i < dr->dr_bio_count; i++) if (dr->dr_bio[i]) bio_put(dr->dr_bio[i]); kmem_free(dr, sizeof (dio_request_t) + sizeof (struct bio *) * dr->dr_bio_count); } static void vdev_classic_dio_get(dio_request_t *dr) { atomic_inc(&dr->dr_ref); } static void vdev_classic_dio_put(dio_request_t *dr) { int rc = atomic_dec_return(&dr->dr_ref); /* * Free the dio_request when the last reference is dropped and * ensure zio_interpret is called only once with the correct zio */ if (rc == 0) { zio_t *zio = dr->dr_zio; int error = dr->dr_error; vdev_classic_dio_free(dr); if (zio) { zio->io_error = error; ASSERT3S(zio->io_error, >=, 0); if (zio->io_error) vdev_disk_error(zio); zio_delay_interrupt(zio); } } } BIO_END_IO_PROTO(vdev_classic_physio_completion, bio, error) { dio_request_t *dr = bio->bi_private; if (dr->dr_error == 0) { #ifdef HAVE_1ARG_BIO_END_IO_T dr->dr_error = BIO_END_IO_ERROR(bio); #else if (error) dr->dr_error = -(error); else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) dr->dr_error = EIO; #endif } /* Drop reference acquired by vdev_classic_physio */ vdev_classic_dio_put(dr); } static inline unsigned int vdev_classic_bio_max_segs(zio_t *zio, int bio_size, uint64_t abd_offset) { unsigned long nr_segs = abd_nr_pages_off(zio->io_abd, bio_size, abd_offset); #ifdef HAVE_BIO_MAX_SEGS return (bio_max_segs(nr_segs)); #else return (MIN(nr_segs, BIO_MAX_PAGES)); #endif } static int vdev_classic_physio(zio_t *zio) { vdev_t *v = zio->io_vd; vdev_disk_t *vd = v->vdev_tsd; struct block_device *bdev = BDH_BDEV(vd->vd_bdh); size_t io_size = zio->io_size; uint64_t io_offset = zio->io_offset; int rw = zio->io_type == ZIO_TYPE_READ ? READ : WRITE; int flags = 0; dio_request_t *dr; uint64_t abd_offset; uint64_t bio_offset; int bio_size; int bio_count = 16; int error = 0; struct blk_plug plug; unsigned short nr_vecs; /* * Accessing outside the block device is never allowed. */ if (io_offset + io_size > bdev->bd_inode->i_size) { vdev_dbgmsg(zio->io_vd, "Illegal access %llu size %llu, device size %llu", (u_longlong_t)io_offset, (u_longlong_t)io_size, (u_longlong_t)i_size_read(bdev->bd_inode)); return (SET_ERROR(EIO)); } retry: dr = vdev_classic_dio_alloc(bio_count); if (!(zio->io_flags & (ZIO_FLAG_IO_RETRY | ZIO_FLAG_TRYHARD)) && zio->io_vd->vdev_failfast == B_TRUE) { bio_set_flags_failfast(bdev, &flags, zfs_vdev_failfast_mask & 1, zfs_vdev_failfast_mask & 2, zfs_vdev_failfast_mask & 4); } dr->dr_zio = zio; /* * Since bio's can have up to BIO_MAX_PAGES=256 iovec's, each of which * is at least 512 bytes and at most PAGESIZE (typically 4K), one bio * can cover at least 128KB and at most 1MB. When the required number * of iovec's exceeds this, we are forced to break the IO in multiple * bio's and wait for them all to complete. This is likely if the * recordsize property is increased beyond 1MB. The default * bio_count=16 should typically accommodate the maximum-size zio of * 16MB. */ abd_offset = 0; bio_offset = io_offset; bio_size = io_size; for (int i = 0; i <= dr->dr_bio_count; i++) { /* Finished constructing bio's for given buffer */ if (bio_size <= 0) break; /* * If additional bio's are required, we have to retry, but * this should be rare - see the comment above. */ if (dr->dr_bio_count == i) { vdev_classic_dio_free(dr); bio_count *= 2; goto retry; } nr_vecs = vdev_classic_bio_max_segs(zio, bio_size, abd_offset); dr->dr_bio[i] = vdev_bio_alloc(bdev, GFP_NOIO, nr_vecs); if (unlikely(dr->dr_bio[i] == NULL)) { vdev_classic_dio_free(dr); return (SET_ERROR(ENOMEM)); } /* Matching put called by vdev_classic_physio_completion */ vdev_classic_dio_get(dr); BIO_BI_SECTOR(dr->dr_bio[i]) = bio_offset >> 9; dr->dr_bio[i]->bi_end_io = vdev_classic_physio_completion; dr->dr_bio[i]->bi_private = dr; bio_set_op_attrs(dr->dr_bio[i], rw, flags); /* Remaining size is returned to become the new size */ bio_size = abd_bio_map_off(dr->dr_bio[i], zio->io_abd, bio_size, abd_offset); /* Advance in buffer and construct another bio if needed */ abd_offset += BIO_BI_SIZE(dr->dr_bio[i]); bio_offset += BIO_BI_SIZE(dr->dr_bio[i]); } /* Extra reference to protect dio_request during vdev_submit_bio */ vdev_classic_dio_get(dr); if (dr->dr_bio_count > 1) blk_start_plug(&plug); /* Submit all bio's associated with this dio */ for (int i = 0; i < dr->dr_bio_count; i++) { if (dr->dr_bio[i]) vdev_submit_bio(dr->dr_bio[i]); } if (dr->dr_bio_count > 1) blk_finish_plug(&plug); vdev_classic_dio_put(dr); return (error); } /* ========== */ BIO_END_IO_PROTO(vdev_disk_io_flush_completion, bio, error) { zio_t *zio = bio->bi_private; #ifdef HAVE_1ARG_BIO_END_IO_T zio->io_error = BIO_END_IO_ERROR(bio); #else zio->io_error = -error; #endif if (zio->io_error && (zio->io_error == EOPNOTSUPP)) zio->io_vd->vdev_nowritecache = B_TRUE; bio_put(bio); ASSERT3S(zio->io_error, >=, 0); if (zio->io_error) vdev_disk_error(zio); zio_interrupt(zio); } static int vdev_disk_io_flush(struct block_device *bdev, zio_t *zio) { struct request_queue *q; struct bio *bio; q = bdev_get_queue(bdev); if (!q) return (SET_ERROR(ENXIO)); bio = vdev_bio_alloc(bdev, GFP_NOIO, 0); if (unlikely(bio == NULL)) return (SET_ERROR(ENOMEM)); bio->bi_end_io = vdev_disk_io_flush_completion; bio->bi_private = zio; bio_set_flush(bio); vdev_submit_bio(bio); invalidate_bdev(bdev); return (0); } #if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE) || \ defined(HAVE_BLKDEV_ISSUE_DISCARD_ASYNC) BIO_END_IO_PROTO(vdev_disk_discard_end_io, bio, error) { zio_t *zio = bio->bi_private; #ifdef HAVE_1ARG_BIO_END_IO_T zio->io_error = BIO_END_IO_ERROR(bio); #else zio->io_error = -error; #endif bio_put(bio); if (zio->io_error) vdev_disk_error(zio); zio_interrupt(zio); } static int vdev_issue_discard_trim(zio_t *zio, unsigned long flags) { int ret; struct bio *bio = NULL; #if defined(BLKDEV_DISCARD_SECURE) ret = - __blkdev_issue_discard( BDH_BDEV(((vdev_disk_t *)zio->io_vd->vdev_tsd)->vd_bdh), zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS, flags, &bio); #else (void) flags; ret = - __blkdev_issue_discard( BDH_BDEV(((vdev_disk_t *)zio->io_vd->vdev_tsd)->vd_bdh), zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS, &bio); #endif if (!ret && bio) { bio->bi_private = zio; bio->bi_end_io = vdev_disk_discard_end_io; vdev_submit_bio(bio); } return (ret); } #endif static int vdev_disk_io_trim(zio_t *zio) { unsigned long trim_flags = 0; if (zio->io_trim_flags & ZIO_TRIM_SECURE) { #if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE) return (-blkdev_issue_secure_erase( BDH_BDEV(((vdev_disk_t *)zio->io_vd->vdev_tsd)->vd_bdh), zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS)); #elif defined(BLKDEV_DISCARD_SECURE) trim_flags |= BLKDEV_DISCARD_SECURE; #endif } #if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE) || \ defined(HAVE_BLKDEV_ISSUE_DISCARD_ASYNC) return (vdev_issue_discard_trim(zio, trim_flags)); #elif defined(HAVE_BLKDEV_ISSUE_DISCARD) return (-blkdev_issue_discard( BDH_BDEV(((vdev_disk_t *)zio->io_vd->vdev_tsd)->vd_bdh), zio->io_offset >> 9, zio->io_size >> 9, GFP_NOFS, trim_flags)); #else #error "Unsupported kernel" #endif } int (*vdev_disk_io_rw_fn)(zio_t *zio) = NULL; static void vdev_disk_io_start(zio_t *zio) { vdev_t *v = zio->io_vd; vdev_disk_t *vd = v->vdev_tsd; int error; /* * If the vdev is closed, it's likely in the REMOVED or FAULTED state. * Nothing to be done here but return failure. */ if (vd == NULL) { zio->io_error = ENXIO; zio_interrupt(zio); return; } rw_enter(&vd->vd_lock, RW_READER); /* * If the vdev is closed, it's likely due to a failed reopen and is * in the UNAVAIL state. Nothing to be done here but return failure. */ if (vd->vd_bdh == NULL) { rw_exit(&vd->vd_lock); zio->io_error = ENXIO; zio_interrupt(zio); return; } switch (zio->io_type) { case ZIO_TYPE_IOCTL: if (!vdev_readable(v)) { rw_exit(&vd->vd_lock); zio->io_error = SET_ERROR(ENXIO); zio_interrupt(zio); return; } switch (zio->io_cmd) { case DKIOCFLUSHWRITECACHE: if (zfs_nocacheflush) break; if (v->vdev_nowritecache) { zio->io_error = SET_ERROR(ENOTSUP); break; } error = vdev_disk_io_flush(BDH_BDEV(vd->vd_bdh), zio); if (error == 0) { rw_exit(&vd->vd_lock); return; } zio->io_error = error; break; default: zio->io_error = SET_ERROR(ENOTSUP); } rw_exit(&vd->vd_lock); zio_execute(zio); return; case ZIO_TYPE_TRIM: zio->io_error = vdev_disk_io_trim(zio); rw_exit(&vd->vd_lock); #if defined(HAVE_BLKDEV_ISSUE_SECURE_ERASE) if (zio->io_trim_flags & ZIO_TRIM_SECURE) zio_interrupt(zio); #elif defined(HAVE_BLKDEV_ISSUE_DISCARD) zio_interrupt(zio); #endif return; case ZIO_TYPE_READ: case ZIO_TYPE_WRITE: zio->io_target_timestamp = zio_handle_io_delay(zio); error = vdev_disk_io_rw_fn(zio); rw_exit(&vd->vd_lock); if (error) { zio->io_error = error; zio_interrupt(zio); } return; default: /* * Getting here means our parent vdev has made a very strange * request of us, and shouldn't happen. Assert here to force a * crash in dev builds, but in production return the IO * unhandled. The pool will likely suspend anyway but that's * nicer than crashing the kernel. */ ASSERT3S(zio->io_type, ==, -1); rw_exit(&vd->vd_lock); zio->io_error = SET_ERROR(ENOTSUP); zio_interrupt(zio); return; } __builtin_unreachable(); } static void vdev_disk_io_done(zio_t *zio) { /* * If the device returned EIO, we revalidate the media. If it is * determined the media has changed this triggers the asynchronous * removal of the device from the configuration. */ if (zio->io_error == EIO) { vdev_t *v = zio->io_vd; vdev_disk_t *vd = v->vdev_tsd; if (!zfs_check_disk_status(BDH_BDEV(vd->vd_bdh))) { invalidate_bdev(BDH_BDEV(vd->vd_bdh)); v->vdev_remove_wanted = B_TRUE; spa_async_request(zio->io_spa, SPA_ASYNC_REMOVE); } } } static void vdev_disk_hold(vdev_t *vd) { ASSERT(spa_config_held(vd->vdev_spa, SCL_STATE, RW_WRITER)); /* We must have a pathname, and it must be absolute. */ if (vd->vdev_path == NULL || vd->vdev_path[0] != '/') return; /* * Only prefetch path and devid info if the device has * never been opened. */ if (vd->vdev_tsd != NULL) return; } static void vdev_disk_rele(vdev_t *vd) { ASSERT(spa_config_held(vd->vdev_spa, SCL_STATE, RW_WRITER)); /* XXX: Implement me as a vnode rele for the device */ } /* * BIO submission method. See comment above about vdev_classic. * Set zfs_vdev_disk_classic=0 for new, =1 for classic */ static uint_t zfs_vdev_disk_classic = 1; /* default classic */ /* Set submission function from module parameter */ static int vdev_disk_param_set_classic(const char *buf, zfs_kernel_param_t *kp) { int err = param_set_uint(buf, kp); if (err < 0) return (SET_ERROR(err)); vdev_disk_io_rw_fn = zfs_vdev_disk_classic ? vdev_classic_physio : vdev_disk_io_rw; printk(KERN_INFO "ZFS: forcing %s BIO submission\n", zfs_vdev_disk_classic ? "classic" : "new"); return (0); } /* * At first use vdev use, set the submission function from the default value if * it hasn't been set already. */ static int vdev_disk_init(spa_t *spa, nvlist_t *nv, void **tsd) { (void) spa; (void) nv; (void) tsd; if (vdev_disk_io_rw_fn == NULL) vdev_disk_io_rw_fn = zfs_vdev_disk_classic ? vdev_classic_physio : vdev_disk_io_rw; return (0); } vdev_ops_t vdev_disk_ops = { .vdev_op_init = vdev_disk_init, .vdev_op_fini = NULL, .vdev_op_open = vdev_disk_open, .vdev_op_close = vdev_disk_close, .vdev_op_asize = vdev_default_asize, .vdev_op_min_asize = vdev_default_min_asize, .vdev_op_min_alloc = NULL, .vdev_op_io_start = vdev_disk_io_start, .vdev_op_io_done = vdev_disk_io_done, .vdev_op_state_change = NULL, .vdev_op_need_resilver = NULL, .vdev_op_hold = vdev_disk_hold, .vdev_op_rele = vdev_disk_rele, .vdev_op_remap = NULL, .vdev_op_xlate = vdev_default_xlate, .vdev_op_rebuild_asize = NULL, .vdev_op_metaslab_init = NULL, .vdev_op_config_generate = NULL, .vdev_op_nparity = NULL, .vdev_op_ndisks = NULL, .vdev_op_type = VDEV_TYPE_DISK, /* name of this vdev type */ .vdev_op_leaf = B_TRUE, /* leaf vdev */ .vdev_op_kobj_evt_post = vdev_disk_kobj_evt_post }; /* * The zfs_vdev_scheduler module option has been deprecated. Setting this * value no longer has any effect. It has not yet been entirely removed * to allow the module to be loaded if this option is specified in the * /etc/modprobe.d/zfs.conf file. The following warning will be logged. */ static int param_set_vdev_scheduler(const char *val, zfs_kernel_param_t *kp) { int error = param_set_charp(val, kp); if (error == 0) { printk(KERN_INFO "The 'zfs_vdev_scheduler' module option " "is not supported.\n"); } return (error); } static const char *zfs_vdev_scheduler = "unused"; module_param_call(zfs_vdev_scheduler, param_set_vdev_scheduler, param_get_charp, &zfs_vdev_scheduler, 0644); MODULE_PARM_DESC(zfs_vdev_scheduler, "I/O scheduler"); int param_set_min_auto_ashift(const char *buf, zfs_kernel_param_t *kp) { uint_t val; int error; error = kstrtouint(buf, 0, &val); if (error < 0) return (SET_ERROR(error)); if (val < ASHIFT_MIN || val > zfs_vdev_max_auto_ashift) return (SET_ERROR(-EINVAL)); error = param_set_uint(buf, kp); if (error < 0) return (SET_ERROR(error)); return (0); } int param_set_max_auto_ashift(const char *buf, zfs_kernel_param_t *kp) { uint_t val; int error; error = kstrtouint(buf, 0, &val); if (error < 0) return (SET_ERROR(error)); if (val > ASHIFT_MAX || val < zfs_vdev_min_auto_ashift) return (SET_ERROR(-EINVAL)); error = param_set_uint(buf, kp); if (error < 0) return (SET_ERROR(error)); return (0); } ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, open_timeout_ms, UINT, ZMOD_RW, "Timeout before determining that a device is missing"); ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, failfast_mask, UINT, ZMOD_RW, "Defines failfast mask: 1 - device, 2 - transport, 4 - driver"); ZFS_MODULE_PARAM(zfs_vdev_disk, zfs_vdev_disk_, max_segs, UINT, ZMOD_RW, "Maximum number of data segments to add to an IO request (min 4)"); ZFS_MODULE_PARAM_CALL(zfs_vdev_disk, zfs_vdev_disk_, classic, vdev_disk_param_set_classic, param_get_uint, ZMOD_RD, "Use classic BIO submission method");