On 6/11/24 07:19, Christoph Hellwig wrote:
Move the cache control settings into the queue_limits so that they
can be set atomically and all I/O is frozen when changing the
flags.
Add new features and flags field for the driver set flags, and internal
(usually sysfs-controlled) flags in the block layer. Note that we'll
eventually remove enough field from queue_limits to bring it back to the
previous size.
The disable flag is inverted compared to the previous meaning, which
means it now survives a rescan, similar to the max_sectors and
max_discard_sectors user limits.
The FLUSH and FUA flags are now inherited by blk_stack_limits, which
simplified the code in dm a lot, but also causes a slight behavior
change in that dm-switch and dm-unstripe now advertise a write cache
despite setting num_flush_bios to 0. The I/O path will handle this
gracefully, but as far as I can tell the lack of num_flush_bios
and thus flush support is a pre-existing data integrity bug in those
targets that really needs fixing, after which a non-zero num_flush_bios
should be required in dm for targets that map to underlying devices.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
.../block/writeback_cache_control.rst | 67 +++++++++++--------
arch/um/drivers/ubd_kern.c | 2 +-
block/blk-core.c | 2 +-
block/blk-flush.c | 9 ++-
block/blk-mq-debugfs.c | 2 -
block/blk-settings.c | 29 ++------
block/blk-sysfs.c | 29 +++++---
block/blk-wbt.c | 4 +-
drivers/block/drbd/drbd_main.c | 2 +-
drivers/block/loop.c | 9 +--
drivers/block/nbd.c | 14 ++--
drivers/block/null_blk/main.c | 12 ++--
drivers/block/ps3disk.c | 7 +-
drivers/block/rnbd/rnbd-clt.c | 10 +--
drivers/block/ublk_drv.c | 8 ++-
drivers/block/virtio_blk.c | 20 ++++--
drivers/block/xen-blkfront.c | 9 ++-
drivers/md/bcache/super.c | 7 +-
drivers/md/dm-table.c | 39 +++--------
drivers/md/md.c | 8 ++-
drivers/mmc/core/block.c | 42 ++++++------
drivers/mmc/core/queue.c | 12 ++--
drivers/mmc/core/queue.h | 3 +-
drivers/mtd/mtd_blkdevs.c | 5 +-
drivers/nvdimm/pmem.c | 4 +-
drivers/nvme/host/core.c | 7 +-
drivers/nvme/host/multipath.c | 6 --
drivers/scsi/sd.c | 28 +++++---
include/linux/blkdev.h | 38 +++++++++--
29 files changed, 227 insertions(+), 207 deletions(-)
diff --git a/Documentation/block/writeback_cache_control.rst b/Documentation/block/writeback_cache_control.rst
index b208488d0aae85..9cfe27f90253c7 100644
--- a/Documentation/block/writeback_cache_control.rst
+++ b/Documentation/block/writeback_cache_control.rst
@@ -46,41 +46,50 @@ worry if the underlying devices need any explicit cache flushing and how
the Forced Unit Access is implemented. The REQ_PREFLUSH and REQ_FUA flags
may both be set on a single bio.
+Feature settings for block drivers
+----------------------------------
-Implementation details for bio based block drivers
---------------------------------------------------------------
+For devices that do not support volatile write caches there is no driver
+support required, the block layer completes empty REQ_PREFLUSH requests before
+entering the driver and strips off the REQ_PREFLUSH and REQ_FUA bits from
+requests that have a payload.
-These drivers will always see the REQ_PREFLUSH and REQ_FUA bits as they sit
-directly below the submit_bio interface. For remapping drivers the REQ_FUA
-bits need to be propagated to underlying devices, and a global flush needs
-to be implemented for bios with the REQ_PREFLUSH bit set. For real device
-drivers that do not have a volatile cache the REQ_PREFLUSH and REQ_FUA bits
-on non-empty bios can simply be ignored, and REQ_PREFLUSH requests without
-data can be completed successfully without doing any work. Drivers for
-devices with volatile caches need to implement the support for these
-flags themselves without any help from the block layer.
+For devices with volatile write caches the driver needs to tell the block layer
+that it supports flushing caches by setting the
+ BLK_FEAT_WRITE_CACHE
-Implementation details for request_fn based block drivers
----------------------------------------------------------
+flag in the queue_limits feature field. For devices that also support the FUA
+bit the block layer needs to be told to pass on the REQ_FUA bit by also setting
+the
-For devices that do not support volatile write caches there is no driver
-support required, the block layer completes empty REQ_PREFLUSH requests before
-entering the driver and strips off the REQ_PREFLUSH and REQ_FUA bits from
-requests that have a payload. For devices with volatile write caches the
-driver needs to tell the block layer that it supports flushing caches by
-doing::
+ BLK_FEAT_FUA
+
+flag in the features field of the queue_limits structure.
+
+Implementation details for bio based block drivers
+--------------------------------------------------
+
+For bio based drivers the REQ_PREFLUSH and REQ_FUA bit are simplify passed on
+to the driver if the drivers sets the BLK_FEAT_WRITE_CACHE flag and the drivers
+needs to handle them.
+
+*NOTE*: The REQ_FUA bit also gets passed on when the BLK_FEAT_FUA flags is
+_not_ set. Any bio based driver that sets BLK_FEAT_WRITE_CACHE also needs to
+handle REQ_FUA.
- blk_queue_write_cache(sdkp->disk->queue, true, false);
+For remapping drivers the REQ_FUA bits need to be propagated to underlying
+devices, and a global flush needs to be implemented for bios with the
+REQ_PREFLUSH bit set.
-and handle empty REQ_OP_FLUSH requests in its prep_fn/request_fn. Note that
-REQ_PREFLUSH requests with a payload are automatically turned into a sequence
-of an empty REQ_OP_FLUSH request followed by the actual write by the block
-layer. For devices that also support the FUA bit the block layer needs
-to be told to pass through the REQ_FUA bit using::
+Implementation details for blk-mq drivers
+-----------------------------------------
- blk_queue_write_cache(sdkp->disk->queue, true, true);
+When the BLK_FEAT_WRITE_CACHE flag is set, REQ_OP_WRITE | REQ_PREFLUSH requests
+with a payload are automatically turned into a sequence of a REQ_OP_FLUSH
+request followed by the actual write by the block layer.
-and the driver must handle write requests that have the REQ_FUA bit set
-in prep_fn/request_fn. If the FUA bit is not natively supported the block
-layer turns it into an empty REQ_OP_FLUSH request after the actual write.
+When the BLK_FEA_FUA flags is set, the REQ_FUA bit simplify passed on for the
+REQ_OP_WRITE request, else a REQ_OP_FLUSH request is sent by the block layer
+after the completion of the write request for bio submissions with the REQ_FUA
+bit set.
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index cdcb75a68989dd..19e01691ea0ea7 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -835,6 +835,7 @@ static int ubd_add(int n, char **error_out)
struct queue_limits lim = {
.max_segments = MAX_SG,
.seg_boundary_mask = PAGE_SIZE - 1,
+ .features = BLK_FEAT_WRITE_CACHE,
};
struct gendisk *disk;
int err = 0;
@@ -882,7 +883,6 @@ static int ubd_add(int n, char **error_out)
}
blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
- blk_queue_write_cache(disk->queue, true, false);
disk->major = UBD_MAJOR;
disk->first_minor = n << UBD_SHIFT;
disk->minors = 1 << UBD_SHIFT;
diff --git a/block/blk-core.c b/block/blk-core.c
index 82c3ae22d76d88..2b45a4df9a1aa1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -782,7 +782,7 @@ void submit_bio_noacct(struct bio *bio)
if (WARN_ON_ONCE(bio_op(bio) != REQ_OP_WRITE &&
bio_op(bio) != REQ_OP_ZONE_APPEND))
goto end_io;
- if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
+ if (!bdev_write_cache(bdev)) {
bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
if (!bio_sectors(bio)) {
status = BLK_STS_OK;
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 2234f8b3fc05f2..30b9d5033a2b85 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -381,8 +381,8 @@ static void blk_rq_init_flush(struct request *rq)
bool blk_insert_flush(struct request *rq)
{
struct request_queue *q = rq->q;
- unsigned long fflags = q->queue_flags; /* may change, cache */
struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
+ bool supports_fua = q->limits.features & BLK_FEAT_FUA;
Shouldn't we have a helper like blk_feat_fua() here?
unsigned int policy = 0;
/* FLUSH/FUA request must never be merged */
@@ -394,11 +394,10 @@ bool blk_insert_flush(struct request *rq)
/*
* Check which flushes we need to sequence for this operation.
*/
- if (fflags & (1UL << QUEUE_FLAG_WC)) {
+ if (blk_queue_write_cache(q)) {
if (rq->cmd_flags & REQ_PREFLUSH)
policy |= REQ_FSEQ_PREFLUSH;
- if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
- (rq->cmd_flags & REQ_FUA))
+ if ((rq->cmd_flags & REQ_FUA) && !supports_fua)
policy |= REQ_FSEQ_POSTFLUSH;
}
@@ -407,7 +406,7 @@ bool blk_insert_flush(struct request *rq)
* REQ_PREFLUSH and FUA for the driver.
*/
rq->cmd_flags &= ~REQ_PREFLUSH;
- if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
+ if (!supports_fua)
rq->cmd_flags &= ~REQ_FUA;
/*
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 770c0c2b72faaa..e8b9db7c30c455 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -93,8 +93,6 @@ static const char *const blk_queue_flag_name[] = {
QUEUE_FLAG_NAME(INIT_DONE),
QUEUE_FLAG_NAME(STABLE_WRITES),
QUEUE_FLAG_NAME(POLL),
- QUEUE_FLAG_NAME(WC),
- QUEUE_FLAG_NAME(FUA),
QUEUE_FLAG_NAME(DAX),
QUEUE_FLAG_NAME(STATS),
QUEUE_FLAG_NAME(REGISTERED),
diff --git a/block/blk-settings.c b/block/blk-settings.c
index f11c8676eb4c67..536ee202fcdccb 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -261,6 +261,9 @@ static int blk_validate_limits(struct queue_limits *lim)
lim->misaligned = 0;
}
+ if (!(lim->features & BLK_FEAT_WRITE_CACHE))
+ lim->features &= ~BLK_FEAT_FUA;
+
err = blk_validate_integrity_limits(lim);
if (err)
return err;
@@ -454,6 +457,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
{
unsigned int top, bottom, alignment, ret = 0;
+ t->features |= (b->features & BLK_FEAT_INHERIT_MASK);
+
t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
t->max_user_sectors = min_not_zero(t->max_user_sectors,
b->max_user_sectors);
@@ -711,30 +716,6 @@ void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
}
EXPORT_SYMBOL(blk_set_queue_depth);
-/**
- * blk_queue_write_cache - configure queue's write cache
- * @q: the request queue for the device
- * @wc: write back cache on or off
- * @fua: device supports FUA writes, if true
- *
- * Tell the block layer about the write cache of @q.
- */
-void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
-{
- if (wc) {
- blk_queue_flag_set(QUEUE_FLAG_HW_WC, q);
- blk_queue_flag_set(QUEUE_FLAG_WC, q);
- } else {
- blk_queue_flag_clear(QUEUE_FLAG_HW_WC, q);
- blk_queue_flag_clear(QUEUE_FLAG_WC, q);
- }
- if (fua)
- blk_queue_flag_set(QUEUE_FLAG_FUA, q);
- else
- blk_queue_flag_clear(QUEUE_FLAG_FUA, q);
-}
-EXPORT_SYMBOL_GPL(blk_queue_write_cache);
-
int bdev_alignment_offset(struct block_device *bdev)
{
struct request_queue *q = bdev_get_queue(bdev);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 5c787965b7d09e..4f524c1d5e08bd 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -423,32 +423,41 @@ static ssize_t queue_io_timeout_store(struct request_queue *q, const char *page,
static ssize_t queue_wc_show(struct request_queue *q, char *page)
{
- if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
- return sprintf(page, "write back\n");
-
- return sprintf(page, "write through\n");
+ if (q->limits.features & BLK_FLAGS_WRITE_CACHE_DISABLED)
Where is the difference between 'flags' and 'features'?
Ie why is is named BLK_FEAT_FUA but BLK_FLAGS_WRITE_CACHE_DISABLED?
And if the feature is the existence of a capability, and the flag is
the setting of that capability, can you make it clear in the documentation?
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
