virtio_blk: set the zone write granularitygrafted

virtblk_read_zoned_limits() reads the write granularity that the device
reports in virtio_blk_zoned_characteristics and assigns it to the
physical block size and to io_min, but never to the limit that is named
after it. queue_limits.zone_write_granularity is left at zero, so
blk_validate_zoned_limits() raises it to the logical block size:

	if (lim->zone_write_granularity < lim->logical_block_size)
		lim->zone_write_granularity = lim->logical_block_size;

A device that reports a granularity coarser than its logical block size,
which is what the field exists to express, therefore has it silently
reduced. A 512e host managed disk passed through to a guest reports a
logical block size of 512 and a write granularity of 4096, and the guest
ends up with a zone write granularity of 512.

bio_split_alignment() returns lim->zone_write_granularity if it is non-zero
and bio_split_io_at() may split a bio with as per bio_split_alignment().
This can real to the write getting rejected by the host drive, as the write
is not aligned to the physical block size.

zonefs also takes its block size from bdev_zone_write_granularity(), so it
would incorrectly use 512 on a disk that requires 4096.

sd_zbc_read_zones() sets the limit from the physical block size for the
same reason. NVMe ZNS and null_blk leave it unset, but the fallback
gives the right answer for them, as their write granularity is the
logical block size. virtio carries a separate value that may exceed it.

Set the zone write granularity from the value that the device reports.

Fixes: 95bfec41bd3d ("virtio-blk: add support for zoned block devices")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://patch.msgid.link/20260918140641.2031075-2-cassel@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 114 insertions, 0 deletions

diff --git a/include/net/dropreason-qdisc.h b/include/net/dropreason-qdisc.h
new file mode 100644
index 000000000..fb151cd31
--- /dev/null
+++ b/include/net/dropreason-qdisc.h
@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_DROPREASON_QDISC_H
+#define _LINUX_DROPREASON_QDISC_H
+#include <net/dropreason.h>
+
+#define DEFINE_QDISC_DROP_REASON(FN, FNe)	\
+	FN(UNSPEC)			\
+	FN(GENERIC)			\
+	FN(OVERLIMIT)			\
+	FN(CONGESTED)			\
+	FN(MAXFLOWS)			\
+	FN(FLOOD_PROTECTION)		\
+	FN(BAND_LIMIT)		\
+	FN(HORIZON_LIMIT)		\
+	FN(FLOW_LIMIT)			\
+	FN(L4S_STEP_NON_ECN)		\
+	FNe(MAX)
+
+#undef FN
+#undef FNe
+#define FN(reason)	QDISC_DROP_##reason,
+#define FNe(reason)	QDISC_DROP_##reason
+
+/**
+ * enum qdisc_drop_reason - reason why a qdisc dropped a packet
+ *
+ * Qdisc-specific drop reasons for packet drops that occur within the
+ * traffic control (TC) queueing discipline layer. These reasons provide
+ * detailed diagnostics about why packets were dropped by various qdisc
+ * algorithms, enabling fine-grained monitoring and troubleshooting of
+ * queue behavior.
+ */
+enum qdisc_drop_reason {
+	/**
+	 * @QDISC_DROP_UNSPEC: unspecified/invalid qdisc drop reason.
+	 * Value 0 serves as analogous to SKB_NOT_DROPPED_YET for enum skb_drop_reason.
+	 * Used for catching zero-initialized drop_reason fields.
+	 */
+	QDISC_DROP_UNSPEC = 0,
+	/**
+	 * @__QDISC_DROP_REASON: subsystem base value for qdisc drop reasons
+	 */
+	__QDISC_DROP_REASON = SKB_DROP_REASON_SUBSYS_QDISC <<
+				SKB_DROP_REASON_SUBSYS_SHIFT,
+	/**
+	 * @QDISC_DROP_GENERIC: generic/default qdisc drop, used when no
+	 * more specific reason applies
+	 */
+	QDISC_DROP_GENERIC,
+	/**
+	 * @QDISC_DROP_OVERLIMIT: packet dropped because the qdisc queue
+	 * length exceeded its configured limit (sch->limit). This typically
+	 * indicates the queue is full and cannot accept more packets.
+	 */
+	QDISC_DROP_OVERLIMIT,
+	/**
+	 * @QDISC_DROP_CONGESTED: packet dropped due to active congestion
+	 * control algorithms (e.g., CoDel, PIE, RED) detecting network
+	 * congestion. The qdisc proactively dropped the packet to signal
+	 * congestion to the sender and prevent bufferbloat.
+	 */
+	QDISC_DROP_CONGESTED,
+	/**
+	 * @QDISC_DROP_MAXFLOWS: packet dropped because the qdisc's flow
+	 * tracking table is full and no free slots are available to allocate
+	 * for a new flow. This indicates flow table exhaustion in flow-based
+	 * qdiscs that maintain per-flow state (e.g., SFQ).
+	 */
+	QDISC_DROP_MAXFLOWS,
+	/**
+	 * @QDISC_DROP_FLOOD_PROTECTION: packet dropped by flood protection
+	 * mechanism detecting unresponsive flows (potential DoS/flood).
+	 * Used by qdiscs implementing probabilistic drop algorithms like
+	 * BLUE (e.g., CAKE's Cobalt AQM).
+	 */
+	QDISC_DROP_FLOOD_PROTECTION,
+	/**
+	 * @QDISC_DROP_BAND_LIMIT: packet dropped because the priority band's
+	 * limit was reached. Used by qdiscs with priority bands that have
+	 * per-band packet limits (e.g., FQ).
+	 */
+	QDISC_DROP_BAND_LIMIT,
+	/**
+	 * @QDISC_DROP_HORIZON_LIMIT: packet dropped because its timestamp
+	 * is too far in the future (beyond the configured horizon).
+	 * Used by qdiscs with time-based scheduling (e.g., FQ).
+	 */
+	QDISC_DROP_HORIZON_LIMIT,
+	/**
+	 * @QDISC_DROP_FLOW_LIMIT: packet dropped because an individual flow
+	 * exceeded its per-flow packet/depth limit. Used by FQ and SFQ qdiscs
+	 * to enforce per-flow fairness and prevent a single flow from
+	 * monopolizing queue resources.
+	 */
+	QDISC_DROP_FLOW_LIMIT,
+	/**
+	 * @QDISC_DROP_L4S_STEP_NON_ECN: DualPI2 qdisc dropped a non-ECN-capable
+	 * packet because the L4S queue delay exceeded the step threshold.
+	 * Since the packet cannot be ECN-marked, it must be dropped to signal
+	 * congestion. See RFC 9332 for the DualQ Coupled AQM step mechanism.
+	 */
+	QDISC_DROP_L4S_STEP_NON_ECN,
+	/**
+	 * @QDISC_DROP_MAX: the maximum of qdisc drop reasons, which
+	 * shouldn't be used as a real 'reason' - only for tracing code gen
+	 */
+	QDISC_DROP_MAX,
+};
+
+#undef FN
+#undef FNe
+
+#endif