STRUCT BLK_MQ_TAG_SET(9)

✨ NAME ✨

okay so bestie, welcome to the struct blk_mq_tag_set(9) page from the Kernel API Manual 💖 and the whole vibe is literally a tag set that can be shared between request queues. that's the name, that's the energy, periodt 💅

🌸 SYNOPSIS 🌸

struct blk_mq_tag_set {
    const struct blk_mq_ops *ops;
    struct blk_mq_queue_map map[HCTX_MAX_TYPES];
    unsigned int            nr_maps;
    unsigned int            nr_hw_queues;
    unsigned int            queue_depth;
    unsigned int            reserved_tags;
    unsigned int            cmd_size;
    int numa_node;
    unsigned int            timeout;
    unsigned int            flags;
    void *driver_data;
    struct blk_mq_tags      **tags;
    struct blk_mq_tags      *shared_tags;
    struct mutex            tag_list_lock;
    struct list_head        tag_list;
    struct srcu_struct      *srcu;
    struct srcu_struct      tags_srcu;
    struct rw_semaphore     update_nr_hwq_lock;
 };

🎀 Members 🎀

here's the member-by-member tour, no skips, no cap 🫶

• ops — pointers to functions that implement block driver behavior. literally the driver's whole move set.
• map — one or more ctx -> hctx mappings. one map exists for each hardware queue type (enum hctx_type) that the driver wishes to support. there are no restrictions on maps being of the same size, and it's perfectly legal to share maps between types — no cap.
• nr_maps — number of elements in the map array. a number in the range [1, HCTX_MAX_TYPES], fr fr.
• nr_hw_queues — number of hardware queues supported by the block driver that owns this data structure.
• queue_depth — number of tags per hardware queue, reserved tags included.
• reserved_tags — number of tags to set aside for BLK_MQ_REQ_RESERVED tag allocations.
• cmd_size — number of additional bytes to allocate per request. the block driver owns these additional bytes.
• numa_node — NUMA node the storage adapter has been connected to.
• timeout — request processing timeout in jiffies.
• flags — zero or more BLK_MQ_F_* flags.
• driver_data — pointer to data owned by the block driver that created this tag set.
• tags — tag sets. one tag set per hardware queue. has nr_hw_queues elements.
• shared_tags — shared set of tags. has nr_hw_queues elements. if set, shared by all tags.
• tag_list_lock — serializes tag_list accesses.
• tag_list — list of the request queues that use this tag set. see also request_queue.tag_set_list.
• srcu — use as lock when type of the request queue is blocking (BLK_MQ_F_BLOCKING).
• tags_srcu — SRCU used to defer freeing of tags page_list to prevent use-after-free when iterating tags. safety first, bestie 🫶
• update_nr_hwq_lock — synchronize updating nr_hw_queues with add/del disk & switching elevator.

💅 SEE ALSO 💅

kernel file ./include/linux/blk-mq.h is the main character here, and you also gotta peek at:

• enum blk_eh_timer_return(9)
• struct blk_mq_hw_ctx(9)
• struct blk_mq_queue_map(9)
• enum hctx_type(9)
• struct blk_mq_queue_data(9)
• struct blk_mq_ops(9)
• blk_mq_rq_state(9)
• blk_mq_add_to_batch(9)
• blk_mq_rq_from_pdu(9)
• blk_mq_rq_to_pdu(9)
• blk_rq_nr_bvec(9)
• blk_rq_passthrough_stats(9)

mwah 💋 this page came from ./include/linux and it's dated October 2026 — slay forever 🌈✨