STRUCT DMA_DEBUG_ENTRY(9)

🎀 struct dma_debug_entry(9) — the Kernel API Manual, bestie edition 🎀

okay so this is struct dma_debug_entry, and it lives in the Kernel API Manual. iykyk. its whole entire job? it tracks a dma_map* or dma_alloc_coherent mapping 💅 like that's literally the assignment and it ate.

✨ SYNOPSIS ✨

here's the shape of it, no cap, copy it exactly:

struct dma_debug_entry {
    struct list_head list;
    struct device    *dev;
    u64 dev_addr;
    u64 size;
    int type;
    int direction;
    int sg_call_ents;
    int sg_mapped_ents;
    phys_addr_t paddr;
    enum map_err_types map_err_type;
    unsigned long    attrs;
  #ifdef CONFIG_STACKTRACE;
    unsigned int    stack_len;
    unsigned long   stack_entries[DMA_DEBUG_STACKTRACE_ENTRIES];
  #endif;
 };

🌸 Members 🌸

breaking it down field by field because every single one of these matters, bestie:

• list — this is the node on the pre-allocated free_entries list 🦋 it's giving backstage pass.
• dev — the device. that's it, that's the field 💜
• dev_addr — the dma address ✨
• size — the length of the mapping, aka how much we're working with 💅
• type — one of single, page, sg, coherent — pick your fighter 🎀
• direction — an enum dma_data_direction, obviously 🙈
• sg_call_ents — sg call entries, it's right there in the name 💀
• sg_mapped_ents — sg mapped entries, same vibe, different field 🌈
• paddr — physical start address of the mapping, lowkey important ⭐
• map_err_type — this one tracks whether dma_mapping_error was checked 👀 yes it's keeping receipts, that's the whole point 🍓
• attrs — dma attributes 💖
• stack_len — the number of backtrace entries in stack_entries 🧚
• stack_entries — the stack of backtrace history, like a little scrapbook of where you've been 😭🔥

real talk: stack_len and stack_entries are tucked inside #ifdef CONFIG_STACKTRACE, so if that's not on, these two are simply not invited to the function 🫶

👑 SEE ALSO 👑

• Kernel file ./kernel/dma/debug.c — go read it, it's the main character 💀

k that's the whole page, you're welcome 💜

sign-off time: this iconic lil doc comes from ./kernel/dma, dated October 2026, and it's filed under struct dma_debug_entry(9). slay, go map some dma safely, and remember to check your errors. periodt. 🌸✨