STRUCT VMCORE_CB(9)

💖 struct vmcore_cb(9) 💖

okay so bestie, welcome to the Kernel API Manual — today's main character is struct vmcore_cb, and it's literally the driver callback squad for /proc/vmcore handling 🎀 like if you're a driver managing physical memory ranges and you need to talk to the vmcore handling code, this is your girl. periodt.

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✨ NAME ✨

struct vmcore_cb — driver callbacks for /proc/vmcore handling 🦋

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🌸 SYNOPSIS 🌸

struct vmcore_cb {
    bool (*pfn_is_ram)(struct vmcore_cb *cb, unsigned long pfn);
    int (*get_device_ram)(struct vmcore_cb *cb, struct list_head *list);
    struct list_head next;
 };

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👑 Members 👑

• pfn_is_ram — this one's job is to check whether a PFN really is RAM and actually should be accessed when reading the vmcore 👀. It returns true if it is RAM, or if the callback genuinely can't tell. But if any callback returns false, then nope — it's not RAM and the page must not be accessed; instead, zeroes should be indicated in the vmcore. Fr fr, think about it: a ballooned page contains no data, and reading from such a page will cause high load in the hypervisor 💀 so yeah, don't do that.
• get_device_ram — this one queries RAM ranges that can only be detected by device drivers, like the virtio-mem driver, so they can be included in the crash dump on architectures that allocate the elfcore hdr in the dump ("2nd") kernel 🌈. And here's the tea: the indicated RAM ranges may contain holes to reduce the total number of ranges — those holes can be detected using the pfn_is_ram callback, just like for other RAM ✨.
• next — list head to manage registered callbacks internally; it gets initialized by register_vmcore_cb 🫶.

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💅 Description 💅

vmcore callbacks allow drivers managing physical memory ranges to coordinate with vmcore handling code — for example, to prevent accessing physical memory ranges that should not be accessed when reading the vmcore, even though they're included in the vmcore header as memory ranges to dump 🦋. it's giving teamwork, it's giving "don't touch that memory", iconic behavior honestly.

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⭐ SEE ALSO ⭐

Kernel file ./include/linux/crash_dump.h 🎀

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ngl bestie, if pfn_is_ram says false, that page is off-limits — zeroes in the vmcore only, no exceptions 🙈

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and that's a wrap, mwah 💋 — this page came from ./include/linux, dated October 2026, and it's struct vmcore_cb(9) in the Kernel API Manual. slay 🧚‍♀️💜