STRUCT VFIO_LOG_OPS(9)

💅 struct vfio_log_ops(9) 💅

okay so bestie, welcome to the kernel API manual page for struct vfio_log_ops — VFIO bus device driver logging callbacks. yes that's a mouthful. we're gonna get through it together 🫶

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✨ NAME ✨

struct vfio_log_ops — literally the VFIO bus device driver logging callbacks. that's the whole vibe. no cap.

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🦋 SYNOPSIS 🦋

struct vfio_log_ops {
    int (*log_start)(struct vfio_device *device, struct rb_root_cached *ranges, u32 nnodes, u64 *page_size);
    int (*log_stop)(struct vfio_device *device);
    int (*log_read_and_clear)(struct vfio_device *device, unsigned long iova, unsigned long length, struct iova_bitmap *dirty);
};

like, three function pointers. that's the girlies. look at them go ✨

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🌸 Members 🌸

• log_start — an optional callback that asks the device to start DMA logging. key word optional, so don't come for me if your driver doesn't have one 💅
• log_stop — another optional callback, this one asking the device to stop DMA logging. cute, simple, iconic.
• log_read_and_clear — the third optional callback, and it's the busy one: it asks the device to read and clear the dirty DMAs in some given range. two jobs, one callback, main character energy fr fr 👑

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💖 Description 💖

okay so this is the part where it gets real. the vfio core implementation of the DEVICE_FEATURE_DMA_LOGGING_ set of features does not track logging state relative to the device. read that again. the core is not keeping score for you. 😭

so because of that, the device implementation of vfio_log_ops has to handle arbitrary user requests. yes, arbitrary. the users are feral and the core is not your mom.

that means, highkey:

• you must reject subsequent calls to log_start without an intervening log_stop (no sneaky double-starts, bestie, that's not the vibe)
• you must gracefully handle log_stop and log_read_and_clear from invalid states (graceful. not dramatic. we don't throw tantrums in kernel space 💀)

that's it. that's the whole contract. slay.

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👑 SEE ALSO 👑

go touch grass in these files and pages, iykyk:

• Kernel file ./include/linux/vfio.h
• struct vfio_device_ops(9)
• struct vfio_migration_ops(9)
• vfio_check_feature(9)
• vfio_check_precopy_ioctl(9)

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⭐ reminder bestie: log_start, log_stop, and log_read_and_clear are all optional callbacks — but the state-handling rules in the Description are not. if the core isn't tracking state for you, you're the one doing the tracking. periodt.

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🌈 that's the page!! this one lives in ./include/linux, dated October 2026 — mwah, take care of her, she's iconic 💜🎀