STRUCT DRM_MODE_GET_PROPERTY(9)

💅 struct drm_mode_get_property — Get property metadata ✨

okay bestie, welcome to the Kernel API Manual, section 9, and honestly? this one's a little iconic. it's struct drm_mode_get_property, and it's literally the answer to "wait, what is this property?" — let's get into it 🎀

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🦋 NAME 🦋

struct drm_mode_get_property — Get property metadata.

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🌸 SYNOPSIS 🌸

struct drm_mode_get_property {
    __u64 values_ptr;
    __u64 enum_blob_ptr;
    __u32 prop_id;
    __u32 flags;
    char name[DRM_PROP_NAME_LEN];
    __u32 count_values;
    __u32 count_enum_blobs;
 };

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✨ Members ✨

so here's the whole cast, no cap — every field, doing its thing 💖

🫶 the fields

• values_ptr — a pointer to a __u64 array. that's it, that's the field. it holds the values ✨
• enum_blob_ptr — a pointer to a struct drm_mode_property_enum array. the enum side of the story 💜
• prop_id — the object ID of the property you want to retrieve. you, the caller, set this one. main character energy 🔥
• flags — a DRM_MODE_PROP_* bitfield. for what all the flags mean, go peek at drm_property.flags — that's where the definitions live 👑
• name — the symbolic property name. user-space, this is literally your field for recognizing properties, use it 💅
• count_values — the number of elements in values_ptr. keep it honest 🍓
• count_enum_blobs — the number of elements in enum_blob_ptr. same energy, different array 🌈

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🧚 DESCRIPTION 🧚

okay so the whole point: user-space can do a GETPROPERTY ioctl to retrieve information about a property. and the same property? it may be attached to multiple objects — see "Modeset Base Object Abstraction" for that whole situation 🦋

here's the spicy bit: the meaning of the values_ptr field changes depending on the property type. yep, it's giving shapeshifter. see drm_property.flags for more details on that 💫

the enum_blob_ptr and count_enum_blobs fields are only meaningful when the property has the type DRM_MODE_PROP_ENUM or DRM_MODE_PROP_BITMASK. and for backwards compatibility, the kernel will always set count_enum_blobs to zero when the property has the type DRM_MODE_PROP_BLOB. so if the property has a different type, user-space must ignore these two fields. not "should", must — we respect the contract 🙈

user-space is expected to retrieve values and enums by doing this ioctl at least twice: first round to get the number of elements, second round to get the elements themselves. two trips, one vibe check ✌️

💖 round one: getting the count

to retrieve the number of elements, set count_values and count_enum_blobs to zero, then call the ioctl. count_values will be updated with the number of elements. and if the property has the type DRM_MODE_PROP_ENUM or DRM_MODE_PROP_BITMASK, count_enum_blobs gets updated too. slay, now you know the size 🎀

💖 round two: getting the goods

to retrieve the elements themselves, allocate an array for values_ptr and set count_values to its capacity. if the property has the type DRM_MODE_PROP_ENUM or DRM_MODE_PROP_BITMASK, allocate an array for enum_blob_ptr and set count_enum_blobs to its capacity. calling the ioctl again will fill the arrays. that's the whole trick, iykyk 🌟

ngl bestie, don't skip the first pass — you genuinely need the counts before you can allocate, and guessing sizes is not the move 💀

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👑 SEE ALSO 👑

the whole friend group, fr fr 🫶

• Kernel file ./include/uapi/drm/drm_mode.h
• overview(9)
• struct drm_mode_modeinfo(9)
• struct drm_mode_get_plane(9)
• struct drm_mode_get_connector(9)
• struct drm_mode_property_enum(9)
• struct drm_mode_fb_cmd2(9)
• enum drm_colorop_type(9)
• enum drm_colorop_lut3d_interpolation_type(9)
• enum drm_colorop_lut1d_interpolation_type(9)
• struct drm_plane_size_hint(9)
• struct hdr_metadata_infoframe(9)
• struct hdr_output_metadata(9)
• DRM_MODE_PAGE_FLIP_EVENT(9)
• DRM_MODE_PAGE_FLIP_ASYNC(9)
• DRM_MODE_PAGE_FLIP_FLAGS(9)
• struct drm_mode_create_dumb(9)
• DRM_MODE_ATOMIC_TEST_ONLY(9)
• DRM_MODE_ATOMIC_NONBLOCK(9)
• DRM_MODE_ATOMIC_ALLOW_MODESET(9)
• DRM_MODE_ATOMIC_FLAGS(9)
• struct drm_mode_create_blob(9)
• struct drm_mode_destroy_blob(9)
• struct drm_mode_create_lease(9)
• struct drm_mode_list_lessees(9)
• struct drm_mode_get_lease(9)
• struct drm_mode_revoke_lease(9)
• struct drm_mode_rect(9)
• struct drm_mode_closefb(9)

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and that's the page, bestie!! 💜 this icon lives in ./include/uapi/drm, dated October 2026 — go forth and GETPROPERTY responsibly, mwah 😘🎀