We have VMap at home already, please (with your eyes) search the rest of the kernel for it. The work for this was pushed to drm-rust-next recently.
On Fri, 2026-07-03 at 04:00 +0100, Mike Lothian wrote: > Framebuffer::vmap() maps a framebuffer's plane-0 backing pages into > the > kernel address space via drm_gem_fb_vmap()/vunmap(), returning an > RAII > FramebufferVmap guard that unmaps on drop. Only single-CPU-visible- > plane > framebuffers are supported (packed formats backed by GEM-shmem/CMA; > multi-plane YUV or an unmapped imported dma-buf return EINVAL). This > is > the driver-side FbVmap guard the v1 series carried, moved into the > layer > proper so every KMS driver gets it instead of hand-rolling the same > map/use/unmap dance. > > Signed-off-by: Mike Lothian <[email protected]> > Assisted-by: Claude:claude-sonnet-5 [Claude-Code] > --- > rust/kernel/drm/kms/framebuffer.rs | 67 > +++++++++++++++++++++++++++++- > 1 file changed, 66 insertions(+), 1 deletion(-) > > diff --git a/rust/kernel/drm/kms/framebuffer.rs > b/rust/kernel/drm/kms/framebuffer.rs > index 54d0391388a9..1ec6779ba7de 100644 > --- a/rust/kernel/drm/kms/framebuffer.rs > +++ b/rust/kernel/drm/kms/framebuffer.rs > @@ -5,7 +5,12 @@ > //! C header: > [`include/drm/drm_framebuffer.h`](srctree/include/drm/drm_framebuffer > .h) > > use super::{KmsDriver, ModeObject, Sealed}; > -use crate::{drm::device::Device, types::*}; > +use crate::{ > + drm::device::Device, > + error::{code::EINVAL, to_result}, > + prelude::*, > + types::*, > +}; > use bindings; > use core::{marker::*, ptr}; > > @@ -67,4 +72,64 @@ pub(super) unsafe fn from_raw<'a>(ptr: *const > bindings::drm_framebuffer) -> &'a > // SAFETY: Our data layout is identical to drm_framebuffer > unsafe { &*ptr.cast() } > } > + > + /// Return the raw `bindings::drm_framebuffer` for this > framebuffer. > + #[inline] > + pub(crate) fn as_raw(&self) -> *mut bindings::drm_framebuffer { > + self.0.get() > + } > + > + /// Map this framebuffer's plane-0 backing pages into the kernel > address space for CPU > + /// access, for the duration of the returned guard. > + /// > + /// Only framebuffers with a single, CPU-visible plane are > supported (i.e. packed formats > + /// backed by GEM-shmem/CMA memory, not multi-plane YUV or an > IMPORTED dma-buf without a > + /// CPU mapping); other cases return `EINVAL`. > + pub fn vmap(&self) -> Result<FramebufferVmap<'_, T>> { > + // SAFETY: `iosys_map` is POD (a pointer union plus a bool); > all-zero is a valid > + // "not mapped" value that `drm_gem_fb_vmap` overwrites for > present planes. > + let mut map: [bindings::iosys_map; 4] = unsafe { > core::mem::zeroed() }; > + let mut data_map: [bindings::iosys_map; 4] = unsafe { > core::mem::zeroed() }; > + // SAFETY: `self.as_raw()` is a valid, GEM-backed > framebuffer for the lifetime of `self`. > + to_result(unsafe { > + bindings::drm_gem_fb_vmap(self.as_raw(), > map.as_mut_ptr(), data_map.as_mut_ptr()) > + })?; > + // SAFETY: `map[0]` was just filled in by `drm_gem_fb_vmap` > above. > + let vaddr = unsafe { map[0].__bindgen_anon_1.vaddr }; > + if vaddr.is_null() { > + // SAFETY: balances the vmap just done, with the same > `map`. > + unsafe { bindings::drm_gem_fb_vunmap(self.as_raw(), > map.as_mut_ptr()) }; > + return Err(EINVAL); > + } > + Ok(FramebufferVmap { fb: self, map, _p: PhantomData }) > + } > +} > + > +/// An RAII guard over a CPU mapping of a [`Framebuffer`]'s plane-0 > backing pages, created by > +/// [`Framebuffer::vmap`]. > +/// > +/// The mapping is torn down when this guard is dropped, so an early > return between mapping and > +/// use can never leak it. > +pub struct FramebufferVmap<'a, T: KmsDriver> { > + fb: &'a Framebuffer<T>, > + map: [bindings::iosys_map; 4], > + _p: PhantomData<T>, > +} > + > +impl<'a, T: KmsDriver> FramebufferVmap<'a, T> { > + /// Plane 0's CPU virtual base address (guaranteed non-null for > the guard's lifetime). > + #[inline] > + pub fn as_ptr(&self) -> *const u8 { > + // SAFETY: set non-null in `Framebuffer::vmap`; `vaddr` is > the active union member. > + (unsafe { self.map[0].__bindgen_anon_1.vaddr }) as *const u8 > + } > +} > + > +impl<'a, T: KmsDriver> Drop for FramebufferVmap<'a, T> { > + fn drop(&mut self) { > + // SAFETY: `self.fb.as_raw()`/`self.map` are exactly the > pair passed to > + // `drm_gem_fb_vmap` in `Framebuffer::vmap`, and the mapping > has not been released > + // since. > + unsafe { bindings::drm_gem_fb_vunmap(self.fb.as_raw(), > self.map.as_mut_ptr()) }; > + } > }
