Module vgabuf 

Lock-free circular buffer for VGA log lines.

The kernel’s log::info! / log::warn! / etc. macros write to this buffer instead of directly locking VGA_WRITER. A background display task (or the panic handler) calls vgabuf_flush_to_framebuffer() to render the buffered lines onto the actual framebuffer.

This decouples the hot logging path from the (comparatively) slow framebuffer drawing, preventing deadlocks and keeping log output fast.

Structs

VgaSlot 🔒

Raw storage: each slot is a fixed-size byte buffer. Wrapped in a newtype that is Sync because we only access slots via atomically-coordinated indices (single writer per slot).

Constants

FLUSH_BATCH 🔒

Maximum number of lines we render in one flush call (to keep frame time bounded).

VGABUF_CAPACITY

Maximum number of lines stored in the circular buffer. 512 gives ample headroom: at 100Hz flush × 30 lines/batch, the writer would need to produce >512 log messages between two reader ticks to overwrite an unread slot.

VGABUF_LINE_LEN

Maximum byte length of a single log line (including trailing newline).

Statics

DISPLAY_IDX 🔒

Slot that the display task has rendered up to (exclusive).

LENS 🔒

Length (in bytes) of each stored line. 0 means the slot is unused.

STORAGE 🔒

TOTAL_WRITTEN 🔒

Total lines written since boot (for ordering / watermark).

WRITE_IDX 🔒

Next slot to write into (monotonic, wraps via % CAPACITY).

Functions

vgabuf_drain_discard 🔒

Drain all pending lines without rendering (e.g. framebuffer not available).

vgabuf_flush_all

Flush all remaining lines (used by the panic handler before halting).

vgabuf_flush_all_direct 🔒

Fallback when VGA_WRITER is locked: use the direct panic drawer. Uses a fixed-size stack buffer to avoid heap allocation in panic context.

vgabuf_flush_to_framebuffer

Read buffered lines and render them onto the framebuffer via crate::arch::x86_64::vga::VGA_WRITER.

vgabuf_total_written

Return the total number of lines written since boot.

vgabuf_write

Write a line into the circular buffer.