52 lines
2.4 KiB
Zig
52 lines
2.4 KiB
Zig
//! The block-device wire protocol — what a filesystem (the FAT server) says to a
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//! block driver (usb-storage) over its well-known `.block` endpoint. A protocol
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//! module like vfs-protocol / usb-transfer-protocol: extern-struct messages, an
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//! `Operation` tag, everything in one IPC message.
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//!
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//! Data path: read and write move whole blocks to or from a **caller-owned DMA
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//! buffer**, named by its physical address — the same physical-address handoff
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//! usb-storage already uses toward the controller, one layer up. So a 512-byte
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//! sector never has to cross the 256-byte IPC boundary; only the small request /
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//! reply headers do. Under an enforcing IOMMU the buffer's physical addresses are
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//! only reachable by the device once the filesystem has `attach`ed the buffer's
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//! capability (the block server forwards it to the controller); see docs/driver-model.md.
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pub const Operation = enum(u32) {
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/// geometry() -> { block_size, block_count }
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geometry = 0,
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/// read(lba, count, physical): read `count` blocks from `lba` into the buffer
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read = 1,
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/// write(lba, count, physical): write `count` blocks at `lba` from the buffer
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write = 2,
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/// flush(): commit any device write cache to stable media (no data transfer).
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/// A filesystem calls this to make prior writes durable — e.g. before power-off,
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/// so a shutdown-time write isn't lost in the USB flash controller's cache.
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flush = 3,
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/// attach(): the caller's DMA-region capability rides the call's cap slot; the
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/// block server forwards it to the controller so the buffer's physical addresses
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/// (named in later read/write) are reachable by the device under an enforcing
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/// IOMMU. Call once per buffer before using it in a transfer.
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attach = 4,
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};
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pub const Request = extern struct {
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operation: u32,
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reserved: u32 = 0,
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lba: u64,
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count: u32, // number of blocks (read/write)
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reserved2: u32 = 0,
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physical: u64, // caller's DMA buffer physical address (read/write)
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};
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pub const Reply = extern struct {
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status: i32, // 0 on success, negative on failure
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reserved: u32 = 0,
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block_size: u32, // geometry: bytes per block (512)
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reserved2: u32 = 0,
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block_count: u64, // geometry: total blocks; read/write: blocks moved
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};
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pub const message_maximum: usize = 256;
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pub const request_size: usize = @sizeOf(Request);
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pub const reply_size: usize = @sizeOf(Reply);
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