60 lines
2.3 KiB
Zig
60 lines
2.3 KiB
Zig
//! The VFS wire protocol — the message format spoken between a client (via the file
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//! API) and the user-space VFS server over IPC. A request is a fixed `Request` header
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//! followed by an inline payload (a path, or write bytes); a reply is a fixed `Reply`
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//! header followed by an inline payload (read bytes, or a FileStatus). Everything fits
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//! in one IPC message (<= ipc MESSAGE_MAXIMUM = 256 bytes).
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//!
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//! This is a danos-native contract, so it uses danos names throughout — the POSIX
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//! spellings (`stat`, `O_CREAT`, ...) live only in the POSIX layer
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//! (library/posix/unistd.zig), which translates to these.
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//!
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//! This is user-space only — the kernel knows nothing of files or paths; it only moves the bytes.
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//! Shared by library/posix/unistd.zig (client) and system/services/vfs/vfs.zig (server).
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pub const Operation = enum(u32) {
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open, // open(path) -> node id
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close, // close(node)
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read, // read(node, offset, len) -> bytes
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write, // write(node, offset, bytes) -> count
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status, // status(node) -> FileStatus
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};
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/// Request header. `node` is the server-side open-file id (from a prior open);
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/// for `open` the path is the payload and `len` is its length. `offset`/`len`
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/// carry the read/write position and count.
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pub const Request = extern struct {
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operation: Operation,
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node: u64,
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offset: u64,
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len: u32,
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flags: u32,
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};
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/// Reply header. `status` is 0 on success or a negative errno; `node` is the new
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/// open-file id (for `open`); `len` is the payload length (bytes read, or the
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/// FileStatus size).
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pub const Reply = extern struct {
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status: i32,
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_padding: u32 = 0,
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node: u64 = 0,
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len: u32 = 0,
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_padding2: u32 = 0,
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};
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/// A file's metadata (the danos-native answer to a `status` request). The POSIX
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/// layer maps this onto `struct stat`.
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pub const FileStatus = extern struct {
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size: u64,
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kind: u32,
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_padding: u32 = 0,
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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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/// Largest inline payload that still fits one IPC message alongside a header.
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pub const maximum_payload: usize = message_maximum - request_size;
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/// Open flags (danos-native; the POSIX layer maps `O_CREAT` onto `create`).
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pub const create: u32 = 1;
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