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io_uring: change read() to use a ReadBuffer instead

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Reads can be done in two ways with io_uring:
* using a simple buffer
* using a automatic buffer selection which requires the user to have
provided a number of buffers before

ReadBuffer let's the caller choose where the data should be read.
This commit is contained in:
Vincent Rischmann 2022-05-16 19:02:22 +02:00
parent 7b3e5ce0b3
commit 52dd468cc3
1 changed files with 27 additions and 6 deletions
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33
lib/std/os/linux/io_uring.zig
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@ -358,17 +358,38 @@ pub const IO_Uring = struct {
return sqe;
}
/// Used to select how the read should be handled.
pub const ReadBuffer = union(enum) {
/// io_uring will read directly into this buffer
buffer: []u8,
/// io_uring will select a buffer that has previously been provided with `provide_buffers`.
/// The buffer group reference by `group_id` must contain at least one buffer for the read to work.
/// `len` controls the number of bytes to read into the selected buffer.
buffer_selection: struct {
group_id: u16,
len: usize,
},
};
/// Queues (but does not submit) an SQE to perform a `read(2)`.
/// Returns a pointer to the SQE.
pub fn read(
self: *IO_Uring,
user_data: u64,
fd: os.fd_t,
buffer: []u8,
buffer: ReadBuffer,
offset: u64,
) !*io_uring_sqe {
const sqe = try self.get_sqe();
io_uring_prep_read(sqe, fd, buffer, offset);
switch (buffer) {
.buffer => |slice| io_uring_prep_read(sqe, fd, slice, offset),
.buffer_selection => |selection| {
io_uring_prep_rw(.READ, sqe, fd, 0, selection.len, offset);
sqe.flags |= linux.IOSQE_BUFFER_SELECT;
sqe.buf_index = selection.group_id;
},
}
sqe.user_data = user_data;
return sqe;
}
@ -1778,7 +1799,7 @@ test "write/read" {
try testing.expectEqual(linux.IORING_OP.WRITE, sqe_write.opcode);
try testing.expectEqual(@as(u64, 10), sqe_write.off);
sqe_write.flags |= linux.IOSQE_IO_LINK;
const sqe_read = try ring.read(0x22222222, fd, buffer_read[0..], 10);
const sqe_read = try ring.read(0x22222222, fd, .{ .buffer = buffer_read[0..] }, 10);
try testing.expectEqual(linux.IORING_OP.READ, sqe_read.opcode);
try testing.expectEqual(@as(u64, 10), sqe_read.off);
try testing.expectEqual(@as(u32, 2), try ring.submit());
@ -2520,7 +2541,7 @@ test "register_files_update" {
var buffer = [_]u8{42} ** 128;
{
const sqe = try ring.read(0xcccccccc, fd_index, &buffer, 0);
const sqe = try ring.read(0xcccccccc, fd_index, .{ .buffer = &buffer }, 0);
try testing.expectEqual(linux.IORING_OP.READ, sqe.opcode);
sqe.flags |= linux.IOSQE_FIXED_FILE;
@ -2541,7 +2562,7 @@ test "register_files_update" {
{
// Next read should still work since fd_index in the registered file descriptors hasn't been updated yet.
const sqe = try ring.read(0xcccccccc, fd_index, &buffer, 0);
const sqe = try ring.read(0xcccccccc, fd_index, .{ .buffer = &buffer }, 0);
try testing.expectEqual(linux.IORING_OP.READ, sqe.opcode);
sqe.flags |= linux.IOSQE_FIXED_FILE;
@ -2558,7 +2579,7 @@ test "register_files_update" {
{
// Now this should fail since both fds are sparse (-1)
const sqe = try ring.read(0xcccccccc, fd_index, &buffer, 0);
const sqe = try ring.read(0xcccccccc, fd_index, .{ .buffer = &buffer }, 0);
try testing.expectEqual(linux.IORING_OP.READ, sqe.opcode);
sqe.flags |= linux.IOSQE_FIXED_FILE;