pub unsafe fn io_uring_prep_read_fixed(
sqe: *mut io_uring_sqe,
fd: c_int,
buf: *mut c_void,
nbytes: c_uint,
offset: u64,
buf_index: c_int,
)Expand description
Prepare I/O read request with registered buffer
§DESCRIPTION
The io_uring_prep_read_fixed prepares an IO read request with a previously registered IO buffer. The submission queue entry sqe is setup to use the file descriptor fd to start reading nbytes into the buffer buf at the specified offset, and with the buffer matching the registered index of buf_index.
This works just like io_uring_prep_read except it requires the use of buffers that have been registered with io_uring_register_buffers. The buf and nbytes arguments must fall within a region specified by buf_index in the previously registered buffer. The buffer need not be aligned with the start of the registered buffer.
After the read has been prepared it can be submitted with one of the submit functions.
§RETURN VALUE
None
§ERRORS
The CQE res field will contain the result of the operation. See the related man page for details on possible values. Note that where synchronous system calls will return -1 on failure and set errno to the actual error value, io_uring never uses errno. Instead it returns the negated errno directly in the CQE res field.
§NOTES
This function accepts an unsigned number of bytes, but io_uring_cqe’s result code is an __s32 value, so in theory a short read with a large enough nbytes value could generate an ambiguous return. But the number of bytes actually transferred has the same limit as read so this cannot happen in practice.