1io_uring_prep_recv(3) liburing Manual io_uring_prep_recv(3)
2
6 io_uring_prep_recv - prepare a recv request
7
9 #include <liburing.h>
10 void io_uring_prep_recv(struct io_uring_sqe *sqe,
12 int sockfd,
13 void *buf,
14 size_t len,
15 int flags);
16 void io_uring_prep_recv_multishot(struct io_uring_sqe *sqe,
18 int sockfd,
19 void *buf,
20 size_t len,
21 int flags);
22
24 The io_uring_prep_recv(3) function prepares a recv request. The submis‐
25 sion queue entry sqe is setup to use the file descriptor sockfd to
26 start receiving the data into the buffer destination buf of size size
27 and with modifier flags flags.
28 This function prepares an async recv(2) request. See that man page for
30 details on the arguments specified to this prep helper.
31 The multishot version allows the application to issue a single receive
33 request, which repeatedly posts a CQE when data is available. It re‐
34 quires length to be 0 , the IOSQE_BUFFER_SELECT flag to be set and no
35 MSG_WAITALL flag to be set. Therefore each CQE will take a buffer out
36 of a provided buffer pool for receiving. The application should check
37 the flags of each CQE, regardless of it's result. If a posted CQE does
38 not have the IORING_CQE_F_MORE flag set then the multishot receive will
39 be done and the application should issue a new request. Multishot
40 variants are available since kernel 6.0.
41 After calling this function, additional io_uring internal modifier
44 flags may be set in the SQE ioprio field. The following flags are sup‐
45 ported:
46 IORING_RECVSEND_POLL_FIRST
48 If set, io_uring will assume the socket is currently empty and
49 attempting to receive data will be unsuccessful. For this case,
50 io_uring will arm internal poll and trigger a receive of the
51 data when the socket has data to be read. This initial receive
52 attempt can be wasteful for the case where the socket is ex‐
53 pected to be empty, setting this flag will bypass the initial
54 receive attempt and go straight to arming poll. If poll does in‐
55 dicate that data is ready to be received, the operation will
56 proceed.
57 Can be used with the CQE IORING_CQE_F_SOCK_NONEMPTY flag, which
59 io_uring will set on CQEs after a recv(2) or recvmsg(2) opera‐
60 tion. If set, the socket still had data to be read after the op‐
61 eration completed. Both these flags are available since 5.19.
62
64 None
65
67 The CQE res field will contain the result of the operation. See the re‐
68 lated man page for details on possible values. Note that where synchro‐
69 nous system calls will return -1 on failure and set errno to the actual
70 error value, io_uring never uses errno. Instead it returns the negated
71 errno directly in the CQE res field.
72
74 io_uring_get_sqe(3), io_uring_submit(3), recv(2)
75liburing-2.2 March 12, 2022 io_uring_prep_recv(3)