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Diffstat (limited to 'man/io_uring_prep_accept.3')
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diff --git a/man/io_uring_prep_accept.3 b/man/io_uring_prep_accept.3 new file mode 100644 index 0000000..3800ccb --- /dev/null +++ b/man/io_uring_prep_accept.3 @@ -0,0 +1,159 @@ +.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk> +.\" +.\" SPDX-License-Identifier: LGPL-2.0-or-later +.\" +.TH io_uring_prep_accept 3 "March 13, 2022" "liburing-2.2" "liburing Manual" +.SH NAME +io_uring_prep_accept \- prepare an accept request +.SH SYNOPSIS +.nf +.B #include <sys/socket.h> +.B #include <liburing.h> +.PP +.BI "void io_uring_prep_accept(struct io_uring_sqe *" sqe "," +.BI " int " sockfd "," +.BI " struct sockaddr *" addr "," +.BI " socklen_t *" addrlen "," +.BI " int " flags ");" +.PP +.BI "void io_uring_prep_accept_direct(struct io_uring_sqe *" sqe "," +.BI " int " sockfd "," +.BI " struct sockaddr *" addr "," +.BI " socklen_t *" addrlen "," +.BI " int " flags "," +.BI " unsigned int " file_index ");" +.PP +.BI "void io_uring_prep_multishot_accept(struct io_uring_sqe *" sqe "," +.BI " int " sockfd "," +.BI " struct sockaddr *" addr "," +.BI " socklen_t *" addrlen "," +.BI " int " flags ");" +.PP +.BI "void io_uring_prep_multishot_accept_direct(struct io_uring_sqe *" sqe "," +.BI " int " sockfd "," +.BI " struct sockaddr *" addr "," +.BI " socklen_t *" addrlen "," +.BI " int " flags ");" +.fi +.SH DESCRIPTION +.PP +The +.BR io_uring_prep_accept (3) +function prepares an accept request. The submission queue entry +.I sqe +is setup to use the file descriptor +.I sockfd +to start accepting a connection request described by the socket address at +.I addr +and of structure length +.I addrlen +and using modifier flags in +.IR flags . + +For a direct descriptor accept request, the offset is specified by the +.I file_index +argument. Direct descriptors are io_uring private file descriptors. They +avoid some of the overhead associated with thread shared file tables and +can be used in any io_uring request that takes a file descriptor. To do so, +.B IOSQE_FIXED_FILE +must be set in the SQE +.I flags +member, and the SQE +.I fd +field should use the direct descriptor value rather than the regular file +descriptor. Direct descriptors are managed like registered files. + +If the direct variant is used, the application must first have registered +a file table using +.BR io_uring_register_files (3) +of the appropriate size. Once registered, a direct accept request may use any +entry in that table, as long as it is within the size of the registered table. +If a specified entry already contains a file, the file will first be removed +from the table and closed. It's consistent with the behavior of updating an +existing file with +.BR io_uring_register_files_update (3). +Note that old kernels don't check the SQE +.I file_index +field, which is not a problem for liburing helpers, but users of the raw +io_uring interface need to zero SQEs to avoid unexpected behavior. This also +means that applications should check for availability of +.B IORING_OP_ACCEPT_DIRECT +before using it, they cannot rely on a +.B -EINVAL +CQE +.I res +return. + +For a direct descriptor accept request, the +.I file_index +argument can be set to +.BR IORING_FILE_INDEX_ALLOC , +In this case a free entry in io_uring file table will +be used automatically and the file index will be returned as CQE +.IR res . +.B -ENFILE +is otherwise returned if there is no free entries in the io_uring file table. + +The multishot version accept and accept_direct allow an application to issue +a single accept request, which will repeatedly trigger a CQE when a connection +request comes in. Like other multishot type requests, the application should +look at the CQE +.I flags +and see if +.B IORING_CQE_F_MORE +is set on completion as an indication of whether or not the accept request +will generate further CQEs. The multishot variants are available since 5.19. + +For multishot with direct descriptors, +.B IORING_FILE_INDEX_ALLOC +must be used as the file descriptor. This tells io_uring to allocate a free +direct descriptor from our table, rather than the application passing one in. +Failure to do so will result in the accept request being terminated with +.BR -EINVAL . +The allocated descriptor will be returned in the CQE +.I res +field, like a non-direct accept request. + +These functions prepare an async +.BR accept4 (2) +request. See that man page for details. + +.SH RETURN VALUE +None +.SH ERRORS +The CQE +.I res +field will contain the result of the operation. For singleshot accept, the +non-direct accept returns the installed file descriptor as its value, the +direct accept returns +.B 0 +on success. The caller must know which direct descriptor was picked for this +request. For multishot accept, the non-direct accept returns the installed +file descriptor as its value, the direct accept returns the file index used on +success. See the related man page for details on possible values for the +non-direct accept. Note that where synchronous system calls will return +.B -1 +on failure and set +.I errno +to the actual error value, io_uring never uses +.IR errno . +Instead it returns the negated +.I errno +directly in the CQE +.I res +field. +.SH NOTES +As with any request that passes in data in a struct, that data must remain +valid until the request has been successfully submitted. It need not remain +valid until completion. Once a request has been submitted, the in-kernel +state is stable. Very early kernels (5.4 and earlier) required state to be +stable until the completion occurred. Applications can test for this +behavior by inspecting the +.B IORING_FEAT_SUBMIT_STABLE +flag passed back from +.BR io_uring_queue_init_params (3). +.SH SEE ALSO +.BR io_uring_get_sqe (3), +.BR io_uring_submit (3), +.BR io_uring_register (2), +.BR accept4 (2) |