73 lines
2.2 KiB
Groff
73 lines
2.2 KiB
Groff
.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
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.\"
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.\" SPDX-License-Identifier: LGPL-2.0-or-later
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.\"
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.TH io_uring_prep_poll_add 3 "March 12, 2022" "liburing-2.2" "liburing Manual"
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.SH NAME
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io_uring_prep_poll_add \- prepare a poll request
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.SH SYNOPSIS
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.nf
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.B #include <poll.h>
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.B #include <liburing.h>
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.PP
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.BI "void io_uring_prep_poll_add(struct io_uring_sqe *" sqe ","
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.BI " int " fd ","
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.BI " unsigned " poll_mask ");"
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.PP
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.BI "void io_uring_prep_poll_multishot(struct io_uring_sqe *" sqe ","
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.BI " int " fd ","
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.BI " unsigned " poll_mask ");"
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.fi
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.SH DESCRIPTION
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.PP
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The
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.BR io_uring_prep_poll_add (3)
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function prepares a poll request. The submission queue entry
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.I sqe
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is setup to use the file descriptor
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.I fd
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that should get polled, with the events desired specified in the
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.I poll_mask
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argument.
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The default behavior is a single-shot poll request. When the specified event
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has triggered, a completion CQE is posted and no more events will be generated
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by the poll request.
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.BR io_uring_prep_multishot (3)
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behaves identically in terms of events, but it persist across notifications
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and will repeatedly post notifications for the same registration. A CQE
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posted from a multishot poll request will have
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.B IORING_CQE_F_MORE
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set in the CQE
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.I flags
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member, indicating that the application should expect more completions from
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this request. If the multishot poll request gets terminated or experiences
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an error, this flag will not be set in the CQE. If this happens, the application
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should not expect further CQEs from the original request and must reissue a
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new one if it still wishes to get notifications on this file descriptor.
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.SH RETURN VALUE
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None
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.SH ERRORS
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The CQE
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.I res
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field will contain the result of the operation, which is a bitmask of the
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events notified. See the
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.BR poll (2)
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man page for details. Note that where synchronous system calls will return
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.B -1
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on failure and set
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.I errno
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to the actual error value, io_uring never uses
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.IR errno .
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Instead it returns the negated
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.I errno
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directly in the CQE
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.I res
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field.
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.SH SEE ALSO
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.BR io_uring_get_sqe (3),
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.BR io_uring_submit (3),
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.BR poll (2),
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.BR epoll_ctl (3)
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