mirror of https://github.com/mkerrisk/man-pages
287 lines
6.6 KiB
Groff
287 lines
6.6 KiB
Groff
.\" Copyright (C) 2003 Free Software Foundation, Inc.
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.\" and Copyright (C) 2017 Goldwyn Rodrigues <rgoldwyn@suse.de>
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.\"
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.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
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.\" This file is distributed according to the GNU General Public License.
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.\" %%%LICENSE_END
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.\"
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.TH IO_SUBMIT 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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io_submit \- submit asynchronous I/O blocks for processing
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.SH SYNOPSIS
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.nf
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.BR "#include <linux/aio_abi.h>" " /* Defines needed types */"
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.PP
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.BI "int io_submit(aio_context_t " ctx_id ", long " nr \
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", struct iocb **" iocbpp );
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.fi
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.PP
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.IR Note :
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There is no glibc wrapper for this system call; see NOTES.
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.SH DESCRIPTION
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.IR Note :
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this page describes the raw Linux system call interface.
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The wrapper function provided by
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.I libaio
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uses a different type for the
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.I ctx_id
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argument.
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See NOTES.
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.PP
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The
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.BR io_submit ()
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system call
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queues \fInr\fP I/O request blocks for processing in
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the AIO context \fIctx_id\fP.
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The
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.I iocbpp
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argument should be an array of \fInr\fP AIO control blocks,
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which will be submitted to context \fIctx_id\fP.
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.PP
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The
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.I iocb
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(I/O control block) structure defined in
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.IR linux/aio_abi.h
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defines the parameters that control the I/O operation.
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.PP
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.in +4n
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.EX
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#include <linux/aio_abi.h>
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struct iocb {
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__u64 aio_data;
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__u32 PADDED(aio_key, aio_rw_flags);
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__u16 aio_lio_opcode;
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__s16 aio_reqprio;
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__u32 aio_fildes;
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__u64 aio_buf;
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__u64 aio_nbytes;
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__s64 aio_offset;
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__u64 aio_reserved2;
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__u32 aio_flags;
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__u32 aio_resfd;
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};
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.EE
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.in
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.PP
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The fields of this structure are as follows:
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.TP
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.I aio_data
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This data is copied into the
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.I data
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field of the
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.I io_event
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structure upon I/O completion (see
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.BR io_getevents (2)).
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.TP
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.I aio_key
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This is an internal field used by the kernel.
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Do not modify this field after an
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.BR io_submit ()
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call.
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.TP
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.I aio_rw_flags
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This defines the R/W flags passed with structure.
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The valid values are:
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.RS
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.TP
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.BR RWF_APPEND " (since Linux 4.16)"
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.\" commit e1fc742e14e01d84d9693c4aca4ab23da65811fb
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Append data to the end of the file.
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See the description of the flag of the same name in
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.BR pwritev2 (2)
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as well as the description of
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.B O_APPEND
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in
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.BR open (2).
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The
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.I aio_offset
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field is ignored.
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The file offset is not changed.
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.TP
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.BR RWF_DSYNC " (since Linux 4.13)"
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Write operation complete according to requirement of
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synchronized I/O data integrity.
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See the description of the flag of the same name in
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.BR pwritev2 (2)
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as well the description of
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.B O_DSYNC
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in
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.BR open (2).
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.TP
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.BR RWF_HIPRI " (since Linux 4.13)"
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High priority request, poll if possible
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.TP
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.BR RWF_NOWAIT " (since Linux 4.14)"
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Don't wait if the I/O will block for operations such as
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file block allocations, dirty page flush, mutex locks,
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or a congested block device inside the kernel.
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If any of these conditions are met, the control block is returned
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immediately with a return value of
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.B \-EAGAIN
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in the
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.I res
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field of the
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.I io_event
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structure (see
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.BR io_getevents (2)).
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.TP
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.BR RWF_SYNC " (since Linux 4.13)"
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Write operation complete according to requirement of
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synchronized I/O file integrity.
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See the description of the flag of the same name in
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.BR pwritev2 (2)
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as well the description of
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.B O_SYNC
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in
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.BR open (2).
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.RE
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.TP
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.I aio_lio_opcode
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This defines the type of I/O to be performed by the
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.I iocb
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structure.
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The
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valid values are defined by the enum defined in
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.IR linux/aio_abi.h :
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.IP
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.in +4n
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.EX
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enum {
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IOCB_CMD_PREAD = 0,
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IOCB_CMD_PWRITE = 1,
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IOCB_CMD_FSYNC = 2,
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IOCB_CMD_FDSYNC = 3,
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IOCB_CMD_POLL = 5,
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IOCB_CMD_NOOP = 6,
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IOCB_CMD_PREADV = 7,
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IOCB_CMD_PWRITEV = 8,
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};
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.EE
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.in
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.TP
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.I aio_reqprio
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This defines the requests priority.
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.TP
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.I aio_fildes
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The file descriptor on which the I/O operation is to be performed.
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.TP
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.I aio_buf
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This is the buffer used to transfer data for a read or write operation.
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.TP
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.I aio_nbytes
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This is the size of the buffer pointed to by
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.IR aio_buf .
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.TP
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.I aio_offset
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This is the file offset at which the I/O operation is to be performed.
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.TP
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.I aio_flags
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This is the set of flags associated with the
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.I iocb
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structure.
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The valid values are:
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.RS
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.TP
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.BR IOCB_FLAG_RESFD
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Asynchronous I/O control must signal the file
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descriptor mentioned in
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.I aio_resfd
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upon completion.
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.TP
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.BR IOCB_FLAG_IOPRIO " (since Linux 4.18)"
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.\" commit d9a08a9e616beeccdbd0e7262b7225ffdfa49e92
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Interpret the
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.I aio_reqprio
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field as an
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.B IOPRIO_VALUE
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as defined by
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.IR linux/ioprio.h .
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.RE
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.TP
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.I aio_resfd
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The file descriptor to signal in the event of asynchronous I/O completion.
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.SH RETURN VALUE
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On success,
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.BR io_submit ()
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returns the number of \fIiocb\fPs submitted (which may be
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less than \fInr\fP, or 0 if \fInr\fP is zero).
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For the failure return, see NOTES.
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.SH ERRORS
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.TP
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.B EAGAIN
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Insufficient resources are available to queue any \fIiocb\fPs.
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.TP
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.B EBADF
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The file descriptor specified in the first \fIiocb\fP is invalid.
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.TP
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.B EFAULT
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One of the data structures points to invalid data.
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.TP
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.B EINVAL
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The AIO context specified by \fIctx_id\fP is invalid.
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\fInr\fP is less than 0.
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The \fIiocb\fP at
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.I *iocbpp[0]
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is not properly initialized, the operation specified is invalid for the file
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descriptor in the \fIiocb\fP, or the value in the
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.I aio_reqprio
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field is invalid.
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.TP
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.B ENOSYS
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.BR io_submit ()
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is not implemented on this architecture.
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.TP
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.B EPERM
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The
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.I aio_reqprio
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field is set with the class
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.BR IOPRIO_CLASS_RT ,
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but the submitting context does not have the
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.B CAP_SYS_ADMIN
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capability.
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.SH VERSIONS
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The asynchronous I/O system calls first appeared in Linux 2.5.
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.SH CONFORMING TO
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.BR io_submit ()
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is Linux-specific and should not be used in
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programs that are intended to be portable.
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.SH NOTES
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Glibc does not provide a wrapper for this system call.
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You could invoke it using
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.BR syscall (2).
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But instead, you probably want to use the
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.BR io_submit ()
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wrapper function provided by
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.\" http://git.fedorahosted.org/git/?p=libaio.git
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.IR libaio .
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.PP
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Note that the
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.I libaio
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wrapper function uses a different type
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.RI ( io_context_t )
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.\" But glibc is confused, since <libaio.h> uses 'io_context_t' to declare
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.\" the system call.
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for the
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.I ctx_id
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argument.
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Note also that the
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.I libaio
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wrapper does not follow the usual C library conventions for indicating errors:
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on error it returns a negated error number
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(the negative of one of the values listed in ERRORS).
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If the system call is invoked via
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.BR syscall (2),
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then the return value follows the usual conventions for
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indicating an error: \-1, with
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.I errno
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set to a (positive) value that indicates the error.
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.SH SEE ALSO
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.BR io_cancel (2),
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.BR io_destroy (2),
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.BR io_getevents (2),
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.BR io_setup (2),
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.BR aio (7)
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.\" .SH AUTHOR
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.\" Kent Yoder.
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