1IO_SUBMIT(2) Linux Programmer's Manual IO_SUBMIT(2)
2
6 io_submit - submit asynchronous I/O blocks for processing
7
9 #include <linux/aio_abi.h> /* Defines needed types */
10 int io_submit(aio_context_t ctx_id, long nr, struct iocb **iocbpp);
12 Note: There is no glibc wrapper for this system call; see NOTES.
14
16 Note: this page describes the raw Linux system call interface. The
17 wrapper function provided by libaio uses a different type for the
18 ctx_id argument. See NOTES.
19 The io_submit() system call queues nr I/O request blocks for processing
21 in the AIO context ctx_id. The iocbpp argument should be an array of
22 nr AIO control blocks, which will be submitted to context ctx_id.
23 The iocb (I/O control block) structure defined in linux/aio_abi.h de‐
25 fines the parameters that control the I/O operation.
26 #include <linux/aio_abi.h>
28 struct iocb {
30 __u64 aio_data;
31 __u32 PADDED(aio_key, aio_rw_flags);
32 __u16 aio_lio_opcode;
33 __s16 aio_reqprio;
34 __u32 aio_fildes;
35 __u64 aio_buf;
36 __u64 aio_nbytes;
37 __s64 aio_offset;
38 __u64 aio_reserved2;
39 __u32 aio_flags;
40 __u32 aio_resfd;
41 };
42 The fields of this structure are as follows:
44 aio_data
46 This data is copied into the data field of the io_event struc‐
47 ture upon I/O completion (see io_getevents(2)).
48 aio_key
50 This is an internal field used by the kernel. Do not modify
51 this field after an io_submit() call.
52 aio_rw_flags
54 This defines the R/W flags passed with structure. The valid
55 values are:
56 RWF_APPEND (since Linux 4.16)
58 Append data to the end of the file. See the description
59 of the flag of the same name in pwritev2(2) as well as
60 the description of O_APPEND in open(2). The aio_offset
61 field is ignored. The file offset is not changed.
62 RWF_DSYNC (since Linux 4.13)
64 Write operation complete according to requirement of syn‐
65 chronized I/O data integrity. See the description of the
66 flag of the same name in pwritev2(2) as well the descrip‐
67 tion of O_DSYNC in open(2).
68 RWF_HIPRI (since Linux 4.13)
70 High priority request, poll if possible
71 RWF_NOWAIT (since Linux 4.14)
73 Don't wait if the I/O will block for operations such as
74 file block allocations, dirty page flush, mutex locks, or
75 a congested block device inside the kernel. If any of
76 these conditions are met, the control block is returned
77 immediately with a return value of -EAGAIN in the res
78 field of the io_event structure (see io_getevents(2)).
79 RWF_SYNC (since Linux 4.13)
81 Write operation complete according to requirement of syn‐
82 chronized I/O file integrity. See the description of the
83 flag of the same name in pwritev2(2) as well the descrip‐
84 tion of O_SYNC in open(2).
85 aio_lio_opcode
87 This defines the type of I/O to be performed by the iocb struc‐
88 ture. The valid values are defined by the enum defined in
89 linux/aio_abi.h:
90 enum {
92 IOCB_CMD_PREAD = 0,
93 IOCB_CMD_PWRITE = 1,
94 IOCB_CMD_FSYNC = 2,
95 IOCB_CMD_FDSYNC = 3,
96 IOCB_CMD_POLL = 5,
97 IOCB_CMD_NOOP = 6,
98 IOCB_CMD_PREADV = 7,
99 IOCB_CMD_PWRITEV = 8,
100 };
101 aio_reqprio
103 This defines the requests priority.
104 aio_fildes
106 The file descriptor on which the I/O operation is to be per‐
107 formed.
108 aio_buf
110 This is the buffer used to transfer data for a read or write op‐
111 eration.
112 aio_nbytes
114 This is the size of the buffer pointed to by aio_buf.
115 aio_offset
117 This is the file offset at which the I/O operation is to be per‐
118 formed.
119 aio_flags
121 This is the set of flags associated with the iocb structure.
122 The valid values are:
123 IOCB_FLAG_RESFD
125 Asynchronous I/O control must signal the file descriptor
126 mentioned in aio_resfd upon completion.
127 IOCB_FLAG_IOPRIO (since Linux 4.18)
129 Interpret the aio_reqprio field as an IOPRIO_VALUE as de‐
130 fined by linux/ioprio.h.
131 aio_resfd
133 The file descriptor to signal in the event of asynchronous I/O
134 completion.
135
137 On success, io_submit() returns the number of iocbs submitted (which
138 may be less than nr, or 0 if nr is zero). For the failure return, see
139 NOTES.
140
142 EAGAIN Insufficient resources are available to queue any iocbs.
143 EBADF The file descriptor specified in the first iocb is invalid.
145 EFAULT One of the data structures points to invalid data.
147 EINVAL The AIO context specified by ctx_id is invalid. nr is less than
149 0. The iocb at *iocbpp[0] is not properly initialized, the op‐
150 eration specified is invalid for the file descriptor in the
151 iocb, or the value in the aio_reqprio field is invalid.
152 ENOSYS io_submit() is not implemented on this architecture.
154 EPERM The aio_reqprio field is set with the class IOPRIO_CLASS_RT, but
156 the submitting context does not have the CAP_SYS_ADMIN capabil‐
157 ity.
158
160 The asynchronous I/O system calls first appeared in Linux 2.5.
161
163 io_submit() is Linux-specific and should not be used in programs that
164 are intended to be portable.
165
167 Glibc does not provide a wrapper for this system call. You could in‐
168 voke it using syscall(2). But instead, you probably want to use the
169 io_submit() wrapper function provided by libaio.
170 Note that the libaio wrapper function uses a different type (io_con‐
172 text_t) for the ctx_id argument. Note also that the libaio wrapper
173 does not follow the usual C library conventions for indicating errors:
174 on error it returns a negated error number (the negative of one of the
175 values listed in ERRORS). If the system call is invoked via
176 syscall(2), then the return value follows the usual conventions for in‐
177 dicating an error: -1, with errno set to a (positive) value that indi‐
178 cates the error.
179
181 io_cancel(2), io_destroy(2), io_getevents(2), io_setup(2), aio(7)
182
184 This page is part of release 5.13 of the Linux man-pages project. A
185 description of the project, information about reporting bugs, and the
186 latest version of this page, can be found at
187 https://www.kernel.org/doc/man-pages/.
188Linux 2021-03-22 IO_SUBMIT(2)