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2bc4bb77 | 1 | .\" This manpage is Copyright (C) 2006 Jens Axboe |
c11b1abf | 2 | .\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
2bc4bb77 | 3 | .\" |
93015253 | 4 | .\" %%%LICENSE_START(VERBATIM) |
2bc4bb77 MK |
5 | .\" Permission is granted to make and distribute verbatim copies of this |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
c13182ef | 13 | .\" |
2bc4bb77 MK |
14 | .\" Since the Linux kernel and libraries are constantly changing, this |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. The author(s) may not | |
18 | .\" have taken the same level of care in the production of this manual, | |
19 | .\" which is licensed free of charge, as they might when working | |
20 | .\" professionally. | |
c13182ef | 21 | .\" |
2bc4bb77 MK |
22 | .\" Formatted or processed versions of this manual, if unaccompanied by |
23 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 24 | .\" %%%LICENSE_END |
2bc4bb77 | 25 | .\" |
f55a6d59 | 26 | .TH VMSPLICE 2 2017-07-13 "Linux" "Linux Programmer's Manual" |
2bc4bb77 MK |
27 | .SH NAME |
28 | vmsplice \- splice user pages into a pipe | |
29 | .SH SYNOPSIS | |
30 | .nf | |
b80f966b | 31 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
2bc4bb77 MK |
32 | .B #include <fcntl.h> |
33 | .B #include <sys/uio.h> | |
34 | ||
52520fb5 MH |
35 | .BI "ssize_t vmsplice(int " fd ", const struct iovec *" iov , |
36 | .BI " unsigned long " nr_segs ", unsigned int " flags ); | |
2bc4bb77 | 37 | .fi |
52520fb5 | 38 | .\" Return type was long before glibc 2.7 |
2bc4bb77 | 39 | .SH DESCRIPTION |
c13182ef MK |
40 | .\" Linus: vmsplice() system call to basically do a "write to |
41 | .\" the buffer", but using the reference counting and VM traversal | |
42 | .\" to actually fill the buffer. This means that the user needs to | |
3b777aff | 43 | .\" be careful not to reuse the user-space buffer it spliced into |
c13182ef | 44 | .\" the kernel-space one (contrast this to "write()", which copies |
3b777aff | 45 | .\" the actual data, and you can thus reuse the buffer immediately |
c13182ef | 46 | .\" after a successful write), but that is often easy to do. |
2bc4bb77 MK |
47 | The |
48 | .BR vmsplice () | |
49 | system call maps | |
50 | .I nr_segs | |
51 | ranges of user memory described by | |
52 | .I iov | |
c13182ef | 53 | into a pipe. |
2bc4bb77 | 54 | The file descriptor |
c13182ef | 55 | .I fd |
2bc4bb77 MK |
56 | must refer to a pipe. |
57 | ||
58 | The pointer | |
59 | .I iov | |
60 | points to an array of | |
61 | .I iovec | |
62 | structures as defined in | |
63 | .IR <sys/uio.h> : | |
64 | ||
a08ea57c | 65 | .in +4n |
2bc4bb77 MK |
66 | .nf |
67 | struct iovec { | |
8031e529 MK |
68 | void *iov_base; /* Starting address */ |
69 | size_t iov_len; /* Number of bytes */ | |
2bc4bb77 | 70 | }; |
a08ea57c | 71 | .in |
2bc4bb77 MK |
72 | .fi |
73 | ||
74 | The | |
75 | .I flags | |
76 | argument is a bit mask that is composed by ORing together | |
77 | zero or more of the following values: | |
68c11e15 | 78 | .RS |
2bc4bb77 MK |
79 | .TP 1.9i |
80 | .B SPLICE_F_MOVE | |
81 | Unused for | |
82 | .BR vmsplice (); | |
83 | see | |
84 | .BR splice (2). | |
85 | .TP | |
86 | .B SPLICE_F_NONBLOCK | |
87 | .\" Not used for vmsplice | |
88 | .\" May be in the future -- therefore EAGAIN | |
c13182ef MK |
89 | Do not block on I/O; see |
90 | .BR splice (2) | |
2bc4bb77 MK |
91 | for further details. |
92 | .TP | |
93 | .B SPLICE_F_MORE | |
c13182ef | 94 | Currently has no effect for |
2bc4bb77 MK |
95 | .BR vmsplice (), |
96 | but may be implemented in the future; see | |
97 | .BR splice (2). | |
98 | .TP | |
99 | .B SPLICE_F_GIFT | |
c13182ef MK |
100 | The user pages are a gift to the kernel. |
101 | The application may not modify this memory ever, | |
bea08fec | 102 | .\" FIXME . Explain the following line in a little more detail: |
8031e529 | 103 | otherwise the page cache and on-disk data may differ. |
2bc4bb77 | 104 | Gifting pages to the kernel means that a subsequent |
0bfa087b | 105 | .BR splice (2) |
2bc4bb77 MK |
106 | .B SPLICE_F_MOVE |
107 | can successfully move the pages; | |
108 | if this flag is not specified, then a subsequent | |
0bfa087b | 109 | .BR splice (2) |
2bc4bb77 MK |
110 | .B SPLICE_F_MOVE |
111 | must copy the pages. | |
112 | Data must also be properly page aligned, both in memory and length. | |
68c11e15 | 113 | .RE |
ced56703 | 114 | .\" FIXME |
68c11e15 MK |
115 | .\" It looks like the page-alignment requirement went away with |
116 | .\" commit bd1a68b59c8e3bce45fb76632c64e1e063c3962d | |
ced56703 | 117 | .\" |
2bc4bb77 MK |
118 | .\" .... if we expect to later SPLICE_F_MOVE to the cache. |
119 | .SH RETURN VALUE | |
120 | Upon successful completion, | |
121 | .BR vmsplice () | |
c13182ef MK |
122 | returns the number of bytes transferred to the pipe. |
123 | On error, | |
d504a994 | 124 | .BR vmsplice () |
2bc4bb77 MK |
125 | returns \-1 and |
126 | .I errno | |
127 | is set to indicate the error. | |
128 | .SH ERRORS | |
129 | .TP | |
56cb0650 MK |
130 | .B EAGAIN |
131 | .B SPLICE_F_NONBLOCK | |
132 | was specified in | |
133 | .IR flags , | |
134 | and the operation would block. | |
135 | .TP | |
2bc4bb77 MK |
136 | .B EBADF |
137 | .I fd | |
138 | either not valid, or doesn't refer to a pipe. | |
139 | .TP | |
140 | .B EINVAL | |
141 | .I nr_segs | |
a2cf8898 | 142 | is greater than |
4df883b9 | 143 | .BR IOV_MAX ; |
2bc4bb77 MK |
144 | or memory not aligned if |
145 | .B SPLICE_F_GIFT | |
146 | set. | |
147 | .TP | |
148 | .B ENOMEM | |
149 | Out of memory. | |
2dd578fd MK |
150 | .SH VERSIONS |
151 | The | |
2777b1ca | 152 | .BR vmsplice () |
c95b6ae1 MK |
153 | system call first appeared in Linux 2.6.17; |
154 | library support was added to glibc in version 2.5. | |
47297adb | 155 | .SH CONFORMING TO |
8382f16d | 156 | This system call is Linux-specific. |
2bc4bb77 MK |
157 | .SH NOTES |
158 | .BR vmsplice () | |
159 | follows the other vectorized read/write type functions when it comes to | |
8031e529 | 160 | limitations on the number of segments being passed in. |
2bc4bb77 MK |
161 | This limit is |
162 | .B IOV_MAX | |
163 | as defined in | |
164 | .IR <limits.h> . | |
8031e529 MK |
165 | Currently, |
166 | .\" UIO_MAXIOV in kernel source | |
167 | this limit is 1024. | |
2bc4bb77 MK |
168 | .SH SEE ALSO |
169 | .BR splice (2), | |
6c97eb40 MK |
170 | .BR tee (2), |
171 | .BR pipe (7) |