1 .\" This manpage is Copyright (C) 2006 Jens Axboe
2 .\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
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26 .TH VMSPLICE 2 2017-07-13 "Linux" "Linux Programmer's Manual"
28 vmsplice \- splice user pages into a pipe
31 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
33 .B #include <sys/uio.h>
35 .BI "ssize_t vmsplice(int " fd ", const struct iovec *" iov ,
36 .BI " unsigned long " nr_segs ", unsigned int " flags );
38 .\" Return type was long before glibc 2.7
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
43 .\" be careful not to reuse the user-space buffer it spliced into
44 .\" the kernel-space one (contrast this to "write()", which copies
45 .\" the actual data, and you can thus reuse the buffer immediately
46 .\" after a successful write), but that is often easy to do.
51 ranges of user memory described by
62 structures as defined in
68 void *iov_base; /* Starting address */
69 size_t iov_len; /* Number of bytes */
76 argument is a bit mask that is composed by ORing together
77 zero or more of the following values:
87 .\" Not used for vmsplice
88 .\" May be in the future -- therefore EAGAIN
89 Do not block on I/O; see
94 Currently has no effect for
96 but may be implemented in the future; see
100 The user pages are a gift to the kernel.
101 The application may not modify this memory ever,
102 .\" FIXME . Explain the following line in a little more detail:
103 otherwise the page cache and on-disk data may differ.
104 Gifting pages to the kernel means that a subsequent
107 can successfully move the pages;
108 if this flag is not specified, then a subsequent
112 Data must also be properly page aligned, both in memory and length.
115 .\" It looks like the page-alignment requirement went away with
116 .\" commit bd1a68b59c8e3bce45fb76632c64e1e063c3962d
118 .\" .... if we expect to later SPLICE_F_MOVE to the cache.
120 Upon successful completion,
122 returns the number of bytes transferred to the pipe.
127 is set to indicate the error.
134 and the operation would block.
138 either not valid, or doesn't refer to a pipe.
144 or memory not aligned if
153 system call first appeared in Linux 2.6.17;
154 library support was added to glibc in version 2.5.
156 This system call is Linux-specific.
159 follows the other vectorized read/write type functions when it comes to
160 limitations on the number of segments being passed in.
166 .\" UIO_MAXIOV in kernel source