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diff --git a/man2/vmsplice.2 b/man2/vmsplice.2 new file mode 100644 index 0000000000..168645ccd9 --- /dev/null +++ b/man2/vmsplice.2 @@ -0,0 +1,154 @@ +.\" Hey Emacs! This file is -*- nroff -*- source. +.\" +.\" This manpage is Copyright (C) 2006 Jens Axboe +.\" and Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net> +.\" +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" +.TH vmsplice 2 2006-04-28 "Linux 2.6.17" "Linux Programmer's Manual" +.SH NAME +vmsplice \- splice user pages into a pipe +.SH SYNOPSIS +.nf +.B #define _GNU_SOURCE +.B #include <fcntl.h> +.B #include <sys/uio.h> + +.BI "long vmsplice(int " fd ", const struct iovec *" iov , +.BI " unsigned long " nr_segs ", unsigned int " flags ); +.fi +.SH DESCRIPTION +.\" Linus: vmsplice() system call to basically do a "write to +.\" the buffer", but using the reference counting and VM traversal +.\" to actually fill the buffer. This means that the user needs to +.\" be careful not to re-use the user-space buffer it spliced into +.\" the kernel-space one (contrast this to "write()", which copies +.\" the actual data, and you can thus re-use the buffer immediately +.\" after a successful write), but that is often easy to do. +The +.BR vmsplice () +system call maps +.I nr_segs +ranges of user memory described by +.I iov +into a pipe. +The file descriptor +.I fd +must refer to a pipe. + +The pointer +.I iov +points to an array of +.I iovec +structures as defined in +.IR <sys/uio.h> : + +.in +0.25i +.nf +struct iovec { + void *iov_base; /* Starting address */ + size_t iov_len; /* Number of bytes */ +}; +.in -0.25i +.fi + +The +.I flags +argument is a bit mask that is composed by ORing together +zero or more of the following values: +.TP 1.9i +.B SPLICE_F_MOVE +Unused for +.BR vmsplice (); +see +.BR splice (2). +.TP +.B SPLICE_F_NONBLOCK +.\" Not used for vmsplice +.\" May be in the future -- therefore EAGAIN +Do not block on I/O; see +.BR splice (2) +for further details. +.TP +.B SPLICE_F_MORE +Currently has no effect for +.BR vmsplice (), +but may be implemented in the future; see +.BR splice (2). +.TP +.B SPLICE_F_GIFT +The user pages are a gift to the kernel. +The application may not modify this memory ever, +.\" FIXME Explain the following line in a little more detail: +or page cache and on-disk data may differ. +Gifting pages to the kernel means that a subsequent +.BR splice () +.B SPLICE_F_MOVE +can successfully move the pages; +if this flag is not specified, then a subsequent +.BR splice () +.B SPLICE_F_MOVE +must copy the pages. +Data must also be properly page aligned, both in memory and length. +.\" .... if we expect to later SPLICE_F_MOVE to the cache. +.SH RETURN VALUE +Upon successful completion, +.BR vmsplice () +returns the number of bytes transferred to the pipe. +On error, +.BR vmplice () +returns \-1 and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EBADF +.I fd +either not valid, or doesn't refer to a pipe. +.TP +.B EINVAL +.I nr_segs +is 0 or greater than +.BR IOV_MAX; +or memory not aligned if +.B SPLICE_F_GIFT +set. +.TP +.B ENOMEM +Out of memory. +.SH NOTES +.BR vmsplice () +follows the other vectorized read/write type functions when it comes to +limitations on number of segments being passed in. +This limit is +.B IOV_MAX +as defined in +.IR <limits.h> . +At the time of this writing, that limit is 1024. +.SH HISTORY +The +.BR vmsplice (2) +system call first appeared in Linux-2.6.17. +.SH "CONFORMING TO" +This system call is Linux specific. +.SH SEE ALSO +.BR splice (2), +.BR tee (2) |