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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2006-09-18 12:35:34 +0000 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2006-09-18 12:35:34 +0000 |
| commit | 2bc4bb77a9adad1d0b307261dd1bafb25bff7b55 (patch) | |
| tree | ef808e751c0ad47b6eae3b4b571bf13155f968bc /man2 | |
| parent | 8231ec7de479133a1b44c8d904e13693c419280f (diff) | |
| download | man-pages-2bc4bb77a9adad1d0b307261dd1bafb25bff7b55.tar.gz | |
New system calls in 2.6.17.
Diffstat (limited to 'man2')
| -rw-r--r-- | man2/splice.2 | 218 | ||||
| -rw-r--r-- | man2/tee.2 | 195 | ||||
| -rw-r--r-- | man2/vmsplice.2 | 154 |
3 files changed, 567 insertions, 0 deletions
diff --git a/man2/splice.2 b/man2/splice.2 new file mode 100644 index 0000000000..9c9674cf39 --- /dev/null +++ b/man2/splice.2 @@ -0,0 +1,218 @@ +.\" 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 +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date.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 splice 2 2006-04-28 "Linux 2.6.17" "Linux Programmer's Manual" +.SH NAME +splice \- splice data to/from a pipe +.SH SYNOPSIS +.nf +.B #define _GNU_SOURCE +.B #include <fcntl.h> + +.BI "long splice(int " fd_in ", off_t *" off_in ", int " fd_out , +.BI " off_t *" off_out ", size_t " len \ +", unsigned int " flags ); +.fi +.SH DESCRIPTION +.BR splice () +moves data between two file descriptors +without copying between kernel address space and user address space. +It transfers up to +.I len +bytes of data from the file descriptor +.I fd_in +to the file descriptor +.IR fd_out , +where one of the descriptors must refer to a pipe. + +If +.I in_fd +refers to a pipe, then +.I in_off +must be NULL. +If +.I in_fd +does not refer to a pipe and +.I in_off +is NULL, then bytes are read from +.I in_fd +starting from the current file offset, +and the current file offset is adjusted appropriately. +If +.I in_fd +does not refer to a pipe and +.I in_off +is not NULL, then +.I in_off +must point to a buffer which specifies the starting +offset from which bytes will be read from +.IR in_fd ; +in this case, the current file offset of +.IR in_fd +is not changed. +Analogous statements apply for +.I out_fd +and +.IR out_off . + +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 +Attempt to move pages instead of copying. +This is only a hint to the kernel: +pages may still be copied if the kernel cannot move the +pages from the pipe, or if +the pipe buffers don't refer to full pages. +.TP +.B SPLICE_F_NONBLOCK +Do not block on I/O. +This makes the splice pipe operations non-blocking, but +.BR splice () +may nevertheless block because the file descriptors that +are spliced to/from may block (unless they have the +.BR O_NONBLOCK +flag set). +.TP +.B SPLICE_F_MORE +More data will be coming in a subsequent splice. +This is a helpful hint when +the +.I fd_out +refers to a socket (see also the description of +.B MSG_MORE +in +.BR send (2), +and the description of +.B TCP_CORK +in +.BR tcp (7)) +.TP +.B SPLICE_F_GIFT +Unused for +.BR splice (); +see +.BR vmsplice (2). +.SH RETURN VALUE +Upon successful completion, +.BR splice () +returns the number of bytes +spliced to or from the pipe. +A return value of 0 means that there was no data to transfer, +and it would not make sense to block, because there are no +writers connected to the write end of the pipe referred to by +.IR fd_in . + +On error, +.BR splice () +returns \-1 and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EBADF +One or both file descriptors are not valid, +or do not have proper read-write mode. +.TP +.B EINVAL +Target file system doesn't support splicing; +neither of the descriptors refers to a pipe; or +offset given for non-seekable device. +.TP +.B ENOMEM +Out of memory. +.TP +.B ESPIPE +Either +.I off_in +or +.I off_out +was not NULL, but the corresponding file descriptor refers to a pipe. +.SH HISTORY +The +.BR splice (2) +system call first appeared in Linux-2.6.17. +.SH NOTES +The three system calls +.BR splice (2), +.BR vmsplice (2), +and +.BR tee (2)), +provide userspace programs with full control over an arbitrary +kernel buffer, implemented within the kernel using the same type +of buffer that is used for a pipe. +In overview, these system calls perform the following tasks: +.TP 1.2i +.BR splice () +moves data from the buffer to an arbitrary file descriptor, or vice versa, +or from one buffer to another. +.TP +.BR tee () +"copies" the data from one buffer to another. +.TP +.BR vmsplice () +"copies" data from user space into the buffer. +.PP +Though we talk of copying, actual copies are generally avoided. +The kernel does this by implementing a pipe buffer as a set +of reference-counted pointers to pages of kernel memory. +The kernel creates "copies" of pages in a buffer by creating new +pointers (for the output buffer) referring to the pages, +and increasing the reference counts for the pages: +only pointers are copied, not the pages of the buffer. +.\" +.\" Linus: Now, imagine using the above in a media server, for example. +.\" Let's say that a year or two has passed, so that the video drivers +.\" have been updated to be able to do the splice thing, and what can +.\" you do? You can: +.\" +.\" - splice from the (mpeg or whatever - let's just assume that the video +.\" input is either digital or does the encoding on its own - like they +.\" pretty much all do) video input into a pipe (remember: no copies - the +.\" video input will just DMA directly into memory, and splice will just +.\" set up the pages in the pipe buffer) +.\" - tee that pipe to split it up +.\" - splice one end to a file (ie "save the compressed stream to disk") +.\" - splice the other end to a real-time video decoder window for your +.\" real-time viewing pleasure. +.\" +.\" Linus: Now, the advantage of splice()/tee() is that you can +.\" do zero-copy movement of data, and unlike sendfile() you can +.\" do it on _arbitrary_ data (and, as shown by "tee()", it's more +.\" than just sending the data to somebody else: you can duplicate +.\" the data and choose to forward it to two or more different +.\" users - for things like logging etc). +.\" +.SH EXAMPLE +See +.BR tee (2). +.SH "CONFORMING TO" +This system call is Linux specific. +.SH SEE ALSO +.BR sendfile (2), +.BR splice (2), +.BR tee (2) diff --git a/man2/tee.2 b/man2/tee.2 new file mode 100644 index 0000000000..672c11192a --- /dev/null +++ b/man2/tee.2 @@ -0,0 +1,195 @@ +.\" 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 tee 2 2006-04-28 "Linux 2.6.17" "Linux Programmer's Manual" +.SH NAME +tee \- duplicating pipe content +.SH SYNOPSIS +.nf +.B #define _GNU_SOURCE +.B #include <fcntl.h> + +.BI "long tee(int " fd_in ", int " fd_out ", size_t " len \ +", unsigned int " flags ); +.fi +.SH DESCRIPTION +.\" Example programs http://brick.kernel.dk/snaps +.\" +.\" +.\" add a "tee(in, out1, out2)" system call that duplicates the pages +.\" (again, incrementing their reference count, not copying the data) from +.\" one pipe to two other pipes. +.BR tee () +duplicates up to +.I len +bytes of data from the pipe referred to by the file descriptor +.I fd_in +to the pipe referred to by the file descriptor +.IR fd_out . +It does not consume the data that is duplicated from +.IR fd_in ; +therefore, that data can be copied by a subsequent +.BR splice (2). + +.I flags +is a series of modifier flags, which share the name space with +.BR splice (2) +and +.BR vmsplice (2): +.TP 1.9i +.B SPLICE_F_MOVE +Currently has no effect for +.BR tee (); +see +.BR splice (2). +.TP +.B SPLICE_F_NONBLOCK +Do not block on I/O; see +.BR splice (2) +for further details. +.TP +.B SPLICE_F_MORE +Currently has no effect for +.BR tee (), +but may be implemented in the future; see +.BR splice (2). +.TP +.B SPLICE_F_GIFT +Unused for +.BR tee (); +see +.BR vmsplice (2). +.SH RETURN VALUE +Upon successful completion, +.BR tee () +returns the number of bytes that were duplicated between the input +and output. +A return value of 0 means that there was no data to transfer, +and it would not make sense to block, because there are no +writers connected to the write end of the pipe referred to by +.IR fd_in . + +On error, +.BR tee () +returns \-1 and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EINVAL +.I fd_in +or +.I fd_out +does not refer to a pipe; or +.I fd_in +and +.I fd_out +refer to the same pipe. +.TP +.B ENOMEM +Out of memory. +.SH NOTES +Conceptually, +.BR tee () +copies the data between the two pipes. +In reality no real data copying takes place though: +under the covers, +.BR tee () +assigns data in the output by merely grabbing +a reference to the input. +.SH EXAMPLE +The following example implements a basic +.BR tee (1) +program using the +.BR tee (2) +system call. +.nf + +#define _GNU_SOURCE +#include <fcntl.h> +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <assert.h> +#include <errno.h> +#include <limits.h> + +int +main(int argc, char *argv[]) +{ + int fd; + int len, slen; + + assert(argc == 2); + + fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); + if (fd == -1) { + perror("open"); + exit(EXIT_FAILURE); + } + + do { + /* + * tee stdin to stdout. + */ + len = tee(STDIN_FILENO, STDOUT_FILENO, + INT_MAX, SPLICE_F_NONBLOCK); + + if (len < 0) { + if (errno == EAGAIN) + continue; + perror("tee"); + exit(EXIT_FAILURE); + } else + if (len == 0) + break; + + /* + * Consume stdin by splicing it to a file. + */ + while (len > 0) { + slen = splice(STDIN_FILENO, NULL, fd, NULL, + len, SPLICE_F_MOVE); + if (slen < 0) { + perror("splice"); + break; + } + len -= slen; + } + } while (1); + + close(fd); + exit(EXIT_SUCCESS); +} +.fi +.SH HISTORY +The +.BR tee (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 vmsplice (2) 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) |