Hello Andrei,
On 11/07/2017 08:34 AM, Andrei Vagin wrote:
The man page describes that vmsplice can splice pages from
memory to a pipe, but it can work to anonther direction as well.
Patch applied. Sorry for the long delay...
Cheers,
Michael
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
---
man2/vmsplice.2 | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)
diff --git a/man2/vmsplice.2 b/man2/vmsplice.2
index e3e61cf27..8f48b8809 100644
--- a/man2/vmsplice.2
+++ b/man2/vmsplice.2
@@ -25,7 +25,7 @@
.\"
.TH VMSPLICE 2 2014-10-02 "Linux" "Linux Programmer's Manual"
.SH NAME
-vmsplice \- splice user pages into a pipe
+vmsplice \- splice user pages to/from a pipe
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
@@ -44,13 +44,25 @@ vmsplice \- splice user pages into a pipe
.\" the kernel-space one (contrast this to "write()", which copies
.\" the actual data, and you can thus reuse the buffer immediately
.\" after a successful write), but that is often easy to do.
-The
+If
+.I fd
+is opened for writting, the
.BR vmsplice ()
system call maps
.I nr_segs
ranges of user memory described by
.I iov
into a pipe.
+.\" commit 6a14b90bb6bc7cd83e2a444bf457a2ea645cbfe7
+If
+.I fd
+is opened for reading, the
+.BR vmsplice ()
+system call fills
+.I nr_segs
+ranges of user memory described by
+.I iov
+from a pipe.
The file descriptor
.I fd
must refer to a pipe.
@@ -70,7 +82,6 @@ struct iovec {
};
.in
.fi
-
The
.I flags
argument is a bit mask that is composed by ORing together
@@ -163,6 +174,13 @@ as defined in
Currently,
.\" UIO_MAXIOV in kernel source
this limit is 1024.
+
+.\" commit 6a14b90bb6bc7cd83e2a444bf457a2ea645cbfe7
+.BR vmsplice ()
+only really supports true splicing from user memory to a pipe. In another
+direction, it actually just copies the data to userspace. But this makes
+the interface nice and symmetric and enables people to build on splice,
+with room for future improvement in performance.
.SH SEE ALSO
.BR splice (2),
.BR tee (2)
--
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