Re: [PATCH] man2/vmsplice: splice pages from pipe to memory

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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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