svn commit: r282417 - head/lib/libc/sys
John Baldwin
jhb at FreeBSD.org
Mon May 4 14:47:01 UTC 2015
Author: jhb
Date: Mon May 4 14:47:00 2015
New Revision: 282417
URL: https://svnweb.freebsd.org/changeset/base/282417
Log:
Various updates to the ftruncate(2) documentation:
- Note that ftruncate(2) can operate on shared memory objects and cross
reference shm_open(2).
- Note that ftruncate(2) does not change the file position pointer (aka
seek pointer) of the file descriptor.
- ftruncate(2) will fail with EINVAL for all sorts of other fd types than
just sockets, so instead note that it fails for all but regular files and
shared memory objects.
- Note that ftruncate(2) also appeared in 4.2BSD along with truncate(2).
(Or at least the manpage for both appeared in 4.2, I did not check the
kernel code itself to see if either predated 4.2.)
PR: 199472 (2)
Submitted by: andrew at ugh.net.au (2)
MFC after: 1 week
Modified:
head/lib/libc/sys/truncate.2
Modified: head/lib/libc/sys/truncate.2
==============================================================================
--- head/lib/libc/sys/truncate.2 Mon May 4 14:23:31 2015 (r282416)
+++ head/lib/libc/sys/truncate.2 Mon May 4 14:47:00 2015 (r282417)
@@ -28,7 +28,7 @@
.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
-.Dd December 13, 2006
+.Dd May 4, 2015
.Dt TRUNCATE 2
.Os
.Sh NAME
@@ -60,9 +60,18 @@ is lost.
If the file was smaller than this size,
it will be extended as if by writing bytes
with the value zero.
-With
-.Fn ftruncate ,
-the file must be open for writing.
+.Pp
+The
+.Fn ftruncate
+system call causes the file or shared memory object backing the file descriptor
+.Fa fd
+to be truncated or extended to
+.Fa length
+bytes in size.
+The file descriptor must be a valid file descriptor open for writing.
+The file position pointer associated with the file descriptor
+.Fa fd
+will not be modified.
.Sh RETURN VALUES
.Rv -std
If the file to be modified is not a directory or
@@ -129,7 +138,7 @@ is not a valid descriptor.
The
.Fa fd
argument
-references a socket, not a file.
+references a file descriptor that is not a regular file or shared memory object.
.It Bq Er EINVAL
The
.Fa fd
@@ -138,11 +147,14 @@ is not open for writing.
.El
.Sh SEE ALSO
.Xr chflags 2 ,
-.Xr open 2
+.Xr open 2 ,
+.Xr shm_open 2
.Sh HISTORY
The
.Fn truncate
-system call appeared in
+and
+.Fn ftruncate
+system calls appeared in
.Bx 4.2 .
.Sh BUGS
These calls should be generalized to allow ranges
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