Date: Mon, 4 May 2015 14:47:00 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r282417 - head/lib/libc/sys Message-ID: <201505041447.t44El03Y050884@svn.freebsd.org>
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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@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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