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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
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=282417
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@ -28,7 +28,7 @@
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.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd December 13, 2006
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.Dd May 4, 2015
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.Dt TRUNCATE 2
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.Os
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.Sh NAME
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@ -60,9 +60,18 @@ is lost.
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If the file was smaller than this size,
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it will be extended as if by writing bytes
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with the value zero.
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With
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.Fn ftruncate ,
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the file must be open for writing.
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.Pp
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The
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.Fn ftruncate
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system call causes the file or shared memory object backing the file descriptor
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.Fa fd
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to be truncated or extended to
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.Fa length
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bytes in size.
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The file descriptor must be a valid file descriptor open for writing.
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The file position pointer associated with the file descriptor
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.Fa fd
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will not be modified.
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.Sh RETURN VALUES
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.Rv -std
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If the file to be modified is not a directory or
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@ -129,7 +138,7 @@ is not a valid descriptor.
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The
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.Fa fd
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argument
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references a socket, not a file.
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references a file descriptor that is not a regular file or shared memory object.
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.It Bq Er EINVAL
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The
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.Fa fd
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@ -138,11 +147,14 @@ is not open for writing.
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.El
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.Sh SEE ALSO
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.Xr chflags 2 ,
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.Xr open 2
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.Xr open 2 ,
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.Xr shm_open 2
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.Sh HISTORY
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The
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.Fn truncate
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system call appeared in
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and
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.Fn ftruncate
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system calls appeared in
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.Bx 4.2 .
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.Sh BUGS
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These calls should be generalized to allow ranges
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