minix/lib/libc/sys/truncate.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

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.\" $NetBSD: truncate.2,v 1.26 2010/05/31 12:16:20 njoly Exp $
.\"
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.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93
.\"
.Dd March 16, 2008
.Dt TRUNCATE 2
.Os
.Sh NAME
.Nm truncate ,
.Nm ftruncate
.Nd truncate a file to a specified length
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn truncate "const char *path" "off_t length"
.Ft int
.Fn ftruncate "int fd" "off_t length"
.Sh DESCRIPTION
.Fn truncate
causes the file named by
.Fa path
or referenced by
.Fa fd
to have a size of
.Fa length
bytes.
If the file previously was larger than this size, the extra data is discarded.
If it was previously shorter than
.Fa length ,
its size is increased to the specified value and
the extended area appears as if it were zero-filled.
.Pp
With
.Fn ftruncate ,
the file must be open for writing; for
.Fn truncate ,
the process must have write permissions for the file.
.Sh RETURN VALUES
A value of 0 is returned if the call succeeds.
If the call fails a \-1 is returned, and the global variable
.Va errno
specifies the error.
.Sh ERRORS
Error return codes common to
.Fn truncate
and
.Fn ftruncate
are:
.Bl -tag -width Er
.It Bq Er EISDIR
The named file is a directory.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er ETXTBSY
The file is a pure procedure (shared text) file that is being executed.
.It Bq Er EIO
An I/O error occurred updating the inode.
.It Bq Er ENOSPC
There was no space in the filesystem to complete the operation.
.El
.Pp
Error codes specific to
.Fn truncate
are:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix, or
the named file is not writable by the user.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EFAULT
.Fa path
points outside the process's allocated address space.
.El
.Pp
Error codes specific to
.Fn ftruncate
are:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
is not a valid descriptor.
.It Bq Er EINVAL
The
.Fa fd
references a socket, not a file, or
the
.Fa fd
is not open for writing.
.El
.Sh SEE ALSO
.Xr open 2
.Sh STANDARDS
Use of
.Fn truncate
to extend a file is an
.St -p1003.1-2004
extension, and is thus not portable.
Files can be extended in a portable way seeking (using
.Xr lseek 2 )
to the required size and writing a single character with
.Xr write 2 .
.Sh HISTORY
The
.Fn truncate
and
.Fn ftruncate
function calls appeared in
.Bx 4.2 .
.Sh BUGS
These calls should be generalized to allow ranges
of bytes in a file to be discarded.