minix/lib/libc/sys/fsync.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

155 lines
4.3 KiB
Groff

.\" $NetBSD: fsync.2,v 1.17 2010/05/17 12:38:04 jruoho Exp $
.\"
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.\" @(#)fsync.2 8.1 (Berkeley) 6/4/93
.\"
.Dd May 17, 2010
.Dt FSYNC 2
.Os
.Sh NAME
.Nm fsync ,
.Nm fsync_range
.Nd "synchronize a file's in-core state with that on disk"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn fsync "int fd"
.Ft int
.Fn fsync_range "int fd" "int how" "off_t start" "off_t length"
.Sh DESCRIPTION
.Fn fsync
causes all modified data and attributes of
.Fa fd
to be moved to a permanent storage device.
This normally results in all in-core modified copies
of buffers for the associated file to be written to a disk.
.Pp
.Fn fsync
should be used by programs that require a file to be
in a known state, for example, in building a simple transaction
facility.
.Pp
.Fn fsync_range
causes all modified data starting at
.Fa start
for length
.Fa length
of
.Fa fd
to be written to permanent storage.
Note that
.Fn fsync_range
requires that the file
.Fa fd
must be open for writing.
.Pp
.Fn fsync_range
may flush the file data in one of two manners:
.Bl -tag -width FDATASYNC -offset indent
.It Dv FDATASYNC
Synchronize the file data and sufficient meta-data to retrieve the
data for the specified range.
.It Dv FFILESYNC
Synchronize all modified file data and meta-data for the specified range.
.El
.Pp
By default,
.Fn fsync_range
does not flush disk caches, assuming that storage media are able to ensure
completed writes are transfered to media.
The
.Dv FDISKSYNC
flag may be included in the
.Fa how
parameter to trigger flushing of all disk caches for the file.
.Pp
If the
.Fa length
parameter is zero,
.Fn fsync_range
will synchronize all of the file data.
.Sh RETURN VALUES
A 0 value is returned on success.
A \-1 value indicates an error.
.Sh ERRORS
.Fn fsync
or
.Fn fsync_range
fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid descriptor.
.It Bq Er EINVAL
.Fa fd
refers to a socket, not to a file.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Pp
Additionally,
.Fn fsync_range
fails if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not open for writing.
.It Bq Er EINVAL
.Fa start
+
.Fa length
is less than
.Fa start .
.El
.Sh NOTES
For optimal efficiency, the
.Fn fsync_range
call requires that the file system containing the file referenced by
.Fa fd
support partial synchronization of file data.
For file systems which do
not support partial synchronization, the entire file will be synchronized
and the call will be the equivalent of calling
.Fn fsync .
.Sh SEE ALSO
.Xr sync 2 ,
.Xr sync 8
.Sh HISTORY
The
.Fn fsync
function call appeared in
.Bx 4.2 .
.Pp
The
.Fn fsync_range
function call first appeared in
.Nx 2.0
and is modeled after the function available in AIX.