xref: /minix3/lib/libc/sys/fsync.2 (revision 84d9c625bfea59e274550651111ae9edfdc40fbd)
1*84d9c625SLionel Sambuc.\"	$NetBSD: fsync.2,v 1.18 2013/09/22 10:02:05 apb Exp $
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302fe8fb19SBen Gras.\"     @(#)fsync.2	8.1 (Berkeley) 6/4/93
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32*84d9c625SLionel Sambuc.Dd September 22, 2013
332fe8fb19SBen Gras.Dt FSYNC 2
342fe8fb19SBen Gras.Os
352fe8fb19SBen Gras.Sh NAME
362fe8fb19SBen Gras.Nm fsync ,
372fe8fb19SBen Gras.Nm fsync_range
382fe8fb19SBen Gras.Nd "synchronize a file's in-core state with that on disk"
392fe8fb19SBen Gras.Sh LIBRARY
402fe8fb19SBen Gras.Lb libc
412fe8fb19SBen Gras.Sh SYNOPSIS
422fe8fb19SBen Gras.In unistd.h
432fe8fb19SBen Gras.Ft int
442fe8fb19SBen Gras.Fn fsync "int fd"
452fe8fb19SBen Gras.Ft int
462fe8fb19SBen Gras.Fn fsync_range "int fd" "int how" "off_t start" "off_t length"
472fe8fb19SBen Gras.Sh DESCRIPTION
482fe8fb19SBen Gras.Fn fsync
492fe8fb19SBen Grascauses all modified data and attributes of
502fe8fb19SBen Gras.Fa fd
51*84d9c625SLionel Sambucto be written to a permanent storage device.
522fe8fb19SBen GrasThis normally results in all in-core modified copies
532fe8fb19SBen Grasof buffers for the associated file to be written to a disk.
542fe8fb19SBen Gras.Pp
55*84d9c625SLionel Sambuc.Fn fsync_range
56*84d9c625SLionel Sambucis similar, but provides control over the region of the file
57*84d9c625SLionel Sambucto be synchronized, and the method of synchronization.
58*84d9c625SLionel Sambuc.Pp
59*84d9c625SLionel SambucThese functions should be used by programs that require a file to be
602fe8fb19SBen Grasin a known state, for example, in building a simple transaction
612fe8fb19SBen Grasfacility.
622fe8fb19SBen Gras.Pp
63*84d9c625SLionel SambucNote that writing the data to a permanent storage device
64*84d9c625SLionel Sambucdoes not necessarily write the data to permanent storage media
65*84d9c625SLionel Sambucwithin that device;
66*84d9c625SLionel Sambucfor example, after writing data to a disk device, the data might
67*84d9c625SLionel Sambucreside in a cache within the device, but not yet on
68*84d9c625SLionel Sambucmore permanent storage within the device.
69*84d9c625SLionel SambucNeither
70*84d9c625SLionel Sambuc.Fn fsync
71*84d9c625SLionel Sambucnor the default behavior of
72*84d9c625SLionel Sambuc.Fn fsync_range
73*84d9c625SLionel Sambuc(without the
74*84d9c625SLionel Sambuc.Dv FDISKSYNC
75*84d9c625SLionel Sambucflag)
76*84d9c625SLionel Sambucwill flush disk caches,
77*84d9c625SLionel Sambucbecause they assume that storage devices are able to ensure that
78*84d9c625SLionel Sambuccompleted writes are transferred to media some time between the
79*84d9c625SLionel Sambucwrite and a power failure or system crash.
80*84d9c625SLionel Sambuc.Pp
812fe8fb19SBen Gras.Fn fsync_range
822fe8fb19SBen Grascauses all modified data starting at
832fe8fb19SBen Gras.Fa start
842fe8fb19SBen Grasfor length
852fe8fb19SBen Gras.Fa length
862fe8fb19SBen Grasof
872fe8fb19SBen Gras.Fa fd
88*84d9c625SLionel Sambucto be written to a permanent storage device.
892fe8fb19SBen GrasIf the
902fe8fb19SBen Gras.Fa length
912fe8fb19SBen Grasparameter is zero,
922fe8fb19SBen Gras.Fn fsync_range
932fe8fb19SBen Graswill synchronize all of the file data.
94*84d9c625SLionel Sambuc.Pp
95*84d9c625SLionel Sambuc.Fn fsync_range
96*84d9c625SLionel Sambuctakes a
97*84d9c625SLionel Sambuc.Fa how
98*84d9c625SLionel Sambucparameter which contains one or more of the following flags:
99*84d9c625SLionel Sambuc.Bl -tag -width FDATASYNC -offset indent
100*84d9c625SLionel Sambuc.It Dv FDATASYNC
101*84d9c625SLionel SambucSynchronize the file data and sufficient meta-data to retrieve the
102*84d9c625SLionel Sambucdata for the specified range.
103*84d9c625SLionel SambucThis is equivalent to
104*84d9c625SLionel Sambuc.Xr fdatasync 2
105*84d9c625SLionel Sambucon the specified range.
106*84d9c625SLionel Sambuc.It Dv FFILESYNC
107*84d9c625SLionel SambucSynchronize all modified file data and meta-data for the specified range.
108*84d9c625SLionel SambucThis is equivalent to
109*84d9c625SLionel Sambuc.Xr fsync 2
110*84d9c625SLionel Sambucon the specified range.
111*84d9c625SLionel Sambuc.It Dv FDISKSYNC
112*84d9c625SLionel SambucRequest the destination device to ensure that the relevant data
113*84d9c625SLionel Sambucand meta-data is flushed from any cache to permanent storage media.
114*84d9c625SLionel SambucIn the present implementation, the entire cache on the affected device will
115*84d9c625SLionel Sambucbe flushed, and this may have a significant impact on performance.
116*84d9c625SLionel Sambuc.El
117*84d9c625SLionel Sambuc.Pp
118*84d9c625SLionel SambucThe
119*84d9c625SLionel Sambuc.Dv FDATASYNC
120*84d9c625SLionel Sambucand
121*84d9c625SLionel Sambuc.Dv FFILESYNC
122*84d9c625SLionel Sambucflags are mutually exclusive.
123*84d9c625SLionel SambucEither of those flags may be combined with the
124*84d9c625SLionel Sambuc.Dv FDISKSYNC
125*84d9c625SLionel Sambucflag.
126*84d9c625SLionel Sambuc.Pp
127*84d9c625SLionel SambucNote that
128*84d9c625SLionel Sambuc.Fn fsync_range
129*84d9c625SLionel Sambucrequires that the file
130*84d9c625SLionel Sambuc.Fa fd
131*84d9c625SLionel Sambucmust be open for writing, whereas
132*84d9c625SLionel Sambuc.Fn fsync
133*84d9c625SLionel Sambucdoes not.
1342fe8fb19SBen Gras.Sh RETURN VALUES
1352fe8fb19SBen GrasA 0 value is returned on success.
1362fe8fb19SBen GrasA \-1 value indicates an error.
1372fe8fb19SBen Gras.Sh ERRORS
1382fe8fb19SBen Gras.Fn fsync
1392fe8fb19SBen Grasor
1402fe8fb19SBen Gras.Fn fsync_range
1412fe8fb19SBen Grasfail if:
1422fe8fb19SBen Gras.Bl -tag -width Er
1432fe8fb19SBen Gras.It Bq Er EBADF
1442fe8fb19SBen Gras.Fa fd
1452fe8fb19SBen Grasis not a valid descriptor.
1462fe8fb19SBen Gras.It Bq Er EINVAL
1472fe8fb19SBen Gras.Fa fd
1482fe8fb19SBen Grasrefers to a socket, not to a file.
1492fe8fb19SBen Gras.It Bq Er EIO
1502fe8fb19SBen GrasAn I/O error occurred while reading from or writing to the file system.
1512fe8fb19SBen Gras.El
1522fe8fb19SBen Gras.Pp
1532fe8fb19SBen GrasAdditionally,
1542fe8fb19SBen Gras.Fn fsync_range
1552fe8fb19SBen Grasfails if:
1562fe8fb19SBen Gras.Bl -tag -width Er
1572fe8fb19SBen Gras.It Bq Er EBADF
1582fe8fb19SBen Gras.Fa fd
1592fe8fb19SBen Grasis not open for writing.
1602fe8fb19SBen Gras.It Bq Er EINVAL
1612fe8fb19SBen Gras.Fa start
1622fe8fb19SBen Gras+
1632fe8fb19SBen Gras.Fa length
1642fe8fb19SBen Grasis less than
1652fe8fb19SBen Gras.Fa start .
1662fe8fb19SBen Gras.El
1672fe8fb19SBen Gras.Sh NOTES
1682fe8fb19SBen GrasFor optimal efficiency, the
1692fe8fb19SBen Gras.Fn fsync_range
1702fe8fb19SBen Grascall requires that the file system containing the file referenced by
1712fe8fb19SBen Gras.Fa fd
1722fe8fb19SBen Grassupport partial synchronization of file data.
1732fe8fb19SBen GrasFor file systems which do
1742fe8fb19SBen Grasnot support partial synchronization, the entire file will be synchronized
1752fe8fb19SBen Grasand the call will be the equivalent of calling
1762fe8fb19SBen Gras.Fn fsync .
1772fe8fb19SBen Gras.Sh SEE ALSO
178*84d9c625SLionel Sambuc.Xr fdatasync 2 ,
1792fe8fb19SBen Gras.Xr sync 2 ,
1802fe8fb19SBen Gras.Xr sync 8
1812fe8fb19SBen Gras.Sh HISTORY
1822fe8fb19SBen GrasThe
1832fe8fb19SBen Gras.Fn fsync
1842fe8fb19SBen Grasfunction call appeared in
1852fe8fb19SBen Gras.Bx 4.2 .
1862fe8fb19SBen Gras.Pp
1872fe8fb19SBen GrasThe
1882fe8fb19SBen Gras.Fn fsync_range
1892fe8fb19SBen Grasfunction call first appeared in
1902fe8fb19SBen Gras.Nx 2.0
1912fe8fb19SBen Grasand is modeled after the function available in AIX.
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