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(-)b/lib/libc/sys/lseek.2 (-6 / +35 lines)
Lines 28-34 Link Here
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.\"     @(#)lseek.2	8.3 (Berkeley) 4/19/94
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.\"     @(#)lseek.2	8.3 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\" $FreeBSD$
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.\"
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.\"
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.Dd April 5, 2007
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.Dd November 21, 2011
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.Dt LSEEK 2
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.Dt LSEEK 2
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.Os
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.Os
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.Sh NAME
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.Sh NAME
Lines 113-122 of the existing end-of-file of the file. Link Here
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If data is later written
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If data is later written
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at this point, subsequent reads of the data in the gap return
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at this point, subsequent reads of the data in the gap return
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bytes of zeros (until data is actually written into the gap).
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bytes of zeros (until data is actually written into the gap).
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.Pp
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However, the
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Some devices are incapable of seeking.
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.Fn lseek
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The value of the pointer
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system call does not, by itself, extend the size of a file.
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associated with such a device is undefined.
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.Pp
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.Pp
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A
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A
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.Qq hole
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.Qq hole
Lines 197-209 is associated with a pipe, socket, or FIFO. Link Here
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The
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The
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.Fn lseek
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.Fn lseek
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system call is expected to conform to
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system call is expected to conform to
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.St -p1003.1-90 .
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.St -p1003.1-2008 .
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.Pp
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The
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.Dv SEEK_HOLE
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and
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.Dv SEEK_DATA
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directives, along with the
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.Er ENXIO
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error, are extensions to that specification.
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.Sh HISTORY
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.Sh HISTORY
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The
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The
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.Fn lseek
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.Fn lseek
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function appeared in
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function appeared in
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.At v7 .
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.At v7 .
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.Sh BUGS
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.Sh BUGS
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If the
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.Fn lseek
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system call is operating on a device which is incapable of seeking,
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it will request the seek operation and return successfully,
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even though no seek was performed.
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Because the
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.Ar offset
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argument will be stored unconditionally in the file descriptor of that device,
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there is no way to confirm, if the seek operation succeeded or not
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(e.g. using the
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.Fn ftell
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function).
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Device types which are known to be incapable of seeking include
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tape drives.
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.Pp
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The
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.Fn lseek
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system call will not detect whether media are present in changeable
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media devices such as DVD or Blu-ray devices.
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A requested seek operation will therefore return sucessfully when no
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medium is present.
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.Pp
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This document's use of
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This document's use of
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.Fa whence
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.Fa whence
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is incorrect English, but is maintained for historical reasons.
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is incorrect English, but is maintained for historical reasons.

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