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Consolidate duplicated information about ut_tv and ut_session 

on biarch platforms.
This commit is contained in:
Michael Kerrisk 2008-06-29 05:24:03 +00:00
parent b40e1143a6
commit 3721bd3f13
1 changed files with 27 additions and 35 deletions
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62
man5/utmp.5
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@ -210,34 +210,6 @@ or
.BR agetty (8)). .BR agetty (8)).
None of these programs creates the file, so if it is None of these programs creates the file, so if it is
removed, record-keeping is turned off. removed, record-keeping is turned off.
.PP
Note that on \fIbiarch\fP platforms, that is, systems which can run both
32-bit and 64-bit applications (x86-64, ppc64, s390x, etc.),
\fIut_tv\fP is the same size in 32-bit mode as in 64-bit mode.
The same goes for \fIut_session\fP and \fIut_time\fP if they are present.
This allows data files and shared memory to be shared between
32-bit and 64-bit applications.
Since \fIut_tv\fP may not be the same as \fIstruct timeval\fP,
then instead of the call:
.in +4n
.nf
.sp
gettimeofday((struct timeval *) &ut.ut_tv, NULL);
.fi
.in
the following method of setting this field is recommended:
.in +4n
.nf
.sp
struct utmp ut;
struct timeval tv;
gettimeofday(&tv, NULL);
ut.ut_tv.tv_sec = tv.tv_sec;
ut.ut_tv.tv_usec = tv.tv_usec;
.fi
.in
.SH FILES .SH FILES
/var/run/utmp /var/run/utmp
.br .br
@ -284,9 +256,12 @@ binaries using the old libc5 struct will corrupt
The file format is machine-dependent, so it is recommended that it be The file format is machine-dependent, so it is recommended that it be
processed only on the machine architecture where it was created. processed only on the machine architecture where it was created.
.PP .PP
Note that on platforms which can run both 32-bit and 64-bit applications Note that on \fIbiarch\fP platforms, that is, systems which can run both
(x86-64, ppc64, s390x, etc.), the sizes of the fields of a \fIutmp\fP struct 32-bit and 64-bit applications (x86-64, ppc64, s390x, etc.),
must be the same in 32-bit mode as in 64-bit mode. \fIut_tv\fP is the same size in 32-bit mode as in 64-bit mode.
The same goes for \fIut_session\fP and \fIut_time\fP if they are present.
This allows data files and shared memory to be shared between
32-bit and 64-bit applications.
This is achieved by changing the type of This is achieved by changing the type of
.I ut_session .I ut_session
to to
@ -299,10 +274,27 @@ fields
.I tv_sec .I tv_sec
and and
.IR tv_usec . .IR tv_usec .
(Thus, in order to fill it, first get the Since \fIut_tv\fP may not be the same as \fIstruct timeval\fP,
time into a real \fIstruct timeval\fP, then instead of the call:
then copy the two fields to .in +4n
.IR ut_tv .) .nf
.sp
gettimeofday((struct timeval *) &ut.ut_tv, NULL);
.fi
.in
the following method of setting this field is recommended:
.in +4n
.nf
.sp
struct utmp ut;
struct timeval tv;
gettimeofday(&tv, NULL);
ut.ut_tv.tv_sec = tv.tv_sec;
ut.ut_tv.tv_usec = tv.tv_usec;
.fi
.in
.SH BUGS .SH BUGS
This man page is based on the libc5 one, things may work differently now. This man page is based on the libc5 one, things may work differently now.
.SH "SEE ALSO" .SH "SEE ALSO"