485889d11c
Provide more details on using mktime(3) in the manpage. Resolves: RHEL-61159 Resolves: RHEL-61136
163 lines
3.8 KiB
Diff
163 lines
3.8 KiB
Diff
commit bd576aaf5fce40100133c1d48c02eacbf25594c8
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Author: Alejandro Colomar <alx@kernel.org>
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Date: Sat Aug 24 00:51:55 2024 +0200
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ctime.3: EXAMPLES: Document how to detect invalid or ambiguous times
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This example documents how to detect some corner cases of mktime(3),
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such as DST transitions and other jumps in the calendar.
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Link: <https://www.redhat.com/en/blog/brief-history-mktime>
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Cc: DJ Delorie <dj@redhat.com>
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Cc: Carlos O'Donell <carlos@redhat.com>
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Cc: Paul Eggert <eggert@cs.ucla.edu>
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Signed-off-by: Alejandro Colomar <alx@kernel.org>
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diff --git a/man3/ctime.3 b/man/man3/ctime.3
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index 53abab6d9..acd6f1565 100644
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--- a/man3/ctime.3
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+++ b/man3/ctime.3
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@@ -467,6 +467,14 @@ For example, a change in the timezone definition
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may cause a clock time to be repeated or skipped
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without a corresponding DST change.
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.SH EXAMPLES
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+The program below defines a wrapper that
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+allows detecting invalid and ambiguous times,
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+with
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+.B EINVAL
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+and
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+.BR ENOTUNIQ ,
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+respectively.
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+.P
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The following shell session shows sample runs of the program:
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.P
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.in +4n
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@@ -482,6 +490,7 @@ $
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.RB $\~ "./a.out 2024 08 23 00 17 53 \-1" ;
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1724365073
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.RB $\~ "./a.out 2024 08 23 00 17 53 0" ;
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+a.out: my_mktime: Invalid argument
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1724368673
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.RB $\~ "./a.out 2024 08 23 00 17 53 1" ;
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1724365073
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@@ -491,12 +500,15 @@ $
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.RB $\~ "./a.out 2024 02 23 00 17 53 0" ;
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1708643873
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.RB $\~ "./a.out 2024 02 23 00 17 53 1" ;
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+a.out: my_mktime: Invalid argument
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1708640273
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$
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.RB $\~ "./a.out 2023 03 26 02 17 53 \-1" ;
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+a.out: my_mktime: Invalid argument
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1679793473
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$
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.RB $\~ "./a.out 2023 10 29 02 17 53 \-1" ;
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+a.out: my_mktime: Name not unique on network
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1698542273
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.RB $\~ "./a.out 2023 10 29 02 17 53 0" ;
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1698542273
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@@ -504,6 +516,7 @@ $
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1698538673
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$
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.RB $\~ "./a.out 2023 02 29 12 00 00 \-1" ;
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+a.out: my_mktime: Invalid argument
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1677668400
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.EE
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.SS Program source: mktime.c
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@@ -511,13 +524,17 @@ $
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.\" SRC BEGIN (mktime.c)
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.EX
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#include <err.h>
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+#include <errno.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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+#include <string.h>
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#include <time.h>
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\&
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#define is_signed(T) ((T) \-1 < 1)
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\&
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+time_t my_mktime(struct tm *tp);
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+\&
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int
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main(int argc, char *argv[])
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{
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@@ -539,10 +556,13 @@ main(int argc, char *argv[])
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tm.tm_sec = atoi(*p++);
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tm.tm_isdst = atoi(*p++);
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\&
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+ errno = 0;
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tm.tm_wday = \-1;
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- t = mktime(&tm);
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+ t = my_mktime(&tm);
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if (tm.tm_wday == \-1)
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err(EXIT_FAILURE, "mktime");
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+ if (errno == EINVAL || errno == ENOTUNIQ)
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+ warn("my_mktime");
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\&
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if (is_signed(time_t))
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printf("%jd\[rs]n", (intmax_t) t);
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@@ -551,6 +571,62 @@ main(int argc, char *argv[])
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\&
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exit(EXIT_SUCCESS);
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}
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+\&
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+time_t
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+my_mktime(struct tm *tp)
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+{
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+ int e, isdst;
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+ time_t t;
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+ struct tm tm;
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+ unsigned char wday[sizeof(tp\->tm_wday)];
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+\&
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+ e = errno;
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+\&
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+ tm = *tp;
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+ isdst = tp\->tm_isdst;
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+\&
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+ memcpy(wday, &tp\->tm_wday, sizeof(wday));
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+ tp\->tm_wday = \-1;
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+ t = mktime(tp);
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+ if (tp\->tm_wday == \-1) {
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+ memcpy(&tp\->tm_wday, wday, sizeof(wday));
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+ return \-1;
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+ }
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+\&
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+ if (isdst == \-1)
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+ tm.tm_isdst = tp\->tm_isdst;
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+\&
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+ if ( tm.tm_sec != tp\->tm_sec
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+ || tm.tm_min != tp\->tm_min
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+ || tm.tm_hour != tp\->tm_hour
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+ || tm.tm_mday != tp\->tm_mday
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+ || tm.tm_mon != tp\->tm_mon
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+ || tm.tm_year != tp\->tm_year
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+ || tm.tm_isdst != tp\->tm_isdst)
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+ {
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+ errno = EINVAL;
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+ return t;
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+ }
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+\&
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+ if (isdst != \-1)
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+ goto out;
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+\&
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+ tm = *tp;
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+ tm.tm_isdst = !tm.tm_isdst;
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+\&
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+ tm.tm_wday = \-1;
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+ mktime(&tm);
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+ if (tm.tm_wday == \-1)
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+ goto out;
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+\&
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+ if (tm.tm_isdst != tp\->tm_isdst) {
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+ errno = ENOTUNIQ;
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+ return t;
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+ }
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+out:
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+ errno = e;
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+ return t;
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+}
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.EE
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.\" SRC END
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.SH SEE ALSO
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