A few days ago, daylight savings time ended, and now
ls --full-time says the timestamps of all the files on
my dos partition have increased by one hour.
For example, ls --full-time says the timestamp of command.com is:
last week: Tue Apr 07 06:00:00 1992
this week: Tue Apr 07 07:00:00 1992
I think the timestamps of a dos filesystem are stored in local
time. So the dos filesystem driver needs to convert the local
time to unix standard time, and then ls converts back to local
time, and displays the timestamp in local time.
I think that the problem is that the dos filesystem driver's
local time to unix standard time algorithm is compensating for
whether or not daylight savings time is in effect NOW. It should
be compensating for whether or not daylight savings time was in
effect at the time of the timestamp.
The time conversion algorithm is function date_dos2unix in file
/usr/src/linux-2.4.19/fs/fat/misc.c. Is there a way to use
tz_minuteswest from the the time of the timestamp instead of the
current tz_minuteswest?
Or before returning the number of seconds, function date_dos2unix
could determine if daylight savings time is in effect now, and if
daylight savings time was in effect at the time of the timestamp.
These determinations could return 0 or 1. Then subtract the two
determinations, which will give us -1, 0, or 1. Multiply by 3600
and add to the number of seconds.
Function fat_date_unix2dos in file
/usr/src/linux-2.4.19/fs/fat/misc.c should have a similar fix.
ls appears to convert unix standard time to local time correctly,
adjusting for whether or not daylight savings time was in effect
at the time being converted. Maybe we should look at the source
for ls, to see how ls converts time.
I am running redhat 7.2 on a pcchips741lmrt/pentiumII, with a
custom 2.4.19 kernel, compiled with gcc version 2.96. My dos
partition is plain dos, not vfat or umsdos.
On Tue, Oct 29, 2002 at 08:08:20PM -0500, Kenneth M. Howlett wrote:
> A few days ago, daylight savings time ended, and now
> ls --full-time says the timestamps of all the files on
> my dos partition have increased by one hour.
>
> For example, ls --full-time says the timestamp of command.com is:
> last week: Tue Apr 07 06:00:00 1992
> this week: Tue Apr 07 07:00:00 1992
>
> I think the timestamps of a dos filesystem are stored in local
> time. So the dos filesystem driver needs to convert the local
> time to unix standard time, and then ls converts back to local
> time, and displays the timestamp in local time.
>
> I think that the problem is that the dos filesystem driver's
> local time to unix standard time algorithm is compensating for
> whether or not daylight savings time is in effect NOW. It should
> be compensating for whether or not daylight savings time was in
> effect at the time of the timestamp.
>
> The time conversion algorithm is function date_dos2unix in file
> /usr/src/linux-2.4.19/fs/fat/misc.c. Is there a way to use
> tz_minuteswest from the the time of the timestamp instead of the
> current tz_minuteswest?
>
> Or before returning the number of seconds, function date_dos2unix
> could determine if daylight savings time is in effect now, and if
> daylight savings time was in effect at the time of the timestamp.
> These determinations could return 0 or 1. Then subtract the two
> determinations, which will give us -1, 0, or 1. Multiply by 3600
> and add to the number of seconds.
>
> Function fat_date_unix2dos in file
> /usr/src/linux-2.4.19/fs/fat/misc.c should have a similar fix.
>
> ls appears to convert unix standard time to local time correctly,
> adjusting for whether or not daylight savings time was in effect
> at the time being converted. Maybe we should look at the source
> for ls, to see how ls converts time.
Yes. But it needs the /usr/share/zoneinfo/`cat /etc/timezone` file for this.
That file contains a record of when daylight saving time was in effect
for that country. It's handling is in standart C library. But kernel
does not use C library and does not load files. Thus it does not know,
weather DST was in effect at some time...
-------------------------------------------------------------------------------
Jan 'Bulb' Hudec <[email protected]>
On Tue, Oct 29, 2002 at 08:08:20PM -0500, Kenneth M. Howlett wrote:
> I think the timestamps of a dos filesystem are stored in local
> time.
Yes, I beleive it does.
> So the dos filesystem driver needs to convert the local time to unix
> standard time, and then ls converts back to local time, and displays
> the timestamp in local time.
Nope.... that's a disgusting ugly hack that won't work (consider that
there are two 2:00am for example in a given time zone, one DST and one
without, does DOS store a bit to say which is which in ambiguous
cases?)
If anything, the FS should know about a tz-offset and just simply add
that to the timestamps before passing the data up to the VFS...
<pause>
Checking the code, it uses sys_tz to do exactly this...
--cw