Re: Problem with boot-time on Cygwin

[Bruno Haible]

Hi Ken,

Thanks for the report.

> > First, there is a comment 
> > saying that /var/run/utmp is empty on Cygwin.  This is not true, at 
> > least on my system.  I'm running Cygwin 3.5.3, the latest stable 
> > release.

In my Cygwin 3.5.3 installation, /var/run/utmp is empty. But anyway,
since you already found the answer:

> Specifically, in 
> boot-time.c:113, ut->ut_type != BOOT_TIME.  As a result, get_boot_time 
> ends up calling get_windows_boot_time, which fails on my system because 
> of the cygdrive problem described in the next paragraph.

OK, nothing to do here.

> > Second, and more serious, is the use of /cygdrive/c to refer to the C: 
> > drive.  In fact, users can set the "cygdrive prefix" to anything they 
> > want in /etc/fstab.  For example, I use /mnt as the cygdrive prefix, so 
> > I would use /mnt/c for the C: drive.  The correct way to use the 
> > cygdrive prefix is to use /proc/cygdrive.  For example, /proc/cygdrive 
> > is a symlink to /mnt/ on my system.

I did not know about /proc/cygdrive; thanks for teaching us. I guess it can be
assumed that /proc/cygdrive exists, because unlike in Linux, there are no
Docker containers and unlike in FreeBSD, there are no jails?

I'm committing this patch:


2024-05-01  Bruno Haible  <bruno@clisp.org>

        readutmp, boot-time: Improve for some Cygwin installations.
        Reported by Ken Brown <kbrown@cornell.edu> in
        <https://lists.gnu.org/archive/html/bug-gnulib/2024-05/msg00008.html>.
        * lib/boot-time-aux.h (get_windows_boot_time): Use /proc/cygdrive/
        instead of /cygdrive/.

diff --git a/lib/boot-time-aux.h b/lib/boot-time-aux.h
index 8b966fe691..a94cdb3f30 100644
--- a/lib/boot-time-aux.h
+++ b/lib/boot-time-aux.h
@@ -306,7 +306,8 @@ get_windows_boot_time (struct timespec *p_boot_time)
      process, namely C:\pagefile.sys.  */
   const char * const boot_touched_file =
     #if defined __CYGWIN__ && !defined _WIN32
-    "/cygdrive/c/pagefile.sys"
+    /* It is more portable to use /proc/cygdrive/c than /cygdrive/c.  */
+    "/proc/cygdrive/c/pagefile.sys"
     #else
     "C:\\pagefile.sys"
     #endif