On 7/18/07, Jean Delvare <[email protected]> wrote:
Hi Greg,
On Tue, 17 Jul 2007 20:38:28 -0700, Greg KH wrote:
> On Tue, Jul 17, 2007 at 11:05:30PM +0200, Jean Delvare wrote:
> > This breaks libsensors. libsensors uses libsysfs, and libsysfs is not
> > very smart in that it will initialize successfully even if sysfs is not
> > mounted.
>
> libsysfs isn't smart at all, and isn't even supported anymore. I'd
> really suggest droping it entirely, it isn't worth it.
Agreed, except that I do not have the time for this right now. I want
to get lm-sensors-3.0.0 ready for a release candidate first. What
really matters for this is to get the API ready. Implementation details
will come later.
> > So I added tests after the initialization, to make sure that
> > sysfs is really there. These tests are:
> > * The mount point exists.
> > * The mount point is really mounted.
>
> Do you know of a 2.6 based distro that does not mount sysfs at /sys? We
> took that check out a long time ago in udev and no one has complained :)
I don't know of any 2.6-based distro not mounting sysfs at /sys, but I
know of 2.4-based distros not mounting sysfs at all ;) libsensors
supports both 2.4 and 2.6 kernels, so being able to tell whether sysfs
is mounted or not, matters.
debian has mounted the sysfs
/etc/rcS.d/S02mountkernfs.sh:
#
# Mount sysfs on /sys
#
# Only mount sysfs if it is supported (kernel >= 2.6)
if grep -E -qs "sysfs\$" /proc/filesystems
then
domount sysfs "" /sys sysfs -onodev,noexec,nosuid
fi
# Mount /var/run and /var/lock as tmpfs if enabled
if [ yes = "$RAMRUN" ] ; then
RUN_OPT=
[ "${RUN_SIZE:=$TMPFS_SIZE}" ] && RUN_OPT=",size=$RUN_SIZE"
domount tmpfs "" /var/run varrun -omode=0755,nosuid$RUN_OPT
touch /var/run/.ramfs
fi
if [ yes = "$RAMLOCK" ] ; then
LOCK_OPT=
[ "${LOCK_SIZE:=$TMPFS_SIZE}" ] && LOCK_OPT=",size=$LOCK_SIZE"
domount tmpfs "" /var/lock varlock -omode=1777,nodev,noexec,nosuid$LOCK_OPT
touch /var/lock/.ramfs
fi
> > The code looks like:
> >
> > if (sysfs_get_mnt_path(sensors_sysfs_mount, NAME_MAX)
> > || stat(sensors_sysfs_mount, &statbuf) < 0
> > || statbuf.st_nlink <= 2) /* Empty directory */
> > return 0; /* Failure */
> >
> > This works OK with 2.6.22.1, but the last test fails with the current
> > git kernel even when sysfs is mounted.
>
> Yeah, but is checking the number of hard links in the directory a safe
> way to always verify that it isn't empty?
I think so, yes. To the best of my knowledge, it has worked on all
Unix-like systems for decades. There are other ways, but this is by far
the less expensive.
> Isn't there some glibc
> function that can detect the mount point of a filesystem or directory?
> Something in glibc parses /proc/mounts for something, I can't remember
> what it is right now though, sorry.
Maybe getmntent(3)? Sure I could use this, but how expensive compared
to a single stat(2).
> Again, I recommend dropping libsysfs, it's gone from some distros
> already :)
Really? I'm curious how such distributions support libsensors and the
other tools which still rely on libsysfs. If they have already
converted libsensors for me, that would be good news :)
> And yes, the bug should be fixed, I agree. Thanks for letting us know.
Tejun already fixed it, that was quick :)
--
Jean Delvare
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