Messages in this thread | | | Date | Wed, 18 Jul 2007 23:21:54 +0200 | From | "Oliver Pinter" <> | Subject | Re: sysfs root link count broken in 2.6.22-git5 |
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On 7/18/07, Jean Delvare <khali@linux-fr.org> 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 > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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