Re: rebuildfstab question
Hello Andrew,
On Fri, Jul 22, 2011 at 04:33:08AM -0400, Andrew wrote:
> Dear Klaus et al,
>
> This pertains to /usr/sbin/rebuildfstab "Jul 2010" as in v6.4.4.
>
> Until recently, Knoppix only added lines to fstab for devices that were
> not already listed. This behavior seemed intentional and I was making
> good use of it.
Before the most recent versions, rebuildfstab was rebuilding fstab
adding _all_ detected block devices on each run, every time a partition
on a newly inserted device was detected. This was somewhat inefficient,
because it would re-detect everyting each time a single partition was
reported via udev.
I changed this behavior so that the environment variables which udev
provides were evaluated, so only the newly detected or changed partition
would trigger a one-line change in /etc/fstab (well, two lines including
the comment).
Since udev also provides file system information using the blkid plugin,
I was also using that in favor of my own filesystem detection script.
At least, that was the idea behind the change. ;-)
> I am studying this script because, unfortunately, this is no longer the
> case. My question pertains to the test which determines the mode of
> operation:
>
> ### We now have two operation modes:
> ### A) do what udev tells us (add/remove partition entries) if DEVNAME and
> ACTION is set
> ### B) scan and add entries automatically
Yes. If called manually (i.e. without udevs environment variables), the
script works as before, scanning all block devices.
> For my empty cdrom drive, udev calls rebuildfstab with DEVNAME='/dev/sr0'
> ACTION='change'
>
> DEVNAME and ACTION are set, so I expect mode "A", but, the actual test is:
>
> if [ -n "$DEVNAME" -a -n "$ID_FS_USAGE" -a -n "$ACTION" ]; then
>
> Therefore, because ID_FS_USAGE is not set, it's mode "B" for the cdrom
> drive. This does not seem correct.
>
> When I insert a disk, udev calls rebuildfstab again; this time with
> ID_FS_USAGE set, and the drive gets mode "A". When I remove the disk, the
> udev event is handled mode "B".
>
> I tried eliminating ID_FS_USAGE from the test, so that it agrees with the
> description in your comment. It seems to work (See fstab entries below.).
Your proposal is good. My original intention here was to only add
partitions that contain a detectable/mountable file system, but since
the old scheme is still being used if the variable is unset, and there
may be cases where you want to add an entry without knowing the file
system in advance, there is no gain in checking for ID_FS_USAGE being
set at that point.
> So, which is the case: (a) detection of blank/absent media/media removal
> is a udev event and is supposed to be handled mode "A" and this is an
> error in the script, (b) should be mode "A", but ID_FS_USAGE should be
> set, so this is an error with udev or my drive, (c) this hybrid behavior
> is intended?
It's (a), a logical error in the script in case of blank/absent/non-fs
partitions. I just uploaded a fixed version to
debian-knoppix.alioth.debian.org. However, the fact that rebuildfstab
adds lines for blank media (which are not mountable) may still be wrong,
though in some cases, partitions with filesystems that just require
additional mount options for being mounted, may be OK to be listed in
/etc/fstab.
Regards
-Klaus
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