when would blkid success but not filesystem type?

when would blkid success but not filesystem type?

[Paul Wise]

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In https://bugs.debian.org/784709 Jérôme Kieffer wrote:

> Here is the answer for the 3.16 kernel:
> 
> jerome@patagonia:~$ sudo blkid -o value -s TYPE /dev/sdb4
> jerome@patagonia:~$ echo $?
> 0
...
> 
> The output is the same on 3.2, as you can see on attached images.

Anyone know when blkid would return success but not the filesystem type?
This is util-linux 2.25.2-6 with Linux 3.16/3.2 and an extended partition.

-- 
bye,
pabs

https://wiki.debian.org/PaulWise


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Re: when would blkid success but not filesystem type?

[Karel Zak]

On Thu, May 21, 2015 at 04:24:38PM +0800, Paul Wise wrote:
> In https://bugs.debian.org/784709 Jérôme Kieffer wrote:
> 
> > Here is the answer for the 3.16 kernel:
> > 
> > jerome@patagonia:~$ sudo blkid -o value -s TYPE /dev/sdb4
> > jerome@patagonia:~$ echo $?
> > 0
> ...
> > 
> > The output is the same on 3.2, as you can see on attached images.
> 
> Anyone know when blkid would return success but not the filesystem type?

 The option '-s' does not affect return code, this option controls 
 output filter only. I have improved the description in the man page 
 to make it more obvious.

 blkid returns success always when it's possible to gather any
 information about the device. The important detail is that the recent
 versions provide also PARTUUID=, so we have information about all
 (including empty) partitions!

 For example (very very old version from e2fsprogs):

    # blkid /dev/sdc1; echo $?
    2

 but the current util-linux upstream:

    #blkid /dev/sdc1; echo $?
    /dev/sdc1: PARTUUID="4b6f59ea-01"
    0


 And yes, we have PARTUUID also for MBR partitions, the method used to
 generate the UUID is the same like kernel uses for root= command
 line option.

 Note that my recommendation is to use lsblk, for example:

    # lsblk --noheading --output FSTYPE /dev/sda1
    vfat

 it reads info from udev db (libblkid is only fallback here), and it
 provides better way how to control output.


  Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: when would blkid success but not filesystem type?

[Paul Wise]

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On Thu, 21 May 2015 13:07:35 +0200 Karel Zak wrote:

> The option '-s' does not affect return code ...  we have information
> about all (including empty) partitions!

Ok, I see. Sounds like the proposed patch is appropriate then.

https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=12;filename=0001-Fix-by-forcing-fs-type-to-not-detected-if-not-named.patch;att=1;bug=784709

>  Note that my recommendation is to use lsblk, for example:

That has the same issue:

$ sudo lsblk --noheading --output FSTYPE /dev/sda2 ; echo $?

0

I think for our purposes we would need --nodeps too.

-- 
bye,
pabs

https://wiki.debian.org/PaulWise


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Re: when would blkid success but not filesystem type?

[Paul Wise]

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On Tue, 2015-05-26 at 12:21 +0800, Paul Wise wrote:
> On Thu, 21 May 2015 13:07:35 +0200 Karel Zak wrote:
> 
> > The option '-s' does not affect return code ...  we have information
> > about all (including empty) partitions!
> 
> Ok, I see. Sounds like the proposed patch is appropriate then.
> 
> https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=12;filename=0001-Fix-by-forcing-fs-type-to-not-detected-if-not-named.patch;att=1;bug=784709

Actually the code in question already contains a code path for when
blkid returns success but an empty string. Needs more investigation.

-- 
bye,
pabs

https://wiki.debian.org/PaulWise


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Bug#784709: Info received (when would blkid success but not filesystem type?)

[Debian Bug Tracking System]

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Re: when would blkid success but not filesystem type?

[Karel Zak]

On Tue, May 26, 2015 at 12:21:36PM +0800, Paul Wise wrote:
> On Thu, 21 May 2015 13:07:35 +0200 Karel Zak wrote:
> 
> > The option '-s' does not affect return code ...  we have information
> > about all (including empty) partitions!
> 
> Ok, I see. Sounds like the proposed patch is appropriate then.
> 
> https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=12;filename=0001-Fix-by-forcing-fs-type-to-not-detected-if-not-named.patch;att=1;bug=784709
> 
> >  Note that my recommendation is to use lsblk, for example:
> 
> That has the same issue:
> 
> $ sudo lsblk --noheading --output FSTYPE /dev/sda2 ; echo $?
> 
> 0

 Why do you want rely on return code? It is not error when 
 FS type is undefined/unknown. All you need is to check result.

  FSTYPE=$(lsblk --nodeps --noheading --output FSTYPE /dev/sda2)
  [ -n "$FSTYPE" ] && echo $FSTYPE

> I think for our purposes we would need --nodeps too.

 Yes.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com