[Bug 1535349] Re: `df /dev/sda1` no longer reports information for /dev/sda1

[Dave Chiluk]

I have been doing some more testing with this, and would appreciate some
more eyes on this before upload.

I have created a ppa with test packages here.
https://launchpad.net/~chiluk/+archive/ubuntu/df

Thanks ahead of time to anyone who can test the PPA.

I've already noticed that on one of my machines I got this unexpected behavior.  Although better this is not expected.
chiluk at bonus:/tmp$ df -h /dev/sda2
Filesystem                                              Size  Used Avail Use% Mounted on
/dev/disk/by-uuid/dc918cc3-dc63-4049-bce1-96fec88f77d1   30G   26G  2.0G  93% /

** Patch removed: "lp1535349.trusty.debdiff"
   https://bugs.launchpad.net/ubuntu/+source/coreutils/+bug/1535349/+attachment/4557958/+files/lp1535349.trusty.debdiff

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https://bugs.launchpad.net/bugs/1535349

Title:
  `df /dev/sda1` no longer reports information for /dev/sda1

Status in coreutils package in Ubuntu:
  Invalid
Status in coreutils source package in Trusty:
  Confirmed

Bug description:
  [Impact]

   * df fails to process devices that are specified on the command line.

  [Test Case]

   * Actual
  $ df -h /dev/sda1
  Filesystem      Size  Used Avail Use% Mounted on
  udev            1.8G  8.0K  1.8G   1% /dev

   * Expected
  $ df -h /dev/sda1
  Filesystem      Size  Used Avail Use% Mounted on
  /dev/sda1       9.9G  978M  8.5G  11% /

  [Regression Potential]

   * This patch is a partial backport of functions as they exist in
  vivid to help minimize the regression potential.

   * That being said I had to do some backporting so as to avoid ui changes.
   
   * This once again significantly changes the mount search and matching
     logic within df, but it is localized to df.

  [Other Info]
   
   * Anything else you think is useful to include
   * Anticipate questions from users, SRU, +1 maintenance, security teams and the Technical Board
   * and address these questions in advance

  
  -------------------- Original Description-----------------------
  It appears that the latest version of coreutils uploaded to trusty-updates has a regression in it.  We have scripting that checks how much space we have left on a partition using `df /dev/sda1`. Using coreutils 8.21-1ubuntu5.1, we can do the following:

  $ df -h /dev/sda1
  Filesystem      Size  Used Avail Use% Mounted on
  /dev/sda1       9.9G  978M  8.5G  11% /

  This is a valid way of using the tool per the manpage: "If  an
  argument is the absolute file name of a disk device node containing a
  mounted file system, df shows the space available on that file system
  rather than on the file system containing the device node"

  It appears that either 8.21-1ubuntu5.2 or 8.21-1ubuntu5.3 broke this,
  however. We now get output for the udev filesystem that is mounted at
  /dev, instead of the device we pass in.

  $ df -h /dev/sda1
  Filesystem      Size  Used Avail Use% Mounted on
  udev            1.8G  8.0K  1.8G   1% /dev

  This is both a behaviour change, and contravenes the manpage, so it
  would be good to get this fixed.

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