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

[Dave Chiluk]

** Also affects: initramfs-tools (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: initramfs-tools (Ubuntu Trusty)
       Status: New => Confirmed

** Changed in: initramfs-tools (Ubuntu Trusty)
     Assignee: (unassigned) => Dave Chiluk (chiluk)

** Changed in: initramfs-tools (Ubuntu)
       Status: New => Invalid

** Changed in: initramfs-tools (Ubuntu Trusty)
   Importance: Undecided => Critical

** Changed in: initramfs-tools (Ubuntu Trusty)
   Importance: Critical => Medium

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

Status in coreutils package in Ubuntu:
  Invalid
Status in initramfs-tools package in Ubuntu:
  Invalid
Status in coreutils source package in Trusty:
  Confirmed
Status in initramfs-tools 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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