[Bug 1818285] Re: [disco desktop] Installation fails with parted_server: No data in infifo. parted_server: Line 2387. CRITICAL ERROR!!! EXITING.

[Iain Lane]

* An archaic GNU extension to scanf, under which '%as', '%aS', and
  '%a[...]' meant to scan a string and allocate space for it with
  malloc, is now restricted to programs compiled in C89 or C++98 mode
  with _GNU_SOURCE defined.  This extension conflicts with C99's use of
  '%a' to scan a hexadecimal floating-point number, which is now
  available to programs compiled as C99 or C++11 or higher, regardless
  of _GNU_SOURCE.

  POSIX.1-2008 includes the feature of allocating a buffer for string input
  with malloc, using the modifier letter 'm' instead.  Programs using
  '%as', '%aS', or '%a[...]' with the old GNU meaning should change to
  '%ms', '%mS', or '%m[...]' respectively.  Programs that wish to use
  the C99 '%a' no longer need to avoid _GNU_SOURCE.

  GCC's -Wformat warnings can detect most uses of this extension, as
  long as all functions that call vscanf, vfscanf, or vsscanf are
  annotated with __attribute__ ((format (scanf, ...))).

I should think the bug is due to this, from the glibc 2.29 update.
partman-base uses '%as' a lot. Indeed the build log does show warnings
along those lines:

parted_server.c: In function ‘scan_device_name’:
parted_server.c:1187:25: warning: format ‘%a’ expects argument of type ‘float *’, but argument 3 has type ‘char **’ [-Wformat=]
         if (1 != iscanf("%as", &device_name))
                         ^~~~~  ~~~~~~~~~~~~

I've locally tested a change to replace '%as' (and one occurrence of
'%a[...]') with '%ms' ('%m[...]') and my first test (running 30parted
directly) works.

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Title:
  [disco desktop] Installation fails with parted_server: No data in
  infifo.  parted_server: Line 2387. CRITICAL ERROR!!!  EXITING.

Status in partman-base package in Ubuntu:
  Confirmed
Status in ubiquity package in Ubuntu:
  Confirmed
Status in partman-base source package in Disco:
  Confirmed
Status in ubiquity source package in Disco:
  Confirmed

Bug description:
  Ubuntu Desktop Disco amd64

  Last known good version: ubiquity 19.04.5

  Automated preseeded tests of Ubuntu Desktop Disco, started failing on
  Feb. 4th with this error in partman log:

  /bin/partman: *******************************************************
  /lib/partman/init.d/30parted: *******************************************************
  parted_server: ======= Starting the server
  parted_server: main_loop: iteration 1
  parted_server: Opening infifo
  /lib/partman/init.d/30parted: IN: OPEN =dev=vda /dev/vda
  parted_server: No data in infifo.
  parted_server: Line 2387. CRITICAL ERROR!!!  EXITING.

  /var/log/ and journal attached to this report.

  Maybe it's a coincidence but it started after the upload of partman-
  crypto.

  Manual installation with Ubiquity fails too with the same error.

  Test Case:
  1. Boot to the live session
  2. Launch Ubiquity
  3. Press 'Next' on all the steps keeping the default

  Actual Result:
  You cannot go beyond the 'Updates and Other software' page.

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