[dm-devel] [PATCH v2 0/9] multipath-tools: use variable-size string buffers

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

Current libmultipath contains a lot of code writing text to pre-allocated
string buffers of fixed size while trying to avoid buffer overflows
or truncation of the output string. This code is, at least in part,
hard to verify and hard to read, as buffer sizes and positions need to
be checked after every additon of text. It requires either allocating large
buffers in advance, or risking to loose data, or re-allocating buffers
and starting over again.

This patch set changes this by switching almost entirely to text buffers
that are dynamically allocated and grow automatically as text is added.

The first patch, which was the initial motivation of the set, doesn't
need growing buffers, it just overcomes the PARAMS_SIZE limitation by
copying data from libdm. However if the PARAMS_SIZE limitation was dropped
when reading from the kernel, it made sense to drop it for constructing
PARAMS, too. This motivated the implementation of the strbuf API (patch 2),
and using it in assemble_map (patch 3). The API was then consequently used
elswhere in libmultipath too, where strings are built up in pieces (patch 4,
5, 8, 9). These additional changes are huge because of large number of
affected "snprint_xyz" functions and respective function calls, but most
of the changes are mechanical and follow always the same overall idea.

Finally, patch 6 and 7 are cleanups which I found necessary while working
on print.c.

Regression testing: added a test suite for strbuf itself, made sure
all tests cases (which involve quite a bit of printf_xyz() functions) still
pass, and compared output of lots of interactive multipathd and multipath
commands before and after the change.

Note that "multipathd show config" / "multipath -t" will show some minor
differences in the output, because the current code omits quotes for some
output value fields. With this patch set, all string values are quoted.

The patch set is available also on my "tip" branch:
https://github.com/openSUSE/multipath-tools/tree/tip.

Changes wrt v1 (thanks to Ben Marzinski for all):

 - 1/9: added missing pointer dereference
 - 2/9: fixed buffer size calculation, simplified code in __append_strbuf_str()
 - 3/9: use STRBUF_ON_STACK() rather than hand-coded __attribute__
        moved free() statement before goto in ev_add_path().
 - 4/9: Fixed return value of snprint_uid_attrs()
 - 5/9: Removed extra '-'

Martin Wilck (9):
  libmultipath: variable-size parameters in dm_get_map()
  libmultipath: strbuf: simple api for growing string buffers
  libmultipath: variable-size parameters in assemble_map()
  libmultipath: use strbuf in dict.c
  libmultipath: use strbuf in print.c
  libmultipath: print.c: fail hard if keywords are not found
  libmultipath: print.h: move macros to print.c
  libmultipath: use strbuf in alias.c.
  multipathd: use strbuf in cli.c

 libmultipath/Makefile                    |    2 +-
 libmultipath/alias.c                     |   84 +-
 libmultipath/blacklist.c                 |   13 +-
 libmultipath/configure.c                 |   18 +-
 libmultipath/configure.h                 |    3 +-
 libmultipath/devmapper.c                 |   44 +-
 libmultipath/devmapper.h                 |    4 +-
 libmultipath/dict.c                      |  314 ++--
 libmultipath/dict.h                      |   19 +-
 libmultipath/discovery.c                 |   13 +-
 libmultipath/dmparser.c                  |   47 +-
 libmultipath/dmparser.h                  |    2 +-
 libmultipath/foreign.c                   |   78 +-
 libmultipath/foreign.h                   |   13 +-
 libmultipath/foreign/nvme.c              |  100 +-
 libmultipath/generic.c                   |   26 +-
 libmultipath/generic.h                   |   17 +-
 libmultipath/libmultipath.version        |   21 +-
 libmultipath/parser.c                    |   50 +-
 libmultipath/parser.h                    |   17 +-
 libmultipath/print.c                     | 1839 ++++++++++------------
 libmultipath/print.h                     |  131 +-
 libmultipath/prioritizers/weightedpath.c |   71 +-
 libmultipath/propsel.c                   |  147 +-
 libmultipath/strbuf.c                    |  207 +++
 libmultipath/strbuf.h                    |  168 ++
 libmultipath/structs.h                   |    1 -
 libmultipath/structs_vec.c               |   11 +-
 libmultipath/util.c                      |    5 +
 libmultipath/util.h                      |    1 +
 multipathd/cli.c                         |   94 +-
 multipathd/cli_handlers.c                |  349 ++--
 multipathd/main.c                        |   20 +-
 tests/Makefile                           |    3 +-
 tests/alias.c                            |   41 +-
 tests/strbuf.c                           |  412 +++++
 36 files changed, 2313 insertions(+), 2072 deletions(-)
 create mode 100644 libmultipath/strbuf.c
 create mode 100644 libmultipath/strbuf.h
 create mode 100644 tests/strbuf.c

-- 
2.32.0