[PATCH v7 00/10] refactor the filter process code into a reusable module

Changes from V6 include:

convert: remove erroneous tests for errno == EPIPE
 - split into separate patch to fix a preexisting bug discovered in the review process

pkt-line: Update packet_read_line() to test for len > 0
 - split into separate patch to deal with errors that return negative lengths

pkt-line: add packet_read_line_gently()
 - update documentation to clarify return values
 - update white space in function definition

Refactor the filter.<driver>.process code into a separate sub-process module that can be used to reduce the cost of starting up a sub-process for multiple commands. It does this by keeping the external process running and processing all commands by communicating over standard input and standard output using the packet format (pkt-line) based protocol. Full documentation is in Documentation/technical/api-sub-process.txt.

This code is refactored from:

	Commit edcc85814c ("convert: add filter.<driver>.process option", 2016-10-16)
	keeps the external process running and processes all commands

Ben Peart (10):
  convert: remove erroneous tests for errno == EPIPE
  pkt-line: fix packet_read_line() to handle len < 0 errors
  pkt-line: add packet_read_line_gently()
  convert: move packet_write_line() into pkt-line as packet_writel()
  convert: split start_multi_file_filter() into two separate functions
  convert: Separate generic structures and variables from the filter
    specific ones
  convert: Update generic functions to only use generic data structures
  convert: rename reusable sub-process functions
  sub-process: move sub-process functions into separate files
  convert: Update subprocess_read_status to not die on EOF

 Documentation/technical/api-sub-process.txt |  59 ++++++++++
 Makefile                                    |   1 +
 convert.c                                   | 161 ++++++----------------------
 pkt-line.c                                  |  33 +++++-
 pkt-line.h                                  |  12 +++
 sub-process.c                               | 106 ++++++++++++++++++
 sub-process.h                               |  49 +++++++++
 7 files changed, 292 insertions(+), 129 deletions(-)
 create mode 100644 Documentation/technical/api-sub-process.txt
 create mode 100644 sub-process.c
 create mode 100644 sub-process.h