[utility perl script] strncmp() -> str_has_prefix() conversions

[Joe Perches <joe@perches.com>]

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On Fri, 2018-12-21 at 23:19 -0500, Steven Rostedt wrote:
> str_has_prefix

A coccinelle script could be more thorough but here
is a trivial perl script that can do most of the
	strncmp() -> str_has_prefix()
conversions where there is a constant string as one of
the first two arguments of strncmp like any of:

	strncmp(foo, "bar", 3)
	strncmp(foo, "bar", strlen("bar"))
	strncmp(foo, "bar", sizeof("bar") - 1)
	strncmp("foo", bar, 3)
	strncmp("foo", bar, strlen("foo"))
	strncmp("foo", bar",
sizeof("foo") - 1)

It could be used with a particular path or file:

$ git grep -w --name-only strncmp <path> | \
  grep -vP '^(tools|scripts)' | \
  while read file ; do \
    echo $file ; \
    perl -i ./strncmp.perl $file ; \
  done

It mostly works, but there are a few uses that
are not converted properly when the non const
string argument to strncmp is an expression like

	strncmp(a+b, "foo", 3)

There are also strncmp uses that remain after
this script is run where strncmp should just
be converted to strcmp instead like:

	strncmp(p, "foo", sizeof(foo))
and
	strncmp(p, "foo", 4)

The script converts the most common cases:

    ## counted length of string
    # strncmp(arg, string, counted length of string) == 0
    # strncmp(arg, string, counted length of string) != 0
    # !strncmp(arg, string, counted length of string)
    # strncmp(arg, string, counted length of string)

    ## Reversed string/arg counted length of string uses
    # strncmp(string, arg, counted length of string) == 0
    # strncmp(string, arg, counted length of string) != 0
    # !strncmp(string, arg, counted length of string)
    # strncmp(string, arg, counted length of string)

    ## strlen uses
    # strncmp(arg, string, strlen(string)) == 0
    # !strncmp(arg, string, strlen(string))

    ## reversed string/arg strlen uses
    # strncmp(string, arg, strlen(string)) == 0
    # !strncmp(string, arg, strlen(string))

    ## 'sizeof(string) - 1' uses
    # strncmp(arg, string, sizeof(string) - 1) == 0
    # !strncmp(arg, string, sizeof(string) - 1)


On linux-next, running the script below

$ git grep -w --name-only strncmp | \
  grep -vP '^(tools|scripts)' | \
  while read file ; do \
    echo $file ; \
    perl -i ./strncmp.perl $file ; \
  done

produces:

$ git diff --shortstat
 437 files changed, 1483 insertions(+), 1500 deletions(-)


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