svn commit: r295523 - head/sys/fs/ext2fs

[Bruce Evans]

On Thu, 11 Feb 2016, Pedro F. Giffuni wrote:

> Log:
>  Ext4: Use boolean type instead of '0' and '1'
>
>  There are precedents of uses of bool in the kernel and
>  it is incorrect style to use integers as replacement for
>  a boolean type.

This is all backwards.

It is correct style to use integers to represent booleans.

There are precedents for breaking this style by using the
bool type, but not many in fs code:

In all of /sys/fs/*, there were just 12 lines of declarations
that use 'bool'.  All of these were in autofs.  Now there are
13 such lines (1 more in ext2fs).  1 use is especially useless
and especially unlikely to be all uses of booleans.

/sys/fs/nfsclient uses boolean_t in 1 whole line.  boolean_t is
an old spelling of 'bool'.  It is a Mach type for representing
booleans in /sys/vm.  I used to like such typedefs 20-30 years ago
(mine was spelled bool_t) and made the mistake of using the Mach
type elsewhere in the kernel.  The use in nfsclient is actually
correct.  It is used to hold the result of a vm function which
returns boolean_t.

/sys/fs/nfsserver uses bool_t in 1 whole line.  bool_t is is
like boolean_t except in is Sun(?) type for reprenting booleans
in rpc.  It use is again correct -- it is used to hold the
result of an rpc function that returns bool_t.

/sys/fs/tmpfs the Mach spelling on 5 lines.  These uses are to
sks for small pessimizations, but inlining and -O usually gives
the same object code as using integers.  The values start as
flags which are naturally represented as integers and are tested
by expressions of the form (de->td_cookie & FLAG).  These simple
flags tests are obfuscated using function calls.  The functions
return boolean_t, so must convert to a logical expression.  They
do this correctly.  Then the compiler should optimize away all
the obfuscations and pessimizations to give the same object code
as if you wrote the tests directly.

ffs and zfs provided perhaps better examples.  /sys/cddl uses
boolean_t on 102 lines.  It isn't clear what this type is.
compat/opensolaris/sys/types.h seems to use the FreeBSD kernel
boolean_t in the kernel, but in userland it uses 2 different
enum types depending on options.  These types are incompatible
so this depends on magic to work.  /sys/cddl also uses bool_t
twice, once each for rpc and nvpair.  /sys/cddl never uses
C99 bool.

ffs used to use a very pure KNF style with integers and no
typedefs, but it now uses C99 bool on 4 lines.  These uses are
correct.

Bruce