linux-ext4 - Re: [PATCH] fsck: fix strange logic

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Message-Id: <0F4CAD2B-88EB-4727-8937-E50D776F3264@dilger.ca>
Date:	Tue, 9 Aug 2016 14:26:21 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Ted Tso <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] fsck: fix strange logic

On Aug 9, 2016, at 2:12 PM, Andreas Dilger <andreas.dilger@...el.com> wrote:
> 
> llvm warns about the confusingly written comparison:
> 
>                              !strncmp(argv[i+1], "-", 1) == 0) {
>    misc/fsck.c:1178 col 9: warning: logical not is only applied to
>      the left hand side of comparison [-Wlogical-not-parentheses]
>    misc/fsck.c:1178 col 9: note: add parentheses after the '!' to
>      evaluate the comparison first
>    misc/fsck.c:1178 col 9: note: add parentheses around left hand
>      side expression to silence this warning
> 
> It makes sense to simplify this to a character comparison
> rather than using strncmp() to check only one character.
> 
> Signed-off-by: Andreas Dilger <andreas.dilger@...el.com>
> ---
> misc/fsck.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/misc/fsck.c b/misc/fsck.c
> index 826aaeb..4f918b7 100644
> --- a/misc/fsck.c
> +++ b/misc/fsck.c
> @@ -1174,8 +1174,8 @@ static void PRS(int argc, char *argv[])
> 						progress_fd = 0;
> 					else
> 						goto next_arg;
> -				} else if ((i+1) < argc &&
> -					   !strncmp(argv[i+1], "-", 1) == 0) {
> +				} else if (argc > i + 1 &&
> +					   argv[i + 1][0] == '-') {
> 					progress_fd = string_to_int(argv[i]);
> 					if (progress_fd < 0)
> 						progress_fd = 0;

Note that it isn't clear whether the original logic also contained a bug,
with both "!strncmp()" and the comparison with "== 0".  At first glance
it appeared that this was a bug to both negate and compare with 0, but
in further review I think that this should _not_ parse negative numbers
and use "-" as the fd.  Unfortunately, it isn't documented what "-" means.

I'll push a v2 patch that keeps the original logic, and Ted can choose
which one is correct.

Cheers, Andreas






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