Messages in this thread | | | Subject | Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup | From | Tiezhu Yang <> | Date | Wed, 11 Dec 2019 11:59:40 +0800 |
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On 12/11/2019 10:48 AM, Eric Biggers wrote: > On Wed, Dec 11, 2019 at 10:20:01AM +0800, Tiezhu Yang wrote: >> diff --git a/include/linux/namei.h b/include/linux/namei.h >> index 7fe7b87..0fd9315 100644 >> --- a/include/linux/namei.h >> +++ b/include/linux/namei.h >> @@ -92,4 +92,14 @@ retry_estale(const long error, const unsigned int flags) >> return error == -ESTALE && !(flags & LOOKUP_REVAL); >> } >> >> +static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len) >> +{ >> + if (unlikely(name[0] == '.')) { >> + if (len == 1 || (len == 2 && name[1] == '.')) >> + return true; >> + } >> + >> + return false; >> +} >> + >> #endif /* _LINUX_NAMEI_H */ > I had suggested adding a len >= 1 check to handle the empty name case correctly. > What I had in mind was > > static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len) > { > if (len >= 1 && unlikely(name[0] == '.')) { > if (len < 2 || (len == 2 && name[1] == '.')) > return true; > } > > return false; > } > > As is, you're proposing that it always dereference the first byte even when > len=0, which seems like a bad idea for a shared helper function. Did you check > whether it's okay for all the existing callers? fscrypt_fname_disk_to_usr() is > called from 6 places, did you check all of them? > > How about keeping the existing optimized code for the hot path in fs/namei.c > (i.e. not using the helper function), while having the helper function do the > extra check to handle len=0 correctly?
Hi Eric,
Thank you for reminding me. How about using the following helper for all callers?
static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len) { if (len == 1 && name[0] == '.') return true;
if (len == 2 && name[0] == '.' && name[1] == '.') return true;
return false; }
Hi Matthew,
How do you think? I think the performance influence is very small due to is_dot_or_dotdot() is a such short static inline function.
Thanks,
Tiezhu Yang
> > - Eric
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