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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