Messages in this thread | | | Subject | Faulty has_zero()? (was: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?) | From | Sven Anderson <> | Date | Sat, 17 Mar 2012 13:29:08 +0100 |
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Hi Linus,
Am 01.03.2012 um 23:42 schrieb Linus Torvalds:
> +/* Return the high bit set in the first byte that is a zero */ > +static inline unsigned long has_zero(unsigned long a) > +{ > + return ((a - ONEBYTES) & ~a) & HIGHBITS; > +}
(I commented this on your google+ posting as well, but I'm not sure if you will notice it there.)
Out of curiosity I studied your code, and if I'm not mistaken your has_zero() function doesn't do what is expected. If there are leading 0x01 bytes in front of a NUL byte, they are also marked in the mask because of the borrow bit. You could argue, that there are no 0x01 bytes in path stings, and I agree (even with UTF-8). But you also use it for slash detection, and there you have the same effect with the '.' char, since '.' ^ '/' == 0x01. So if you have a directory name like "foobar.../" it will get handled the same as "foobar////".
Best regards
Sven
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