| Message ID | 20200317222555.29974-2-pali@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fixes for exfat driver | expand |
On Tue, Mar 17, 2020 at 11:25:52PM +0100, Pali Rohár wrote: > Function partial_name_hash() takes long type value into which can be stored > one Unicode code point. Therefore conversion from UTF-32 to UTF-16 is not > needed. Hmm... You might want to update the comment in stringhash.h...
On Wednesday 18 March 2020 00:09:25 Al Viro wrote: > On Tue, Mar 17, 2020 at 11:25:52PM +0100, Pali Rohár wrote: > > Function partial_name_hash() takes long type value into which can be stored > > one Unicode code point. Therefore conversion from UTF-32 to UTF-16 is not > > needed. > > Hmm... You might want to update the comment in stringhash.h... Well, initially I have not looked at hashing functions deeply. Used hashing function in stringhash.h is defined as: static inline unsigned long partial_name_hash(unsigned long c, unsigned long prevhash) { return (prevhash + (c << 4) + (c >> 4)) * 11; } I guess it was designed for 8bit types, not for long (64bit types) and I'm not sure how effective it is even for 16bit types for which it is already used. So question is, what should we do for either 21bit number (one Unicode code point = equivalent of UTF-32) or for sequence of 16bit numbers (UTF-16)? Any opinion?
On Wednesday 18 March 2020 10:32:51 Pali Rohár wrote: > On Wednesday 18 March 2020 00:09:25 Al Viro wrote: > > On Tue, Mar 17, 2020 at 11:25:52PM +0100, Pali Rohár wrote: > > > Function partial_name_hash() takes long type value into which can be stored > > > one Unicode code point. Therefore conversion from UTF-32 to UTF-16 is not > > > needed. > > > > Hmm... You might want to update the comment in stringhash.h... > > Well, initially I have not looked at hashing functions deeply. Used > hashing function in stringhash.h is defined as: > > static inline unsigned long > partial_name_hash(unsigned long c, unsigned long prevhash) > { > return (prevhash + (c << 4) + (c >> 4)) * 11; > } > > I guess it was designed for 8bit types, not for long (64bit types) and > I'm not sure how effective it is even for 16bit types for which it is > already used. > > So question is, what should we do for either 21bit number (one Unicode > code point = equivalent of UTF-32) or for sequence of 16bit numbers > (UTF-16)? > > Any opinion? So what to do with that hashing function? Anyway, "[PATCH 4/4] exfat: Fix discard support" should be reviewed as currently discard support in exfat is broken.
diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c index a8681d91f569..e0ec4ff366f5 100644 --- a/fs/exfat/namei.c +++ b/fs/exfat/namei.c @@ -147,16 +147,10 @@ static int exfat_utf8_d_hash(const struct dentry *dentry, struct qstr *qstr) return charlen; /* - * Convert to UTF-16: code points above U+FFFF are encoded as - * surrogate pairs. * exfat_toupper() works only for code points up to the U+FFFF. */ - if (u > 0xFFFF) { - hash = partial_name_hash(exfat_high_surrogate(u), hash); - hash = partial_name_hash(exfat_low_surrogate(u), hash); - } else { - hash = partial_name_hash(exfat_toupper(sb, u), hash); - } + hash = partial_name_hash(u <= 0xFFFF ? exfat_toupper(sb, u) : u, + hash); } qstr->hash = end_name_hash(hash);
Function partial_name_hash() takes long type value into which can be stored one Unicode code point. Therefore conversion from UTF-32 to UTF-16 is not needed. Signed-off-by: Pali Rohár <pali@kernel.org> --- fs/exfat/namei.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)