[PREVIEW] [PATCH chao/erofs-dev 1/3] staging: erofs: harden inode lookup for 32-bit platforms

[Gao Xiang]

Hi Chao,

On 2018/10/1 9:57, Chao Yu wrote:
> On 2018-9-21 11:43, Gao Xiang wrote:
>> This patch introduces inode hash function, test and set callbacks,
>> and iget5_locked to find the right inode for 32-bit platforms.
>>
>> Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
>> ---
>>  drivers/staging/erofs/inode.c    | 37 ++++++++++++++++++++++++++++++++++++-
>>  drivers/staging/erofs/internal.h | 10 ++++++++++
>>  2 files changed, 46 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c
>> index da8693a..a2fa2aa 100644
>> --- a/drivers/staging/erofs/inode.c
>> +++ b/drivers/staging/erofs/inode.c
>> @@ -232,10 +232,45 @@ static int fill_inode(struct inode *inode, int isdir)
>>  	return err;
>>  }
>>  
>> +/*
>> + * erofs nid is 64bits, but i_ino is 'unsigned long', therefore
>> + * we should do more for 32-bit platform to find the right inode.
>> + */
>> +#if BITS_PER_LONG < 64
> 
> #if BITS_PER_LOG == 32

OK.

> 
>> +static int erofs_ilookup_test_actor(struct inode *inode, void *opaque)
>> +{
>> +	const erofs_nid_t nid = *(erofs_nid_t *)opaque;
>> +
>> +	return EROFS_V(inode)->nid == nid;
>> +}
>> +
>> +static int erofs_iget_set_actor(struct inode *inode, void *opaque)
>> +{
>> +	const erofs_nid_t nid = *(erofs_nid_t *)opaque;
>> +
>> +	inode->i_ino = erofs_inode_hash(nid);
>> +	return 0;
>> +}
>> +#endif
>> +
>> +static inline struct inode *erofs_iget_locked(struct super_block *sb,
>> +					      erofs_nid_t nid)
>> +{
>> +	const unsigned long hashval = erofs_inode_hash(nid);
>> +
>> +#if BITS_PER_LONG >= 64
>> +	/* it is safe to use iget_locked for >= 64-bit platform */
>> +	return iget_locked(sb, hashval);
>> +#else
>> +	return iget5_locked(sb, hashval, erofs_ilookup_test_actor,
>> +		erofs_iget_set_actor, &nid);
> 
> How about just using iget5_locked? and then we can only handle 32/64-bit
> platforms difference in erofs_inode_hash()?

It seems iget_locked is faster than iget5_locked because it has
more fast paths and no indirect callbacks for each inode...

> 
>> +#endif
>> +}
>> +
>>  struct inode *erofs_iget(struct super_block *sb,
>>  	erofs_nid_t nid, bool isdir)
>>  {
>> -	struct inode *inode = iget_locked(sb, nid);
>> +	struct inode *inode = erofs_iget_locked(sb, nid);
>>  
>>  	if (unlikely(inode == NULL))
>>  		return ERR_PTR(-ENOMEM);
>> diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
>> index c2cc4a016..823929a 100644
>> --- a/drivers/staging/erofs/internal.h
>> +++ b/drivers/staging/erofs/internal.h
>> @@ -511,6 +511,16 @@ struct erofs_map_blocks_iter {
>>  }
>>  
>>  /* inode.c */
>> +static inline unsigned long erofs_inode_hash(erofs_nid_t nid)
>> +{
>> +	u64 h = nid;
> 
> unsigned long h;
> 
>> +
>> +#if BITS_PER_LONG == 32
>> +	h = (h >> 32) ^ (h & 0xffffffff);
> 
> h = (nid >> 32) ^ (nid & 0xffffffff);
> 
>> +#endif
>> +	return (unsigned long)h;
> 
> return h;

OK, will fix soon.

Thanks,
Gao Xiang

> 
> Thanks,
> 
>> +}
>> +
>>  extern struct inode *erofs_iget(struct super_block *sb,
>>  	erofs_nid_t nid, bool dir);
>>  
>>