Re: [osd-dev] [PATCH 6/8] exofs: super_operations and file_system_type

From: Benny Halevy <bhalevy@panasas.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Boaz Harrosh <bharrosh@panasas.com>,
	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
	Jeff Garzik <jeff@garzik.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	Avishay Traeger <avishay@gmail.com>,
	open-osd <osd-dev@open-osd.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Evgeniy Polyakov <zbr@ioremap.net>
Subject: Re: [osd-dev] [PATCH 6/8] exofs: super_operations and	file_system_type
Date: Tue, 31 Mar 2009 21:52:10 +0300	[thread overview]
Message-ID: <49D2665A.9090500@panasas.com> (raw)
In-Reply-To: <20090331010430.72e8137e.akpm@linux-foundation.org>

On Mar. 31, 2009, 11:04 +0300, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 18 Mar 2009 20:09:51 +0200 Boaz Harrosh <bharrosh@panasas.com> wrote:
> 
>> This patch ties all operation vectors into a file system superblock
>> and registers the exofs file_system_type at module's load time.
>>
>> * The file system control block (AKA on-disk superblock) resides in
>>   an object with a special ID (defined in common.h).
>>   Information included in the file system control block is used to
>>   fill the in-memory superblock structure at mount time. This object
>>   is created before the file system is used by mkexofs.c It contains
>>   information such as:
>> 	- The file system's magic number
>> 	- The next inode number to be allocated
>>
>>
>> ...
>>
>> +static int exofs_statfs(struct dentry *dentry, struct kstatfs *buf)
>> +{
>> +	struct super_block *sb = dentry->d_sb;
>> +	struct exofs_sb_info *sbi = sb->s_fs_info;
>> +	struct osd_obj_id obj = {sbi->s_pid, 0};
>> +	struct osd_attr attrs[] = {
>> +		ATTR_DEF(OSD_APAGE_PARTITION_QUOTAS,
>> +			OSD_ATTR_PQ_CAPACITY_QUOTA, sizeof(__be64)),
>> +		ATTR_DEF(OSD_APAGE_PARTITION_INFORMATION,
>> +			OSD_ATTR_PI_USED_CAPACITY, sizeof(__be64)),
>> +	};
>> +	uint64_t capacity = ~0;
>> +	uint64_t used = ~0;
> 
> My brain hurts.
> 
> ~0 is signed 0xffffffff.
> 
> When assigning to a u64 it gets signed extended to signed
> 0xffffffffffffffff and then converted to unsigned 0xffffffffffffffff.

Right (I think, I'm not sure in what order)

> 
> I think.  Just as with plain old "-1".  Perhaps using plain old "-1"
> would be clearer here.

or maybe ~0ULL or ~(uint64_t)0 to be extremely anal about it.

Benny

> 
>> ...
>>
>> +const struct super_operations exofs_sops = {
> 
> This can in fact be made static, I believe.
> 
>> ...
>>
> 
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