Re: [PATCH -V7 6/9] ext4: Add get_fsid callback

[Coly Li <coly.li@suse.de>]

On 05/15/2010 02:21 AM, Aneesh Kumar K. V Wrote:
> On Sat, 15 May 2010 01:32:35 +0800, Coly Li <coly.li@suse.de> wrote:
>>
>>
>> On 05/12/2010 11:50 PM, Aneesh Kumar K.V Wrote:
>>> Acked-by: Serge Hallyn <serue@us.ibm.com>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>>> ---
>>>  fs/ext4/super.c |   15 +++++++++++++++
>>>  1 files changed, 15 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>> index e14d22c..fc7d464 100644
>>> --- a/fs/ext4/super.c
>>> +++ b/fs/ext4/super.c
>>> @@ -1049,6 +1049,19 @@ static int bdev_try_to_free_page(struct super_block *sb, struct page *page,
>>>  	return try_to_free_buffers(page);
>>>  }
>>>  
>>> +static int ext4_get_fsid(struct super_block *sb, struct uuid *fsid)
>>> +{
>>> +	struct ext4_sb_info *sbi = EXT4_SB(sb);
>>> +	struct ext4_super_block *es = sbi->s_es;
>>> +
>>> +	memcpy(fsid->uuid, es->s_uuid, sizeof(fsid->uuid));
>>> +	/*
>>> +	 * We may want to make sure we return error if the s_uuid is not
>>> +	 * exactly unique
>>> +	 */
>>> +	return 0;
>>> +}
>>> +
>>>  #ifdef CONFIG_QUOTA
>>>  #define QTYPE2NAME(t) ((t) == USRQUOTA ? "user" : "group")
>>>  #define QTYPE2MOPT(on, t) ((t) == USRQUOTA?((on)##USRJQUOTA):((on)##GRPJQUOTA))
>>> @@ -1109,6 +1122,7 @@ static const struct super_operations ext4_sops = {
>>>  	.quota_write	= ext4_quota_write,
>>>  #endif
>>>  	.bdev_try_to_free_page = bdev_try_to_free_page,
>>> +	.get_fsid	= ext4_get_fsid,
>>>  };
>>>  
>>>  static const struct super_operations ext4_nojournal_sops = {
>>> @@ -1128,6 +1142,7 @@ static const struct super_operations ext4_nojournal_sops = {
>>>  	.quota_write	= ext4_quota_write,
>>>  #endif
>>>  	.bdev_try_to_free_page = bdev_try_to_free_page,
>>> +	.get_fsid	= ext4_get_fsid,
>>>  };
>>>  
>>
>> Hi Aneesh,
>>
>> Just wondering why not call sb->s_op->statfs() to get the fsid in do_sys_name_to_handle() ?
>> The overhead is a little bit more code to get fsid from struct kstatfs, but we can gain,
>> 1) avoid to have one more callback in struct super_operations.
>> 2) more file system can be supported (since most of file systems have statfs() call back)
>>
> 
> sb->s_op->statfs returns fsid of type __kernel_fsid_t which is just
> 64bits.
> 

I don't check the user space code of the patch series, anyway f_fsid from statfs(2) is designed to identify a file
system volume within a single system. Correct me if I am wrong, I guess handle->fsid is invisible from other systems,
maybe the f_fsid is enough here ?

Thanks.

-- 
Coly Li
SuSE Labs