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

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

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)

Thanks.
-- 
Coly Li
SuSE Labs