linux-kernel - Re: [PATCH -V7 6/9] ext4: Add get

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Date:	Fri, 14 May 2010 23:51:56 +0530
From:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	coly.li@...e.de
Cc:	hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
	corbet@....net, serue@...ibm.com, neilb@...e.de,
	linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
	philippe.deniel@....FR, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V7 6/9] ext4: Add get_fsid callback

On Sat, 15 May 2010 01:32:35 +0800, Coly Li <coly.li@...e.de> wrote:
> 
> 
> On 05/12/2010 11:50 PM, Aneesh Kumar K.V Wrote:
> > Acked-by: Serge Hallyn <serue@...ibm.com>
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.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.

-aneesh
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