Re: what's the real meaning of fsid?

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Dec 17, 2008 at 01:36:12PM +0800, lioupayphone wrote:
> Hello, everyone. 
> 
> fsid in /etc/exports was used for identifying a file system. if a file system which exported 2 directories, it seems that we should tag the two export entries with same fsid.
> 
> eg
> on one machine (server   10.10.37.147,  Centos5.2 with linux2.6.18):
> 
> #mkfs.ext3 /dev/sdc; mount /dev/sdc /mnt/;mkdir -p /mnt/dir1 /mnt/dir2; touch /mnt/dir1/wall-e /mnt/dir2/eva;
> #echo "/mnt/dir1 *(rw,async,root_squash,fsid=2)" > /etc/exports
> #echo "/mnt/dir2 *(rw,async,root_squash,fsid=2)" >> /etc/exports

That's an odd thing to do; could you explain what you're trying to
accomplish?

--b.

> #service nfs start && exportfs -r
> 
> on another machine (client   10.10.37.154):
> #mount  10.10.37.147:/mnt/dir1 /mnt/1/ && mount 10.10.37.147:/mnt/dir2 /mnt/2/
> 
> i am puzzled:   on the client (10.10.37.154), i found both "/mnt/1/" and "/mnt/2/" have the same child ---- "wall-e".
> 
> so i browsed the code of 2.6.18 and found: exp_export(), fs/nfsd/export.c . i have taged a comment on this code listed below. please give me some suggestions. thx.
> 
> /*
>  * Export a file system.
>  */
> int
> exp_export(struct nfsctl_export *nxp)
> {
> 	svc_client	*clp;
> 	struct svc_export	*exp = NULL;
> 	struct svc_export	new;
> 	struct svc_expkey	*fsid_key = NULL;
> 	struct nameidata nd;
> 	int		err;
> 
> 	/* Consistency check */
> 	err = -EINVAL;
> 	if (!exp_verify_string(nxp->ex_path, NFS_MAXPATHLEN) ||
> 	    !exp_verify_string(nxp->ex_client, NFSCLNT_IDMAX))
> 		goto out;
> 
> 	dprintk("exp_export called for %s:%s (%x/%ld fl %x).\n",
> 			nxp->ex_client, nxp->ex_path,
> 			(unsigned)nxp->ex_dev, (long)nxp->ex_ino,
> 			nxp->ex_flags);
> 
> 	/* Try to lock the export table for update */
> 	exp_writelock();
> 
> 	/* Look up client info */
> 	if (!(clp = auth_domain_find(nxp->ex_client)))
> 		goto out_unlock;
> 
> 
> 	/* Look up the dentry */
> 	err = path_lookup(nxp->ex_path, 0, &nd);
> 	if (err)
> 		goto out_unlock;
> 	err = -EINVAL;
> 
> 	exp = exp_get_by_name(clp, nd.mnt, nd.dentry, NULL);
> 
> 	/* must make sure there won't be an ex_fsid clash */
> 	if ((nxp->ex_flags & NFSEXP_FSID) &&
> 	    (fsid_key = exp_get_fsid_key(clp, nxp->ex_dev)) &&
> 	    !IS_ERR(fsid_key) &&
> 	    fsid_key->ek_mnt &&
> 		/* 
> 		 * --> HERE.  "nd.mnt of "/mnt/dir1" and "/mnt/dir2" are same, but nd.dentry not.
> 		 * "(fsid_key->ek_mnt != nd.mnt || fsid_key->ek_dentry != nd.dentry)" will be 1 in such
> 		 * a situation. but they are different exp-entries in "/var/lib/nfs/etab"
> 		* it should be "(fsid_key->ek_dentry != nd.dentry || fsid_key->ek_mnt != nd.mnt)" ??
> 		 */
> 	    (fsid_key->ek_mnt != nd.mnt || fsid_key->ek_dentry != nd.dentry) )        
> 		goto finish;
> 
> 	if (exp) {
> 		/* just a flags/id/fsid update */
> 
> 		exp_fsid_unhash(exp);
> 		exp->ex_flags    = nxp->ex_flags;
> 		exp->ex_anon_uid = nxp->ex_anon_uid;
> 		exp->ex_anon_gid = nxp->ex_anon_gid;
> 		exp->ex_fsid     = nxp->ex_dev;
> 
> 		err = exp_fsid_hash(clp, exp);
> 		goto finish;
> 	}
> 
> 	err = check_export(nd.dentry->d_inode, nxp->ex_flags);
> 	if (err) goto finish;
> 
> 	err = -ENOMEM;
> 
> 	dprintk("nfsd: creating export entry %p for client %p\n", exp, clp);
> 
> 	new.h.expiry_time = NEVER;
> 	new.h.flags = 0;
> 	new.ex_client = clp;
> 	new.ex_mnt = nd.mnt;
> 	new.ex_dentry = nd.dentry;
> 	new.ex_flags = nxp->ex_flags;
> 	new.ex_anon_uid = nxp->ex_anon_uid;
> 	new.ex_anon_gid = nxp->ex_anon_gid;
> 	new.ex_fsid = nxp->ex_dev;
> 
> 	exp = svc_export_lookup(&new);
> 	if (exp)
> 		exp = svc_export_update(&new, exp);
> 
> 	if (!exp)
> 		goto finish;
> 
> 	if (exp_hash(clp, exp) ||
> 	    exp_fsid_hash(clp, exp)) {
> 		/* failed to create at least one index */
> 		exp_do_unexport(exp);
> 		cache_flush();
> 		err = -ENOMEM;
> 	}
> 
> finish:
> 	if (exp)
> 		exp_put(exp);
> 	if (fsid_key && !IS_ERR(fsid_key))
> 		cache_put(&fsid_key->h, &svc_expkey_cache);
> 	if (clp)
> 		auth_domain_put(clp);
> 	path_release(&nd);
> out_unlock:
> 	exp_writeunlock();
> out:
> 	return err;
> }
> 	
> 	
>  				
> Best Regards! 
> lioupayphone
> 
> 
> --
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