[PATCH] knfsd: Break the hard linkage from svc_expkey to svc_export

Current svc_expkey holds a pointer to the svc_export structure, so updates to
that structure have to be in-place, which is a wart on the whole cache
infrastruct.  So we break that linkage and just do a second lookup.

If this became a performance issue, it would be possible to put a direct link
back in which was only used conditionally.  i.e.  when an object is replaced
in the cache, we set a flag in the old object.  When dereferencing the link
from svc_expkey, if the flag is set, we drop the reference and do a fresh
lookup.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 44 insertions, 36 deletions

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index ac0997731fce..587829ed651c 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -73,8 +73,10 @@ void expkey_put(struct cache_head *item, struct cache_detail *cd)
         if (cache_put(item, cd)) {
                 struct svc_expkey *key = container_of(item, struct svc_expkey, h);
                 if (test_bit(CACHE_VALID, &item->flags) &&
-                    !test_bit(CACHE_NEGATIVE, &item->flags))
-                        exp_put(key->ek_export);
+                    !test_bit(CACHE_NEGATIVE, &item->flags)) {
+                        dput(key->ek_dentry);
+                        mntput(key->ek_mnt);
+                }
                 auth_domain_put(key->ek_client);
                 kfree(key);
         }
@@ -164,26 +166,18 @@ static int expkey_parse(struct cache_detail *cd, char *mesg, int mlen)
         } else {
                 struct nameidata nd;
                 struct svc_expkey *ek;
-                struct svc_export *exp;
                 err = path_lookup(buf, 0, &nd);
                 if (err)
                         goto out;
 
                 dprintk("Found the path %s\n", buf);
-                exp = exp_get_by_name(dom, nd.mnt, nd.dentry, NULL);
-
-                err = -ENOENT;
-                if (!exp)
-                        goto out_nd;
-                key.ek_export = exp;
-                dprintk("And found export\n");
+                key.ek_mnt = nd.mnt;
+                key.ek_dentry = nd.dentry;
                 
                 ek = svc_expkey_lookup(&key, 1);
                 if (ek)
                         expkey_put(&ek->h, &svc_expkey_cache);
-                exp_put(exp);
                 err = 0;
-        out_nd:
                 path_release(&nd);
         }
         cache_flush();
@@ -214,7 +208,7 @@ static int expkey_show(struct seq_file *m,
         if (test_bit(CACHE_VALID, &h->flags) && 
             !test_bit(CACHE_NEGATIVE, &h->flags)) {
                 seq_printf(m, " ");
-                seq_path(m, ek->ek_export->ex_mnt, ek->ek_export->ex_dentry, "\\ \t\n");
+                seq_path(m, ek->ek_mnt, ek->ek_dentry, "\\ \t\n");
         }
         seq_printf(m, "\n");
         return 0;
@@ -252,8 +246,8 @@ static inline void svc_expkey_init(struct svc_expkey *new, struct svc_expkey *it
 
 static inline void svc_expkey_update(struct svc_expkey *new, struct svc_expkey *item)
 {
-        cache_get(&item->ek_export->h);
-        new->ek_export = item->ek_export;
+        new->ek_mnt = mntget(item->ek_mnt);
+        new->ek_dentry = dget(item->ek_dentry);
 }
 
 static DefineSimpleCacheLookup(svc_expkey,0) /* no inplace updates */
@@ -519,7 +513,8 @@ static int exp_set_key(svc_client *clp, int fsid_type, u32 *fsidv,
         key.ek_client = clp;
         key.ek_fsidtype = fsid_type;
         memcpy(key.ek_fsid, fsidv, key_len(fsid_type));
-        key.ek_export = exp;
+        key.ek_mnt = exp->ex_mnt;
+        key.ek_dentry = exp->ex_dentry;
         key.h.expiry_time = NEVER;
         key.h.flags = 0;
 
@@ -741,8 +736,8 @@ exp_export(struct nfsctl_export *nxp)
         if ((nxp->ex_flags & NFSEXP_FSID) &&
             (fsid_key = exp_get_fsid_key(clp, nxp->ex_dev)) &&
             !IS_ERR(fsid_key) &&
-            fsid_key->ek_export &&
-            fsid_key->ek_export != exp)
+            fsid_key->ek_mnt &&
+            (fsid_key->ek_mnt != nd.mnt || fsid_key->ek_dentry != nd.dentry) )
                 goto finish;
 
         if (exp) {
@@ -912,6 +907,24 @@ out:
         return err;
 }
 
+struct svc_export *
+exp_find(struct auth_domain *clp, int fsid_type, u32 *fsidv,
+         struct cache_req *reqp)
+{
+        struct svc_export *exp;
+        struct svc_expkey *ek = exp_find_key(clp, fsid_type, fsidv, reqp);
+        if (!ek || IS_ERR(ek))
+                return ERR_PTR(PTR_ERR(ek));
+
+        exp = exp_get_by_name(clp, ek->ek_mnt, ek->ek_dentry, reqp);
+        expkey_put(&ek->h, &svc_expkey_cache);
+
+        if (!exp || IS_ERR(exp))
+                return ERR_PTR(PTR_ERR(exp));
+        return exp;
+}
+
+
 /*
  * Called when we need the filehandle for the root of the pseudofs,
  * for a given NFSv4 client.   The root is defined to be the
@@ -922,6 +935,7 @@ exp_pseudoroot(struct auth_domain *clp, struct svc_fh *fhp,
                struct cache_req *creq)
 {
         struct svc_expkey *fsid_key;
+        struct svc_export *exp;
         int rv;
         u32 fsidv[2];
 
@@ -933,8 +947,14 @@ exp_pseudoroot(struct auth_domain *clp, struct svc_fh *fhp,
         if (!fsid_key || IS_ERR(fsid_key))
                 return nfserr_perm;
 
-        rv = fh_compose(fhp, fsid_key->ek_export, 
-                          fsid_key->ek_export->ex_dentry, NULL);
+        exp = exp_get_by_name(clp, fsid_key->ek_mnt, fsid_key->ek_dentry, creq);
+        if (exp == NULL)
+                rv = nfserr_perm;
+        else if (IS_ERR(exp))
+                rv = nfserrno(PTR_ERR(exp));
+        else
+                rv = fh_compose(fhp, exp,
+                                fsid_key->ek_dentry, NULL);
         expkey_put(&fsid_key->h, &svc_expkey_cache);
         return rv;
 }
diff --git a/include/linux/nfsd/export.h b/include/linux/nfsd/export.h
index 6bad4766d3d9..d52e0b7ad37b 100644
--- a/include/linux/nfsd/export.h
+++ b/include/linux/nfsd/export.h
@@ -67,7 +67,8 @@ struct svc_expkey {
         int                     ek_fsidtype;
         u32                     ek_fsid[3];
 
-        struct svc_export *     ek_export;
+        struct vfsmount *       ek_mnt;
+        struct dentry *         ek_dentry;
 };
 
 #define EX_SECURE(exp)          (!((exp)->ex_flags & NFSEXP_INSECURE_PORT))
@@ -114,22 +115,9 @@ static inline void exp_get(struct svc_export *exp)
 {
         cache_get(&exp->h);
 }
-static inline struct svc_export *
+extern struct svc_export *
 exp_find(struct auth_domain *clp, int fsid_type, u32 *fsidv,
-         struct cache_req *reqp)
-{
-        struct svc_expkey *ek = exp_find_key(clp, fsid_type, fsidv, reqp);
-        if (ek && !IS_ERR(ek)) {
-                struct svc_export *exp = ek->ek_export;
-                int err;
-                exp_get(exp);
-                expkey_put(&ek->h, &svc_expkey_cache);
-                if ((err = cache_check(&svc_export_cache, &exp->h, reqp)))
-                        exp = ERR_PTR(err);
-                return exp;
-        } else
-                return ERR_PTR(PTR_ERR(ek));
-}
+         struct cache_req *reqp);
 
 #endif /* __KERNEL__ */