smb: client: optimize referral walk on failed link targets

If a link referral request sent to root server was successful but
client failed to connect to all link targets, there is no need to
retry same link referral on a different root server.  Set an end
marker for the DFS root referral so the client will not attempt to
re-send link referrals to different root servers on failures.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Paulo Alcantara

fs/smb/client/dfs.c

@@ -98,15 +98,16 @@ static inline int parse_dfs_target(struct smb3_fs_context *ctx,
 	return rc;
 }
 
-static int setup_dfs_ref(struct cifs_mount_ctx *mnt_ctx,
-			 struct dfs_info3_param *tgt,
-			 struct dfs_ref_walk *rw)
+static int setup_dfs_ref(struct dfs_info3_param *tgt, struct dfs_ref_walk *rw)
 {
-	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
-	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
+	struct cifs_sb_info *cifs_sb = rw->mnt_ctx->cifs_sb;
+	struct smb3_fs_context *ctx = rw->mnt_ctx->fs_ctx;
 	char *ref_path, *full_path;
 	int rc;
 
+	set_root_smb_session(rw->mnt_ctx);
+	ref_walk_ses(rw) = ctx->dfs_root_ses;
+
 	full_path = smb3_fs_context_fullpath(ctx, CIFS_DIR_SEP(cifs_sb));
 	if (IS_ERR(full_path))
 		return PTR_ERR(full_path);
@@ -123,35 +124,22 @@ static int setup_dfs_ref(struct cifs_mount_ctx *mnt_ctx,
 	}
 	ref_walk_path(rw) = ref_path;
 	ref_walk_fpath(rw) = full_path;
-	ref_walk_ses(rw) = ctx->dfs_root_ses;
-	return 0;
+
+	return dfs_get_referral(rw->mnt_ctx,
+				ref_walk_path(rw) + 1,
+				ref_walk_tl(rw));
 }
 
-static int __dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx,
-			       struct dfs_ref_walk *rw)
+static int __dfs_referral_walk(struct dfs_ref_walk *rw)
 {
-	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
+	struct smb3_fs_context *ctx = rw->mnt_ctx->fs_ctx;
+	struct cifs_mount_ctx *mnt_ctx = rw->mnt_ctx;
 	struct dfs_info3_param tgt = {};
 	int rc = -ENOENT;
 
 again:
 	do {
 		ctx->dfs_root_ses = ref_walk_ses(rw);
-		if (ref_walk_empty(rw)) {
-			rc = dfs_get_referral(mnt_ctx, ref_walk_path(rw) + 1,
-					      NULL, ref_walk_tl(rw));
-			if (rc) {
-				rc = cifs_mount_get_tcon(mnt_ctx);
-				if (!rc)
-					rc = cifs_is_path_remote(mnt_ctx);
-				continue;
-			}
-			if (!ref_walk_num_tgts(rw)) {
-				rc = -ENOENT;
-				continue;
-			}
-		}
-
 		while (ref_walk_next_tgt(rw)) {
 			rc = parse_dfs_target(ctx, rw, &tgt);
 			if (rc)
@@ -162,32 +150,29 @@ static int __dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx,
 			if (rc)
 				continue;
 
-			ref_walk_set_tgt_hint(rw);
 			if (tgt.flags & DFSREF_STORAGE_SERVER) {
 				rc = cifs_mount_get_tcon(mnt_ctx);
 				if (!rc)
 					rc = cifs_is_path_remote(mnt_ctx);
-				if (!rc)
+				if (!rc) {
+					ref_walk_set_tgt_hint(rw);
 					break;
+				}
 				if (rc != -EREMOTE)
 					continue;
 			}
 
-			set_root_smb_session(mnt_ctx);
 			rc = ref_walk_advance(rw);
 			if (!rc) {
-				rc = setup_dfs_ref(mnt_ctx, &tgt, rw);
-				if (!rc) {
-					rc = -EREMOTE;
-					goto again;
-				}
+				rc = setup_dfs_ref(&tgt, rw);
+				if (rc)
+					break;
+				ref_walk_mark_end(rw);
+				goto again;
 			}
-			if (rc != -ELOOP)
-				goto out;
 		}
 	} while (rc && ref_walk_descend(rw));
 
-out:
 	free_dfs_info_param(&tgt);
 	return rc;
 }
@@ -204,10 +189,10 @@ static int dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx,
 		return rc;
 	}
 
-	ref_walk_init(*rw);
-	rc = setup_dfs_ref(mnt_ctx, NULL, *rw);
+	ref_walk_init(*rw, mnt_ctx);
+	rc = setup_dfs_ref(NULL, *rw);
 	if (!rc)
-		rc = __dfs_referral_walk(mnt_ctx, *rw);
+		rc = __dfs_referral_walk(*rw);
 	return rc;
 }
 
@@ -297,7 +282,7 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 	 * to respond with PATH_NOT_COVERED to requests that include the prefix.
 	 */
 	if (!nodfs) {
-		rc = dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL, NULL);
+		rc = dfs_get_referral(mnt_ctx, ctx->UNC + 1, NULL);
 		if (rc) {
 			cifs_dbg(FYI, "%s: no dfs referral for %s: %d\n",
 				 __func__, ctx->UNC + 1, rc);
@@ -317,10 +302,8 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 		cifs_mount_put_conns(mnt_ctx);
 		rc = get_session(mnt_ctx, NULL);
 	}
-	if (!rc) {
-		set_root_smb_session(mnt_ctx);
+	if (!rc)
 		rc = __dfs_mount_share(mnt_ctx);
-	}
 	return rc;
 }
 

fs/smb/client/dfs.h

@@ -12,6 +12,7 @@
 #include "dfs_cache.h"
 #include "cifs_unicode.h"
 #include <linux/namei.h>
+#include <linux/errno.h>
 
 #define DFS_INTERLINK(v) \
 	(((v) & DFSREF_REFERRAL_SERVER) && !((v) & DFSREF_STORAGE_SERVER))
@@ -25,8 +26,9 @@ struct dfs_ref {
 };
 
 struct dfs_ref_walk {
-	struct dfs_ref *ref;
-	struct dfs_ref refs[MAX_NESTED_LINKS];
+	struct cifs_mount_ctx	*mnt_ctx;
+	struct dfs_ref		*ref;
+	struct dfs_ref		refs[MAX_NESTED_LINKS];
 };
 
 #define ref_walk_start(w)	((w)->refs)
@@ -35,7 +37,6 @@ struct dfs_ref_walk {
 #define ref_walk_descend(w)	(--ref_walk_cur(w) >= ref_walk_start(w))
 
 #define ref_walk_tit(w)	(ref_walk_cur(w)->tit)
-#define ref_walk_empty(w)	(!ref_walk_tit(w))
 #define ref_walk_path(w)	(ref_walk_cur(w)->path)
 #define ref_walk_fpath(w)	(ref_walk_cur(w)->full_path)
 #define ref_walk_tl(w)		(&ref_walk_cur(w)->tl)
@@ -51,9 +52,11 @@ static inline struct dfs_ref_walk *ref_walk_alloc(void)
 	return rw;
 }
 
-static inline void ref_walk_init(struct dfs_ref_walk *rw)
+static inline void ref_walk_init(struct dfs_ref_walk *rw,
+				 struct cifs_mount_ctx *mnt_ctx)
 {
 	memset(rw, 0, sizeof(*rw));
+	rw->mnt_ctx = mnt_ctx;
 	ref_walk_cur(rw) = ref_walk_start(rw);
 }
 
@@ -93,15 +96,23 @@ static inline int ref_walk_advance(struct dfs_ref_walk *rw)
 static inline struct dfs_cache_tgt_iterator *
 ref_walk_next_tgt(struct dfs_ref_walk *rw)
 {
-	struct dfs_cache_tgt_iterator *tit;
 	struct dfs_ref *ref = ref_walk_cur(rw);
+	struct dfs_cache_tgt_iterator *tit;
+
+	if (IS_ERR(ref->tit))
+		return NULL;
 
 	if (!ref->tit)
 		tit = dfs_cache_get_tgt_iterator(&ref->tl);
 	else
 		tit = dfs_cache_get_next_tgt(&ref->tl, ref->tit);
+
+	if (!tit) {
+		ref->tit = ERR_PTR(-ENOENT);
+		return NULL;
+	}
 	ref->tit = tit;
-	return tit;
+	return ref->tit;
 }
 
 static inline int ref_walk_get_tgt(struct dfs_ref_walk *rw,
@@ -112,11 +123,6 @@ static inline int ref_walk_get_tgt(struct dfs_ref_walk *rw,
 					  ref_walk_tit(rw), tgt);
 }
 
-static inline int ref_walk_num_tgts(struct dfs_ref_walk *rw)
-{
-	return dfs_cache_get_nr_tgts(ref_walk_tl(rw));
-}
-
 static inline void ref_walk_set_tgt_hint(struct dfs_ref_walk *rw)
 {
 	dfs_cache_noreq_update_tgthint(ref_walk_path(rw) + 1,
@@ -136,6 +142,15 @@ static inline void ref_walk_set_tcon(struct dfs_ref_walk *rw,
 	}
 }
 
+static inline void ref_walk_mark_end(struct dfs_ref_walk *rw)
+{
+	struct dfs_ref *ref = ref_walk_cur(rw) - 1;
+
+	WARN_ON_ONCE(ref < ref_walk_start(rw));
+	dfs_cache_noreq_update_tgthint(ref->path + 1, ref->tit);
+	ref->tit = ERR_PTR(-ENOENT); /* end marker */
+}
+
 int dfs_parse_target_referral(const char *full_path, const struct dfs_info3_param *ref,
 			      struct smb3_fs_context *ctx);
 int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx);
@@ -145,15 +160,16 @@ static inline char *dfs_get_path(struct cifs_sb_info *cifs_sb, const char *path)
 	return dfs_cache_canonical_path(path, cifs_sb->local_nls, cifs_remap(cifs_sb));
 }
 
-static inline int dfs_get_referral(struct cifs_mount_ctx *mnt_ctx, const char *path,
-				   struct dfs_info3_param *ref, struct dfs_cache_tgt_list *tl)
+static inline int dfs_get_referral(struct cifs_mount_ctx *mnt_ctx,
+				   const char *path,
+				   struct dfs_cache_tgt_list *tl)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
 	struct cifs_ses *rses = ctx->dfs_root_ses ?: mnt_ctx->ses;
 
 	return dfs_cache_find(mnt_ctx->xid, rses, cifs_sb->local_nls,
-			      cifs_remap(cifs_sb), path, ref, tl);
+			      cifs_remap(cifs_sb), path, NULL, tl);
 }
 
 /*