cifs: Add DFS cache routines

* Add new dfs_cache.[ch] files

* Add new /proc/fs/cifs/dfscache file
  - dump current cache when read
  - clear current cache when writing "0" to it

* Add delayed_work to periodically refresh cache entries

The new interface will be used for caching DFS referrals, as well as
supporting client target failover.

The DFS cache is a hashtable that maps UNC paths to cache entries.

A cache entry contains:
- the UNC path it is mapped on
- how much the the UNC path the entry consumes
- flags
- a Time-To-Live after which the entry expires
- a list of possible targets (linked lists of UNC paths)
- a "hint target" pointing the last known working target or the first
  target if none were tried. This hint lets cifs.ko remember and try
  working targets first.

* Looking for an entry in the cache is done with dfs_cache_find()
  - if no valid entries are found, a DFS query is made, stored in the
    cache and returned
  - the full target list can be copied and returned to avoid race
    conditions and looped on with the help with the
    dfs_cache_tgt_iterator

* Updating the target hint to the next target is done with
  dfs_cache_update_tgthint()

These functions have a dfs_cache_noreq_XXX() version that doesn't
fetches referrals if no entries are found. These versions don't
require the tcp/ses/tcon/cifs_sb parameters as a result.

Expired entries cannot be used and since they have a pretty short TTL
[1] in order for them to be useful for failover the DFS cache adds a
delayed work called periodically to keep them fresh.

Since we might not have available connections to issue the referral
request when refreshing we need to store volume_info structs with
credentials and other needed info to be able to connect to the right
server.

1: Windows defaults: 5mn for domain-based referrals, 30mn for regular
links

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 97 insertions, 0 deletions

diff --git a/fs/cifs/dfs_cache.h b/fs/cifs/dfs_cache.h
new file mode 100644
index 000000000000..22f366514f3a
--- /dev/null
+++ b/fs/cifs/dfs_cache.h
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DFS referral cache routines
+ *
+ * Copyright (c) 2018 Paulo Alcantara <palcantara@suse.de>
+ */
+
+#ifndef _CIFS_DFS_CACHE_H
+#define _CIFS_DFS_CACHE_H
+
+#include <linux/nls.h>
+#include <linux/list.h>
+#include "cifsglob.h"
+
+struct dfs_cache_tgt_list {
+	int tl_numtgts;
+	struct list_head tl_list;
+};
+
+struct dfs_cache_tgt_iterator {
+	char *it_name;
+	struct list_head it_list;
+};
+
+extern int dfs_cache_init(void);
+extern void dfs_cache_destroy(void);
+extern const struct file_operations dfscache_proc_fops;
+
+extern int dfs_cache_find(const unsigned int xid, struct cifs_ses *ses,
+			  const struct nls_table *nls_codepage, int remap,
+			  const char *path, struct dfs_info3_param *ref,
+			  struct dfs_cache_tgt_list *tgt_list);
+extern int dfs_cache_noreq_find(const char *path, struct dfs_info3_param *ref,
+				struct dfs_cache_tgt_list *tgt_list);
+extern int dfs_cache_update_tgthint(const unsigned int xid,
+				    struct cifs_ses *ses,
+				    const struct nls_table *nls_codepage,
+				    int remap, const char *path,
+				    const struct dfs_cache_tgt_iterator *it);
+extern int
+dfs_cache_noreq_update_tgthint(const char *path,
+			       const struct dfs_cache_tgt_iterator *it);
+extern int dfs_cache_get_tgt_referral(const char *path,
+				      const struct dfs_cache_tgt_iterator *it,
+				      struct dfs_info3_param *ref);
+extern int dfs_cache_add_vol(struct smb_vol *vol, const char *fullpath);
+extern int dfs_cache_update_vol(const char *fullpath,
+				struct TCP_Server_Info *server);
+extern void dfs_cache_del_vol(const char *fullpath);
+
+static inline struct dfs_cache_tgt_iterator *
+dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,
+		       struct dfs_cache_tgt_iterator *it)
+{
+	if (!tl || list_empty(&tl->tl_list) || !it ||
+	    list_is_last(&it->it_list, &tl->tl_list))
+		return NULL;
+	return list_next_entry(it, it_list);
+}
+
+static inline struct dfs_cache_tgt_iterator *
+dfs_cache_get_tgt_iterator(struct dfs_cache_tgt_list *tl)
+{
+	if (!tl)
+		return NULL;
+	return list_first_entry_or_null(&tl->tl_list,
+					struct dfs_cache_tgt_iterator,
+					it_list);
+}
+
+static inline void dfs_cache_free_tgts(struct dfs_cache_tgt_list *tl)
+{
+	struct dfs_cache_tgt_iterator *it, *nit;
+
+	if (!tl || list_empty(&tl->tl_list))
+		return;
+	list_for_each_entry_safe(it, nit, &tl->tl_list, it_list) {
+		list_del(&it->it_list);
+		kfree(it->it_name);
+		kfree(it);
+	}
+	tl->tl_numtgts = 0;
+}
+
+static inline const char *
+dfs_cache_get_tgt_name(const struct dfs_cache_tgt_iterator *it)
+{
+	return it ? it->it_name : NULL;
+}
+
+static inline int
+dfs_cache_get_nr_tgts(const struct dfs_cache_tgt_list *tl)
+{
+	return tl ? tl->tl_numtgts : 0;
+}
+
+#endif /* _CIFS_DFS_CACHE_H */