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, 12 insertions, 0 deletions

diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index ba178b09de0b..593fb422d0f3 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -30,6 +30,9 @@
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "cifsfs.h"
+#ifdef CONFIG_CIFS_DFS_UPCALL
+#include "dfs_cache.h"
+#endif
 #ifdef CONFIG_CIFS_SMB_DIRECT
 #include "smbdirect.h"
 #endif
@@ -629,6 +632,11 @@ cifs_proc_init(void)
 		    &cifs_security_flags_proc_fops);
 	proc_create("LookupCacheEnabled", 0644, proc_fs_cifs,
 		    &cifs_lookup_cache_proc_fops);
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	proc_create("dfscache", 0644, proc_fs_cifs, &dfscache_proc_fops);
+#endif
+
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	proc_create("rdma_readwrite_threshold", 0644, proc_fs_cifs,
 		&cifs_rdma_readwrite_threshold_proc_fops);
@@ -663,6 +671,10 @@ cifs_proc_clean(void)
 	remove_proc_entry("SecurityFlags", proc_fs_cifs);
 	remove_proc_entry("LinuxExtensionsEnabled", proc_fs_cifs);
 	remove_proc_entry("LookupCacheEnabled", proc_fs_cifs);
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	remove_proc_entry("dfscache", proc_fs_cifs);
+#endif
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	remove_proc_entry("rdma_readwrite_threshold", proc_fs_cifs);
 	remove_proc_entry("smbd_max_frmr_depth", proc_fs_cifs);