smb3: add mount option to allow RW caching of share accessed by only 1 client

If a share is known to be only to be accessed by one client, we
can aggressively cache writes not just reads to it.

Add "cache=" option (cache=singleclient) for mounting read write shares
(that will not be read or written to from other clients while we have
it mounted) in order to improve performance.

Signed-off-by: Steve French <[e-mail]>

fs/cifs/cifs_fs_sb.h

···
 #define CIFS_MOUNT_NO_DFS 0x8000000 /* disable DFS resolving */
 #define CIFS_MOUNT_MODE_FROM_SID 0x10000000 /* retrieve mode from special ACE */
 #define CIFS_MOUNT_RO_CACHE	0x20000000  /* assumes share will not change */
+#define CIFS_MOUNT_RW_CACHE	0x40000000  /* assumes only client accessing */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;

fs/cifs/cifsfs.c

···
 		seq_puts(s, "strict");
 	else if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_DIRECT_IO)
 		seq_puts(s, "none");
+	else if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RW_CACHE)
+		seq_puts(s, "singleclient"); /* assume only one client access */
 	else if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RO_CACHE)
 		seq_puts(s, "ro"); /* read only caching assumed */
 	else

fs/cifs/cifsglob.h

···
 	bool direct_io:1;
 	bool strict_io:1; /* strict cache behavior */
 	bool cache_ro:1;
+	bool cache_rw:1;
 	bool remap:1;      /* set to remap seven reserved chars in filenames */
 	bool sfu_remap:1;  /* remap seven reserved chars ala SFU */
 	bool posix_paths:1; /* unset to not ask for posix pathnames. */
···
 			 CIFS_MOUNT_CIFS_BACKUPUID | CIFS_MOUNT_CIFS_BACKUPGID | \
 			 CIFS_MOUNT_UID_FROM_ACL | CIFS_MOUNT_NO_HANDLE_CACHE | \
 			 CIFS_MOUNT_NO_DFS | CIFS_MOUNT_MODE_FROM_SID | \
-			 CIFS_MOUNT_RO_CACHE)
+			 CIFS_MOUNT_RO_CACHE | CIFS_MOUNT_RW_CACHE)
 
 /**
  * Generic VFS superblock mount flags (s_flags) to consider when
···
 
 #define CIFS_CACHE_READ(cinode) ((cinode->oplock & CIFS_CACHE_READ_FLG) || (CIFS_SB(cinode->vfs_inode.i_sb)->mnt_cifs_flags & CIFS_MOUNT_RO_CACHE))
 #define CIFS_CACHE_HANDLE(cinode) (cinode->oplock & CIFS_CACHE_HANDLE_FLG)
-#define CIFS_CACHE_WRITE(cinode) (cinode->oplock & CIFS_CACHE_WRITE_FLG)
+#define CIFS_CACHE_WRITE(cinode) ((cinode->oplock & CIFS_CACHE_WRITE_FLG) || (CIFS_SB(cinode->vfs_inode.i_sb)->mnt_cifs_flags & CIFS_MOUNT_RW_CACHE))
 
 /*
  * One of these for each file inode

fs/cifs/connect.c

···
 	Opt_cache_strict,
 	Opt_cache_none,
 	Opt_cache_ro,
+	Opt_cache_rw,
 	Opt_cache_err
 };
 
···
 	{ Opt_cache_strict, "strict" },
 	{ Opt_cache_none, "none" },
 	{ Opt_cache_ro, "ro" },
+	{ Opt_cache_rw, "singleclient" },
 	{ Opt_cache_err, NULL }
 };
 
···
 		vol->direct_io = false;
 		vol->strict_io = false;
 		vol->cache_ro = false;
+		vol->cache_rw = false;
 		break;
 	case Opt_cache_strict:
 		vol->direct_io = false;
 		vol->strict_io = true;
 		vol->cache_ro = false;
+		vol->cache_rw = false;
 		break;
 	case Opt_cache_none:
 		vol->direct_io = true;
 		vol->strict_io = false;
 		vol->cache_ro = false;
+		vol->cache_rw = false;
 		break;
 	case Opt_cache_ro:
 		vol->direct_io = false;
 		vol->strict_io = false;
 		vol->cache_ro = true;
+		vol->cache_rw = false;
+		break;
+	case Opt_cache_rw:
+		vol->direct_io = false;
+		vol->strict_io = false;
+		vol->cache_ro = false;
+		vol->cache_rw = true;
 		break;
 	default:
 		cifs_dbg(VFS, "bad cache= option: %s\n", value);
···
 	if (pvolume_info->cache_ro) {
 		cifs_dbg(VFS, "mounting share with read only caching. Ensure that the share will not be modified while in use.\n");
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_RO_CACHE;
+	} else if (pvolume_info->cache_rw) {
+		cifs_dbg(VFS, "mounting share in single client RW caching mode. Ensure that no other systems will be accessing the share.\n");
+		cifs_sb->mnt_cifs_flags |= (CIFS_MOUNT_RO_CACHE |
+					    CIFS_MOUNT_RW_CACHE);
 	}
 	if (pvolume_info->mfsymlinks) {
 		if (pvolume_info->sfu_emul) {
···
 			if (tcon->fsDevInfo.DeviceCharacteristics &
 			    FILE_READ_ONLY_DEVICE)
 				cifs_dbg(VFS, "mounted to read only share\n");
-			else
+			else if ((cifs_sb->mnt_cifs_flags &
+				  CIFS_MOUNT_RW_CACHE) == 0)
 				cifs_dbg(VFS, "read only mount of RW share\n");
+			/* no need to log a RW mount of a typical RW share */
 		}
 	}