[RFC][SMB3][PATCH] Allow share to be mounted with "cache=ro" if immutable share

[Steve French <smfrench@gmail.com>]

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Increases performance a lot in cases where we know that the share is
not changing



-- 
Thanks,

Steve

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From a2c56fa07718ec7de30866919c7ae442a72f8a5f Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Tue, 27 Aug 2019 23:58:54 -0500
Subject: [PATCH] smb3: add mount option to allow forced caching of read only
 share

If a share is immutable (at least for the period that it will
be mounted) it would be helpful to not have to revalidate
dentries repeatedly that we know can not be changed remotely.

Add "cache=" option (cache=ro) for mounting read only shares
in order to improve performance in cases in which we know that
the share will not be changing while it is in use.

Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/cifs_fs_sb.h |  1 +
 fs/cifs/cifsfs.c     |  2 ++
 fs/cifs/cifsglob.h   |  3 ++-
 fs/cifs/connect.c    | 14 ++++++++++++++
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index b326d2ca3765..286a104c4761 100644
--- a/fs/cifs/cifs_fs_sb.h
+++ b/fs/cifs/cifs_fs_sb.h
@@ -53,6 +53,7 @@
 #define CIFS_MOUNT_NO_HANDLE_CACHE 0x4000000 /* disable caching dir handles */
 #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 */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 3289b566463f..970251bc0661 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -400,6 +400,8 @@ cifs_show_cache_flavor(struct seq_file *s, struct cifs_sb_info *cifs_sb)
 		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_RO_CACHE)
+		seq_puts(s, "ro"); /* read only caching assumed */
 	else
 		seq_puts(s, "loose");
 }
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index fe610e7e3670..f2ee201ec98a 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -559,6 +559,7 @@ struct smb_vol {
 	bool server_ino:1; /* use inode numbers from server ie UniqueId */
 	bool direct_io:1;
 	bool strict_io:1; /* strict cache behavior */
+	bool cache_ro: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. */
@@ -1366,7 +1367,7 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
 #define CIFS_CACHE_RW_FLG	(CIFS_CACHE_READ_FLG | CIFS_CACHE_WRITE_FLG)
 #define CIFS_CACHE_RHW_FLG	(CIFS_CACHE_RW_FLG | CIFS_CACHE_HANDLE_FLG)
 
-#define CIFS_CACHE_READ(cinode) (cinode->oplock & CIFS_CACHE_READ_FLG)
+#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)
 
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 4fe559821aff..81cebf4c2269 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -298,6 +298,7 @@ enum {
 	Opt_cache_loose,
 	Opt_cache_strict,
 	Opt_cache_none,
+	Opt_cache_ro,
 	Opt_cache_err
 };
 
@@ -305,6 +306,7 @@ static const match_table_t cifs_cacheflavor_tokens = {
 	{ Opt_cache_loose, "loose" },
 	{ Opt_cache_strict, "strict" },
 	{ Opt_cache_none, "none" },
+	{ Opt_cache_ro, "ro" },
 	{ Opt_cache_err, NULL }
 };
 
@@ -1418,14 +1420,22 @@ cifs_parse_cache_flavor(char *value, struct smb_vol *vol)
 	case Opt_cache_loose:
 		vol->direct_io = false;
 		vol->strict_io = false;
+		vol->cache_ro = false;
 		break;
 	case Opt_cache_strict:
 		vol->direct_io = false;
 		vol->strict_io = true;
+		vol->cache_ro = false;
 		break;
 	case Opt_cache_none:
 		vol->direct_io = true;
 		vol->strict_io = false;
+		vol->cache_ro = false;
+		break;
+	case Opt_cache_ro:
+		vol->direct_io = false;
+		vol->strict_io = false;
+		vol->cache_ro = true;
 		break;
 	default:
 		cifs_dbg(VFS, "bad cache= option: %s\n", value);
@@ -4040,6 +4050,10 @@ int cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
 		cifs_dbg(FYI, "mounting share using direct i/o\n");
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_DIRECT_IO;
 	}
+	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;
+	}
 	if (pvolume_info->mfsymlinks) {
 		if (pvolume_info->sfu_emul) {
 			/*
-- 
2.20.1