From 3e049c6058278ac80a21a370e0d5e06b68b20aa7 Mon Sep 17 00:00:00 2001
From: Alexey Makhalov <amakhalov@vmware.com>
Date: Mon, 2 Mar 2020 21:12:50 +0000
Subject: [PATCH] 9p: file attributes caching support
The motivation behind this change is to support
open-unlink-fstat sequence.
The idea of the implementation is to avoid sending GETATTR
command to the server if file attributes can be fetched
from the inode struct of dentry.
In other words, this is a minimalistic cache implementation
to store GETATTR/STAT metadata.
To enable this caching mechanism, use "cache=stat" mount
option.
Consider:
fd = open("file", O_RDONLY);
remove("file);
fstat(fd, &stat);
Translated to 9P2000.L with cache=none
TWALK tag 0 fid 1 newfid 26 nwname 1 'file'
TGETATTR tag 0 fid 26 request_mask 0x17ff
TWALK tag 0 fid 26 newfid 27 nwname 0
TLOPEN tag 0 fid 27 flags 0100000
TUNLINKAT tag 0 dirfid 1 name 'file' flags 0
TWALK tag 0 fid 26 newfid 28 nwname 0
TREMOVE tag 0 fid 28
TGETATTR tag 0 fid 26 request_mask 0x3fff
RLERROR tag 0 ecode 2 <-- ENOENT error code
TCLUNK tag 0 fid 27
TCLUNK tag 0 fid 26
With cache=stat
TWALK tag 0 fid 1 newfid 26 nwname 1 'file'
TGETATTR tag 0 fid 26 request_mask 0x17ff <-- save fid 26 stat here
TWALK tag 0 fid 26 newfid 27 nwname 0
TLOPEN tag 0 fid 27 flags 0100000
TUNLINKAT tag 0 dirfid 1 name 'file' flags 0
TWALK tag 0 fid 26 newfid 28 nwname 0
TREMOVE tag 0 fid 28
<-- use saved fid 26 stat
TCLUNK tag 0 fid 27
TCLUNK tag 0 fid 26
Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
---
Documentation/filesystems/9p.rst | 4 ++++
fs/9p/v9fs.c | 10 +++++++++-
fs/9p/v9fs.h | 1 +
fs/9p/vfs_inode.c | 3 ++-
fs/9p/vfs_inode_dotl.c | 3 ++-
5 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/Documentation/filesystems/9p.rst b/Documentation/filesystems/9p.rst
index 7b5964b..b2fe1d1 100644
--- a/Documentation/filesystems/9p.rst
+++ b/Documentation/filesystems/9p.rst
@@ -92,6 +92,10 @@ Options
minimal cache that is only used for read-write
mmap. Northing else is cached, like cache=none
+ stat
+ minimal cache that is only used for file
+ attributes. Northing else is cached.
+
debug=n specifies debug level. The debug level is a bitmask.
===== ================================
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 39def02..7a8d963 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -43,7 +43,7 @@ enum {
/* Options that take no arguments */
Opt_nodevmap,
/* Cache options */
- Opt_cache_loose, Opt_fscache, Opt_mmap,
+ Opt_cache_loose, Opt_fscache, Opt_stat, Opt_mmap,
/* Access options */
Opt_access, Opt_posixacl,
/* Lock timeout option */
@@ -63,6 +63,7 @@ static const match_table_t tokens = {
{Opt_cache, "cache=%s"},
{Opt_cache_loose, "loose"},
{Opt_fscache, "fscache"},
+ {Opt_stat, "stat"},
{Opt_mmap, "mmap"},
{Opt_cachetag, "cachetag=%s"},
{Opt_access, "access=%s"},
@@ -73,6 +74,7 @@ static const match_table_t tokens = {
static const char *const v9fs_cache_modes[nr__p9_cache_modes] = {
[CACHE_NONE] = "none",
+ [CACHE_STAT] = "stat",
[CACHE_MMAP] = "mmap",
[CACHE_LOOSE] = "loose",
[CACHE_FSCACHE] = "fscache",
@@ -92,6 +94,9 @@ static int get_cache_mode(char *s)
} else if (!strcmp(s, "mmap")) {
version = CACHE_MMAP;
p9_debug(P9_DEBUG_9P, "Cache mode: mmap\n");
+ } else if (!strcmp(s, "stat")) {
+ version = CACHE_STAT;
+ p9_debug(P9_DEBUG_9P, "Cache mode: stat\n");
} else if (!strcmp(s, "none")) {
version = CACHE_NONE;
p9_debug(P9_DEBUG_9P, "Cache mode: none\n");
@@ -272,6 +277,9 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
case Opt_fscache:
v9ses->cache = CACHE_FSCACHE;
break;
+ case Opt_stat:
+ v9ses->cache = CACHE_STAT;
+ break;
case Opt_mmap:
v9ses->cache = CACHE_MMAP;
break;
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index 7b76377..afa7a68 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -49,6 +49,7 @@ enum p9_session_flags {
enum p9_cache_modes {
CACHE_NONE,
+ CACHE_STAT,
CACHE_MMAP,
CACHE_LOOSE,
CACHE_FSCACHE,
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index ae0c38a..d76685f 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -1005,7 +1005,8 @@ v9fs_vfs_getattr(const struct path *path, struct kstat *stat,
p9_debug(P9_DEBUG_VFS, "dentry: %p\n", dentry);
v9ses = v9fs_dentry2v9ses(dentry);
- if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
+ if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE ||
+ (v9ses->cache == CACHE_STAT && d_really_is_positive(dentry))) {
generic_fillattr(&init_user_ns, d_inode(dentry), stat);
return 0;
}
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 0028ecc..09d9638 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -465,7 +465,8 @@ v9fs_vfs_getattr_dotl(const struct path *path, struct kstat *stat,
p9_debug(P9_DEBUG_VFS, "dentry: %p\n", dentry);
v9ses = v9fs_dentry2v9ses(dentry);
- if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
+ if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE ||
+ (v9ses->cache == CACHE_STAT && d_really_is_positive(dentry))) {
generic_fillattr(&init_user_ns, d_inode(dentry), stat);
return 0;
}
--
2.7.4