[PATCH 20/23] fuse4fs: add cache to track open files

Darrick J. Wong
2025-11-06T22:48:24Z

Add our own inode cache so that we can track open files.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
lib/support/cache.h | 7 +++
fuse4fs/Makefile.in | 3 +
fuse4fs/fuse4fs.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 141 insertions(+), 1 deletion(-)

diff --git a/lib/support/cache.h b/lib/support/cache.h
index c7c8298c115d50..71fb9762f97866 100644
--- a/lib/support/cache.h
+++ b/lib/support/cache.h
@@ -6,6 +6,13 @@
#ifndef __CACHE_H__
#define __CACHE_H__

+/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
+#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
+#ifndef CACHE_LINE_SIZE
+/* if the system didn't tell us, guess something reasonable */
+#define CACHE_LINE_SIZE 64
+#endif
+
/*
* initialisation flags
*/
diff --git a/fuse4fs/Makefile.in b/fuse4fs/Makefile.in
index 6b41d1dd5ffe8d..9f3547c271638f 100644
--- a/fuse4fs/Makefile.in
+++ b/fuse4fs/Makefile.in
@@ -146,7 +146,8 @@ fuse4fs.o: $(srcdir)/fuse4fs.c $(top_builddir)/lib/config.h \
$(top_srcdir)/lib/ext2fs/ext2_ext_attr.h $(top_srcdir)/lib/ext2fs/hashmap.h \
$(top_srcdir)/lib/ext2fs/bitops.h $(top_srcdir)/lib/ext2fs/ext2fsP.h \
$(top_srcdir)/lib/ext2fs/ext2fs.h $(top_srcdir)/version.h \
- $(top_srcdir)/lib/e2p/e2p.h
+ $(top_srcdir)/lib/e2p/e2p.h $(top_srcdir)/lib/support/cache.h \
+ $(top_srcdir)/lib/support/list.h $(top_srcdir)/lib/support/xbitops.h
journal.o: $(srcdir)/../debugfs/journal.c $(top_builddir)/lib/config.h \
$(top_builddir)/lib/dirpaths.h $(srcdir)/../debugfs/journal.h \
$(top_srcdir)/e2fsck/jfs_user.h $(top_srcdir)/e2fsck/e2fsck.h \
diff --git a/fuse4fs/fuse4fs.c b/fuse4fs/fuse4fs.c
index 7585f1ff346d84..038d6126dbfde1 100644
--- a/fuse4fs/fuse4fs.c
+++ b/fuse4fs/fuse4fs.c
@@ -26,6 +26,7 @@
#include <sys/ioctl.h>
#include <unistd.h>
#include <ctype.h>
+#include <assert.h>
#define FUSE_DARWIN_ENABLE_EXTENSIONS 0
#ifdef __SET_FOB_FOR_FUSE
# error Do not set magic value __SET_FOB_FOR_FUSE!!!!
@@ -49,6 +50,8 @@
#include "ext2fs/ext2_fs.h"
#include "ext2fs/ext2fsP.h"
#include "support/bthread.h"
+#include "support/list.h"
+#include "support/cache.h"

#include "../version.h"
#include "uuid/uuid.h"
@@ -206,6 +209,7 @@ int journal_enable_debug = -1;
#define FUSE4FS_FILE_MAGIC (0xEF53DEAFUL)
struct fuse4fs_file_handle {
unsigned long magic;
+ struct fuse4fs_inode *fi;
ext2_ino_t ino;
int open_flags;
int check_flags;
@@ -261,6 +265,7 @@ struct fuse4fs {
int timing;
#endif
struct fuse_session *fuse;
+ struct cache inodes;
};

#define FUSE4FS_CHECK_HANDLE(req, fh) \
@@ -353,6 +358,115 @@ static inline int u_log2(unsigned int arg)
return l;
}

+struct fuse4fs_inode {
+ struct cache_node i_cnode;
+ ext2_ino_t i_ino;
+ unsigned int i_open_count;
+};
+
+struct fuse4fs_ikey {
+ ext2_ino_t i_ino;
+};
+
+#define ICKEY(key) ((struct fuse4fs_ikey *)(key))
+#define ICNODE(node) (container_of((node), struct fuse4fs_inode, i_cnode))
+
+static unsigned int
+icache_hash(cache_key_t key, unsigned int hashsize, unsigned int hashshift)
+{
+ uint64_t hashval = ICKEY(key)->i_ino;
+ uint64_t tmp;
+
+ tmp = hashval ^ (GOLDEN_RATIO_PRIME + hashval) / CACHE_LINE_SIZE;
+ tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> hashshift);
+ return tmp % hashsize;
+}
+
+static int icache_compare(struct cache_node *node, cache_key_t key)
+{
+ struct fuse4fs_inode *fi = ICNODE(node);
+ struct fuse4fs_ikey *ikey = ICKEY(key);
+
+ if (fi->i_ino == ikey->i_ino)
+ return CACHE_HIT;
+
+ return CACHE_MISS;
+}
+
+static struct cache_node *icache_alloc(struct cache *c, cache_key_t key)
+{
+ struct fuse4fs_ikey *ikey = ICKEY(key);
+ struct fuse4fs_inode *fi;
+
+ fi = calloc(1, sizeof(struct fuse4fs_inode));
+ if (!fi)
+ return NULL;
+
+ fi->i_ino = ikey->i_ino;
+ return &fi->i_cnode;
+}
+
+static bool icache_flush(struct cache *c, struct cache_node *node)
+{
+ return false;
+}
+
+static void icache_relse(struct cache *c, struct cache_node *node)
+{
+ struct fuse4fs_inode *fi = ICNODE(node);
+
+ assert(fi->i_open_count == 0);
+ free(fi);
+}
+
+static unsigned int icache_bulkrelse(struct cache *cache,
+ struct list_head *list)
+{
+ struct cache_node *cn, *n;
+ int count = 0;
+
+ if (list_empty(list))
+ return 0;
+
+ list_for_each_entry_safe(cn, n, list, cn_mru) {
+ icache_relse(cache, cn);
+ count++;
+ }
+
+ return count;
+}
+
+static const struct cache_operations icache_ops = {
+ .hash = icache_hash,
+ .alloc = icache_alloc,
+ .flush = icache_flush,
+ .relse = icache_relse,
+ .compare = icache_compare,
+ .bulkrelse = icache_bulkrelse,
+ .resize = cache_gradual_resize,
+};
+
+static errcode_t fuse4fs_iget(struct fuse4fs *ff, ext2_ino_t ino,
+ struct fuse4fs_inode **fip)
+{
+ struct fuse4fs_ikey ikey = {
+ .i_ino = ino,
+ };
+ struct cache_node *node = NULL;
+
+ cache_node_get(&ff->inodes, &ikey, 0, &node);
+ if (!node)
+ return ENOMEM;
+
+ *fip = ICNODE(node);
+ return 0;
+}
+
+static void fuse4fs_iput(struct fuse4fs *ff, struct fuse4fs_inode *fi)
+{
+ cache_node_put(&ff->inodes, &fi->i_cnode);
+}
+
static inline blk64_t FUSE4FS_B_TO_FSBT(const struct fuse4fs *ff, off_t pos)
{
return pos >> ff->blocklog;
@@ -1137,6 +1251,11 @@ static void fuse4fs_unmount(struct fuse4fs *ff)
errcode_t err;

if (ff->fs) {
+ if (cache_initialized(&ff->inodes)) {
+ cache_purge(&ff->inodes);
+ cache_destroy(&ff->inodes);
+ }
+
uuid_unparse(ff->fs->super->s_uuid, uuid);
err = ext2fs_close_free(&ff->fs);
if (err)
@@ -1268,6 +1387,10 @@ static errcode_t fuse4fs_open(struct fuse4fs *ff)
log_printf(ff, "%s %s.\n", _("mounted filesystem"), uuid);
}

+ err = cache_init(CACHE_AUTO_SHRINK, 1U << 10, &icache_ops, &ff->inodes);
+ if (err)
+ return translate_error(ff->fs, 0, err);
+
ff->fs->priv_data = ff;
ff->blocklog = u_log2(ff->fs->blocksize);
ff->blockmask = ff->fs->blocksize - 1;
@@ -2326,6 +2449,7 @@ static int fuse4fs_remove_inode(struct fuse4fs *ff, ext2_ino_t ino)
if (inode.i_links_count)
goto write_out;

+
if (ext2fs_has_feature_ea_inode(fs->super)) {
ret = fuse4fs_remove_ea_inodes(ff, ino, &inode);
if (ret)
@@ -3282,6 +3406,13 @@ static int fuse4fs_open_file(struct fuse4fs *ff, const struct fuse_ctx *ctxt,
goto out;
}

+ err = fuse4fs_iget(ff, file->ino, &file->fi);
+ if (err) {
+ ret = translate_error(fs, 0, err);
+ goto out;
+ }
+ file->fi->i_open_count++;
+
file->check_flags = check;
fuse4fs_set_handle(fp, file);

@@ -3470,6 +3601,7 @@ static void op_release(fuse_req_t req, fuse_ino_t fino EXT2FS_ATTR((unused)),
ret = translate_error(fs, fh->ino, err);
}

+ fuse4fs_iput(ff, fh->fi);
fp->fh = 0;
fuse4fs_finish(ff, ret);