[Qemu-devel] [PATCH 3/5] virtiofsd: rename inode->refcount to inode->nlookup

[Stefan Hajnoczi]

This reference counter plays a specific role in the FUSE protocol.  It's
not a generic object reference counter and the FUSE kernel code calls it
"nlookup".

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 contrib/virtiofsd/passthrough_ll.c | 36 ++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/contrib/virtiofsd/passthrough_ll.c 
b/contrib/virtiofsd/passthrough_ll.c
index e1d729d26b..135123366a 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -97,7 +97,19 @@ struct lo_inode {
        int fd;
        bool is_symlink;
        struct lo_key key;
-       uint64_t refcount; /* protected by lo->mutex */
+
+       /* This counter keeps the inode alive during the FUSE session.
+        * Incremented when the FUSE inode number is sent in a reply
+        * (FUSE_LOOKUP, FUSE_READDIRPLUS, etc).  Decremented when an inode is
+        * released by requests like FUSE_FORGET, FUSE_RMDIR, FUSE_RENAME, etc.
+        *
+        * Note that this value is untrusted because the client can manipulate
+        * it arbitrarily using FUSE_FORGET requests.
+        *
+        * Protected by lo->mutex.
+        */
+       uint64_t nlookup;
+
        uint64_t version_offset;
        uint64_t ireg_refid;
        fuse_ino_t fuse_ino;
@@ -485,7 +497,7 @@ retry:
        if (last == path) {
                p = &lo->root;
                pthread_mutex_lock(&lo->mutex);
-               p->refcount++;
+               p->nlookup++;
                pthread_mutex_unlock(&lo->mutex);
        } else {
                *last = '\0';
@@ -688,8 +700,8 @@ static struct lo_inode *lo_find(struct lo_data *lo, struct 
stat *st)
        pthread_mutex_lock(&lo->mutex);
        p = g_hash_table_lookup(lo->inodes, &key);
        if (p) {
-               assert(p->refcount > 0);
-               p->refcount++;
+               assert(p->nlookup > 0);
+               p->nlookup++;
        }
        pthread_mutex_unlock(&lo->mutex);
 
@@ -797,7 +809,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, 
const char *name,
                        goto out_err;
 
                inode->is_symlink = S_ISLNK(e->attr.st_mode);
-               inode->refcount = 1;
+               inode->nlookup = 1;
                inode->fd = newfd;
                newfd = -1;
                inode->key.ino = e->attr.st_ino;
@@ -1051,7 +1063,7 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, 
fuse_ino_t parent,
                goto out_err;
 
        pthread_mutex_lock(&lo->mutex);
-       inode->refcount++;
+       inode->nlookup++;
        pthread_mutex_unlock(&lo->mutex);
        e.ino = inode->fuse_ino;
        update_version(lo, inode);
@@ -1200,9 +1212,9 @@ static void unref_inode(struct lo_data *lo, struct 
lo_inode *inode, uint64_t n)
                return;
 
        pthread_mutex_lock(&lo->mutex);
-       assert(inode->refcount >= n);
-       inode->refcount -= n;
-       if (!inode->refcount) {
+       assert(inode->nlookup >= n);
+       inode->nlookup -= n;
+       if (!inode->nlookup) {
                lo_map_remove(&lo->ino_map, inode->fuse_ino);
                 g_hash_table_remove(lo->inodes, &inode->key);
                if (g_hash_table_size(inode->posix_locks)) {
@@ -1225,7 +1237,7 @@ static int unref_all_inodes_cb(gpointer key, gpointer 
value,
        struct lo_inode *inode  = value;
        struct lo_data *lo = user_data;
 
-       inode->refcount = 0;
+       inode->nlookup = 0;
        lo_map_remove(&lo->ino_map, inode->fuse_ino);
        close(inode->fd);
 
@@ -1252,7 +1264,7 @@ static void lo_forget_one(fuse_req_t req, fuse_ino_t ino, 
uint64_t nlookup)
        if (lo_debug(req)) {
                fuse_debug("  forget %lli %lli -%lli\n",
                           (unsigned long long) ino,
-                          (unsigned long long) inode->refcount,
+                          (unsigned long long) inode->nlookup,
                           (unsigned long long) nlookup);
        }
 
@@ -2581,7 +2593,7 @@ static void setup_root(struct lo_data *lo, struct 
lo_inode *root)
        root->fd = fd;
        root->key.ino = stat.st_ino;
        root->key.dev = stat.st_dev;
-       root->refcount = 2;
+       root->nlookup = 2;
 }
 
 static void setup_proc_self_fd(struct lo_data *lo)
-- 
2.21.0