Re: [PATCH 090/104] virtiofsd: rename inode->refcount to inode->nlookup

[Philippe Mathieu-Daudé]

On 12/12/19 5:38 PM, Dr. David Alan Gilbert (git) wrote:
> From: Stefan Hajnoczi <address@hidden>
>
> 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>
> ---
>   tools/virtiofsd/passthrough_ll.c | 37 +++++++++++++++++++++-----------
>   1 file changed, 25 insertions(+), 12 deletions(-)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> index 7663e574d8..b19c9ee328 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -101,7 +101,20 @@ 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;
> +
>       fuse_ino_t fuse_ino;
>       pthread_mutex_t plock_mutex;
>       GHashTable *posix_locks; /* protected by lo_inode->plock_mutex */
> @@ -570,7 +583,7 @@ retry:
>       if (last == path) {
>           p = &lo->root;
>           pthread_mutex_lock(&lo->mutex);
> -        p->refcount++;
> +        p->nlookup++;
>           pthread_mutex_unlock(&lo->mutex);
>       } else {
>           *last = '\0';
> @@ -788,8 +801,8 @@ 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);
>   
> @@ -857,7 +870,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
>           }
>   
>           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;
> @@ -1097,7 +1110,7 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, 
> fuse_ino_t parent,
>       }
>   
>       pthread_mutex_lock(&lo->mutex);
> -    inode->refcount++;
> +    inode->nlookup++;
>       pthread_mutex_unlock(&lo->mutex);
>       e.ino = inode->fuse_ino;
>   
> @@ -1226,9 +1239,9 @@ static void unref_inode_lolocked(struct lo_data *lo, struct lo_inode *inode,
>       }
>   
>       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)) {
> @@ -1249,7 +1262,7 @@ static int unref_all_inodes_cb(gpointer key, gpointer 
> value, gpointer user_data)
>       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);
>   
> @@ -1274,7 +1287,7 @@ static void lo_forget_one(fuse_req_t req, fuse_ino_t ino, uint64_t nlookup)
>       }
>   
>       fuse_log(FUSE_LOG_DEBUG, "  forget %lli %lli -%lli\n",
> -             (unsigned long long)ino, (unsigned long long)inode->refcount,
> +             (unsigned long long)ino, (unsigned long long)inode->nlookup,
>                (unsigned long long)nlookup);
>   
>       unref_inode_lolocked(lo, inode, nlookup);
> @@ -2642,7 +2655,7 @@ 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 guint lo_key_hash(gconstpointer key)

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>